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GSM_P&O__01_200904 GSM Capacity PlanningObjective Learn about the basic concepts and prediction methods of capacity planning. Master the network planning flow. Master how to increase network capacity and plan locationsReference GSM BasicsContents1Chapter 1 Basic Concepts of GSM Capacity Planning

11.1 Traffic and BHCA

31.2 Call Congestion Ratio and Erlang-B Table

7Chapter 2 Capacity Prediction

72.1 Overview

72.2 Capacity Prediction Method

72.2.1 Growth Trend

102.2.2 Population Penetration Rate

122.2.3 Growth Curve

152.2.4 Conic

172.3 Traffic Distribution Prediction

19Chapter 3 Capacity Planning Flow

193.1 Capacity Planning Ideas

203.2 Prerequisites for Capacity Planning

203.3 Capacity Planning Calculation Method

213.4 Channel Capacity Planning

213.4.1 SDCCH Capacity Planning

243.4.2 CCCH Channel Configuration Principle

253.4.3 Recommended Assignment Principles for CCCH Channels and TCH Channels

27Chapter 4 Capacity Planning Optimization

29Chapter 5 Network Capacity Improvement

295.1 Method of Improving the Network Capacity

295.2 Analysis of Improving the Network Capacity

295.2.1 Principle of Cell Splitting

305.2.2 More Aggressive Frequency Reuse Pattern

305.2.3 Adding Microcellular Equipment

305.2.4 Expanding Frequency Band

315.2.5 Adopting Half Rate

33Chapter 6 Location Area Planning

336.1 Demarcating Boundary of LA

346.2 Paging Capacity of LA

346.2.1 Analysis of Paging Principle

356.2.2 Paging Policy

356.2.3 Setting Paging Parameters

386.2.4 Calculating LA Capacity

406.2.5 Effect of SMS on Paging Capacity of LA

Chapter 1 Basic Concepts of GSM Capacity PlanningThis document describes capacity planning of base stations on the BSS side of the GSM network, which serves as the basis for capacity planning of others.1.1 Traffic and BHCA

When a user makes a call and how long the call lasts are random events, but there are certain statistical rules for such random events. To indicate how often a user makes a call and how long the call lasts, a concept of traffic is introduced to telephony exchange. Traffic refers to the conversation volume generated by a user within a period of time. It is a dimensionless value and is generally expressed by Erlang (an Erlang refers to traffic load generated when a conversation circuit is 100% continuously occupied for an hour). Busy traffic refers to traffic load when the system or line is busiest within a day.The average traffic of every user, that is, , can be expressed as:

Here,

, also called by call arrival rate, is the average number of calls made by every user within a unit of time.

is the average conversation duration of every user, in the unit of second. is the call completion rate. Traffic of every cell, that is, , can be expressed as:

Here,

is the average traffic of every user (Erlang/user).

is the user density (user amount/ km2).

is the acreage of the cell (km2).In actual environments, traffic varies with time. Even though the possible traffic changes in the long-term development process are not considered, yet traffic still changes periodically in the short term (on a daily or weekly basis).In general, one hour when traffic is heaviest is called busy hour. Accordingly, the number of calls with the one hour is the busy hour call amount or busy hour call attempt, that is, BHCA for short. Busy traffic (that is, traffic within the busy hour) can be expressed as:

In network planning, busy traffic is generally a design index and it is believed that a GSM network, if supporting busy traffic, is certainly able to deal with common traffic. In network planning and design, busy traffic of every user is generally used as an index. Busy traffic of every user can be expressed as:

Here,

is busy traffic of every user.

is the number of calls made by every user within a day.

is the busy hour factor (ratio of busy traffic to total traffic within a day).Busy traffic of the system can also be expressed as:

N is the total number of users in the system.

is a very important formula for capacity planning. It is obvious that during system planning, the expected capacity of the system must exceed the estimated .In the current system, the average busy traffic of every user can be obtained generally from the statistical data of the existing network. It can be known from the preceding formula that the average busy traffic of every user in the current system is the total busy traffic divided by the number of registered users on the VLR during the busy hour. During network planning, however, some margins are generally reserved for the average busy traffic of every user in the current system.In China, the experience in operating the common mobile telephone network in recent years shows that the acceptable average busy traffic of every user is 0.025 to 0.03 Erl/user. This equals 6 calls (including incoming and outgoing calls) made by every user every day and 2 minutes per call.1.2 Call Congestion Ratio and Erlang-B TableCall loss or congestion: When a call is made on condition that all the channels of a wireless communications system have already been occupied, the call is unsuccessful and then is lost or congested. The call congestion ratio refers to the probability that such a call is congested.Grade of service (GOS) indicates the congestion level and is defined as the probability of congestion. During planning of a GSM system, GOS of a traffic channel (TCH) is generally 2% or 5%.As specified in the Technical Mechanism for the Common Mobile Telephone Network, the call congestion ratio of a wireless channel is smaller than or equal to 5%. In a high-density traffic area, 2% is used. In general, all common mobile telephone networks are the call congestion systems. During system designs, although a user within a cell (or sector) is designed to continue his or her call attempt if his or her first call cannot occupy the idle channel, yet the sector sharing or directed retry function diverts the congested call of the user to another sector for searching for an idle channel, that is, the user leaves the sector that he or she originally accesses. Therefore, for users of every sector, every call of users is lost if there is no idle channel, and the result is that the overall congestion feature is comparatively close to the Erlang-B call rules.According to the Erlang call congestion formula and the call congestion calculation table, a call must have the following characteristics: Every call is random, which is independent of or irrelevant to other calls. Every call has the same probability in terms of time. When a call cannot occupy the idle channel, the call is lost, instead of waiting a period of time for the channel to become idle. The Erlang-B formula is:

This formula provides the relationship between the call congestion ratio B, traffic A, and channel amount n. According to this formula, you can calculate traffic at different call congestion ratios and on different channels. The calculated traffic values form an Erlang-B table. If knowing any two of the preceding B, A, and n, you can calculate the value of the third one.The following table is an Erlang-B table formed according to calculation via the Erlang formula and is used for convenient query.N1.0%1.2%1.5%2%3%5%

