dn9814144_iuo

Nokia Siemens Networks GSM/EDGE BSS, rel. RG10(BSS), operating documentation, issue 04

Feature description

Intelligent Underlay-Overlay

DN9814144

Issue 11-1Approval Date 15/12/2006 00:00:00

2 DN9814144Issue 11-1


Id:0900d8058058fc8e

The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia Siemens Networks customers only for the purposes of the agreement under which the document is submitted, and no part of it may be used, reproduced, modified or transmitted in any form or means without the prior written permission of Nokia Siemens Networks. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation.

The information or statements given in this documentation concerning the suitability, capacity, or performance of the mentioned hardware or software products are given "as is" and all liability arising in connection with such hardware or software products shall be defined conclusively and finally in a separate agreement between Nokia Siemens Networks and the customer. However, Nokia Siemens Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Siemens Networks will, if deemed necessary by Nokia Siemens Networks, explain issues which may not be covered by the document.

Nokia Siemens Networks will correct errors in this documentation as soon as possible. IN NO EVENT WILL Nokia Siemens Networks BE LIABLE FOR ERRORS IN THIS DOCUMENTA-TION OR FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, DIRECT, INDI-RECT, INCIDENTAL OR CONSEQUENTIAL OR ANY LOSSES, SUCH AS BUT NOT LIMITED TO LOSS OF PROFIT, REVENUE, BUSINESS INTERRUPTION, BUSINESS OPPORTUNITY OR DATA,THAT MAY ARISE FROM THE USE OF THIS DOCUMENT OR THE INFORMATION IN IT.

This documentation and the product it describes are considered protected by copyrights and other intellectual property rights according to the applicable laws.

The wave logo is a trademark of Nokia Siemens Networks Oy. Nokia is a registered trademark of Nokia Corporation. Siemens is a registered trademark of Siemens AG.

Other product names mentioned in this document may be trademarks of their respective owners, and they are mentioned for identification purposes only.

Copyright © Nokia Siemens Networks 2009. All rights reserved

f Important Notice on Product Safety Elevated voltages are inevitably present at specific points in this electrical equipment. Some of the parts may also have elevated operating temperatures.

Non-observance of these conditions and the safety instructions can result in personal injury or in property damage.

Therefore, only trained and qualified personnel may install and maintain the system.

The system complies with the standard EN 60950 / IEC 60950. All equipment connected has to comply with the applicable safety standards.

The same text in German:

Wichtiger Hinweis zur Produktsicherheit

In elektrischen Anlagen stehen zwangsläufig bestimmte Teile der Geräte unter Span-nung. Einige Teile können auch eine hohe Betriebstemperatur aufweisen.

Eine Nichtbeachtung dieser Situation und der Warnungshinweise kann zu Körperverlet-zungen und Sachschäden führen.

Deshalb wird vorausgesetzt, dass nur geschultes und qualifiziertes Personal die Anlagen installiert und wartet.

Das System entspricht den Anforderungen der EN 60950 / IEC 60950. Angeschlossene Geräte müssen die zutreffenden Sicherheitsbestimmungen erfüllen.

DN9814144Issue 11-1

3


Id:0900d8058058fc8e

Table of ContentsThis document has 53 pages.

Summary of changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 Overview of Intelligent Underlay-Overlay. . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Technical description of Intelligent Underlay-Overlay . . . . . . . . . . . . . . 102.1 Regular and super-reuse frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2 Interworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 RF power control and handover algorithm with Intelligent Underlay-Overlay19

3.1 Intelligent Underlay-Overlay handover strategy. . . . . . . . . . . . . . . . . . . 193.2 RF power control strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.3 Processing of radio link measurements . . . . . . . . . . . . . . . . . . . . . . . . . 243.4 C/I evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.5 Threshold comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.6 Handover decision algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4 Radio resource allocation and Intelligent Underlay-Overlay . . . . . . . . . 47

5 User interface of Intelligent Underlay-Overlay . . . . . . . . . . . . . . . . . . . . 495.1 Parameters and MMLs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.2 Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4 DN9814144Issue 11-1


Id:0900d8058058fc8e

List of FiguresFigure 1 Method of baseband hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Figure 2 Method of radio frequency hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

DN9814144Issue 11-1

5


Id:0900d8058058fc8e

List of TablesTable 1 Correspondence between the measurement results of the interfering cells

of the TRX (k) and the averaged results. . . . . . . . . . . . . . . . . . . . . . . . 25

6 DN9814144Issue 11-1


Id:0900d8058058fc8e

DN9814144Issue 11-1

7

Intelligent Underlay-Overlay Summary of changes

Id:0900d8058058fc7c

Summary of changesChanges between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues.

Changes made between issues 11–1 and 11Information on direct access from a SDCCH of a parent cell to a child cell has been removed from RF power control and handover algorithm with Intelligent Underlay-Overlay, Radio resource allocation and Intelligent Underlay-Overlay, and User interface of Intelligent Underlay-Overlay.

Changes made between issues 11 and 10–1Information on Dual Transfer Mode (DTM) interworking has been added.

In Overview of Intelligent Underlay-Overlay, a list of related topics has been added.

Advanced Multilayer Handling (AMH) related information has been removed to the AMH description document.

Changes made between issues 10–1 and 10Editorial changes.

8 DN9814144Issue 11-1


Id:0900d8058058fc7f

Overview of Intelligent Underlay-Overlay

1 Overview of Intelligent Underlay-OverlayIntelligent Underlay-Overlay (IUO) is an application software in the base station control-ler (BSC). It allows you to reuse frequencies very intensively and hence achieve a higher radio network capacity.

To avoid interference caused by an increased level of frequency reuse, the BSC esti-mates the degree of interference on different frequencies and directs the mobile stations to those frequencies that are 'clean' enough to sustain a good radio connection quality.

The interference estimation that the BSC makes is based on the measurement results that the mobile station (MS) reports via the base transceiver station (BTS) and on various adjustable parameters.

Related topics in Intelligent Underlay-Overlay

• Technical description of Intelligent Underlay-Overlay • RF power control and handover algorithm with Intelligent Underlay- Overlay • Radio resource allocation and Intelligent Underlay-Overlay • User interface of Intelligent Underlay-Overlay

Other related topics in BSC/TCSM documentation

• Test and Activate • Radio Network Performance

• BSS6114: TCH Assignment of Super-reuse TRX in IUO • Activating and Testing BSS6114: TCH Assignment of Super-reuse TRX

in IUO • Reference

• Commands • MML Commands

• EH – Handover Control Parameter Handling • EQ – Base Transceiver Station Handling in BSC • ER – Transceiver Handling

• Counters/Performance Indicators • Call Control Measurements (CSW)

• 1 Traffic Measurement • 4 Handover Measurement • 5 Power Control Measurement • 14 RX Quality Statistics Measurement • 51 BSC Level Clear Code (PM) Measurement • 52 Underlay-Overlay Statistics Measurement • 53 RX Level Statistics Measurement • 60 C/I Ratio Measurement

• Observations • 18 Handover Observation

• Parameters • BSS Radio Network Parameter Dictionary

• Descriptions • Functional Area Descriptions

• Radio Network Performance

DN9814144Issue 11-1

9

Intelligent Underlay-Overlay Overview of Intelligent Underlay-Overlay

Id:0900d8058058fc7f

• Radio Channel Allocation • RF Power Control and Handover Algorithm • Traffic Reason Handover in BSC

• Operability • Radio Network Configuration Management • Radio Network Recovery and State Management

• Feature Descriptions • Radio Network Performance

• Advanced Multilayer Handling • Directed Retry in BSC • Dual Band Network Operation • Frequency Hopping

• Data • HSCSD and 14.4 kbit/s Data Services

• Value Added Services • Radio Resource Pre-emption and Queueing in BSC • Trunk Reservation

10 DN9814144Issue 11-1


Id:0900d8058058fc82

Technical description of Intelligent Underlay-Overlay

2 Technical description of Intelligent Underlay-Overlay

2.1 Regular and super-reuse frequenciesTo achieve a higher radio network capacity with Intelligent Underlay-Overlay, the oper-ating spectrum of the network is divided into regular frequencies and super-reuse fre-quencies.

Regular frequencies compose the overlay network which provides the continuous coverage area of the radio network. The frequency planning of the overlay network is based on conventional planning criteria such as low probability of co-channel and adjacent channel interference, and overlapping cell areas required for handover control. The regular frequencies are intended to serve mobile stations mainly at cell boundary areas and other locations where the carrier-to-interference (C/I) ratio is the worst.

Super-reuse frequencies compose the underlay network where frequencies are reused very intensively to produce extended capacity. To avoid the interference caused by the increased level of frequency reuse, the super-reuse frequencies should serve mobile stations that are close to the BTS, inside buildings and other locations where the radio conditions are less vulnerable to the interference.

The parameter TRX frequency type (FRT) controls the division into regular and super-reuse frequencies within a cell on a transceiver-by-transceiver basis. The trans-ceivers (TRXs) of the cell are identified as either regular TRXs or super-reuse TRXs:

Regular TRX: the radio frequency of the transceiver belongs to regular frequencies

Super-reuse TRX: the radio frequency of the transceiver belongs to super-reuse fre-quencies

g The type of the radio frequency is a cell-associated definition. For example, a radio frequency which belongs to the super-reuse frequency group 1 in one cell, may belong to the super-reuse frequency group 2 in another cell.

An ordinary cell (regular cell) is typically equipped with both types of TRXs. The regular TRXs allocated to the cell belong to a regular frequency group. A super-reuse TRX allo-cated to the cell belongs to a specified super-reuse frequency group. The super-reuse TRXs of the cell may belong to the same super-reuse frequency group, or they may belong to different super-reuse frequency groups. The groups are selected with the parameter TRX frequency type (FRT). For example, the super-reuse TRXs allo-cated to the cell may be divided into super-reuse frequency groups according to the source of interference. Those super-reuse TRXs which belong to the same super-reuse frequency group have the same sources of interference.

The BSC uses radio resource allocation at call set-up and handover during the call to control traffic between regular and super-reuse frequencies.

The BSC normally allocates a traffic channel (TCH) for a call or for an inter-cell handover attempt to a regular cell from a regular TRX, that is, a regular cell must have at least one regular TRX, typically a broadcast control channel (BCCH) TRX. If there are no free channels available on regular TRXs, a TCH on a super-reuse TRX may be assigned for the call (but never for the inter-cell handover attempt to a regular cell) if the downlink C/I ratio of the super-reuse TRX is good enough. The parameter enable TCH

DN9814144Issue 11-1

11

Intelligent Underlay-Overlay Technical description of Intelligent Underlay-Overlay

Id:0900d8058058fc82

assignment super IUO (ETA) indicates if the BSC can allocate a TCH for a call from a super-reuse TRX when the regular TRX is congested.

The BSC may also allocate a TCH for a call or for an inter-cell handover attempt to a regular cell from a super-reuse TRX when the downlink signal level of the super-reuse TRX exceeds a certain predetermined threshold (controlled by the parameter direct access level (DAL)). In this case the high downlink signal level (well above the worst expected interference level) ensures that the downlink C/I ratio on the super-reuse TRX is good enough.

During the call, the BSC monitors the downlink C/I ratio continuously on each super-reuse frequency group of the regular cell for every ongoing call. The call is always handed over from a regular TRX to a super-reuse TRX when the downlink C/I ratio of the super-reuse TRX is good enough. If the downlink C/I ratio of a super-reuse TRX becomes worse, the call is handed over from the super-reuse TRX back to a regular TRX. The BSC uses the profile of interference each mobile is exposed to when deter-mining the most appropriate frequency group to be assigned for the conversation.

Child cells and parent cellsMicrocells may be equipped solely with super-reuse frequencies. By establishing appro-priate handover connections, a microcell at a location with heavy traffic (traffic hot spot) can handle more traffic than the regular cells in its vicinity. With such an arrangement, the surrounding regular cells are called parent cells and the microcell is called a child cell.

A child cell has only super-reuse TRXs. They are defined by the parameter TRX frequency type (FRT). The super-reuse TRXs of the child cell may belong to the same super-reuse frequency group or they may belong to different super-reuse fre-quency groups.

g Because a child cell does not have any regular TRXs, the call set-up through the child cell is not possible; for that reason, access to the child cell must be denied with the parameter cell barred (BAR). The type of the BCCH TRX cannot be deter-mined as a super-reuse TRX until the cell is barred and, correspondingly, if the type of the BCCH TRX is super-reuse, the barred information cannot be changed.

For more information, see Base Transceiver Station Handling in BSC (EQ command group) and Radio Network Configuration Management.

The BSC continuously monitors the downlink C/I ratio on each super-reuse frequency group of the child cell, adjacent to the regular/serving cell, during every call. The call is handed over from a regular cell to a child cell when the downlink C/I ratio of the child cell is good enough. If the downlink C/I ratio of a child cell becomes worse, the call is handed over from the child cell to one regular/parent cell adjacent to the child cell.

Downlink C/I ratio of super-reuse TRXThe BSC calculates the downlink C/I ratio of the super-reuse TRX from the measure-ment results reported by the MS via the BTS.

By comparing the downlink signal level of the serving cell (carrier) and the downlink signal level of those neighbouring cells which use the same super-reuse frequencies as the serving cell (interference), the BSC can calculate the C/I ratio on the super-reuse frequencies at the location of each active mobile station.

12 DN9814144Issue 11-1


Id:0900d8058058fc82


Example: Super-reused frequency 90 has been allocated to cells A and B, and the cells are close enough to each other to cause interference. When the downlink signal level of the serving cell A is -70 dBm and the signal level of the adjacent cell B is -86 dBm, the downlink C/I ratio of the super-reuse TRX (frequency 90) of the cell A is 16 dB.

