rf cellular planning

1 7/18/2014 RF CELLULAR

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Handoff - a basic mobile network capability for dynamic support of terminal migration• Handoff Management - the process of initiating and ensuring a seamless and lossless handoff of a mobile terminal from the region covered by one base station to another base station



  • **GSM RF Cellular ConceptContents:

    Handover HCS Dual Band NetworkPower Control

  • **1. Handover

  • **Handover (HO) Handover (HO): Kemampuan dasar suatu network untuk mendukung secara dinamis perpindahan dari MS.

    Managemen HO: Proses HO suatu MS dari awal dan terkontrol secara konsisten dan tanpa kerugian dari area yg dicover satu BTS ke BTS lain.

  • **Basic Handover (HO) Measurements Secara UL and DL dan neighbor BTSs

    Decision Kapan dan dimana MS akan HO

    Execution Transfer Traffic dan control ke BTS lain.

  • **Location (HO)

    NetworkMSMeasurementEvaluasi HOEvaluasi HODecisionInisiasi HOInisiasi HOExecution

  • **Basic HO Process in Single Layer Networks Measurement acquisition/reportingPre-processing, exampleIdle channel measurementsHO initiation due to radio criteriapriorities, static / dynamic rankingrelationship between parametersIntercell HOHO Prevention Algorithmsprevention of Back-HO due to PBGT prevention of HO failure repetitionlimitation of Intracell HO repetitionTarget Cell List generation/ranking criteria

  • **Why is HO necessary? Mengatur suatu progress call ketika MS meninggalkan suatu coverage area dan masuk ke coverage area dari neighbor cell.

    Network Managemen Efisiensi:high quality of servicemaximum capacityhigh spectrum efficiency

  • **Basic Handover Process Overview

  • **Handover Types

  • **Measurement Reporting

  • **Idle Channel Measurements (ICM)

  • **Handover Initiation Criteria Overview

  • **Basic Handover Initiation Criteria

    handover criterion

    handover class

    handover type

    evaluated on

    Extended Cell Handover




    Quality Intercell Handover




    RXLEV Handover




    Distance Handover




    Power Budget Handover




    Quality Intracell Handover




    Forced Handover




  • **Basic Handover Initiation Criteria

    Handover CauseInitiation CriteriaIntercell HO due to Quality1. RXQUAL_XX > L_RXQUAL_XX_H 2. RXLEV_XX < L_RXLEV_XX_IH 3. XX_TXPWR = Min ( XX_TXPWR_MAX, P )HO due to Level1. RXLEV_XX < L_RXLEV_XX_H 2. XX_TXPWR = Min ( XX_TXPWR_MAX, P )HO due to Distance1. MS_BS_DIST > MS_RANGE_MAXHO due to Power Budget1. RXLEV_NCELL(n) > RXLEV_MIN(n) + Max ( 0, MS_TXPWR_MAX(n) - P ) 2. PBGT(n) > HO_MARGIN(n)Intracell HO due to Quality1. RXQUAL_XX > L_RXQUAL_XX_H 2. RXLEV_XX > L_RXLEV_XX_IH

  • **Imperative HO Defined by Level and Quality Thresholds

  • **Relations between HO Level Thresholds

  • **Cell Border Design by Handover Thresholds

  • **Conditions for TCL Generation in Single Layer Networks

    HandoverConditions for neighbor cells to enter the Target Cell List (TCL) ClassImperative HORXLEV_NCELL(n) > RXLEVMIN(n) + max (0, Pa)Forced HORXLEV_NCELL(n) > RXLEVMIN(n) + max (0, Pa) + FHORLMO(n)Power Budget HORXLEV_NCELL(n) > RXLEVMIN(n) + max (0, Pa)andBCV(n) = PBGT(n) HO_MARGIN(n) > 0

  • **Handover Prevention Algorithms Prevention of Back-HO due to Power Budget to the old (Original) cell in case of: imperative HO out of the original cell forced HO (Directed Retry) out of the original cell After specific number of consecutive unsuccessful HOs

    After specific number of consecutive successful HOs

  • **Prevention of Back-HO due to Power BudgetBack-HO prevention is triggered by the BSC by including the old (original) cell (e.g. cell A) and the previous HO-cause (e.g. quality, forced ...) in the Channel Activation message sent to cell B: A timer is started in the BTS of the new cell (cell B) Until the timer for the original cell (A) expires: the evaluation of the HO condition due to Power Budget to cell (A) is suspended this cell (A) is excluded from the target cell list in case of a HO request due to Power Budget to other cells

  • **Intra-cell HO evaluationNot performed at assignment and otherwise only performed if intra cell handover is allowed for the current subcell.