10.01010.01210.01520.02040.03090.0526

20.1530.1680.190.2230.2820.381

30.4550.4890.5350.6020.7150.899

40.8690.9220.9921.091.261.52

51.361.431.521.661.882.22

61.9122.112.282.542.96

72.52.62.742.943.253.74

83.133.253.43.633.994.54

93.783.924.094.344.755.37

104.464.614.815.085.536.22

115.165.325.545.846.337.08

125.886.056.296.617.147.95

136.616.87.057.47.978.83

147.357.567.828.28.89.73

158.118.338.619.019.6510.6

168.889.119.419.8310.511.5

179.659.8910.210.711.412.5

1810.410.71111.512.213.4

1911.211.511.812.313.114.3

201212.312.713.21415.2

2112.813.113.51414.916.2

2213.71414.314.915.817.1

2314.514.815.215.816.718.1

2415.315.61616.617.619

2516.116.516.917.518.520

261717.317.818.419.420.9

2717.818.218.619.320.321.9

2818.61919.520.221.222.9

2919.519.920.42122.123.8

3020.320.721.221.923.124.8

3121.221.622.122.82425.8

322222.52323.724.926.7

3322.923.323.924.625.827.7

3423.824.224.825.526.828.7

3524.625.125.626.427.729.7

3625.52626.527.328.630.7

3726.426.827.428.329.631.6

3827.327.728.329.230.532.6

3928.128.629.230.131.533.6

402929.530.13132.434.6

4129.930.43131.933.435.6

4230.831.331.932.834.336.6

4331.732.232.833.835.337.6

4432.533.133.734.736.238.6

4533.43434.635.637.239.6

4634.334.935.636.538.140.5

4735.235.836.537.539.141.5

4836.136.737.438.44042.5

493737.638.339.34143.5

5037.938.539.240.341.944.5

5138.839.440.141.242.945.5

5239.740.34142.143.946.5

5340.641.24243.144.847.5

5441.542.142.94445.848.5

5542.44343.844.946.749.5

5643.343.944.745.947.750.5

5744.244.845.746.848.751.5

5845.145.846.647.849.652.6

594646.747.548.750.653.6

6046.947.648.449.651.654.6

6147.948.549.450.652.555.6

6248.849.450.351.553.556.6

6349.750.451.252.554.557.6

6450.651.352.253.455.458.6

Chapter 2 Capacity Prediction2.1 OverviewIn terms of cellular network planning, the system capacity requirements must be determined first, that is, how many users will be in the system and how much traffic the users will generate. This serves as the basis of designs on the whole cellular network. The prediction analysis of system capacity aims to reflect the actual and future capacity requirements in the system so as to estimate the number of channels required in the system. Network planning is implemented based on the distribution of initial and future traffic requirements obtained through various statistics and calculations. Capacity prediction needs to take into consideration the following factors: 1 Incoming status2 Distribution of population at different age groups and incoming groups 3 As-is economic status of the region4 Introduction of service competition5 Reduced or preferential mobile service expanses6 Publicity and development goals of mobile operators2.2 Capacity Prediction Method7 Short-term prediction (1 to 2 years) or long-term prediction (3 to 5 years)8 Population penetration rate9 Growth trend 10 Growth curve 11 Conic2.2.1 Growth Trend (1) As-is mobile communications outside of ChinaIn June 2003, the number of mobile users worldwide has hit 1.3 billion, with a penetration rate of over 18%. Replacement of fixed with mobile has become an increasingly obvious trend. Currently, over 100 countries worldwide have seen more mobile users than fixed-line users.In Europe, the average penetration rate of mobile phones is about 75% and the market penetration rate is almost saturated. European operators are raising service ARPU to compensate for loss incurred by slow growth of the user base. What is delightful is that the data services are on the continuous increase. In 2002, revenues from the data services accounted for 13.6% of the total revenues in Europe, of which the short message service took up the major part and such services as GPRS and WAP held less than 5%. Prior to July 2001, America was the worlds largest mobile communications market and its penetration rate of mobile phones was about 50%. However, due to fierce market competition, revenues from mobile services are constrained and the overall growth of the mobile user base is not promising. At the same time, along with the slowdown of American economy, operators in America were confronted with many difficulties. Under such circumstances, it was a possible way out of the economy shadow for the mobile communications industry to seek out cooperation and collaboration and develop new service models.Unlike Europe and America, Japan and South Korea witnessed good results. Although the proportion of mobile uses in Japan and South Korea had already exceeded 60% early, the enriched data services, however, brought in continuous service revenues. Particularly, in Japan, the mobile data users accounted for 70% to 80% of the total mobile users and the proportion of revenues from the data services exceeded 20%, with the short message service taking up only 3%. In the developing countries and certain under-developing countries, the mobile communications services are still growing astonishingly. Specifically, in over half of African countries, the number of mobile users has exceeded that of fixed-line users. In addition, 85% of the total mobile users are prepaid users. In 2002, the average proportion of prepaid users was about 50% worldwide and this figure is still on the increase.(2) As-is mobile communications in ChinaIn China, the mobile communications services have been maintaining a momentum of rapid growth. By July 2001, the number of mobile users in China surpassed that in America and China became the worlds largest mobile communications market. Two years later, Chinas mobile user base has exceeded 257 million by October 2003 and this was the first time that the mobile user base exceeded the fixed line user base (255 million). Currently, the penetration rate of mobile communications in China is about 20%. In the next five years, this figure will be increased greatly. China still lags far behind her European and American counterparts in terms of the overall country power and especially, the development in China is imbalanced. All these trigger the shift of mobile communications from high-end users to common users. The short message service is widely accepted and is explosively growing. In 2003, the total number of short messages hit 180 billion. In addition, the multimedia message service (MMS) is gradually burgeoning. It is believed in the telecommunications industry that the MMS service is a rising star and also a runner for fostering the 3G service markets.(3) Overall development trend of mobile communications Within a period of time in the future, the mobile user base continues to be expanded and its dominance role will be future fortified. However, the continuous efforts are still required for the compliance of mobile services with application standards. The ARPU will continue to fall until the data services are widely accepted and booming. The voice and its value-added services will also continue to grow and in addition, the data services will develop continuously. All these require a cost-effective 3G network. The 3G network, however, will grow in a step-by-step manner because considerable 2G networks exist and the data services do not growth astonishingly. For a long period of time, 2G/2.5G and 3G technologies will coexist.The following describes an example of the growth trend prediction method:In a region, the number of mobile users grows as shown in the following table.Region1992199319941995

User Amount Growth Rate (%)User Amount Growth Rate (%)User Amount Growth Rate (%)User Amount Growth Rate (%)