2.2 InterworkingAdvanced Multilayer HandlingAdvanced Multilayer Handling (AMH) can be applied with Intelligent Underlay-Overlay to avoid congestion in the overlay layer and thus it provides more trunking gain. You can also use AMH to prevent the use of Intelligent Underlay-Overlay during very light traffic, and therefore keep the mobile stations only in the overlay network. For more information on AMH, see Advanced Multilayer Handling.

Directed retry to super-reuse TRXWhen Directed Retry is enabled, the BSC may assign a TCH on a super-reuse TRX for the call when the regular TRX is congested. Directed Retry is enabled with the param-eter directed retry used (DR), which is controlled on a cell-by-cell basis.

The BSC starts the directed retry procedure after the assignment request (this message is sent from the MSC to the BSC to request the BSC to allocate a radio resource) in con-gestion situations. When Intelligent Underlay-Overlay is employed, the radio resource management may allocate a traffic channel (TCH) for a call from a regular TRX only. If no TCHs are available on regular TRXs when requested, the BSC starts the directed retry. In this case the BSC performs either:

1. Inter-cell handover from a stand-alone dedicated control channel (SDCCH) of the serving cell to a TCH on a regular TRX of an adjacent (regular) cell when the signal level of the adjacent cell is good enough. For more information, see Directed Retry in BSC and RF Power Control and Handover Algorithm.The parameter min time limit directed retry (MIDR) determines the period starting from the assignment request during which the handover in question is not allowed. The parameter is controlled on a cell-by-cell basis. The period is allowed for the mobile station to decode the base station identity code (BSIC) of the adjacent cells before the handover decision. The period also increases the possibil-ity of allocating a TCH (on a regular TRX or on a super-reuse TRX) from the serving cell before the execution of handover to an adjacent cell. The BSC may perform the handover after the period has expired.

2. Intra/inter-cell handover from a SDCCH of the serving cell to a TCH on a super-reuse TRX of a serving/child cell when the downlink C/I ratio of the super-reuse TRX is good enough. See section Handover decision algorithm.The handover from a SDCCH to a super-reuse TRX is enabled with the parameter enable TCH assignment super IUO (ETA), which is controlled on a cell-by-cell basis.The parameter also determines the period starting from the assignment request during which the C/I evaluation is considered unreliable and the handover to a super-reuse TRX is not allowed. This period is allowed for the mobile station to

DN9814144Issue 11-1

13


Id:0900d8058058fc82

decode the BSIC of the interfering cells before the handover decision. The BSC may perform the handover to a super-reuse TRX after the period has expired.If the directed retry attempt to a super-reuse TRX was not successful, the BSC may perform the directed retry.

If it is possible to perform a handover both to a regular TRX and to a super-reuse TRX simultaneously, the BSC prefers the super-reuse TRXs of the serving/child cell to the regular TRXs of the adjacent cells. Note the effect of the parameters min time limit directed retry (MIDR) and enable TCH assignment super IUO (ETA).

The BSC can monitor the signal level of the adjacent cells and the C/I ratio of the super-reuse TRXs and perform the handover from the SDCCH until the maximum period allowed for the directed retry procedure expires. The period starts from the assignment request and it is controlled by the parameter max time limit directed retry (MADR). The parameter is controlled on a cell-by-cell basis. If the call cannot be handed over from a SDCCH during the period, the BSC discontinues the call setup pro-cedure: the possibly ongoing queueing is terminated and the call attempt is cleared.

g Radio resource queueing increases the possibility of allocating a TCH on a regular TRX of the serving cell before the maximum period allowed for the directed retry pro-cedure expires. If a TCH on a regular TRX of the serving cell can be assigned for the call, the BSC discontinues the directed retry procedure. For more information on queueing, see Radio Resource Pre-emption and Queueing in BSC.

Dual Transfer ModeThe BSC does not support super-reuse frequencies for GPRS, and therefore Dual Transfer Mode (DTM) is not supported, either. The BSC does not initiate handovers towards super-reuse resources for ongoing DTM connections.

If a DTM call establishment is started on a regular cell’s super layer, the call is handed over to the regular layer during the call establishment. It is not possible to start a DTM call from a child cell.

For more information on DTM, see Dual Transfer Mode in BSC.

Pre-emption procedure

• In call assignment and inter-cell and intra-cell handover to a regular TRX: if a forced call release or a forced handover is required in congestion situations, the actions to be taken concern calls on regular TRXs only. In the case of forced handover, the call is handed over to a TCH on a regular TRX, never to a TCH on a super-reuse TRX.A handover attempt (inter-cell or intra-cell) which leads to the pre-emption procedure can take place either from a super-reuse TRX or from a regular TRX.

• In inter-cell and intra-cell handover to a super-reuse TRX, the pre-emption proce-dure is not employed.

For more information, see Radio Resource Pre-emption and Queueing in BSC.

Radio resource queueing

• In call assignment and inter-cell and intra-cell handover to a regular TRX, the queued radio resource is always a TCH on the regular TRX of the BSS cell, never a TCH on a super-reuse TRX.

• In inter-cell and intra-cell handover to a super-reuse TRX, radio resource queueing is not employed.

For more information on queueing, see:

14 DN9814144Issue 11-1


Id:0900d8058058fc82


• the section Radio resource allocation and Intelligent Underlay-Overlay. • Radio Resource Pre-emption and Queueing in BSC.

Rotation of allocatable resources

• In call assignment and inter-cell and intra-cell handover to a regular TRX, the rotation of allocatable radio resources concerns regular TRXs inside a cell and TCHs inside a regular TRX.

• In inter-cell and intra-cell handover to a super-reuse TRX, the rotation of allocatable radio resources concerns the TCHs inside the super-reuse TRX.

Trunk reservation

• In call assignment: when the radio resource management verifies the number of unallocated TCHs for the trunk reservation procedure in a call, it only takes into account the unallocated TCHs on the regular TRXs of the BSS cell.

• In inter-cell and intra-cell handover to a regular TRX, the radio resource manage-ment applies the trunk reservation procedure in an inter-cell handover attempt only. The target of the inter-cell handover must be a regular TRX of the regular cell but the type of the TRX of the source cell may be regular or super-reuse.When the radio resource management verifies the number of unallocated TCHs for the trunk reservation procedure in the handover attempt in question, it takes into account only the unallocated TCHs on the regular TRXs of the BSS cell.

• In inter-cell and intra-cell handover to a super-reuse TRX, the trunk reservation pro-cedure is not employed.

For more information, see Trunk Reservation.

High speed circuit switched data (HSCSD)

• In call assignment and inter-cell and intra-cell handover to a regular TRX, radio resource management may allocate multiple TCHs (time slots) for a high speed circuit switched data (HSCSD) call from a regular TRX. The load threshold where the multislot TCH allocation is stopped and the single slot TCH allocation is started (parameter HSCSD regular cell load upper limit (HRCU)), is determined independently for the regular TRXs of the cell.When the radio resource management verifies the load of the cell for the HSCSD resource allocation in a call or in a handover attempt to a regular TRX, it takes into account only the allocated TCHs on the regular TRXs of the BSS cell. If the number of allocated TCHs exceeds the load threshold, the multislot TCH allocation is not allowed, and a new resource request initiates the resource downgrade procedure for one of the existing multislot HSCSD calls on the regular TRXs.g When a HSCSD call is on a regular TRX, the radio resource management may

not upgrade the number of time slots that have been allocated to the HSCSD call in question.

• In inter-cell and intra-cell handover to a super-reuse TRX, radio resource manage-ment may allocate multiple TCHs (time slots) for a HSCSD call from a super-reuse TRX if either: • the number of TCHs that have been allocated for the HSCSD calls has not

reached the minimum TCH capacity (parameter HSCSD TCH capacity minimum (HTM)) which is offered to the HSCSD calls (see the following Note), or

DN9814144Issue 11-1

15


Id:0900d8058058fc82

• the number of allocated TCHs on the regular and super-reuse TRXs of the cell has not exceeded the upper load threshold (parameter HSCSD cell load upper limit (HCU)).

When the multislot TCH allocation is allowed, the radio resource management may also perform resource upgrade procedures for those HSCSD calls on super-reuse TRXs that have less allocated resources (time slots) than requested.The multislot TCH allocation on a super-reuse TRX is not allowed, and a new resource request initiates the resource downgrade procedure for one of the existing multislot HSCSD calls (on a regular TRX or on a super-reuse TRX) if the following conditions are fulfilled simultaneously: • the number of TCHs that have been allocated for the HSCSD calls, exceeds the

minimum TCH capacity which is offered to the HSCSD calls (see the following note)

• the number of allocated TCHs on the regular and super-reuse TRXs of the cell exceeds the upper load threshold.

Once the single slot TCH allocation has been started, it is not possible to resume the multislot TCH allocation (or the resource upgrade procedure) until the number of allocated TCHs on the regular and super-reuse TRXs of the cell has decreased below the lower load threshold (parameter HSCSD cell load lower limit (HCL)).

g When the radio resource management verifies the minimum TCH capacity that is offered to the HSCSD calls, it takes into account the TCHs both on the regular TRXs and on the super-reuse TRXs of the BSS cell.

For more information on HSCSD, see HSCSD and 14.4 kbit/s Data Services in BSC.

Dual band network operationIntelligent Underlay-Overlay does not have any special requirements for the Dual Band Network Operation. However, it is possible to prevent the dual band mobile stations from using the super-reuse TRXs of the serving/child cell when the serving cell has adjacent cells from another frequency band.

The parameter DualBandMSSuperReuseUsage indicates whether the super-reuse TRXs of the serving/child cell are barred from the dual band MSS the serving cell has adjacent cells from another frequency band. For information on the parameter values, see section User inferface of Intelligent Underlay-Overlay.

For more information on Dual Band, see Dual Band Network Operation.

Frequency HoppingIntelligent Underlay-Overlay and Frequency Hopping can be used together to further improve the capacity of the radio network.

When Intelligent Underlay-Overlay is employed in the BSC, the frequency hopping is controlled on a frequency group-by-group basis. The regular TRXs of the cell compose one hopping group and the super-reuse TRXs of the cell compose another hopping group, and frequency hopping can be used independently in both frequency/hopping groups.

g It is not possible to use baseband hopping and radio frequency hopping in a base station at the same time.

16 DN9814144Issue 11-1


Id:0900d8058058fc82


• Baseband hoppingFigure Method of baseband hopping shows the method of frequency hopping when baseband (BB) hopping is used in the cell: • HSN1 (hopping sequence) is used with hopping group 1. Time slot 0 of each

regular TRX, except the BCCH TRX, belongs to this group. • HSN2 is used with the hopping group 2. Time slots 1 - 7 of each regular TRX,

including the BCCH TRX, belong to this group. • HSN3 is used with the hopping group 3. Time slots 0 - 7 of each super-reuse

TRX of the cell belong to this group.

Figure 1 Method of baseband hopping • Radio frequency hopping

Figure Method of radio frequency hopping shows the method of frequency hopping when radio frequency (RF) hopping is used in the cell: • HSN1 is used with the hopping group 1. Time slots 0 - 7 of each regular TRX,

except the BCCH TRX, belong to this group. The BCCH TRX does not hop when RF hopping has been selected.

• HSN3 is used with the hopping group 3. Time slots 0 - 7 of each super-reuse TRX of the cell belong to this group.

Both the mobile allocation (MA) frequency list and the mobile allocation index offset (MAIO) are set separately for the regular frequency group and for the super-reuse frequency group.

LAYER

Regular TRXs

TRX

TRX-1

TRX-2

TRX-3

RTSL0

RTSL1

RTSL2

RTSL3

RTSL4

RTSL5

RTSL6

RTSL7

BCCH

HSN1

Super-reuseTRXs

TRX-4

TRX-5

TRX-6

HSN3

HSN2

DN9814144Issue 11-1

17


Id:0900d8058058fc82

Figure 2 Method of radio frequency hopping

TRX recoveryTo maintain the traffic efficiency of the cell (equipped with both super-reuse and regular TRXs) as high as possible, the BSC always replaces a faulty regular TRX by a working super-reuse TRX when there is such a super-reuse TRX available. For more informa-tion, see Radio Network Recovery and State Management.

When a regular TRX becomes faulty, the BSC swaps both the frequencies and the types of the faulty and working TRXs as follows:

• Regular frequency is allocated to the working TRX and the type of the working TRX is changed into regular.

• Super-reuse frequency is allocated to the faulty TRX and the type of the faulty TRX is changed into super-reuse.

The faulty TRX is blocked after the recovery procedure. When a faulty super-reuse (ex-regular) TRX is repaired and it is deblocked, the type of the TRX remains unchanged with the exception of the preferred BCCH TRX. If a faulty TRX has been determined as a preferred BCCH TRX, the BSC automatically restores the preferred TRX configuration to its former condition after the fault has been repaired.

g In order for the recovery procedure to become possible, the BSC must clear those ongoing calls which cannot be handed over from the working TRX which replaces the faulty TRX.

For more information, see Frequency Hopping.

Resource indication to the MSCThe resource indication procedure does not handle super-reuse TRXs any differently from regular TRXs. The number of available resources in a BSS cell consists of the unal-located traffic channels on the regular TRXs and on the super-reuse TRXs.

LAYER

Regular TRXs

TRX

TRX-1

TRX-2

TRX-3

RTSL0

RTSL1

RTSL2

RTSL3

RTSL4

RTSL5

RTSL6

RTSL7

BCCH

Super-reuseTRXs

TRX-4

TRX-5

TRX-6

(BCCH frequencydoes not hop)

HSN1

HSN3

18 DN9814144Issue 11-1


Id:0900d8058058fc82


For more information, see Traffic Reason Handover in BSC.

Traffic Reason HandoverWhen the BSC examines the calls that can be handed over from the serving cell to some of the specified adjacent cells, the BSC does not handle the calls on the regular TRXs any differently from those on super-reuse TRXs. For more information, see Traffic Reason Handover in BSC.