    Based on uplink and downlink quality and signal strength measurements from the serving cell.

    Fulfilled when the quality is worse than could be expected from the signal strength level.

  • **Intra-cell HO evaluation

  • **Limitation of Intracell HO RepetitionPre-condition: Specific counter in the BSC for the number of successfully performed Intracell HOs for the same connection Specific Timer in the BTS for the duration of which no HO Condition Indication for Intracell HO is generated Adapted Channel Activation message on the Abis IF (cell id, HO-cause=HO successful) from the BSC to the BTS

  • **2. HCS (Hierarchical Cell Structure)

  • **IntroductionProblem in capacitySmall cells give limited coverage Large cells give limited capacity Situation :Combined microcell/macrocell Dualband GSM 900/GSM 1800

  • **HCS (Hierarchical Cell Structure)Concept of hierarchical networks has been developed to meet the increasing traffic demand in certain areas. Full HCS option8 layers distributed in ascending orderone or several layers can belong to one of 8 bandsReduced HCS option one band and 3 layers

  • **What Can Be Achieved Network in layers and bands The assignment of band and layer is based ontraffic distribution strategy among different cellsmaximum traffic capacity for the cellsinfluence of interference on the cells Large cells as umbrella cells and small cells to provide extra hot spot capacity HCS makes it possible to pass between layers in a controlled way Traffic is directed to lower layers. Priority of a cell is given by associating a layer to the cell.Maximum utilization of given capacity by maintaining sufficient quality (eg. GSM 1800/900)

  • **Cell LayerCells that have similarities in function and size can be seen as belonging to the same cell layer. HCS can be used to give different priority to different layers.Examples of layers are; macrocells, providing the main coverage and often main capacitystreet cells or microcells with their lower antennas, less expensive and more shielded sitesindoor/picocellsmacro-, micro- or picocells of another system type in a multiband network

  • **Frequency Band The available frequencies can be grouped into different bands that do not cause interference to each otherThe 900 and 1800 MHz frequencies naturally form different bands. These bands can be further divided into sub bands.

  • **HCS Bands and LayersAn example of how layers can be grouped into bands

  • **HCS Bands and Layers

  • **Locating

  • **Locating

  • **AlgorithmThe layer threshold decides if the cell should be prioritize over stronger cells of the same HCS band.For each cell: Signal strength threshold, LAYERTHR Hysteresis, LAYERHYST

    The band threshold decides if the cell should be prioritized over stronger cells from other HCS bands.For each band: Signal strength threshold, HCSBANDTHR Hysteresis, HCSBANDHYST

  • **Algorithm - Example 1

  • **Basic Ranking Only

  • **

  • **HCS rankingThere will be prioritized candidates even if the LAYERTHR is not fulfilled for any cell (must be above HCSBANDTHR). If there is congestion in the BEST candidate, HCS will cause a handover/assignment to a cell in another layer (one cell per layer)Maximum capacity utilization not possible in this caseMethod optimized to get an interference safe candidate that belongs to same band ONLY (BQOFFSET & AWOFFSET)Congestion can be elevated through CLS OR putting cells of same type in different layers within same HCS band.

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    *** Handoff - a basic mobile network capability for dynamic support of terminal migration

    Handoff Management - the process of initiating and ensuring a seamless and lossless handoff of a mobile terminal from the region covered by one base station to another base station

    ****The HO process is one of the fundamental principles in cellular mobile networks.Main objectives:1. Automatic transfer of the connection in progress from one cell to the other while the mobile subscriber is moving through the service area of the network based on radio criteria.2. Automatic transfer of the connection in progress from one cell to the other based network management criteria aiming at maximizing capacity, relieving congestion, providing dedicated service etc.

    The optimal design of the HO process is of great importance because an MS communicating with the wrong BTS will not only suffer from poor link quality, but it will also increase interference in reuse cells.

    *The HO process is based upon the basic concept outlined in GSM TS 05.08, Annex A.The HO decision mainly relies on radio criteria based on radio link measurements performed by the TRX in the BTS (uplink) and by the MS (downlink).The following sub-processes are running for each call in progress in the serving TRX:- measurement preprocessing and neighbour cell book keeping (averaging, power budget calculation)Preprocessing is started every SACCH block period (e.g. 480 ms for TCH)- HO detection and generation of the preferred target cell listRecognizing the necessity to request a HO the TRX sends a HO Condition Indication message to the BSCcontaining the HO cause and the ranked list of target cells.- Target Cell List evaluationIf the first target cell belongs to the same BSC and the equipment is capable of and configured to perform an Intra-BSC HO, this type of HO will be attempted.If the target cell belongs to another BSC an Intra MSC or even an Inter-MSC HO will be required.