HX1085303318073671431453997

1996199719981999

311801144976160939228917765989

As shown in this table, the growth rate from 1992 to 1999 is not on a year-on-year decrease. Instead, the growth rate fluctuates irregularly. Therefore, in 2000, the average growth rate from 1992 to 1999, that is, 70%, is used as the growth rate. In 2001, the growth rate uses 40%, slightly higher the average national level 38.85%. This also complies with the actual conditions of the region (the region is a medium-sized city). In 2002, the growth rate uses 30%. Based on the growth trend prediction method, the prediction of mobile users in this region from 2000 to 2002 is shown in the following table.Region200020012002

User Amount Growth Rate (%)User Amount Growth Rate (%)User Amount Growth Rate (%)

HX302021704228294054967830

2.2.2 Population Penetration RateWhen determining the penetration rate, take into consideration the following factors:12 Penetration rate of mobile phones in moderately developed countries in the world13 Expected attainable index in the next several years across the country 14 Market penetration rates of operators in the current region 15 Economic development status in the current region The following table lists national penetration rate of mobile phones from 1995 to 2002.Year19951996199719981999200020012002

User amount (10, 000)362.9684.8136424963432505370169219

Penetration rate (%)0.3020.571.142.082.643.895.407.69

As estimated by relevant experts, in the next 2 to 3 years, the penetration rate of mobile phones will hit 10%. For example, in Lanzhou, an important city in Northwest China and also a moderately developed city across the country in terms of economic development status, the penetration rate has reached 6%. It is expected that the 10% goal will come 2 to 3 years in advance, that is, in 2000, Lanzhou will see the penetration rate 10%. The following tables show the penetration rates in Lanzhou and across the country in recent several years.The following table shows the as-is penetration rate of mobile phones in a certain region.SNRegion1996199719981999

User Amount (10, 000)Penetration Rate (%)User Amount (10, 000)Penetration Rate (%)User Amount (10, 000)Penetration Rate (%)User Amount (10, 000)Penetration Rate (%)

1GL311801.13497611.77939223.251776596.12

As shown in the table above, in 1998, the penetration rate in this region is already higher than the national average. This also reflects the regions role as a provincial capital city. In 1999, the penetration rate is three-fold higher than the national average. Based on such a proportion, from 2000 to 2002, the penetration rate in this region will be about 10%, 15%, and 20% respectively.In Shanghai and Beijing, the penetration rate of mobile users has exceeded 15%. This region is a moderately developed city and it is possible that its penetration rate is two years behind Bejing, that is, 15% in 2001. Therefore, it is acceptable that this regions penetration rate in the next three years is 10%, 15%, and 20% respectively. Currently, China Unicom holds a market share of 10% throughout the country and its goal is to hit 20% to 30% market share. After the restructuring of China Telecom, China Mobile will turn out a new picture to compete with China Unicom. And it is estimated that China Unicoms growth of market share will slow down. Based on such an analysis, the market share of China Unicom in this region in the next three years is estimated to be 10%, 15%, and 20% respectively. Along with market development, the supportive measures taken by the nation for China Unicom will be phased out and the market goes in a more standardized manner. As a result, in the future, what is more appealing to users is service quality and new service offerings.The following table shows the estimated population of this region from 2000 to 2002.SNRegion 199619971998200020012002

Population (10,000) Population (10,000)Population (10,000)Natural Growth Rate ()Population (10,000)Population (10,000)Population (10,000)

1Lanzhou276.09280.46288.565.90291.98293.70295.43

According to the estimated population and China Mobiles estimated market share in the next several years, the estimated user base of China Mobile in three city of this region from 2000 to 2002 is shown in the following table (the population penetration method is used). Region 200020012002

Population (10,000)Penetration Rate (%)Market Share (%)User Amount

Population (10,000)Penetration Rate (%)Market Share (%)User Amount

Population (10,000)Penetration Rate (%)Market Share (%)User Amount

GL291.9810.090262778293.7015.085374465295.4320.080472689

GW192.420.89814448194.501.19220564196.591.58826510

DX293.630.510013236296.401.09829459299.191.89047336

2.2.3 Growth CurveDuring the research on prediction methods, a lot of facts show that there are certain similarities in the development of the technical equipments functions and features and the market requirements. For example, within a city, when the penetration rate of phones reaches a certain value and then the market in the city begins to be gradually saturated, rather than to simply increase exponentially or linearly. The commonly used equation to indicate such a saturation curve is Gompertz and Logistic. The following considers the Gompertz curve equation as an example. The Gompertz curve equation is expressed as:

The following shows the Gompertz curve diagram.

The Gompertz curve parameters can be determined as follows: Determine the peak saturation value L and then perform the logarithm on both sides of the equation. Then, lnln (L/Yt) = lnb-kt is obtained. Assume that A = lnb, and Yt = lnln (L/Yt). Then, lnln (L/Yt) = lnb-kt is changed to Yt = A + Bt. Then, obtain the values of A and B by using the least square method.The following shows an example of such a method of determining Gompertz curve parameters.

Step 1: Determine the peak saturation value L. Mobile phones feature convenient mobility. The population mobility is relevant to ages. Specifically, population of 15 to 64 years old has a great mobility and is the most probable to use mobile phones. Population of 0-14 years old or 65 years old or above has a relatively fixed activity range and fixed-line phones can basically meet their communications requirements. Therefore, when conducting a user prediction, mainly take into consideration population of 15 to 64 years old. Seen from Chinas changes to the population structure with different age groups, population of 15 to 64 years old in 2000 is 67.7% of the total population. This proportion can be considered as the peak saturation value L for the penetration rate of mobile phones. The following table shows Chinas population structure from 1995 to 2010. YearTotal Population0-14 Years Old15-64 Years Old65 Years Old or Above

Population ProportionPopulation Amount (10, 000) Population ProportionPopulation Amount (10, 000) Population ProportionPopulation Amount (10, 000) Population ProportionPopulation Amount (10, 000)

199510012112126.73230366.6807276.78091

199610012224826.43227366.8816626.88313

199710012338526.13220367826686.98514

199810012453225.83212967.28368678717

200010012685925.33210567.78584178913

200510013143822.93009969.5913507.69989

201010013618320.72824871.1967998.211136

Step 2: Calculate the values of A and B. The following table considers a city GL as an example.YearSN (t)User Amount (Yt)Yt'=lnln(L/Yt)Ytt'=t*Yt't2

19961311801.4229661.4229660421

19972497611.3034442.606887644

19983939221.1140663.3421985239

199941776590.8793443.51737701416

Sum 103525224.71982010.8894292230

Obtain the values of A and B by using the least square method and set up a mathematic model as shown below:

Predict the user amount of the city GL in 2000 and apply t=5 to the preceding formula. Then, obtain y2000=250804. Likewise, apply t=6 and t=7, then obtain y2001=353629 and y2002=470899 respectively.The following table shows the predicted mobile user amount of the city GL from 2000 to 2002 by using the growth curve method.SNRegion User Amount

2000 2001 2002

1GL250804353629470899

Any type of telecommunications service needs to go through four phases, debut, growth, saturation, and degradation. For any service having such four phases, you can use the growth curve method to perform prediction and this method is very suitable to medium-term prediction. 2.2.4 ConicFor many engineering problems, it is a common practice to search out an approximate expression for the function relationship of two variables according to several groups of lab data for these two variables. The approximate expression is generally called empirical formula. After an empirical formula is set up, certain experience accumulated during production and experiments can be raised to the theory for analysis. During a mobile user prediction, an empirical formula can be set up based on the user development over the last several years and through the empirical formula, the next several years user development can be predicted.In a city, the growth of mobile users can be expressed by the following empirical formula:

Here, x represents the year and y the amount of mobile users.Apply the user amount of the last several years and select constants a, b, and c by using the least square method.

The values of a, b, and c are calculated as follows:

Apply the mobile user data of the city GL from 1996 to 1999 and then calculate the values of a, b, and c. Then, based on the values, you can predict the mobile user amount of the city GL in the next three years.The following table shows the predicated mobile user amount of the city GL from 2000 to 2002 by using the conic method.SNRegion User Amount

200020012002

1GL287371430790606184

2.3 Traffic Distribution PredictionTraffic is mainly centralized in medium and large-sized cities. Especially, in the center of an urban area, there is a comparatively high-density traffic region. Within the region, an area with extremely heavy traffic generally exists. In the suburban areas, traffic is low. When constructing a network, take into consideration all the preceding factors and deploy nodes properly; otherwise, the equipment resources for the low traffic areas will be wasted and the capacity in the heavy traffic areas will be insufficient, thus adversely affecting the return on investments (ROI) and service quality of the network. To avoid the preceding adverse impact, conduct a prediction and survey of traffic distribution beforehand and then based on the prediction and survey result, deploy base stations and determine the frequency multiplexing mode.At early stages, you can use such statistical data as population distribution, incoming status, vehicle use distribution, and phone use to predict the geographic distribution of traffic requirements. After a network is built out and runs in the normal state, you can use the traffic statistical report of OMC to obtain a comparatively comprehensive traffic distribution of the mobile service area for future optimization and capacity expansion.Three methods are currently available to the traffic density prediction: percentage-based method, linear prediction method, and linear prediction+manual adjustment.Percentage-based method: The service area is divided into several sub-areas, such as, high-density user sub-area, medium-density user sub-area, and low-density user area (for example, densely populated urban area, common urban area, and suburban area) and then different percentages are allocated to these areas during the mobile user prediction. Then, multiply the predicated user amount by the percentage of an area to obtain the total user amount of the area, and then divide this total user amount by the acreage of the area to obtain the user density of the region. Linear prediction method: Based on the cell planning software and the digital map, allocate the actual statistical busy traffic of the existing base stations to every cell, and then import the total traffic in the target year to the PC. Then, the cell planning software can generate the traffic distribution diagram in the target year according to the existing traffic distribution.Chapter 3 Capacity Planning Flow Based on the preceding traffic prediction and traffic distribution prediction, you can obtain the total traffic requirements within the service area and the traffic distribution and acreage within every specific area. After a correct predication of user development within the planned area, select a proper frequency multiplexing mode according to the available frequency band resources. In addition, after considering the configured capabilities of wireless system products as well as the wireless environment/user distribution characteristics within the planned area, determine site-type configuration for different types of area and ultimately obtain the site quantity that meets capacity requirements. Capacity planning needs to yield the following results:Number of base stations that meet traffic requirements within the planned areaSite-type configuration of every base stationNumber of traffic channels and users and traffic provided by every sectorNumber of traffic channels and users and traffic provided by every base stationNumber of traffic channels and users and traffic provided by the whole networkThe preceding planning is an initial planning. That is, after wireless coverage planning and analysis, certain base stations may be added or deleted. Then, the number of base stations and their locations are finally determined after repeated planning and analysis.3.1 Capacity Planning IdeasA common capacity planning flow is: conducting capacity prediction -> analyzing traffic distribution -> determining site-type configuration -> determining the number of base stations -> determining the layout of base stations. At different stages of network planning, the work focuses are also different: At the elementary stage of network development, there are a few capacity requirements, the site is generally small, and the network is relatively simple. In this case, mainly consider the basic coverage. At the intermediate stage of network development, there are a large number of capacity requirements, the coverage requirements are high, and the network is relatively complex. In this case, take such measures as capacity expansion of base stations and cell splitting.At the advanced stage of network development, there are enormous capacity requirements, the hole-free coverage is required, and the network is complex. In this case, take such measures as adding micro cells and setting up dual-frequency networks. 3.2 Prerequisites for Capacity Planning Before a prediction of total traffic and traffic distribution, the following prerequisites are met: GOS provided by the system (call congestion ratio)

Available frequency band resources and frequency multiplexing mode 3.3 Capacity Planning Calculation MethodEstimate the number of base stations and their types and capacity in the capacity-constrained area.Estimate the maximum site type for different types of area according to the available frequency band resources and frequency multiplexing mode.Obtain the capacity of every base station according to the traffic model and Erlang-B table.Obtain the number of required base stations by dividing the total traffic by the maximum capacity (sum of capacity of all cells) of a base station.Estimate the number of base stations and their types and capacity in the coverage-constrained area.Obtain the total number of base stations required by a type of area by dividing the area acreage by the coverage acreage (estimated) of every base station. Obtain the required traffic within a cell by multiplying the coverage acreage (estimated) of the cell by the corresponding traffic density.Estimate the number of required voice channels and control channels according to the Erlang-B table.Obtain the number of required carrier frequencies of a cell by dividing the sum of the voice channels and control channels by 8.The output results are total number of base stations and their types.The following is an example of calculating capacity of a base station.In an S4/4/4 base station, every cell has 32 channels, of which 29 are traffic channels. Assume that the call congestion ratio is 2%. According to the Erlang-B table, it is found that traffic carried in this base station is 21.03 Erl. Assume that the average busy traffic of every user is 0.025 Erl, then, it is calculated that 841 users can be accommodated. Then, the whole base station can accommodate 2523 users (841 x 3 = 2523).3.4 Channel Capacity Planning3.4.1 SDCCH Capacity Planning1. SDCCH channel structure and service type An SDCCH channel has two types of structure: SDCCH/4 and SDCCH/8. These two types of structure are applied to the hybrid control channel and independent control channel respectively. In a GSM system, the cell broadcast service can be provisioned. That is, within an area, the short messages of the short message service center are broadcast to all registered users within the area. When the cell broadcast service is provisioned, the broadcast traffic channel CBCH of every cell must occupy an SDCCH channel.Combined channel: BCCH+CCCH+SDCCH/4(TS0)Non-combined (independent) channel: BCCH+CCCH (TS0)+X x SDCCH/8 (timeslots for BCCH carriers frequencies 1-7 or any timeslot for other carrier frequencies)During network designs, X can be configured according to the number of carrier frequencies (that is, number of TCH channels) and the proportion of TCH traffic to SDCCH traffic. An SDCCH channel mainly carries the following types of services: Location update or periodic location update IMSI attachment/separation