When the radio network recovery management initiates a handover (intra-cell or inter-cell) to empty a cell or a TRX (forced handover), the call is handed over to a TCH on a regular TRX, never to a TCH on a super-reuse TRX. For more information, see Radio Network Recovery and State Management.

Load information from channel administration to HO algorithmIntelligent Underlay-Overlay does not have any special requirements for the procedure in question. The load information is collected equally from both the regular and the super-reuse TRXs of the cell. For more information, see RF Power Control and Handover Algorithm.

For an overview, see Overview of Intelligent Underlay-Overlay.

DN9814144Issue 11-1

19

Intelligent Underlay-Overlay RF power control and handover algorithm with Intelli-gent Underlay-Overlay

Id:0900d8058058fc85

3 RF power control and handover algorithm with Intelligent Underlay-OverlayIntelligent Underlay-Overlay has special requirements for every stage of the radio fre-quency (RF) power control and handover algorithm:

• processing of radio link measurements • threshold comparison • decision of power control and handover in the BSC

Intelligent Underlay-Overlay is, however, compatible with the basic handover algorithm.

For more information on the RF power control and handover algorithm, see RF Power Control and Handover Algorithm.

g Whenever the RF power control and handover algorithm uses a corrected RxQual in power control and handover decision making, it uses the thresholds defined for non-AMR calls also for AMR calls. Moreover, whenever a basic HR call is in ques-tion, RF power control and handover algorithm uses thresholds defined for AMR HR calls. For more information on the corrected RxQual, see Using FEP in HO and PC decisions in the document RF Power Control and Handover Algorithm.

3.1 Intelligent Underlay-Overlay handover strategyWhen the BSC uses Intelligent Underlay-Overlay, the handover algorithm is able to perform handovers for the following reasons:

• traffic control between regular and super-reuse frequencies during the call set-up phase in congestion situations (underlay-overlay assignment)

• traffic control between regular and super-reuse frequencies during a call (underlay-overlay handover)

• traffic control between regular and super-reuse frequencies without the C/I evalua-tion (direct access procedure)

• conventional radio criteria such as power budget, low signal level and bad signal quality

• other reasons than radio criteria such as directed retry procedure, traffic reason han-dover, umbrella handover, and an order from the channel administration to empty a cell with the handover procedure

The BSC uses different handover decision algorithms for handovers caused by:

• traffic control between regular and super-reuse frequencies • handovers caused by conventional radio criteria • handovers caused by other reasons than radio criteria

Handover caused by radio criteria Intelligent Underlay-Overlay does not affect the handover decisions that the BSC makes when the cause of the handover attempt is conventional radio criteria or when other reasons than radio criteria cause the handover attempt. For more information, see RF Power Control and Handover Algorithm.

The possible handover types are the following:

• intra-cell handover within a regular frequency group • inter-cell handover from a regular cell to another regular cell

20 DN9814144Issue 11-1


Id:0900d8058058fc85

RF power control and handover algorithm with Intelli-gent Underlay-Overlay

• inter-cell handover from a child cell to a regular cell

The inter-cell handover can start either from a regular TRX or from a super-reuse TRX. The list of preferred HO candidates consists of regular cells that meet the requirements for the radio link properties. The target cells are ranked according to priority levels and the load of the target cells as usual.

g When a call is on a super-reuse TRX, the following handover causes are not con-sidered conventional radio criteria, but they are related to traffic control between regular and super-reuse frequencies:

• downlink quality • downlink interference and • uplink interference

A call may be handed over from a traffic channel (TCH) to a TCH on a regular TRX. An intra-cell handover can take place either to a TCH on a new regular TRX or to a different TCH on the same regular TRX. A handover may also take place during the initial signal-ling period of call set-up when a call is handed over from a stand-alone dedicated control channel (SDCCH) to a SDCCH on a regular TRX.

During the call set-up phase in congestion situations, a handover can take place from a SDCCH of the serving cell to a traffic channel on a regular TRX of an adjacent cell.

Underlay-overlay handoverThe underlay-overlay handover can take place during a call from a TCH to a TCH. An intra-cell handover can take place either to a TCH on a new TRX or to a different TCH on the same TRX.

Intelligent Underlay-Overlay does not affect the actual performance of the handover. For example, the optimisation of the MS power level in the handover may also be employed in the underlay-overlay handover.

The BSC makes underlay-overlay handover decisions based on the measurement results reported by the MS/BTS and various parameters.

The parameters control the underlay-overlay handover in the BSC. By changing the values of the parameters, it is possible to affect the handover decisions at all stages of the underlay-overlay handover procedure.

The handover decision algorithm for the underlay-overlay handover consists of the fol-lowing four stages:

1. processing of radio link measurements2. C/I evaluation procedure3. HO threshold comparison4. HO candidate selection

The BSC monitors the downlink C/I ratio on the super-reuse frequencies continuously. It determines the most appropriate frequency group, regular or super-reuse, to be assigned for the conversation and performs the underlay-overlay handover between fre-quency groups when necessary.

The possible types of the underlay-overlay handover are the following:

• intra-cell handover from a regular TRX to a super-reuse TRX • intra-cell handover from a super-reuse TRX to a regular TRX • intra-cell handover within a super-reuse frequency group

DN9814144Issue 11-1

21


Id:0900d8058058fc85

• inter-cell handover from a parent cell to a child cell • inter-cell handover from a child cell to a parent cell • intra-cell handover between super-reuse frequency groups • inter-cell handover between super-reuse frequency groups

When a call is on a regular TRX, the handover algorithm monitors every super-reuse fre-quency group of the serving cell and those child cells that are adjacent to the serving cell. The BSC performs the handover from a regular TRX to a super-reuse TRX if the C/I ratio of the super-reuse TRX is greater than or equals a specified HO threshold.

If there are appropriate super-reuse frequency groups both in the serving cell and in the child cell, the handover algorithm prefers the super-reuse frequency groups of the child cell to those of the serving cell. If there are several super-reuse frequency groups in the target (serving or child) cell that meet the requirements for the C/I ratio, the BSC ranks the groups according to the load and the radio link properties of the super-reuse fre-quency groups.

g The alternative priorities of the intra-cell and inter-cell handover have no effect on the underlay-overlay handover procedure.

When a call is on a super-reuse TRX, the handover algorithm monitors every super-reuse frequency group of the serving cell and those child cells that are adjacent to the serving (parent or child) cell in the same way as when a call is on a regular TRX. The BSC performs the handover from a super-reuse TRX to a regular TRX if the C/I ratio of the super-reuse TRX or the signal quality becomes worse than the relevant handover threshold. If a handover back to a regular TRX is not possible, for example, because of TCH congestion, the BSC may perform a handover from the serving super-reuse fre-quency group to another super-reuse frequency group that meets the requirements for the C/I ratio.

You can control the handover between super-reuse frequency groups with the parame-ter enable inter FRT handover (EFHO). The parameter also determines which type of handover, a handover to another super-reuse frequency group, or a handover to a regular TRX, is preferable when the downlink C/I ratio on the serving super-reuse fre-quency group becomes worse.

The BSC performs underlay-overlay handovers autonomously according to the list of preferred frequency groups within one target cell. The underlay-overlay handover is always an intra-BSC handover.

g The BSC may perform underlay-overlay handovers between frequency groups within the serving cell although intra-cell handovers caused by conventional radio criteria are disabled. Nevertheless, the parameter enable intracell handover interference UL (EIC) indicates if an intra-cell handover within the frequency group caused by uplink interference is enabled.

Underlay-overlay assignmentDuring the call setup phase, the BSC may assign a TCH on a super-reuse TRX for the call when the regular TRX is congested (the call is handed over from a SDCCH to a TCH on a super-reuse TRX). The parameter enable TCH assignment super IUO (ETA) indicates whether the BSC may allocate a TCH for a call from a super-reuse TRX when the regular TRX is congested.

22 DN9814144Issue 11-1


Id:0900d8058058fc85


g Directed Retry is essential for the underlay-overlay assignment procedure. If Directed Retry is not employed, the second attempt is not allowed and thus the underlay-overlay assignment is not possible. For more information, see:

• Directed Retry to super-reuse TRX in section Technical description of Intelligent Underlay-Overlay

• Directed Retry in BSC

The BSC performs the underlay-overlay assignment as a handover procedure. Both the principle and the stages of the handover decision algorithm for the underlay-overlay assignment are exactly the same as for the underlay-overlay handover. The possible types of underlay-overlay assignment are the following:

• intra-cell handover from a SDCCH to a super-reuse TRX • inter-cell handover from a SDCCH to a child cell

The BSC monitors the downlink C/I ratio on the super-reuse frequencies during the call setup phase. The BSC monitors every super-reuse frequency group of the serving cell and those child cells that are adjacent to the serving cell. When the regular TRX is con-gested, the BSC performs the handover from a SDCCH to a super-reuse TRX if the C/I ratio of the super-reuse TRX is greater than or equal to a specified HO threshold.

If there are appropriate super-reuse frequency groups both in the serving cell and in the child cell, the handover algorithm prefers the super-reuse frequency groups of the child cell to those of the serving cell. If there are several super-reuse frequency groups in the target (serving or child) cell that meet the requirements for the C/I ratio, the BSC ranks the groups according to the load and the radio link properties of the super-reuse fre-quency groups.

The underlay-overlay assignment is always an intra-BSC procedure.

g The alternative priorities of the intra-cell and inter-cell handover have no effect on the underlay-overlay assignment procedure.

Direct access procedureThe BSC allocates a TCH for the handover attempt in question according to the list of preferred super-reuse frequency groups within one target cell. The list is composed of a maximum of 16 super-reuse TRXs of the specified super-reuse frequency groups.

The basic procedure is that the traffic control between regular and super-reuse frequen-cies is based on the downlink C/I ratio. This means that a call is handed over to a super-reuse TRX when the downlink C/I ratio of the super-reuse TRX is good enough to sustain a good radio link.

However, the BSC may ignore the C/I evaluation procedure when the downlink signal level of the super-reuse TRX exceeds a certain predetermined threshold. In this case the high downlink signal level (the carrier is well above the worst expected interference level) ensures that the downlink C/I ratio of the super-reuse TRX is good enough, and the BSC may perform a handover to the super-reuse TRX without the C/I evaluation (direct access procedure).

The signal level which the downlink signal of the super-reuse TRX must exceed for the direct access to the super-reuse TRX (frequency group) to become possible is con-trolled on a transceiver-by-transceiver basis with the parameter direct access level (DAL).

The direct access procedure can be applied during the call setup phase and in an inter-cell handover attempt to a regular cell. The BSC performs the direct access to a super-

DN9814144Issue 11-1

23


Id:0900d8058058fc85

reuse TRX as a handover procedure. The possible types of the direct access are the following:

• intra-cell handover (direct access) from a SDCCH to a super-reuse TRX • inter-cell handover (direct access) from a regular/child cell to a super-reuse TRX of

a regular/parent cell

If there are no free traffic channels available on super-reuse TRXs, the BSC allocates a TCH for the call or for the inter-cell handover attempt from a regular TRX.

The direct access procedure is always an intra-BSC procedure.

3.2 RF power control strategyIntelligent Underlay-Overlay has two requirements for the RF power control strategy: BTS power reduction due to good signal level and due to good signal quality. For more information, see RF Power Control and Handover Algorithm.

On the super-reuse layer, the BTS power reduction is allowed only if the new C/I ratio remains over the threshold super reuse good C/I threshold with the new RX level. The C/I ratio must be over the super reuse good C/I threshold to prevent handover to a regular layer due to bad signal quality.

When the BTS power is reduced because of good signal level or good signal quality, and the current TRX is in the super-reuse layer, interference caused by interfering cells must be taken into account. Before the power reduction, the power control and handover algo-rithm calculates a new downlink signal level, that is RXLEV_DL – PWR_DECR_STEP.

RXLEV_DL is the size of the current downlink signal level measured by the MS.

BTS power reduction is allowed in the super-reuse TRX(k), if the following equation is true:

SuperReuseGoodCiThreshold < New estimated downlink signal level — MAX( ( AV_RXLEV_INTF1(k) + LEV_ADJ_INTF1(k) ) ,( AV_RXLEV_INTF2(k) + LEV_ADJ_INTF2(k) ) ,( AV_RXLEV_INTF3(k) + LEV_ADJ_INTF3(k) ) ... ,( AV_RXLEV_INTFn(k) + LEV_ADJ_INTFn(k) ))

The comparison between the threshold super reuse good C/I threshold and the new estimated C/I ratio is made the same way in the average-based C/I method and the maximum-based C/I method.

If the value of the new estimated downlink signal level would be too low in the super-reuse layer, the BTS power is decreased to the value that maintains C/I ratio above the value which the parameter super reuse good C/I threshold defines. In that case, the BTS power step size is calculated as follows:

PWR_DECR_STEP = RXLEV_DL — ( SuperReuseGoodCiThreshold + 1 + MAX( ( AV_RXLEV_INTF1(k) + LEV_ADJ_INTF1(k) ) ,( AV_RXLEV_INTF2(k) + LEV_ADJ_INTF2(k) ) ,( AV_RXLEV_INTF3(k) + LEV_ADJ_INTF3(k) ) ... ,( AV_RXLEV_INTFn(k) + LEV_ADJ_INTFn(k) )) )

24 DN9814144Issue 11-1


Id:0900d8058058fc85


g The RF power control strategy works the same way if the system-level application software Adaptive Multi Rate (AMR) speech codec is activated.

• The parameter super reuse good C/I threshold AMR FR is used instead of super reuse good C/I threshold for the FR AMR set and the param-eter super reuse good C/I threshold AMR HR for the HR AMR set.

• The current Nx and Px values of super reuse good C/I threshold are used.

• The threshold values for HR AMR also serve the basic HR. The parameter super reuse good C/I threshold serves the basic FR.