    *Different types of HO are distinguished with respect to the area controlled by the respective network entitiy:1. Intracell HO - requests allocation of another dedicated channel within the serving cell. In other words, MS is handed over from one channel/timeslot in the serving cell to another channel/timeslot in the same cell. 2. Intercell HO- requests allocation of a dedicated channel in a neighbour cell2.1 Intercell Intra-BSC HO- the serving cell and the target cell belong to the same BSC controlled area 2.2 Intercell Intra-MSC HO- the serving cell and the target cell belong to different BSCs, but are within the same MSC controlled area. 2.3 Intercell Inter-MSC HO- the serving and the target cell belong to different MSC. This is the most complicated case and requires adequate signalling between the different MSCs.*For each call in progress the MS performes downlink measurements on each burst of the TCH including : - received signal quality (BER:bit error rate),- received signal level (RSSI: received signal strength intensity), and - received signal level on the BCCH carriers of the surrounding cells.The number of samples on each BCCH carrier depends on the number of carriers defined in the BCCH Allocation (BA), see note on the slide.For each call in progress the serving TRX performes uplink measurements on each burst of the TCH including : - received signal quality (BER:bit error rate),- received signal level (RSSI: received signal strength intensity) - absolute distance between MS and serving BTS (BS: burst shift) The burst samples over one SACCH block period are averaged and mapped on the corresponding physical parameters according to GSM TS 05.08 Chapter 8. These values are referred to as measurement results.Every SACCH block period the MS transmits to the serving BTS via the Measurement Report message (4 SACCH bursts) the measurement results including the RXQUAL, RXLEV on the DL of the serving cell and the RXLEV on the BCCH carriers of the six strongest neighbor cells with known and allowed BSIC (Base Station Identity Code).When sending the measurement report MS includes certain flags to give additional information for the data processing: DTX_USED: indicates uplink DTX in the previous reporting period MEAS_VALID: indicates whether the measurements are validBA_USED: value of BA_IND for BCCH Allocation usedEvery SACCH block period the serving TRX compiles the measurement results including the RXQUAL, RXLEV on the UL and the MS-BS distance.Note: Implementation of the HO process within the BTS avoids transmission of the Measurement Report (MR) messages via the Abis interface to the BCS. Optionally MR messages can be sent for performance measurement reasons. The frequency of sending is controlled by an O&M parameter.

    *Uplink signal strength measurements on traffic channels in idle mode are mapped to RXLEV, then averaged and mapped to interference level classes. BTS sends periodically to BSC an RF RESOURCE INDICATION message (specified in [GSM 08.58]) including the interference level classes of all idle channels. Averaging is done in averaging windows in the way described above.The averaged RXLEV values are mapped into five interference categories (band 1 to band 5). The values x1 to x4 constitute the right boundaries of the interference bands and are strictly increasing (0 x1 < x2 < x3 < x4 < 63). The definition of the bands is shown below .

    Interference bandRXLEV_IDLE10 ... Interf boundary x12Interf boundary x1 < ... Interf boundary x23Interf boundary x2 < ... Interf boundary x34Interf boundary x3 < ... Interf boundary x45Interf boundary x4 < ... 63

    *Two categories of HO initiation criteria are distinguished:1. Radio criteria: based on threshold comparison of absolute or relative measurements of the radio parameters (e.g. Quality , level, distance, power budget)2. Network criteria: based on resource and traffic management criteria to maintain a required grade of service and improve the capacity of the network; usually these criteria invoke traditional or modified radio criteria to answer the handover request of the networkThe radio criteria are classified into alarm or imperative criteria for maintaining the call in progress in case of bad link quality; the purpose of these criteria is to prevent the interruption of the call (e.g. bad quality, bad level); the excessive distance criterion is of an imperative type but the main purpose of it is to prevent excessive interference to other cells normal or power budget criterion; it is exclusively designed to ensure that the MS is connected to the cell with the minimum pathloss, thus the radiated interference to other cell will be kept at a minimum level

    *The table above gives an overview fo the evaluated HO initiation criteria on the SDCCH and TCH.A forced handover is a network requested one. The BTS is triggered by the BSC to answer with a handover request. A forced HO may only be initiated on the SDCCH in case of Directed Retry.Directed Retry is the HO from a SDCCH in the congested cell to a TCH in a neighbor cell during call setup because of lack of resources in the first cell.