Call set-up

Short message

Fax and supplementary services For networks with different structures and user habits and for different traffic models, time when the preceding various events are occupying the SDCCH channel is also different. 2. SDCCH GOS and SDCCH/TCH capacity proportionWhen the number of SDCCH channels is defined, the call congestion ratios of SDCCH channels and TCH channels must be comprehensively considered. This is because in a conversation, SDCCH channels are used to transmit the call connection signaling and TCH channels are used to transmit voice or data information. SDCCH channels and TCH channels are equally important for set-up of a conversation. SDCCH, however, can utilize the physical channels of carrier frequencies in a more effective manner. Therefore, the call congestion ratio of SDCCH channels must be lower than that of TCH channels.The basic principles for determining the call congestion ratio of SDCCH channels are as follows: The call congestion ratio of SDCCH channels must be 25% of that of TCH channels. If the call congestion ratio of SDCCH channels is higher than 25% of that of TCH channels, more SDCCH channels must be defined. For the SDCCH/4 structure, the call congestion ratio of SDCCH channels must be 50% of that of TCH channels.In general, the GOS of the SDCCH/8 structure is calculated as 1/4 of the GOS of TCH. The GOS of the SDCCH/4 structure is calculated as 1/2 of the GOS of TCH.For example, when the GOS of TCH is 2%: SDCCH/4 GOS = 1%

SDCCH/8 GOS = 0.5%Based on the channel assignment algorithm of BSC, signaling can be transmitted on the TCH channels. No matter which channel assignment method (pre-assignment or dynamic assignment) is used, signaling both can be transmitted on the TCH channels. During set-up of a call, TCH channels are immediately assigned for transmitting call connecting signaling. This can reduce call congestion ratio and improve GOS.3. SDCCH Capacity PredictionSDCCH traffic prediction is calculated according to common service models. Different networks and traffic models have different SDCCH traffic models. During actual SDCCH planning, make calculations according to the service models provided by operators.If the service models have already been provided, you can calculate per-user traffic of every type of phone action.The corresponding calculation formula is as follows:

The following shows the calculation process (only considering location update, short message, and call set-up):Conventions: Location update factor: L Proportion of short message amount to call amount: S Average call duration: T Cell traffic: Acell Location update duration: TLU Call set-up duration: TC Short message duration: TSMS SDCCH clear protection duration: TG

Then, Busy call amount of a cell: CALL = Acell x 3600/T Busy location update amount: LU = L x Acell x 3600/T Busy short message amount: SMS = S x Acell x 3600/T = 6Acell

Then, traffic carried by SDCCH is: ASDCCH = [CALL x TC + LU x (TLU + TG) + SMS x (TSMS + TG)]/3600

After traffic is obtained, you can obtain the number of required SDCCH channels from the Erlang-B table according to the corresponding GOS.The following table shows the recommended SDCCH configuration.TRX AmountChannel AmountSDCCH Structure SDCCH Amount TCH AmountTCH Traffic (GOS = 2%)

18SDCCH/8162.28

216SDCCH/88148.2

3242*SDCCH/8162114.9

4322*SDCCH/8162921

5402*SDCCH/8163728.3

6482*SDCCH/8164535.6

7563*SDCCH/8245243.1

8643*SDCCH/8246049.6

9723*SDCCH/8246857.2

10804*SDCCH/8327564.9

3.4.2 CCCH Channel Configuration Principle1. CCCH channel structureCommon control channels (CCCHs) mainly include the access granted channel (AGCH), paging channel (PCH), and random access channel (RACH).The uplink channel transmits the channel request message and the downlink channel transmits the granted access (that is, immediate assignment) and paging messages. All traffic channels of every cell share the CCCH channels. 2. CCCH channel configurationCCCH-CONFMeaningNumber of CCCH Messages in a BCCH Multiframe

0One basic physical channel used by CCCH9

Not used with SDCCH

1One basic physical channel used by CCCH3

Used with SDCCH

2Two basic physical channels used by CCCH 18

Not used with SDCCH

4Three basic physical channels used by CCCH 27

Not used with SDCCH

6Four basic physical channels used by CCCH 36

Not used with SDCCH

3.4.3 Recommended Assignment Principles for CCCH Channels and TCH ChannelsAssume that the average busy traffic of mobile users is 0.025 Erl/user and the GOS of wireless channels is 2%. According to the recommended SDCCH configuration and CCCH channel structure, you can obtain the maximum traffic in different amount of carrier frequencies of every cell from the Erlang-B table. Based on the maximum traffic, you can calculate the maximum number of users supported by every cell and then finally the maximum number of users supported by the entire system. Carrier Frequency AmountChannel AmountCCCHControl Channel Amount (SDCCH)TCH Channel AmountCapacity (Erlang)