3.3 Processing of radio link measurementsIntelligent Underlay-Overlay does not have any special requirements for the following basic averaging procedures:

• weighted averaging of quality and level • averaging of distance • bookkeeping and averaging of the signal level (RXLEV) of the adjacent cell

For more information, see RF Power Control and Handover Algorithm.

The BSC uses a special averaging procedure for the bookkeeping and averaging of the RXLEV of the interfering cell to produce a reliable interference level estimate for the C/I evaluation procedure.

New averaged values are calculated for the C/I evaluation procedure whenever the BSC receives measurement results from the BTS. The BSC receives measurement results either in every SACCH multiframe or in every second, third, or fourth SACCH multiframe if preprocessing is used in the BTS. You can control the preprocessing in the BTS on a cell-by-cell basis with the parameter BTS measure average (BMA).

Bookkeeping and averaging of RXLEV of interfering cellYou can define at most 10 interfering cells for a super-reuse TRX or for a super-reuse frequency group. The BSC is able to maintain a table of up to 32 interfering cells per each call and store the levels as they arrive. The BSC is able to monitor several super-reuse TRXs simultaneously.

When a super-reuse frequency group consists of two or more super-reuse TRXs:

• an interfering cell that has been defined for one super-reuse TRX is associated with all super-reuse TRXs which belong to the same super-reuse frequency group

• it is not possible to define more than 10 different interfering cells for the super-reuse TRXs which belong to the same super-reuse frequency group.

g The interfering cells must be adjacent to the serving cell, otherwise the mobile station is not able to measure and report the signal levels of the interfering cells. For more information, see Radio Network Configuration Management.

The MS is able to report the measurement results of the six strongest neighbouring cells it receives best. The interfering cells are often weaker than the six strongest neighbour-ing cells. Because of this and the possibility of a base station identity code (BSIC) decoding failure, the RXLEV of the interfering cell may be available intermittently.

When the RXLEV of the interfering cell is missing from the measurement sample, the actions vary depending on whether the RXLEV is regarded as a directly-measured inter-ference level or as a reference value that is used for calculating an interference level

DN9814144Issue 11-1

25


Id:0900d8058058fc85

estimate (parameter C/I estimation type 1-10 (T1-T10), which is set for each interfering cell).

1. RXLEV regarded as directly-measured interference level:When the MS reports the measurement results of the six neighbouring cells (the six positions in the measurement sample are fully occupied), the weakest RXLEV of the six reported cells is entered as the measurement value for the interfering cell if it is missing from the measurement sample.When the MS reports the measurement results of less than six neighbouring cells (the six positions in the measurement sample are not fully occupied), a zero is entered as the measurement value for the interfering cell if it is missing from the measurement sample.

2. RXLEV regarded as reference value used for calculating an interference level esti-mate:For those cells of which the measurement values are used for calculating an inter-ference level estimate and are missing from the measurement sample, a zero is entered as the measurement value.

To diminish the distortion of the results of the averaging procedure caused by the zero values among the measurement results, the parameter interfering cell number of zero results (ZERO) indicates how many (maximum) zero values the BSC can ignore over the averaging interval.

The parameter all interfering cells averaged (AVER) indicates whether the measurement results are averaged either for every interfering cell of the TRX or only for those interfering cells that are among the six best neighbouring cells as measured in the latest sample.

The parameter interfering cell averaging window size (SIZE) defines the size of the averaging window on a cell-by-cell basis. The sliding window technique takes into account a maximum of 32 most recent measurement samples. The averaging pro-cedure can start as soon as the BSC receives the first measurement result from the BTS.

g When selecting the appropriate averaging window size, consider whether prepro-cessing is used in the BTS or not. Otherwise it is possible that the averaging window size accidentally becomes much longer than expected.

Example: The parameter interfering cell averaging window size (SIZE) has the value 8 and the parameter interfering cell number of zero results

MEASUREMENT RESULT AVERAGED RESULT

RXLEV_INTF1(k) AV_RXLEV_INTF1(k)



... ...

RXLEV_INTFn(k) AV_RXLEV_INTFn(k)

Table 1 Correspondence between the measurement results of the interfering cells of the TRX (k) and the averaged results.

26 DN9814144Issue 11-1


Id:0900d8058058fc85


(ZERO) has the value 2, and the BSC has received eight measurement results from the interfering cell at SACCH multiframe i:

AV_RXLEV_INTF3(k) = 1/8 (RXLEV_INTF3(k)(i) +RXLEV_INTF3(k)(i-1) +...+ RXLEV_INTF3(k)(i-7))

If the result i-1 was zero, the effective averaging window size would be 7:

AV_RXLEV_INTF3(k) = 1/7 (RXLEV_INTF3(k)(i) + 0 +RXLEV_INTF3(k)(i-2) +...+ RXLEV_INTF3(k)(i-7))

Example: interfering cell averaging window size (SIZE) is 8 and interfering cell number of zero results (ZERO) is 7, and the BSC has received one mea-surement result (RxLev 40) from the interfering cell. all interfering cells averaged (AVER) is 'yes' and C/I estimation type 1-10 (T1-T10) of the interfering cell is 'estimate'.

In this case the average is

40/(interfering cell averaging window size - interfering cell number of zero results)= 40/(8 - 7) = 40.

Example: interfering cell averaging window size (SIZE) is 8 and interfering cell number of zero results (ZERO) is 7, and the BSC has received one mea-surement result (RxLev 40) from the interfering cell. all interfering cells averaged (AVER) is 'no' and C/I estimation type 1-10 (T1–T10) of the inter-fering cell is 'estimate'.

If the most recent measurement sample includes the RXLEV of the interfering cell, the average is 40/(8 - 7) = 40. If the most recent measurement sample does not include the RXLEV of the interfering cell, a zero is entered as the average value for the interfering cell that is missing from the measurement sample.

Example: all interfering cells averaged (AVER) is 'yes' and C/I estimation type 1-10 (T1–T10) of the interfering cell is 'estimate'. interfering cell averaging window size (SIZE) is 8 and interfering cell number of zero results (ZERO) is 7, and the BSC has received five measurement results (RxLev 40, 42, 39, 40 and 43) from the interfering cell (thus there are 3 measurement results missing and they are fewer than the interfering cell number of zero results; the number of missing results is subtracted from the interfering cell averaging window size).

In this case the average is (40 + 42 + 39 + 40 + 43)/(8 - 3) = 41.

Example: all interfering cells averaged (AVER) is 'yes' and C/I estimation type 1-10 (T1–T10) of the interfering cell is 'estimate'. interfering cell averaging window size (SIZE) is 12 and interfering cell number of zero results (ZERO) is 5, and the BSC has received three measurement results (RxLev 40, 42, and 43) from the interfering cell (thus there are 9 measurement results missing, and that is more than the interfering cell number of zero results; the interfering cell number of zero results value is subtracted from the interfering cell averaging window size.)

DN9814144Issue 11-1

27


Id:0900d8058058fc85

In this case the average is (40 + 42 + 43)/(12 - 5) = 17.

Example: all interfering cells averaged (AVER) is 'yes' and C/I estimation type 1-10 (T1–T10) of the interfering cell is 'measured'. interfering cell averaging window size (SIZE) is 8 and interfering cell number of zero results (ZERO) is 7, and the BSC has received five measurement results (RxLev 40, 42, 39, 40, and 43) from the interfering cell.

In those cases in which the signal level of the interfering cell was missing from the mea-surement sample (3 times), the MS reported signal levels of six neighbouring cells two times and signal levels of five neighbouring cells one time. When the MS reported the measurement results of the six neighbouring cells, the weakest RXLEV of the six reported cells was 36 (entered as the measurement value for the interfering cell when it is missing from the measurement sample).

In this case the average is (40 + 42 + 39 + 40 + 36 + 43 + 36)/(8 - 1) = 39.

Example: all interfering cells averaged (AVER) is 'no' and C/I estimation type 1-10 (T1–T10) of the interfering cell is 'measured'. interfering cell averaging window size (SIZE) is 8 and interfering cell number of zero results (ZERO) is 7, and the BSC has received five measurement results (RxLev 40, 42, 39, 40, and 43) from the interfering cell.

In those cases in which the signal level of the interfering cell was missing from the mea-surement sample (three times), the MS reported signal levels of six neighbouring cells two times and signal levels of five neighbouring cells one time. When the MS reported the measurement results of the six neighbouring cells, the weakest RXLEV of the six reported cells was 36 (entered as the measurement value for the interfering cell when it is missing from the measurement sample).

If the most recent measurement sample includes the RXLEV of the interfering cell, the average is (40 + 42 + 39 + 40 + 43 + 36)/(8 -1 ) = 39. If the most recent measurement sample does not include the RXLEV of the interfering cell, a zero (equals the interfer-ence level -110dBm) is entered as the average value for the interfering cell that is missing from the measurement sample.

Variable averaging window sizeThe variable averaging window size functionality affects the averaging of the RXLEV of the interfering cell in the following way:

• If the MS is considered a slow-moving MS or the MS speed cannot be determined, the BSC uses the normal values of the averaging parameters interfering cell averaging window size (SIZE) and interfering cell number of zero results (ZERO).

• If the MS is considered a fast-moving MS, the BSC uses the scaled values of the averaging parameters interfering cell averaging window size and interfering cell number of zero results.

For more information on the variable averaging window size functionality, see RF Power Control and Handover Algorithm.

The parameter MS speed detection state (SDS) indicates how much the values of the averaging parameters are scaled down if the mobile station is considered a fast-

28 DN9814144Issue 11-1


Id:0900d8058058fc85


moving MS. The range is from 1% to 100% and the scaling of the averaging parameters is disabled when the value is zero.

For example, when the parameter MS speed detection state has the value 80% and the parameter interfering cell averaging window size has the value 10, the scaled averaging window size is 8 (80 * 10/100 = 8).

3.4 C/I evaluationWhen the intelligent underlay-overlay procedure is employed with the parameter super reuse estimation method (METH) set for each cell, the BSC calculates the downlink C/I ratio on super-reuse TRXs whenever it receives measurement results from the BTS. For more information, see RF Power Control and Handover Algorithm.

The BSC receives measurement results after every SACCH multiframe or, if prepro-cessing is used in the BTS, every second, third, or fourth SACCH multiframe.

The C/I evaluation concerns every super-reuse TRX of the serving cell and those child cells that are adjacent to the serving (parent or child) cell.

The BSC calculates the downlink C/I ratio of the super-reuse TRX from the following pro-cessed measurement results (averages):

• downlink RXLEV of the serving cell • downlink RXLEV of the interfering cells • downlink RXLEV of the adjacent cell

The following parameters control the C/I evaluation procedure:

• super reuse estimation method (METH)

• level adjustment 1-10 (L1-L10)

• C/I estimation weight 1-10 (W1-W10)

• C/I estimation type 1-10 (T1-T10)

By comparing the downlink RXLEV of the super-reuse TRX and the downlink interfer-ence level, the BSC can calculate the C/I ratio of the super-reuse TRX.

RXLEV of super-reuse TRXIt is possible to allocate a super-reuse TRX to a regular cell or a child cell.

1. Super-reuse TRX of a regular cell:The average downlink RXLEV of the super-reuse TRX AV_RXLEV_TRX(k) is cal-culated as follows:

AV_RXLEV_TRX(k) = AV_RXLEV_DL_HO + (BsTxPwrMax - BS_TXPWR)AV_RXLEV_DL_HO is the average downlink RXLEV of the serving cell. BS TX pwr max-BS_TXPWR is the difference between the maximum downlink RF power per-mitted in the serving cell (parameter BS TX pwr max) and the actual downlink power (BS_TXPWR) determined by the BTS power control.BsTxPwrMax = BS TX pwr max if the serving cell is GSM 900 or GSM 800.BsTxPwrMax = BS TX pwr max1x00 if the serving cell is GSM 1800 or GSM 1900.

2. Super-reuse TRX of a child cell when the child cell is adjacent to the serving cell:The average downlink RXLEV of the super-reuse TRX AV_RXLEV_TRX(k) equals the average downlink RXLEV of the child (adjacent) cell AV_RXLEV_NCELL(n).

3. Super-reuse TRX of a child cell when the child cell is the serving cell:The average downlink RXLEV of the super-reuse TRX AV_RXLEV_TRX(k) is cal-culated as follows:

DN9814144Issue 11-1

29


Id:0900d8058058fc85

AV_RXLEV_TRX(k) = AV_RXLEV_DL_HO + (BsTxPwrMax - BS_TXPWR)BsTxPwrMax = BS TX pwr max if the serving cell is GSM 900 or GSM 800. BsTxPwrMax = BS TX pwr max1x00 if the serving cell is GSM 1800 or GSM 1900.

RXLEV of interfering cellThe parameter C/I estimation type 1-10 (T1–T10) indicates whether the signal level of the interfering cell is regarded as a directly-measured interference level or as a reference value that is used for calculating an interference level estimate (the interfering cell is actually a reference cell).

If the averaging procedure has only been done for those interfering cells that are among the best six neighbouring cells according to the latest measurement sample (parameter all interfering cells averaged (AVER)), a zero (equals the interference level -110dBm) is used as the interference level for those interfering cells that are missing from the measurement sample.

• Directly-measured interference levelThe most common situation is that the interfering cell is a regular cell that is adjacent to the serving cell and has the same set of super-reuse frequencies as the serving cell, and the location of the interfering cell is also close enough to cause interfer-ence. In this situation, the downlink RXLEV of the interfering cell corresponds directly to the interference level on the super-reuse TRX caused by the interfering cell.