    *Every SACCH reporting period for each cell in the book-keeping list the threshold comparison process is run for the HO initiation criteria.XX stands in general for UL and DLXX_TXPWR stands for MS_TXPWR or BS_TXPWR respectivelyThe radio parameters RXQUAL, RXLEV, MS_BS_DIST are the averaged measurement results from the preprocessing.Note that imperative HO due to quality and level require that the capability of the Power Control has been exhausted. PBGT(n) is calculated according to the formula in GSM 05.08 Annex A:PBGT (n) = RXLEV_NCELL (n) - (RXLEV_DL + PWR_C_D) + Min(MS_TXPWR_MAX , P) - Min(MS_TXPWR(n) , P)RXLEV_DL : average value on the DL traffic channel in the Serving CellPWR_C_D : BS_TXPWR_MAX[dBm] - BS_TXPWR [dBm] Averaged difference taken as correction factor due to power control in the serving cell. Neighbor BCCHs are measured at full transmit power RXLEV_NCELL(n) : Average value measured on neighbor cell (n)PBGT(n)-HO_MARGIN(n) > 0 means that the path loss of the serving cell is greater than the path loss of the adjacent cell by the HO_MARGIN, i.e. the adjacent cell is considered as a better cell.Note: Implementation for a HO initiation due to PBGT unlike the proposal in GSM 05.08 both the RXLEV_MIN and the PBGT condition have to be fulfilled. This avoids an initiation of HO due to better cell to a cell which does not provide the absolute minimum required level. Recall that PBGT is a relative comparison of the signal levels in two cells. If any of the threshold comparisons is fulfilled a HO CONDITION INDICATION message including the cause and the Target Cell List is generated by the BTS and sent to the BSC. *The diagram above show the partitioning of the RXLEV/RXQUAL plane in the defined range by the O&M parameters (thresholds).Bad quality (RXQUAL above the threshold L_RXQUAL_XX_H) will cause an Intracell HO if at the same time the RXLEV on the same link is above the threshold L_RXLEV_XX_IH. The latter indicates that the bad quality is due to excessive interference of the link caused by other users on the same channel or adjacent channels. An Intercell HO due to quality will be caused if the level on the same link is below the threshold L_RXLEV_XX_IH and the transmit power can not be increased.Insufficient level (RXLEV below the threshold L_RXLEV_XX_H) will cause an Intercell HO due to LEVEL if the transmit power can not be increased.If neither of the above conditions are met (lower right domain) of the RXLEV/RXQUAL plane other types of HO, e.g. HO due to PBGT might be detected.

    *This diagram shows the qualitative relation between the relevant O&M parameters (thresholds) as well as the idealized circled area around a BS where the received signal level (RXLEV) will be greater than the assumed threshold.

    This figure should help setting the threshold values properly in the database.

    Especially it is important to satisfy the relation between the required minimum received level RXLEV_MIN of a HO candidate cell and the level threshold L_RXLEV_XX_H for the same cell. If this condition is not met, after a HO to this cell (independent of the cause) a HO due to Level out of that cell will be most probably initiated.

    *This diagram shows three different borders of three cells as defined by the O&M parameters:RXLEV_MIN, L_RXLEV_XX_H and HO_MARGIN = 0While the first two parameters (similar to the previous slide) define the idealized circled area around a BS where the received signal level (RXLEV) in each cell will be greater than the assumed threshold the third parameter defines the locations (straight lines) of equal received power from the respective pair of cells.Thus L_RXLEV_XX_H defines the cell border for HO due to level out of the cell, RXLEV_MIN defines the cell border for the neighbor cell to be a suitable HO candidate. Finally HO_MARGIN = 0 defines the ideal Power Budget HO border between two cells. It should be noted that these cell borders in a real propagation environment are strongly shaped by diffraction, shadowing, scattering reflection of the radio waves. Anyway, what is very important for the design of the HO borders is to keep in mind the relevant relations between the parameters. As shown in the Figure above a certain overlap of the cells is required in order to satisfy the relevant relations. In other words, bad coverage planning cannot be compensated by judicious HO parameter setting for an acceptable HO performance.

    *Every SACCH reporting period for each neighbor cell in the book-keeping list the conditions in the Table above are checked in order to enter the respective neighbor cell into the Target Cell List on a HO detection. The condition to be met depends on the class of the HO criterion which caused the HO indication, i.e. imperative, forced, better cell. Note that for an imperative and forced HO it is not necessary for a neighbor cell to be a better cell than the serving cell (BCV>0) in order to put this neighbor cell into the target cell list, i.e. a neighbor cell with a BCV