Channel Structure GOS=2%

18 (1BCCH+9CCCH)+SDCCH/8162.28

216(1BCCH+9CCCH)+SDCCH/81148.2

324(1BCCH+9CCCH)+2*SDCCH/822114.9

432(1BCCH+9CCCH)+2*SDCCH/822922

540(1BCCH+9CCCH)+2*SDCCH/823728

648(1BCCH+9CCCH)+2*SDCCH/824535.5

756(1BCCH+9CCCH)+3*SDCCH/835242.12

864(1BCCH+9CCCH)+3*SDCCH/836049.64

972(1BCCH+9CCCH)+3*SDCCH/836857.2

1080(1BCCH+9CCCH)+4*SDCCH/847564.9

For different traffic models and GOSs, you can obtain the channel configuration and traffic according to the recommended configurations listed in the table above.Chapter 4 Capacity Planning OptimizationThe initial capacity planning is mainly based on various predications and assumptions. As network planning and network construction are implemented, traffic models may change and these changes to traffic models (such as change to the size of a traffic model) have a direct and important impact on capacity planning. In actual conditions, the initial capacity planning will be adjusted and optimized, thereby laying a good foundation for future network optimization and reducing investments under certain conditions.The recommended traffic model calculation method on the exiting network is as follows:

When any of the following factors occurs, you need to consider adjusting and optimizing capacity planning: Changes to user behavior: Mainly consider the user capacity offset caused by mobility of users in the local network. Use behavior includes user traffic behavior and user mobility behavior. These two types of behavior lead to user traffic offset from the macro and micro perspectives respectively. As for the extent to which the traffic offset affects the network, we can use the fluctuation coefficient (1.05-1.1 in general) for measurement. The network margins caused by such offset cannot be saved during network construction.Non-linear channel configuration: Channel configuration is calculated according to the number of carrier frequencies rather than linearly based on requirements. This certainly leads to wastes. For example, a cell only needs 9 TCH channels, but we need to configure 2 TRXs (that is, 14 TCH channels). This means that 5 TCH channels are wasted. According to domestic network research and experience and statistics of several local networks, non-linear channel configuration decreases network utilization by 20% to 25%. For provincial capital cities, the figure is 20% and for common cities, the figure is 25%. Especially, for the backward areas, the figure is 30% because there are many single-carrier-frequency cells. At early stages of network construction, if heavy traffic congestion occurs, you need to consider the suppressed traffic requirements due to traffic congestion when performing a traffic model prediction. Specifically, add the traffic required for solving traffic congestion as the actual traffic to the traffic model. Then, the traffic model is a true traffic model that meets actual conditions.At different stages of network construction, it is proper to carry out an analysis and prediction of traffic models periodically. If the predicted proportion of activated mobile users is relatively proper, take into consideration this proportion. This can reduce the traffic model value of every user, and reduce costs of base stations or compensate for impact caused by other uncontrollable factors.Other impacts. Chapter 5 Network Capacity ImprovementIn the initial stage of a GSM network, the number of users is limited, and in this case, fewer BTSs with small model are suitable for the network capacity. In this situation, the main problem is network coverage. With the rapid user development and new service promotion, cell congestion is more and more severe and the network quality is attacked. Therefore, it is urgent to improve the network capacity. The process of the capacity design is:

BTS with small model->BTS expansion and cell splitting->Microcellular increase in hot stop->Two frequency construction->Half rate provisioning

5.1 Method of Improving the Network CapacityAdopting cell splitting

Adopting the more aggressive frequency multiplexing pattern

Adding microcellular equipment

Expanding frequency band

Adopting half rate

5.2 Analysis of Improving the Network Capacity5.2.1 Principle of Cell SplittingIn the initial stage of a GSM network, the network coverage is the main problem. This is because the antenna height is high, distance between BTSs is large, and the coverage radius is large.

With the user increment, the original cell can be split into cells with smaller coverage area.

Shorten the distance between BTSs, lower the antenna height, or increase the antenna downtilt angle appropriately, so as to narrow the coverage radius.

Through cell splitting, increase the number of BTSs in the network, and then the carrier frequencies and channels of the entire network increase, accordingly, the traffic and users are accommodated.

Method of implementing cellular splitting

Add a new BTS at the center point of the connection line between two existing BTSs.

Use half of the radius of the existing cell as the radius of the split cell and the antenna direction of sectors after splitting remains unchanged.

Cell splitting is limited and the distance of macro-cellular BTSs is at least 400m.

The antenna height of a BTS cannot be very high. That is, in a medium size city, the antenna height is about 25m.

For a BTS with high antenna height, lower the height in cell splitting.

5.2.2 More Aggressive Frequency Multiplexing PatternIf the network capacity cannot be increased through cell splitting, the more aggressive frequency multiplexing pattern can be used. That is, improve the frequency band usage and enlarge the BTS model supported by the network, so as to improve the network capacity. The common aggressive frequency multiplexing patterns are:Multiple multiplexing pattern (MRP)

1 x 3 (or 1 x 1) multiplexingConcentric circle

5.2.3 Adding Microcellular EquipmentTwo cases for microcellular: One is to improve the coverage blind zone and the other is to solve the problem of traffic overflow of the hot spot with high traffic.

The macro-cellular with large coverage is in the lower layer and absorbs the main traffic. The micro-cellular is with a higher layer and is the supplement of the macro-cellular coverage, which improves the indoor coverage, absorbs the traffic of the hot spot, and improves the network quality.

5.2.4 Expanding Frequency BandThrough expanding the frequency band, increase the carrier frequency of each cell so as to increase the system capacity.

When the 900M frequency resources are used for the GSM system, to improve the network capacity, the 1800M frequency band is needed to set up a two frequency to absorb the traffic.

The two frequency network of the same vendor uses the co-bcch technology to economize a common control channel (CCCH).

5.2.5 Adopting Half RateThe frequency resources are limited, so expansion in increasing carrier frequencies is hard to be achieved. In addition, frequency point increase means diseconomy. When half rate traffic channel TCH/HS (half rate speech) is adopted, the channel that carries one TCH/FS or one TCH/EFS carries two TCH/HS. That is, the channel capacity doubles.The half rate voice uses the VSELP coding. To adapt to the half rate bandwidth, the coding rate decreases to 5.6 kbps. Compared with the full rate voice coding 13 kbps, the voice quality degrades.

Chapter 6 Location Area PlanningLocation area (LA) is an important concept in GSM. According to the GSM protocol, the entire mobile communication network is divided into different service areas based on location area code (LAC). LA is the unit for paging scope in a GSM system. That is, the paging message pages in the unit of LA. The paging message of a mobile subscriber is sent in all the cells of an LA. One LA may contain one or more base station controllers (BSC) but it belongs to only one mobile switch center (MSC). In addition, one BSC or MSC may contain multiple LAs.