• Estimated interference levelIf the call is on a super-reuse TRX (BCCH frequency) of the child cell or the child cell is a handover candidate, and the potential source of interference is another child cell with the same super-reuse frequency (also a BCCH frequency), the MSS are unable to measure and report the corresponding interference level because of the same BCCH frequencies. In this case the BSC can only estimate the interference level caused by the other child cell.When the RF signal profile of a regular adjacent cell is similar to the interference profile within the coverage area of the serving cell, the regular adjacent cell may be defined as the interfering cell (reference cell) instead of the true source of interfer-ence. The RF signal profile is considered the same as the interference profile when the ratio between the RF signal level and the interference level (for example 6 dB) remains relatively unchanged within the service area of the serving cell. The param-eter level adjustment 1-10 (L1-L10) represents the ratio set for each inter-fering/reference cell.A super-reuse TRX may have several reference cells to increase the reliability of the estimation. The estimated downlink interference level AV_RXLEV_ESTM(k) and the downlink C/I ratio of the super-reuse TRX are calculated by using similar evaluation methods.

C/I calculation methodsThe handover algorithm uses two alternative methods to calculate the downlink C/I ratio of the super-reuse TRX or the estimated downlink interference level:

• average-based C/I method • maximum-based C/I method

The parameter super reuse estimation method (METH) defines the C/I estima-tion method on a cell-by-cell basis.

30 DN9814144Issue 11-1


Id:0900d8058058fc85


• Average-based C/I methodThe average-based C/I method calculates the estimated downlink interference level AV_RXLEV_ESTM(k) as follows. Only the RXLEVs of the reference cells are taken into account:AV_RXLEV_ESTM(k) =(W1(k) * ( AV_RXLEV_INTF1(k) + LEV_ADJ_INTF1(k) )+ W2(k) * ( AV_RXLEV_INTF2(k) + LEV_ADJ_INTF2(k) )+ W3(k) * ( AV_RXLEV_INTF3(k) + LEV_ADJ_INTF3(k) )+ ... Wn(k) * ( AV_RXLEV_INTFn(k) + LEV_ADJ_INTFn(k) ))/ ( W1(k) + W2(k) + W3(k) + ... + Wn(k) )The average-based C/I method calculates the downlink C/I ratio CI_RATIO(k) of a super-reuse TRX (k) as follows. Only the RXLEVs of the interfering cells are taken into account; instead of the RXLEVs of the reference cells, the estimated downlink interference level AV_RXLEV_ESTM(k) is used:

CI_RATIO(k) =(W1(k)*(AV_RXLEV_TRX(k)-AV_RXLEV_INTF1(k)-LEV_ADJ_INTF1(k))+ W2(k)*(AV_RXLEV_TRX(k)-AV_RXLEV_INTF2(k)-LEV_ADJ_INTF2(k))+ W3(k)*(AV_RXLEV_TRX(k)-AV_RXLEV_INTF3(k)-LEV_ADJ_INTF3(k))+ ... Wn(k)*(AV_RXLEV_TRX(k)-AV_RXLEV_INTFn(k)-LEV_ADJ_INTFn(k))+ 5 *(AV_RXLEV_TRX(k)-AV_RXLEV_ESTM(k) ))/ ( W1(k) + W2(k) + W3(k) + ... + Wn(k) + 5 )

LEV_ADJ_INTFx(k) is the adjustment parameter level adjustment 1-10 (L1-L10) of the interfering/reference cell and Wx(k) is the weighting coefficient of the interfering/reference cell. Parameter C/I estimation weight 1-10 (W1-W10) is set for each interfering cell.

• Maximum-based C/I methodThe maximum-based C/I method calculates the estimated downlink interference level AV_RXLEV_ESTM(k) as follows. Only the RXLEVs of the reference cells are taken into account:

AV_RXLEV_ESTM(k) =MAX(( AV_RXLEV_INTF1(k) + LEV_ADJ_INTF1(k) ) ,( AV_RXLEV_INTF2(k) + LEV_ADJ_INTF2(k) ) ,( AV_RXLEV_INTF3(k) + LEV_ADJ_INTF3(k) ) ... ,( AV_RXLEV_INTFn(k) + LEV_ADJ_INTFn(k) ))

The maximum-based C/I method calculates the downlink C/I ratio CI_RATIO(k) of a super-reuse TRX(k) as follows. Only the RXLEVs of the interfering cells are taken into account; instead of the RXLEVs of the reference cells, the estimated downlink interference level AV_RXLEV_ESTM(k) is used:

CI_RATIO(k) =MIN((AV_RXLEV_TRX(k)-AV_RXLEV_INTF1(k)-LEV_ADJ_INTF1(k)) ,(AV_RXLEV_TRX(k)-AV_RXLEV_INTF2(k)-LEV_ADJ_INTF2(k)) ,(AV_RXLEV_TRX(k)-AV_RXLEV_INTF3(k)-LEV_ADJ_INTF3(k)) ... ,(AV_RXLEV_TRX(k)-AV_RXLEV_INTFn(k)-LEV_ADJ_INTFn(k)) ,(AV_RXLEV_TRX(k)-AV_RXLEV_ESTM(k)))

The principle of this method is exactly the same as in the average-based C/I method except that the maximum-based C/I method takes into account the worst C/I ratio and the maximum interference instead of the weighted average.

DN9814144Issue 11-1

31


Id:0900d8058058fc85

3.5 Threshold comparisonRF power controlIntelligent Underlay-Overlay does not have any special requirements for the power control threshold comparison.

HandoverIntelligent Underlay-Overlay introduces two special HO thresholds in addition to the basic HO thresholds.

• super reuse good C/I threshold

• super reuse bad C/I threshold

For more information, see RF Power Control and Handover Algorithm.

g The threshold comparison works the same way if the system-level application software Adaptive Multi Rate (AMR) speech codec is activated.

• The parameter super reuse good C/I threshold AMR FR is used instead of super reuse good C/I threshold for the FR AMR set and super reuse good C/I threshold AMR HR for the HR AMR set.

• The parameter super reuse bad C/I threshold AMR FR is used instead of super reuse good C/I threshold for the FR AMR set and super reuse bad C/I threshold AMR HR for the HR AMR set.

• Current Nx and Px values of super reuse good C/I threshold and super reuse bad C/I threshold are used.

• The threshold values for HR AMR also serve the basic HR. The parameter super reuse good C/I threshold and the parameter super reuse bad C/I threshold serve the basic FR.

Both handover (HO) thresholds have three parts:

• the threshold itself (CiRatio) • the total number of comparisons (Nx) to be taken into account before a decision is

possible and • the number of comparisons out of total comparisons (Px) where the downlink C/I

ratio must be lower/greater than or equal to the threshold before actions are possi-ble.

The BSC compares the downlink C/I ratio of specified super-reuse TRXs with a specified HO threshold whenever it receives measurement results from the BTS. The BSC receives measurement results from the BTS after every SACCH multiframe period or, if preprocessing is used in the BTS, every second, third, or fourth SACCH multiframe.

When the call is on a regular TRX, the BSC performs the threshold comparison of good downlink C/I ratio (HO threshold super reuse good C/I threshold). The thresh-old comparison of good downlink C/I ratio concerns every super-reuse TRX of the serving cell and those child cells that are adjacent to the serving cell.

If the call has been handed over to a super-reuse TRX, the BSC performs both the threshold comparison of bad downlink C/I ratio (HO threshold super reuse bad C/I threshold) and the threshold comparison of good downlink C/I ratio (HO threshold super reuse good C/I threshold). The threshold comparison of bad downlink C/I ratio concerns only the super-reuse TRX itself, whereas the threshold comparison of good downlink C/I ratio concerns every super-reuse frequency group of the serving cell,

32 DN9814144Issue 11-1


Id:0900d8058058fc85


except the serving frequency group, and those child cells which are adjacent to the serving (parent or child) cell.

The direct access procedure does not have any special requirements for the HO thresh-old comparison.

The threshold comparison and the actions to be taken are the following:

1. Comparison of CI_RATIO(k) with super reuse good C/I threshold when the call is on a regular TRXThe following basic HO thresholds affect this comparison: • threshold qual downlink Rx qual

• threshold qual uplink Rx qual

• MS distance threshold param ms max range.If at least in Px comparisons out of Nx comparisons the downlink C/I ratio of the super-reuse TRX CI_RATIO(k) is greater than or equal to the threshold CiRatio and if the signal quality on the regular TRX or the MS-BS distance has not reached the relevant HO threshold, a handover (cause: good C/I ratio) from a regular TRX to a super-reuse TRX (k) can be performed.When the comparison of signal quality and MS-BS distance are associated directly with the threshold comparison of good downlink C/I ratio, the comparison of signal quality and MS-BS distance only includes the checking of the latest averaged values. Px and Nx factors are not taken into consideration.In this case the BSC checks the MS-BS distance regardless of whether a handover caused by the MS-BS distance is enabled or not.

2. Comparison of CI_RATIO(k) with super reuse good C/I threshold when the call is on a super-reuse TRX:The following basic HO threshold affects this comparison: MS distance threshold param ms max rangeIf at least in Px comparisons out of Nx comparisons the downlink C/I ratio of the super-reuse TRX CI_RATIO(k) is greater than or equal to the threshold CiRatio and if the MS-BS distance has not reached the relevant HO threshold, a handover (cause: good C/I ratio) between super-reuse frequency groups can be performed.When the comparison of MS-BS distance is associated directly with the threshold comparison of good downlink C/I ratio, the comparison of MS-BS distance only includes the checking of the latest averaged values. Px and Nx factors are not taken into consideration.In this case the BSC checks the MS-BS distance regardless of whether a handover caused by the MS-BS distance is enabled or not.

3. Comparison of CI_RATIO(k) with super reuse bad C/I threshold:The following basic HO threshold affects this comparison: MS distance threshold param ms max range, Px, NxIf at least in Px comparisons out of Nx comparisons the downlink C/I ratio of the super-reuse TRX CI_RATIO(k) is lower than or equal to the threshold CiRatio or if the MS-BS distance has reached the relevant HO threshold, a handover (cause: bad C/I ratio) from a super-reuse TRX (k) to a regular TRX is required.g The MS-BS distance may initiate the underlay-overlay handover from a super-

reuse TRX to a regular TRX only if it is not employed as a criterion in the imper-

DN9814144Issue 11-1

33


Id:0900d8058058fc85

ative handover or in the call release (parameter enable ms distance process (EMS)).

When the comparison of MS-BS distance is associated directly with the threshold comparison of bad downlink C/I ratio, the comparison of MS-BS distance takes into consideration both the threshold MSRangeMax and the Pxand Nx factors.

Handover priorityIf two or more criteria for a handover are present simultaneously, the priority order is the following:

For a regular TRX:

1. HO: Interference (uplink or downlink)2. HO: Uplink quality3. HO: Downlink quality4. HO: Uplink level5. HO: Downlink level6. HO: MS-BS distance7. HO: Turn-around-corner MS8. HO: Rapid field drop9. HO: Fast/Slow-moving MS10. HO: Better cell (PBGT or Umbrella)11. HO: Good C/I ratio12. PC: lower signal quality thresholds (uplink and downlink)13. PC: lower signal level thresholds (uplink and downlink)14. PC: upper signal quality thresholds (uplink and downlink)15. PC: upper signal level thresholds (uplink and downlink)

For a super-reuse TRX:

1. HO: Better cell (PBGT)2. HO: Downlink interference3. HO: Downlink quality4. HO: Bad C/I ratio5. HO: Uplink interference6. HO: Uplink quality7. HO: Uplink level8. HO: Downlink level9. HO: MS-BS distance10. HO: Turn-around-corner MS11. HO: Rapid field drop12. HO: Fast/Slow-moving MS13. HO: Better cell (Umbrella)14. PC: lower signal quality thresholds (uplink and downlink)15. PC: lower signal level thresholds (uplink and downlink)16. PC: upper signal quality thresholds (uplink and downlink)17. PC: upper signal level thresholds (uplink and downlink)

34 DN9814144Issue 11-1


Id:0900d8058058fc85


3.6 Handover decision algorithm Underlay-overlay handover to a super-reuse TRXThe relevant types of the underlay-overlay handover are the following:

• intra-cell handover from a regular TRX to a super-reuse TRX • inter-cell handover from a parent cell to a child cell

The BSC recognises the possibility of making the underlay-overlay handover when the HO threshold comparison indicates that a handover because of good C/I ratio can be made from a regular TRX to a specified super-reuse TRX (frequency group) of the serv-ing/child cell. In other words, the following conditions are fulfilled:

1. Downlink C/I ratio of the super-reuse TRX is good enough to sustain a good radio link.

2. Both uplink and downlink signal quality on the regular TRX is good.3. MS-BS distance has not reached the HO threshold.

The BSC considers a super-reuse frequency group as the target of the handover although it performs the C/I evaluation procedure and the HO threshold comparison for the C/I ratio on a transceiver-by-transceiver basis.

• Intra-cell handover from a regular TRX to a super-reuse TRXThe BSC performs an intra-cell handover from a regular TRX to a super-reuse TRX of the serving cell if no child cell is good enough for the handover.If there are several super-reuse frequency groups (TRXs) in the serving cell that meet the requirements for the C/I ratio simultaneously, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.If there are appropriate super-reuse frequency groups both in the serving cell and in the child cell, the BSC prefers the child cell to the super-reuse frequency groups of the serving cell. In other words, the BSC performs an inter-cell handover to the child cell instead of an intra-cell handover.

• Inter-cell handover from a parent cell to a child cellIn order for the handover to the child cell to become possible, the child (adjacent) cell must also satisfy the following requirements for the radio link properties:1. AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) where Pa = ( MsTxPwrMaxCell(n) - P )2. PBGT(n) > HoMarginPBGT(n)RxLevMinCell(n) is the level which the signal level AV_RXLEV_NCELL(n) in the child (adjacent) cell (n) must exceed before the handover is possible.MsTxPwrMaxCell(n)-P is the difference between the maximum RF power that an MS is permitted to use on a traffic channel in the child cell (n) and the maximum power of the MS (P).MsTxPwrMaxCell(n) = MsTxPwrMaxGSM(ADJ)(n) if the adjacent cell is GSM 900 or GSM 800.MsTxPwrMaxCell(n) = MsTxPwrMaxGSM1x00(ADJ)(n) if the adjacent cell is GSM 1800 or GSM 1900.HoMarginPBGT(n) is the margin which the power budget PBGT(n) of the child cell (n) must exceed before the handover is possible.If the child cell is a low layer cell, the handover algorithm verifies the radio link prop-erties of the child cell with the following equation (1') instead of the equation (1) and the PBGT equation (2):

1'. AV_RXLEV_NCELL(n) > HoLevelUmbrella(n)

DN9814144Issue 11-1

35


Id:0900d8058058fc85

For more information on the child cell as low layer cell, see Handover due to fast/slow-moving MS in RF Power Control and Handover Algorithm.HoLevelUmbrella(n) is the level which the signal level in the low layer child cell (n) must exceed. In addition, the MS must be considered as a slow-moving MS in order for the underlay-overlay handover to a low layer child cell to become possible.If there are appropriate super-reuse frequency groups in many child cells, the BSC ranks the child cells according to priority levels and the load of the child cells, and selects the best child cell to be the target cell. Signal strength conditions have an effect only between cells that have the same priority level.If there are several super-reuse frequency groups (TRXs) in the target (child) cell that meet the requirements for the C/I ratio simultaneously, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.

• Time allowed for BSIC decodingThe parameter minimum BSIC decode time (TIM) determines the period starting from call set-up or handover (inter-cell or intra-cell) during which the C/I evaluation is considered unreliable and the handover to a super-reuse TRX is not allowed. The BSC, however, performs the averaging, C/I evaluation and HO thresh-old comparison procedures normally during this period. This period allows the mobile station to decode the BSIC of the interfering (adjacent) cells before the HO decision.

Underlay-overlay handover from a super-reuse TRXThe relevant types of the underlay-overlay handover are the following:

• intra-cell handover from a super-reuse TRX to a regular TRX • intra-cell handover within a super-reuse frequency group • inter-cell handover from a child cell to a parent cell • intra-cell handover between super-reuse frequency groups • inter-cell handover between super-reuse frequency groups

The BSC recognises the need to make an underlay-overlay handover from or within the serving super-reuse frequency group when the HO threshold comparison indicates that some of the following criteria for a handover are present:

1. downlink quality/interference2. uplink interference3. bad C/I ratio4. MS-BS distance has reached the HO threshold

g The MS-BS distance may initiate an underlay-overlay handover from a super-reuse TRX to a regular TRX only if it is not employed as a criterion in the imper-ative handover or in the call release (parameter enable ms distance process (EMS)). A handover between super-reuse frequency groups is not possible when the cause of the handover attempt is MS-BS distance.

• Order of preference of handover typesThe order of preference of the possible types of handover is related to the cause of the handover attempt as follows. The cause of the handover is downlink qual-ity/interference:1. Handover from a super-reuse TRX to a regular TRX2. Handover between super-reuse frequency groups:

The handover is enabled with the parameter enable inter FRT handover (EFHO)

36 DN9814144Issue 11-1


Id:0900d8058058fc85


3. Imperative handover to a regular cellThe cause of the handover is uplink interference:1. Handover within a super-reuse frequency group:

The handover is enabled with the parameter enable intracell handover interference UL (EIC)

2. Handover from a super-reuse TRX to a regular TRX3. Handover between super-reuse frequency groups:

The handover is enabled with the parameter enable inter FRT handover (EFHO)

4. Imperative handover to a regular cellThe cause of the handover is bad C/I ratio:It is possible to determine which handover is preferable when the C/I ratio on the serving super-reuse frequency group becomes worse: • handover between super-reuse frequency groups, or • handover to a regular frequency groupThe parameter enable inter FRT handover determines the priority order of the handover types. The parameter also indicates if a handover between super-reuse frequency groups is enabled.The cause of the handover is MS-BS distance: handover from a super-reuse TRX to a regular TRX.If it is not possible to perform a handover back to a regular frequency group or if a handover to a regular frequency group is not preferable in case of a bad C/I ratio, the BSC can perform a handover from a serving super-reuse frequency group to another super-reuse frequency group.If the handover between super-reuse frequency groups is disabled, there are no such super-reuse frequency groups available whose C/I ratio is good enough, or the handover is not allowed as a result of a handover failure or bad quality experience, the BSC can perform an imperative (inter-cell) handover to a regular cell to maintain the call.

• Intra-cell handover from a super-reuse TRX to a regular TRXThe BSC always performs an intra-cell handover from a super-reuse TRX to a regular TRX of the serving cell when it is required and when it is possible.The BSC may perform a handover from the serving super-reuse frequency group to another super-reuse frequency group if: • the intra-cell handover back to a regular TRX is not possible due to TCH con-

gestion or it is not allowed as a result of a handover failure (see Interval between handovers and handover attempts)

• or if a handover to a regular frequency group is not preferable in case of a bad C/I ratio.

• Inter-cell handover from a child cell to a parent cellAn inter-cell handover from a super-reuse TRX of the child cell to a regular TRX of the parent cell is considered imperative and it is sufficient for the parent cell to satisfy the following equation (1):1. AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) where Pa = ( MsTxPwrMaxCell(n) - P )

DN9814144Issue 11-1

37


Id:0900d8058058fc85

RxLevMinCell(n) is the level which the signal level AV_RXLEV_NCELL(n) in the parent (adjacent) cell (n) must exceed before the handover is possible.MsTxPwrMaxCell(n)-P is the difference between the maximum RF power that an MS is permitted to use on a traffic channel in the parent cell (n) and the maximum power of the MS (P).MsTxPwrMaxCell(n) = MsTxPwrMaxGSM(ADJ)(n) if the adjacent cell is GSM 900 or GSM 800.MsTxPwrMaxCell(n) = MsTxPwrMaxGSM1x00(ADJ)(n) if the adjacent cell is GSM 1800 or GSM 1900.If there are several parent cells available that meet the requirements for the signal level simultaneously, the BSC selects the parent cell that has the best signal strength condition to be the target cell.The BSC performs a handover from the child cell to the parent cell autonomously. If there are no parent cells available within the BSC and a handover between super-reuse frequency groups is not possible, the BSC initiates an inter-BSC handover caused by the conventional radio criteria to maintain the call.

• Intra-cell handover within a super-reuse frequency groupThe parameter enable intracell handover interference UL indicates if an intra-cell handover within a super-reuse frequency group caused by uplink inter-ference is enabled. When the handover is enabled, the BSC always performs an intra-cell handover within a super-reuse frequency group when it is required.The BSC performs a handover from a super-reuse TRX to a regular TRX if • the intra-cell handover within a super-reuse frequency group is not possible due

to TCH congestion or it is not allowed as a result of a handover failure or a bad quality experience (see Interval between handovers and handover attempts)

• or if the handover is not enabled • Intra-cell handover between super-reuse frequency groups

In order for the handover to another super-reuse frequency group of the serving cell to become possible, the HO threshold comparison must indicate that a handover whose cause is good C/I ratio can be made to the super-reuse frequency group in question.If there are several super-reuse frequency groups (TRXs) in the serving cell that simultaneously meet the requirements for the C/I ratio, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.If there are appropriate super-reuse frequency groups both in the serving cell and in the child cell, the handover algorithm prefers the super-reuse frequency groups of the child cell to those of the serving cell. In other words, the BSC performs an inter-cell handover to the child cell instead of an intra-cell handover.

• Inter-cell handover between super-reuse frequency groupsIn order for the handover to a super-reuse frequency group of the child cell to become possible, the HO threshold comparison must indicate that a handover whose cause is good C/I ratio can be done to the super-reuse frequency group in question.In order for the handover to the child cell to become possible, the child (adjacent) cell must also satisfy the following requirements for the radio link properties:1. AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) where Pa = ( MsTxPwrMaxCell(n) - P )2. PBGT(n) > HoMarginPBGT(n)

38 DN9814144Issue 11-1


Id:0900d8058058fc85


RxLevMinCell(n) is the level which the signal level AV_RXLEV_NCELL(n) in the child (adjacent) cell (n) must exceed before the handover is possible.MsTxPwrMaxCell(n)-P is the difference between the maximum RF power that an MS is permitted to use on a traffic channel in the child cell (n) and the maximum power of the MS (P).MsTxPwrMaxCell(n) = MsTxPwrMaxGSM(ADJ)(n) if the adjacent cell is GSM 900 or GSM 800.MsTxPwrMaxCell(n) = MsTxPwrMaxGSM1x00(ADJ)(n) if the adjacent cell is GSM 1800 or GSM 1900.HoMarginPBGT(n) is the margin which the power budget PBGT(n) of the child cell (n) must exceed before the handover is possible.If the child cell is a low layer cell , the handover algorithm verifies the radio link prop-erties of the child cell with the following equation (1') instead of the equation (1) and the PBGT equation (2):

1'. AV_RXLEV_NCELL(n) > HoLevelUmbrella(n)For more information on child cell as low layer cell, see section Handover due to fast/slow-moving MS in RF Power Control and Handover Algorithm.HoLevelUmbrella(n) is the level which the signal level in the low layer child cell (n) must exceed. In addition, the MS must be considered as a slow-moving MS in order for the underlay-overlay handover to a low layer child cell to become possible.If there are appropriate super-reuse frequency groups in many child cells, the BSC ranks the child cells according to priority levels and the load of the child cells, and selects the best child cell to be the target cell. Signal strength conditions have an effect only between child cells that have the same priority level.If there are several super-reuse frequency groups (TRXs) in the target (child) cell that meet the requirements for the C/I ratio simultaneously, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.g It is possible to perform the handover between super-reuse frequency groups

from a parent cell to a child cell or from a child cell to another child cell but it is not possible to perform the handover from a child cell to a super-reuse frequency group of a parent cell.

Handover from SDCCH to super-reuse TRXDuring the call setup phase, a TCH on a super-reuse TRX may be assigned for the call when the regular TRX is congested. This means that the call is handed over from a stand alone dedicated control channel (SDCCH) to a TCH on a super-reuse TRX. The parameter enable TCH assignment super IUO (ETA) indicates if the BSC may allocate a TCH for a call from a super-reuse TRX when the regular TRX is congested.

g Directed Retry is essential for the handover from a SDCCH to a super-reuse TRX. If the directed retry procedure is not employed, the second attempt is not allowed and thus the handover from a SDCCH to a super-reuse TRX is not possible. For more information, see:

• Directed Retry to super-reuse TRX in section Technical description of Intelligent Underlay-Overlay

• Directed Retry in BSC

The BSC performs the underlay-overlay assignment procedure as a handover proce-dure. The possible types of underlay-overlay assignment are the following:

• intra-cell HO from a SDCCH to a super-reuse TRX • inter-cell HO from a SDCCH to a child cell

DN9814144Issue 11-1

39


Id:0900d8058058fc85

The BSC recognises the possibility to make the underlay-overlay assignment when the HO threshold comparison indicates that a handover whose cause is good C/I ratio can be performed from a SDCCH to a specified super-reuse TRX (frequency group) of the serving/child cell. In other words, the following conditions are fulfilled:

1. Downlink C/I ratio of the super-reuse TRX is good enough to sustain a good radio link.

2. Both uplink and downlink signal quality on the regular TRX is good.3. MS-BS distance has not reached the HO threshold.

The BSC considers a super-reuse frequency group as the target of the handover although it performs the C/I evaluation procedure and the HO threshold comparison for the C/I ratio on a transceiver-by-transceiver basis.

• Intra-cell HO from a SDCCH to a super-reuse TRXThe BSC performs an intra-cell handover from a SDCCH to a super-reuse TRX of the serving cell if no child cell is good enough for the handover.If there are several super-reuse frequency groups (TRXs) in the serving cell that simultaneously meet the requirements for the C/I ratio, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.If there are appropriate super-reuse frequency groups both in the serving cell and in the child cell, the BSC prefers the child cell to the super-reuse frequency groups of the serving cell. In other words, the BSC performs an inter-cell handover to the child cell instead of an intra-cell handover.

• Inter-cell HO from a SDCCH to a child cellIn order for the handover to the child cell to become possible, the child (adjacent) cell must also satisfy the following requirements for the radio link properties.1. AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) where Pa = ( MsTxPwrMaxCell(n) - P )2. PBGT(n) > HoMarginPBGT(n)RxLevMinCell(n) is the level which the signal level AV_RXLEV_NCELL(n) in the child (adjacent) cell (n) must exceed before the handover is possible.MsTxPwrMaxCell(n)-P is the difference between the maximum RF power that an MS is permitted to use on a traffic channel in the child cell (n) and the maximum power of the MS (P).MsTxPwrMaxCell(n) = MsTxPwrMaxGSM(ADJ)(n) if the adjacent cell is GSM 900 or GSM 800.MsTxPwrMaxCell(n) = MsTxPwrMaxGSM1x00(ADJ)(n) if the adjacent cell is GSM 1800 or GSM 1900.HoMarginPBGT(n) is the margin which the power budget PBGT(n) of the child cell (n) must exceed before the handover is possible.If the child cell is a low layer cell, the handover algorithm verifies the radio link prop-erties of the child cell with the following equation (1') instead of the equation (1) and the PBGT equation (2):

1'. AV_RXLEV_NCELL(n) > HoLevelUmbrella(n)For more information on child cell as low layer cell, see Handover due to fast/slow-moving MS in RF Power Control and Handover Algorithm.HoLevelUmbrella(n) is the level which the signal level in the low layer child cell (n) must exceed. In addition, the MS must be considered as a slow-moving MS in

40 DN9814144Issue 11-1


Id:0900d8058058fc85


order for the underlay-overlay assignment to a low layer child cell to become possi-ble.If there are appropriate super-reuse frequency groups in many child cells, the BSC ranks the child cells according to priority levels and the load of the child cells, and selects the best child cell to be the target cell. Signal strength conditions have an effect only between cells that have the same priority level.If there are several super-reuse frequency groups (TRXs) in the target (child) cell that meet the requirements for the C/I ratio simultaneously, the handover algorithm ranks the super-reuse frequency groups according to the C/I ratios.