The size of an LA, the coverage of an LAC, is a key factor in the system. In the aspect of decreasing the location update frequency and economizing the channel resources of a system, the bigger the LA is the better. This is because the more the location update, the bigger the SDCCH load, which wastes the channel resources and increases the MSC and HLR load. In addition, the mobile station requires about 10s to update cells. In this period of time, a call cannot be made. However, if an LA is over size and is beyond the paging capability of the system, the paging signaling load in the system is very high, which leads to paging message loss and decrement of the paging success ratio. The low paging success ratio generates the second call for a subscriber. In this case, the paging load in the system increases and the paging success ratio deteriorates. Therefore, the LA cannot be set to a large value. In network planning, consider and balance the LA capacity, channel resources and paging capability in the system. In the case that the paging load is not very high, decrease the update frequency of the LA to a minimized value.

6.1 Demarcating Boundary of LAIn the initial stage of a GSM network, BTSs in multiple BSCs can be divided into an LA. With the increase of traffic and carrier frequency capacity, the traffic carried by each BSC increases greatly and LA demarcation approaches to BSC demarcation. That is, one BSC is demarcated to one LA. In a fewer cases, one BSC can be demarcated to multiple LAs. However, problems may arise because of the very small LA. For example, inter-LA update occurs more frequently and thus the switch load increases.

When location update occurs in different LAs, a mobile phone cannot communicate normally. In density urban areas with high traffic, a mobile phone is active in the overlap areas of different LAs. In this case, a high requirement for boundary setting of two LAs or multiple LAs is required. With the network development, user density increases and the effect of inter-LA update on the system load increases. Therefore, the boundary setting of LAs is more important. According to features of the normal location update, boundary demarcation of the LA needs to comply with the following principles:

Try not to set the boundary away from the areas with high traffic such as urban areas, instead, set it in areas with low traffic or for low-end users such as rural areas and factories. These areas are with low density, location update scope of the mobile phone narrows, and inter-LA update has relatively lower load for the network. When the LA boundary should cover the urban areas, try to set the boundary in the areas with low mobility such as residential areas.

Set the LA boundary and the road with an angle and try to prevent the overlap areas of the LA from being in the areas with high mobility. This avoids a large amount of toggle location update in inter-LA. If the setting is improper, the system will be severely affected.

The boundary of multiple LAs is avoided in the same small area, and this prevents the mobile phone from frequently updating among location areas in the small area.

When demarcating the boundary, the traffic increase trend needs to be taken into consideration. In addition, in designing paging capacity and traffic capacity of an LA, the expansion margin needs to be considered, so as to prevent the LA from demarcating and splitting frequently.

6.2 Paging Capacity of LA6.2.1 Analysis of Paging PrincipleWhen a mobile station of an LAC is paged, the MSC initiates the paging request for all the cells corresponding to the LAC through BSC. Currently, the GSM network provides two paging modes: TMSI and IMSI.

In the GSM system, each user is allocated with a unique IMSI. The IMSI is written in the SIM card of a mobile phone, and it is with eight bytes and is used for identity identification. The TMSI is allocated temporarily by the VLR for the visited mobile subscriber after successful authentication. The TMSI is temporarily used for the air interface instead of the IMSI only in the VLR jurisdictional areas. In addition, TMSI corresponds to IMSI and is with four bytes. In this case, when the paging channel of the air interface adopts IMSI, the paging request contains only two IMSI numbers; but if TMSI is adopted, four TMSI numbers are contained. Therefore, paging load of IMSI is twice more than that of TMSI.

When obtaining current LAI of the mobile station from VLR, MSC initiates the paging message to all the BSCs in the LA. After receiving the paging message, BSCs send the paging message to all the cells belonging to the LA of the BSCs. When receiving the paging message, BTS sends the paging request to paging sub-channels where the paging group is located. The paging request carries IMSI or TMSI of the paged user. After receiving the paging request, the mobile station uses the random access channel (RACH) to allocate SDCCH. In addition, after confirming that the BTS activates the required SDCCH, BSC assigns the SDCCH to the mobile station by assigning the message in the access grant channel (AGCH). Then, the mobile station uses the SDCCH to send the paging response to BSC and BSC forwards the paging response to MSC. In this case, a successful radio paging is complete.

6.2.2 Paging PolicyIf the MS LA is known in VLR, the first paging message is broadcasted in the LAs that are registered in MS, that is, local paging. If MS does not respond to the first paging, MSC initiates the second paging. Usually, the second paging is broadcasted in the original LA. However, the second paging can be performed in all the cells in the entire MSC, that is, global paging. The global paging is with a higher success ratio. In paging, TMSI or IMSI can be used to differentiate MS.

6.2.3 Setting Paging ParametersAccording to the GMS specifications, CCCH has two configurations:

Shared CCCH and SDCCH, also called combined BCCH. In this configuration, each multiframe transfers three paging groups.

Un-shared CCCH and SDCCH, also called un-combined BCCH. In this configuration, each multiframe transfers nine paging groups.

The paging group can be used as the paging channel (PCH) to broadcast the paging request, and can be used as the AGCH to respond the access request of a mobile phone. In operation, multiple multiframes can be combined together so as to form a paging cycle to increase the number of paging groups in a cell. In this case, the mobile phone senses its belonged paging group periodically. Therefore, when the mobile phone is called, it monitors the paging request sent from the BTS and responds.

If there are many paging groups, a long time will be cost before the mobile phone monitors the correct paging group. This increases the paging time. If there are fewer paging groups, the paging setup time will be shortened because the mobile phone answers the paging group frequently. This wastes electricity of the mobile phone. The number of paging groups of a cell can be adjusted through the following two parameters:

Access grant reserved blocks (BS-AG-BLK-RES)

This parameter defines the number of paging groups that are configured with the dedicated AGCH of each multiframe. For the cell with combined BCCH, BS-AG-BLK-RES ranges from 0 to 2. For the cell with un-combined BCCH, BS-AG-BLK-RES ranges from 0 to 7. If the cell broadcast channel (CBCH) is used, BS-AG-BLK-RES ranges from 1 to 7. The value of BS-AG-BLK-RES can be 0, it indicates that no dedicated AGCH is used, and all the paging groups are shared by PCH and AGCH. If BS-AG-BLK-RES is equal to or larger than 1, it indicates that a paging group is reserved as the dedicated AGCH. This is determined by the traffic of the cell.

The following figure lists the number of CCCHs contained in each BCCH multiframe (including 51 frames) when different CCCHs are configured.