• Time allowed for BSIC decodingThe parameter enable TCH assignment super IUO determines the period starting from call set-up during which the C/I evaluation is considered unreliable and the handover from a stand alone dedicated control channel (SDCCH) to a super-reuse TRX is not allowed. However, the BSC normally performs the averaging, C/I evaluation and HO threshold comparison procedures during this period. This period allows the mobile station to decode the BSIC of the interfering (adjacent) cells before the HO decision.

Direct access to a super-reuse TRXThe direct access procedure can be applied during the call setup phase and in an inter-cell handover attempt to a regular cell. The BSC performs the direct access to a super-reuse TRX as a handover procedure. The possible types of direct access are the follow-ing:

• intra-cell direct access to a super-reuse TRXDuring the call setup phase, a TCH on a specified super-reuse TRX (frequency group) can be assigned for the call when the following radio link conditions are ful-filled:1. Downlink signal level of the serving cell is high enough to ensure a good radio

link on the super-reuse TRX (frequency group):RXLEV_DL > direct access level(k)RXLEV_DL is the downlink signal level of the serving cell. The parameter direct access level(k) is the signal level which the downlink signal on the super-reuse TRX (k) must exceed before the direct access to the super-reuse TRX (k) is possible.

2. Both uplink and downlink signal quality on the stand alone dedicated control channel (SDCCH) is good.

3. The MS-BS distance has not reached the HO threshold.The radio link conditions are verified during the initial signalling period of call set-up after the BSC has received the first valid downlink measurement report from the MS via the BTS (the measurement results are not averaged).If the value of the parameter direct access level (DAL) varies between the TRXs of the super-reuse frequency group, the BSC selects the highest value for the equation. If the value of the parameter varies between the frequency groups, the handover algorithm ranks the groups according to the value of the parameter. In other words, the frequency group which has the highest value for the parameter, has the highest priority.g If there are appropriate super-reuse frequency groups both in the serving cell

and in the child cell, the BSC prefers the child cell to the super-reuse frequency groups of the serving cell. In other words, the BSC allocates a TCH for a call from the child cell.

DN9814144Issue 11-1

41


Id:0900d8058058fc85

• inter-cell direct access to a regular cellThe BSC may allocate a TCH on a super-reuse TRX for an inter-cell handover attempt to a regular cell if the parameter super reuse estimation method (METH) is set on for the target cell and when the cause of the handover attempt is either: • turn-around-corner MS • fast/slow-moving MS or • better cell (PBGT or Umbrella)First, the handover algorithm defines and selects those cells that meet the relevant requirements for the radio link properties (for example, the PBGT equation). Second, the handover algorithm ranks the cells according to the priority levels and the load of the neighbouring cells as usual.The BSC may perform the direct access only to the super-reuse TRX of the best target cell. The handover algorithm examines if there are any super-reuse TRXs (frequency groups) in the best target cell that can be assigned for the handover attempt. The BSC may allocate a TCH on a super-reuse TRX for an inter-cell handover attempt to a regular cell when the following conditions are fulfilled:1. Downlink signal level of the best target cell is high enough to ensure a good radio

link on the super-reuse TRX (frequency group):AV_RXLEV_NCELL(n) > direct access level(k)AV_RXLEV_NCELL(n) is the averaged downlink signal level of the target (adja-cent) cell (n). The parameter direct access level(k) is the level which the downlink signal level on the super-reuse TRX (k) must exceed before the direct access to the super-reuse TRX (k) of the target cell (n) is possible.

2. Both uplink and downlink signal quality in the serving cell is good.If there are several super-reuse frequency groups (TRXs) in the best target cell that meet the requirements for the downlink signal level, the handover algorithm ranks the groups according to the value of the parameter direct access level. Note that the value of the parameter direct access level may vary between the fre-quency groups: the frequency group which has the highest value for the parameter, has the highest priority.The inter-cell direct access to a regular cell is not possible when: • there are no super-reuse TRXs in the best target cell • direct access to the best target cell is disabled • downlink signal level is not high enough • direct access is not allowed as a result of either a handover failure or a direct

access failure or • there are no TCHs available on the appropriate super-reuse TRXsIf the direct access procedure is not possible, the BSC initiates a normal inter-cell handover attempt according to the list of the preferred target cells.

Interval between handovers and handover attemptsThe BSC normally controls the intervals between handovers and handover attempts with the following two timers:

1. To prevent repetitive handovers for the same MS, there is a timer for the minimum interval between handovers related to the same connection (parameter min int between HO req (MIH)).

2. If a handover attempt fails for some reason, for example, if there are no free channels available, there is a timer for the minimum interval between an unsuccess-

42 DN9814144Issue 11-1


Id:0900d8058058fc85


ful handover attempt and the following handover attempt related to the same con-nection (parameter min int between unsucc HO attempt (MIU)).

The averaging and HO threshold comparison do not stop during these intervals although handovers are not possible. The timer for the minimum interval between handovers concerns all types of handover attempts (see the following Note). The timer for the minimum interval between an unsuccessful handover attempt and the following handover attempt can also concern all types of handover attempts, or only specified cells or specified frequency groups.

g The timer for the minimum interval between handovers is not applied if the call has been handed over to a super-reuse TRX, or if the call has been handed over from a super-reuse TRX to a regular TRX within a cell.

The BSC also determines extra guard timers for specified frequency groups (TRXs) as a result of handover failures, direct access failures and bad quality experience. The extra guard timers are controlled with the following two parameters:

1. The parameter min interval between unsucc IUO HO (MIO) determines the minimum interval between an unsuccessful (reversion to old channel) handover attempt to a super-reuse TRX (frequency group) and the following handover attempt to the super-reuse frequency group in question.

2. The parameter min interval between IUO HO req BQ (MIR) determines the period during which a handover to one specified super-reuse frequency group is not allowed because of bad quality experience on the super-reuse frequency group in question.

The guard timers that have been determined for specified super-reuse frequency groups as a result of handover failures or bad quality experience are also involved in the direct access procedure.

When the BSC performs an underlay-overlay handover or an intra-cell handover within the serving cell, the BSC maintains all timers that have been determined as a result of

• handover failures • direct access failures or • bad quality experience

When a call is handed over from the serving cell to a regular cell, the BSC maintains all timers that have been determined for a super-reuse frequency group as a result of handover failure (excluding fails due to TCH congestion) or bad quality experience. In this case the BSC resets timers which concern regular cells and regular frequency groups, and timers which have been determined as a result of direct access failures.

• Timers related to handover failures:1. Unsuccessful intra-cell handover attempt from a regular TRX to a super-reuse

TRXREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts is not applied.To prevent repetitive unsuccessful intra-cell handover attempts to the same super-reuse frequency group, there is a guard time during which a handover is not allowed to the super-reuse frequency group that was the target of the unsuc-cessful handover attempt. The guard timer concerns only intra-cell handover attempts from a regular TRX to this super-reuse frequency group. The duration of the guard time depends on the number of handover failures related to the

DN9814144Issue 11-1

43


Id:0900d8058058fc85

same super-reuse frequency group during the same connection. The guard time is determined as follows:

GUARD_TIME =NUMBER_OF_HO_FAIL * MinIntUnsuccIuoHo

NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only intra-cell handover attempts from a regular TRX to this super-reuse frequency group.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

2. Unsuccessful intra-cell handover attempt from a super-reuse TRX to a regular TRXREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts concerns only intra-cell handover attempts from a super-reuse TRX to a regular frequency group.NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only intra-cell handover attempts from a super-reuse TRX to a regular frequency group.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

3. Unsuccessful intra-cell handover attempt within a super-reuse frequency groupREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts is not applied.To prevent repetitive unsuccessful intra-cell handover attempts within the same super-reuse frequency group, there is a guard time during which a handover is not allowed within a super-reuse frequency group. The guard timer concerns only intra-cell handover attempts within the super-reuse frequency group in question. The guard time is determined as follows:

GUARD_TIME = MinIntUnsuccIuoHoNO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only intra-cell handover attempts within a super-reuse frequency group.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

4. Unsuccessful inter-cell handover attempt from a parent cell to a child cellREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts is not applied.To prevent repetitive unsuccessful inter-cell handover attempts to the same super-reuse frequency group of the child cell, there is a guard time during which a handover is not allowed to the super-reuse frequency group that was the target of the unsuccessful handover attempt. The guard timer concerns only handover attempts from a regular TRX to the super-reuse frequency group in question. The duration of the guard time depends on the number of handover failures related to the same super-reuse frequency group during the same connection. The guard time is determined as follows:

44 DN9814144Issue 11-1


Id:0900d8058058fc85



NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only inter-cell handover attempts from a parent cell to the super-reuse frequency group of the child cell that was the target of the unsuccessful handover attempt.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

5. Unsuccessful inter-cell handover attempt from a child cell to a parent cellREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts concerns only inter-cell handover attempts from a child cell to the parent cell that was the target of the unsuccessful handover attempt.NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only inter-cell handover attempts from a child cell to the parent cell that was the target of the unsuccessful handover attempt.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

6. Unsuccessful intra-cell handover attempt between super-reuse frequency groupsREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts is not applied.To prevent repetitive unsuccessful handover attempts to the same super-reuse frequency group, there is a guard time during which a handover is not allowed to the super-reuse frequency group that was the target of the unsuccessful handover attempt. The guard timer concerns only handover attempts to this super-reuse frequency group. The duration of the guard time depends on the number of handover failures related to the same super-reuse frequency group during the same connection. The guard time is determined as follows:


NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only handover attempts to this super-reuse frequency group.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

7. Unsuccessful inter-cell handover attempt from a super-reuse TRX of a parent cell to a child cellREVERSION TO OLD CHANNEL:The timer for the minimum interval between handover attempts is not applied.To prevent repetitive unsuccessful handover attempts to the same super-reuse frequency group of the child cell, there is a guard time during which a handover is not allowed to the super-reuse frequency group that was the target of the unsuccessful handover attempt. The guard timer concerns only handover attempts to the super-reuse frequency group in question. The duration of the guard time depends on the number of handover failures related to the same

DN9814144Issue 11-1

45


Id:0900d8058058fc85

super-reuse frequency group during the same connection. The guard time is determined as follows:


NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts concerns only handover attempts to the super-reuse frequency group of the child cell that was the target of the unsuccessful handover attempt.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns all types of handover attempts.

• Timers related to direct access failures:Unsuccessful inter-cell direct access attempt to a regular cell:REVERSION TO OLD CHANNEL:To prevent repetitive unsuccessful direct access attempts to the same super-reuse frequency group of the target cell, there is a guard time (fixed 255 seconds) during which a direct access is not allowed from the serving cell to the super-reuse fre-quency group that was the target of the unsuccessful direct access attempt. The guard timer concerns only direct access attempts to the super-reuse frequency group in question.NO RADIO RESOURCE AVAILABLE:The timer for the minimum interval between handover attempts is not applied. The BSC initiates a normal inter-cell handover attempt immediately after the unsuccess-ful direct access attempt.OTHER FAILURE CASES:The timer for the minimum interval between handover attempts concerns both all types of handover attempts and direct access attempts.

• Timers related to bad quality experience on a source cell sideIn addition to (or instead of) the timer for the minimum interval between handovers, the BSC may determine an extra guard timer for a specified cell or super-reuse fre-quency group:1. Inter-cell handover from a child cell to a regular/parent cell due to the following

reasons: downlink quality, downlink interference.Underlay-overlay handover back to the super-reuse frequency group of the child cell is not allowed during a guard time which is determined as follows:

GUARD_TIME =( 1 + MAX(0,Qa) ) * MinIntIuoHoReqBQwhere Qa = RXQUAL_DL - HoThresholdsQualDL

RXQUAL_DL is the signal quality band on the child cell just before the handover to a regular cell. HoThresholdsQualDL indicates the quality band which corresponds to the quality threshold for the handover. The range of the quality band varies from 0 to 7, where 0 indicates the best quality and 7 indicates the worst quality. For more information, see RF Power Control and Handover Algorithm.

2. Intra-cell handover from a super-reuse TRX to a regular frequency group due to the following reasons: downlink quality, downlink interference.Underlay-overlay handover back to this super-reuse frequency group is not allowed during a guard time which is determined as follows:

46 DN9814144Issue 11-1


Id:0900d8058058fc85



RXQUAL_DL is the signal quality band on the super-reuse TRX just before the handover to a regular TRX. The parameter threshold qual downlink Rx qual indicates the quality band which corresponds to the quality threshold for the handover. The range of the quality band varies from 0 to 7, where 0 indicates the best quality and 7 indicates the worst quality.

3. Intra-cell handover within a super-reuse frequency group.Underlay-overlay handover within this super-reuse frequency group is not allowed during a guard time which is determined as follows:

GUARD_TIME = MinIntIuoHoReqBQ

4. Intra-cell or inter-cell handover from a super-reuse frequency group to another super-reuse frequency group due to the following reasons: downlink quality, downlink interference.Underlay-overlay handover back to the original super-reuse frequency group is not allowed during a guard time which is determined as follows:


RXQUAL_DL is the signal quality band on the super-reuse TRX just before the handover to another super-reuse frequency group. The parameter threshold qual downlink Rx qual indicates the quality band which corresponds to the quality threshold for the handover. The range of the quality band varies from 0 to 7 where 0 indicates the best quality and 7 indicates the worst quality.


DN9814144Issue 11-1

47

Intelligent Underlay-Overlay Radio resource allocation and Intelligent Underlay-Overlay

Id:0900d8058058fc88

4 Radio resource allocation and Intelligent Underlay-OverlayRadio channel allocation searches and allocates available radio environment resources according to the requirements included in the resource requests. For more information, see Radio Channel Allocation.

Traffic channel allocation in callThe radio resource management may allocate a traffic channel (TCH) for a call from a regular TRX only (see the following Note). If no TCHs are available on regular TRXs when requested or in the case of queueing after the queueing timer has expired, the radio resource management rejects the TCH request because of lack of resources although there may be free TCHs available on super-reuse TRXs.

If no TCHs are available on regular TRXs when requested, the BSC may allow the MS to make a second attempt at gaining access in parallel with queueing. See Directed retry to super-reuse TRX in section Technical description of Intelligent Underlay-Overlay. In this case the following handovers are possible:

• inter-cell handover from a SDCCH of the serving cell to a TCH on a regular TRX of an adjacent (regular) cell. See section TCH allocation in inter-cell and intra-cell handover to regular TRX.

• intra/inter-cell handover from a SDCCH of the serving cell to a TCH on a super-reuse TRX of a serving/child cell. See section TCH allocation in inter-cell and intra-cell handover to super-reuse TRX.

g The BSC performs the direct access from a SDCCH to a TCH on a super-reuse TRX as a handover procedure. For more information, see section TCH allocation in inter-cell and intra-cell handover to super-reuse TRX .

TCH allocation in inter-cell and intra-cell handover attempt to a regular TRXA handover attempt to a regular TRX can be either

• an intra-BSC (inter-cell or intra-cell) handover, or • an inter-BSC handover.

The call can be handed over to the regular TRX of the target cell either from a regular TRX or from a super-reuse TRX of another cell (regular or child cell), or an intra-cell handover can take place either from a super-reuse TRX to a regular TRX or within a regular frequency group. The following handovers are possible:

• intra-cell handover within a regular frequency group • intra-cell handover from a super-reuse TRX to a regular TRX • inter-cell handover from a regular cell to another regular cell • inter-cell handover from a child cell to a regular cell • inter-cell handover from a child cell to a parent cell

Radio resource management may allocate a TCH for the handover attempt in question from a regular TRX only. If no TCHs are available on regular TRXs when requested or in the case of queueing after the queueing timer has expired, the radio resource man-agement rejects the TCH request because of lack of resources although there may be free TCHs available on super-reuse TRXs.

48 DN9814144Issue 11-1


Id:0900d8058058fc88

Radio resource allocation and Intelligent Underlay-Overlay

TCH allocation in inter-cell and intra-cell handover to a super-reuse TRXA handover attempt to a super-reuse TRX is always an intra-BSC handover (intra-cell or inter-cell). The handover candidate can be either a super-reuse TRX of the regular cell or a super-reuse TRX of the child cell. The possible types of handover are the fol-lowing:

• intra-cell handover from a regular TRX to a super-reuse TRX • intra-cell handover within a super-reuse frequency group • inter-cell handover from a parent cell to a child cell • intra-cell handover between super-reuse frequency groups • inter-cell handover between super-reuse frequency groups • intra-cell handover from a SDCCH to a super-reuse TRX • inter-cell handover from a SDCCH to a child cell • intra-cell direct access from a SDCCH to a super-reuse TRX • inter-cell direct access from a regular/child cell to a super-reuse TRX of a regu-

lar/parent cell

The radio resource management allocates a TCH for the handover attempt in question according to the list of preferred super-reuse frequency groups within one target cell. The list is composed of a maximum of 16 super-reuse TRXs of the specified super-reuse frequency groups.

The TCH is allocated primarily from the super-reuse frequency group that has the highest number of unallocated TCHs whose interference level is either within or lower than the recommended interference band. For more information, see Channel allocation criteria based on the minimum acceptable C/N ratio in RF Power Control and Handover Algorithm.

If there are no TCHs available in the specified super-reuse frequency groups of which the interference level is either within or lower than the recommended interference band, the radio resource management rejects the TCH request.

If there are two (or more) specified super-reuse frequency groups that have the same number of unallocated TCHs of which the interference level is acceptable, the TCH is allocated from that frequency group that has priority over the other frequency groups according to the list of preferred super-reuse frequency groups.

In an intra-cell handover within the super-reuse frequency group, the radio resource management allocates the TCH primarily from a new TRX and secondly from the serving TRX.

If the uplink interference level of the unallocated TCH on a super-reuse TRX cannot be determined, the BSC uses the highest possible interference level as a default value. The default value is applied after the TCH is released until the BSC receives the real measured interference level from the BTS.

Related topicsFor interworking information, see section Technical description of Intelligent Underlay-Overlay.


DN9814144Issue 11-1

49

Intelligent Underlay-Overlay User interface of Intelligent Underlay-Overlay

Id:0900d8058058fc8b

5 User interface of Intelligent Underlay-Overlay

5.1 Parameters and MMLsThe parameters are stored in BSS Radio Network Configuration Database (BSDATA). You can control the parameters by using the BSC MMI or the network service and man-agement system, Nokia NetAct.

For more information on the use of the parameters, see

• Technical description of Intelligent Underlay-Overlay • Functionality of Intelligent Underlay-Overlay

For parameter descriptions, see BSS Radio Network Parameter Dictionary.

Handover control parametersThe handover control parameters are controlled on a cell-by-cell basis.

The parameters can be handled with the Handover Control Parameter Handling MML commands (EH).

• super reuse estimation method (METH)

• super reuse good C/I threshold (GCI)

• super reuse good C/I threshold AMR FR (GCIF) • super reuse good C/I threshold AMR HR (GCIH) • super reuse bad C/I threshold (BCI)

• super reuse bad C/I threshold AMR FR (BCIF)

• super reuse bad C/I threshold AMR HR (BCIH)

• interfering cell averaging window size (SIZE) • interfering cell number of zero results (ZERO) • all interfering cells averaged (AVER)

• minimum BSIC decode time (TIM)

• enable TCH assignment super IUO (ETA)

• enable inter FRT handover (EFHO)

• min int between HO req (MIH)

• min int between unsucc HO attempt (MIU)

• min interval between unsucc IUO HO (MIO)

• min interval between IUO HO req BQ (MIR)

• enable intracell handover interference UL (EIC)

• enable ms distance process (EMS)

Transceiver parametersThe transceiver parameters are controlled on a transceiver-by-transceiver basis. The parameters can be handled with the Transceiver Handling MML commands (ER).

• TRX frequency type (FRT)

g When both regular and super-reuse frequency layers are hopping, the TRX frequency type modification from a regular to a super-reuse frequency hopping TRX or vice versa is recommended to be done with a BTS which is in the locked state. This is required to eliminate possible MAIO inconsistency.

50 DN9814144Issue 11-1


Id:0900d8058058fc8b

User interface of Intelligent Underlay-Overlay

• direct access level (DAL)It is possible to define 10 interfering cells for every transceiver and the following parameters for each of the 10 interfering cells (see the following Note).

• cell identification of interfering cell 1-10 (CI1-CI10)

• level adjustment 1-10 (L1-L10)

• C/I estimation weight 1-10 (W1-W10)

• C/I estimation type 1-10 (T1-T10)

g When a super-reuse frequency group consists of two or more super-reuse TRXs:

• An interfering cell which has been defined for one super-reuse TRX, is associ-ated with all super-reuse TRXs which belong to the same super-reuse frequency group.

• It is not possible to define more than 10 different interfering cells for the super-reuse TRXs which belong to the same super-reuse frequency group.

Base transceiver station parametersThe base transceiver station parameters are controlled on a cell-by-cell basis. The parameters can be handled with the Base Transceiver Station Handling in BSC MML commands (EQ).

• cell barred (BAR)

• directed retry used (DR)

• min time limit directed retry (MIDR)

• max time limit directed retry (MADR)

UTPFIL parametersThe UTPFIL parameters are stored in the Unit-type-associated Parameter File (UTPFIL) of the BCSU unit.

The UTPFIL file is empty when it is taken to the BSC. You can change the UTPFIL parameter default values by adding the data into the UTPFIL file of the unit in question.

A record of the UTPFIL consists of the identifier of the parameter (double word) and the parameter value (double word). The records of the UTPFIL file are filled from the first free record onwards with the local MMI on the BSC site.

The parameter DualBandMSSuperReuseUsage indicates whether the super-reuse TRXs of the serving/child cell are barred from the dual band MSS when the serving cell has adjacent cells from another frequency band. The alternative values are the follow-ing:

0 No effect on IUO, default value.

1 Super-reused TRXs are barred from the dual band MSS if the frequency band of the serving cell is GSM 900.

2 Super-reused TRXs are barred from the dual band MSS if the frequency band of the serving cell is GSM 1800 or GSM 1900.

3 Super-reused TRXs are barred from the dual band MSS regardless of the frequency of the serving cell.

4 Super-reused TRXs are barred from the dual band MSS if the frequency band of the serving cell is GSM 800.

The identifier of the parameter is 06601B3H (hexadecimal).

DN9814144Issue 11-1

51


Id:0900d8058058fc8b

5.2 StatisticsUnderlay-overlay statisticsIntelligent Underlay-Overlay introduces a measurement type Underlay-Overlay Statis-tics.

For more information on the counters, see 52 Underlay-Overlay Statistics Measure-ment.

Intelligent Underlay-Overlay also has special requirements for the following measure-ments and observations.

Traffic measurementIn the traffic measurement, an intra-cell direct access to a super-reuse TRX is handled as a traffic channel (TCH) request for a call attempt, whereas an inter-cell direct access to a regular cell is handled as a TCH request for a handover attempt. An underlay-overlay assignment is also handled as a TCH request for a handover attempt.

For more information on the counters, see 1 Traffic Measurement.

Resource availability measurements per BSS cellThe measurement does not handle super-reuse TRXs differently from regular TRXs within the BSS cell, for example, the TCH congestion time does not start until both regular and super-reuse TRXs are occupied.

Handover measurementHandover measurement counters that are related only to Intelligent Underlay-Overlay belong to the Intra-cell handover and Handover cause counter classes. The other handover measurement counters (BSC controlled incoming/outgoing handovers) are incremented both due to conventional handovers and underlay-overlay handovers.

g In the handover measurement, an intra-cell direct access is considered an intra-cell SDCCH-TCH handover. When the BSC performs an inter-cell direct access from a regular/child cell to a super-reuse TRX of a regular/parent cell, the statistics are updated on the basis of the original cause of the handover, for example, power budget (PBGT). An underlay-overlay assignment from SDCCH to a super-reuse TRX is considered (Handover cause) a directed retry procedure.

For more information on the counters, see 4 Handover Measurement.

RX quality statistics (optional)The RX quality statistics measurement collects statistics of the performance of the underlay-overlay procedure by measuring traffic intensity (erlang) and signal quality in different frequency groups.

The measurement includes the identifications of the frequency groups which the TRXs belong to. A TRX belongs either to a regular frequency group (regular TRX) or to one of the sixteen super-reuse frequency groups (super-reuse TRX).

g Statistics on frequency groups are collected from TRXs which belong to the fre-quency group in question.

For more information on the counters, see 14 RX Quality Statistics Measurement.

52 DN9814144Issue 11-1


Id:0900d8058058fc8b

User interface of Intelligent Underlay-Overlay

RX level statistics (optional)The RX level statistics measurement collects statistics of the performance of the underlay-overlay procedure by measuring traffic intensity (erlang) and the relationship between signal quality and signal level in different frequency groups.

The measurement includes the identifications of the frequency groups which the TRXs belong to. A TRX belongs to either a regular frequency group (regular TRX) or to one of the sixteen super-reuse frequency groups (super-reuse TRX).


For more information on the counters, see 53 RX Level Statistics Measurement.

C/I ratio statistics (optional)For information on the counters, see 60 C/I Ratio Measurement.

Power control measurementThe power control measurement collects statistics of the performance of the RF power control. Statistics are compiled in counters reserved for each TRX.

The power control measurement measures the interference level of unallocated TCHs in different frequency groups.

The measurement includes the identifications of the frequency groups which the TRXs belong to. A TRX either belongs to a regular frequency group (regular TRX) or to one of the sixteen super-reuse frequency groups (super-reuse TRX).


For more information on the counters, see 5 Power Control Measurement.

BSC level clear code (PM) measurementThe counters of BSC level clear code (PM) measurement that are related to Intelligent Underlay-Overlay belong to the handover counter class.

For more information on the counters, see 51 BSC Level Clear Code (PM) Measure-ment.

Handover observationThe following special values for handover causes (BSC internal cause) are introduced with Intelligent Underlay-Overlay:

1. good C/I ratio on super-reuse frequency2. bad C/I ratio on super-reuse frequency3. direct access procedure

The handover observation report also includes the type of underlay-overlay handover, assignment and direct access attempts. The possible handovers are:

• intra-cell handover from a regular TRX to a super-reuse TRX • intra-cell handover from a super-reuse TRX to a regular TRX • intra-cell handover within a super-reuse frequency group • inter-cell handover from a parent cell to a child cell • inter-cell handover from a child cell to a parent cell • intra-cell handover between super-reuse frequency groups

DN9814144Issue 11-1

53


Id:0900d8058058fc8b

• inter-cell handover between super-reuse frequency groups • intra-cell handover from a SDCCH to a super-reuse TRX • inter-cell handover from a SDCCH to a child cell • intra-cell direct access to a super-reuse TRX • inter-cell direct access to a regular cell

g When the BSC performs an inter-cell handover (direct access) from a regular/child cell to a super-reuse TRX of a regular/parent cell, the original cause of the handover (for example, power budget) is used as the BSC internal handover cause.

g Observation reports do not include the identification of the frequency group to which the TRX belongs.

For more information on the counters, see 18 Handover Observation.


dn9814144_iuo

Documents