CCCH_CONFBS_AG_BLK_RESNumber of CCCHs in Each BCCH Multiframe That Are Reserved for AGCHNumber of CCCHs in Each BCCH Multiframe That Are Reserved for PCH

1003

112

221

Others (invalid)--

Others009

118

227

336

445

554

663

772

Paging channel multiframes (BS-PA-MFRAMS)

This parameter defines multiframes in 51 TDMA frames of MS of the same paging group that are sent by the transmission paging message. According to the GSM specifications, each mobile subscriber (corresponding to each IMSI) belongs to a paging group. In every cell, each paging group corresponds to a paging sub-channel. The mobile station calculates to which paging group it belongs based on its IMSI. Then, it calculates the location of the paging sub-channel that belongs to the paging group. In an actual network, the mobile station just listens the paging sub-channel to which it belongs but not listen the contents of other paging sub-channels. In addition, disable the power of certain hardware components of the mobile station to save the power cost (source of DRX). BsPaMframes refers to a cycle with how many multiframes that are used as the paging sub-channels. Actually, this parameter determines the number of paging sub-channels of the paging channels in a cell. Calculation of this parameter is mainly used to calculate the paging group of MS, so as to sense the corresponding paging sub-channels.

The following tables lists the relation between AGCH and MFRMS, and number of paging group and paging group interval.

BS_PA_MFRAMSPaging Group Interval (s)Number of Paging Groups in Combined BCCHNumber of Paging Groups in Un-combined BCCH

AGCH=0AGCH=1AGCH=0AGCH=1

20.47641816

30.71962724

40.941283632

51.1815104540

61.4118125448

71.6521146356

81.8924167264

92.1227188172

6.2.4 Calculating LA CapacityThe method of calculating the LA capacity is as follows:Paging blocks/s x Paging messages/paging block = Maximum pagings/s->Supported pagings/h->Permitted traffic/LA->Supported carrier frequencies/LA

Paging blocks/s:One frame = 4.615 ms and one multiframe = 0.2354s. Assume that AGB access grant reserved blocks are permitted, paging blocks each second are: For the un-combined BCCH: Paging blocks/s = (9-AGB) / 0.2354 (paging blocks/s)

For the combined BCCH: Paging blocks/s = (3-AGB) / 0.2354 (paging blocks/s)

For the un-combined BCCH, ZTE configures AGB = 2, that is, paging blocks/s = 29.7/s. For the combined BCCH, ZTE configures AGB = 1, that is, paging blocks/s = 8.5/s. Note that in an LA, it is not suitable to configure the combined BCCH cell and un-combined BCCH cell concurrently, and the access grant reserved blocks must be the same in the same LA. Otherwise, the paging capacity degrades to be the lowest paging capacity of an LA. However, if the capacity of a cell is small, and the LAC resources are in short supply, the combine BCCH cell and un-combined BCCH cell can be configured in a same LA. This increases the number of traffic channels of BTSs in 01 and S111 models.

Pagings/paging blocks (X)

When a BTS broadcasts a paging request through a paging group, there are following configurations: two IMSIs, two TMSIs and one IMSI, and four TMSIs. In this case, the average pagings X sent by each paging block is:

X = 2 pagings/paging block

IMSI is used.

X = 4 pagings/paging block

TMSI is used.

The maximum pagings P sent each second

can be calculated:

For the un-combined BCCH: P = (9-AGB) / 0.2354 (paging blocks/s) x X (pagings/paging block)

For the combined BCCH: P = (3-AGB) / 0.2354 (paging blocks/s) x X (pagings/paging block)

For IMSI, when the un-combined BCCH is used, if AGB = 2, P = 59.47 pagings/s; when the combined BCCH is used, if AGB = 1, P = 16.99 pagings/s.

For TMSI, when the un-combined BCCH is used, if AGB = 2, P = 118.95 pagings/s; when the combined BCCH is used, if AGB = 1, P = 33.98 pagings/s.

Permitted traffic/LA (T)

When designing the LA capacity, note that the LA size cannot exceed the maximum paging capacity it can be bore. In the case of a running network, paging messages issued by BSC in the basic measurement can be collected from the server, and then converts the result to paging messages/s. The paging messages/s cannot exceed the preceding calculated result.

When there is no traffic data to be used as reference, if a new network is created, calculate the traffic according to an assumed traffic model.

Average communication time: 60s, that is, 1/60 Erl.

Proportion of successful called MSs + pagings generated by SMS and total pagings + SMS pagings is 30%. If the USSD service is provisioned in the network, the SMS pagings generated by the USSD service should be contained in the preceding SMS pagings.

Assume that 75% MSs respond in the first paging, 25% MSs respond in the second paging, and MSs that respond in the third paging are not taken into account. In this case, successful called MS each time needs 1.25 pagings.

( Caution:The above-mentioned traffic model data is for reference. If a new network is pre-planned, and no existing network data or data from other carriers for reference, confirm with the office's engineers. If an existing network is planned, calculation must be performed based on the statistics of the server, including the average communication time, proportion of pagings, and proportion of the first and second pagings. Where, proportion of pagings = successful called MSs (leading to paging and generating TCH traffic) + pagings generated by SMS / total pagings + SMS pagings. Assume that the paging channel is congested after pagings exceed 50% of the theoretical maximum paging capacity. That is, under the condition that pagings do not exceed 50% of the maximum paging capacity, the original paging messages are not lost because of full paging queues in a BTS. In this case, the paging capacity in a second is P x 50%.

When IMSI is used, if AGB = 2 and the un-combined BCCH is used, the traffic permitted in an LA is: T x 30% / (1 / 60) x 1.25 = P x 50% = 59.47 x 3600 x 50%T = 4757.6 Erl

(AGB = 2 and un-combined BCCH is used)In the same way:

T= 1359.39 Erl

(AGB = 1 and the combined BCCH is used)

When TMSI is used, the traffic permitted in an LA is:

T= 9515.72 Erl

(AGB = 2 and un-combined BCCH is used)

T= 2718.78 Erl

(AGB = 1 and the combined BCCH is used)

6.2.5 Effect of SMS on Paging Capacity of LAThe SMS can be sent through SDCCH or SACCH. The sending process can be divided into the SMS calling process and SMS called process according to differences between the sent SMS and the received SMS. The effect of SMS on the paging capacity of an LA represents in the effect on receiving SMS by a mobile phone. That is, when a mobile phone receives SMS, the systems pages the mobile phone just like that the mobile phone serves as the called party. Therefore, it can be determined that the effect on receiving a short message by a mobile phone is the same as the effect that the mobile phone serves as the called party. The following calculates SMS and analyzes the effect of the SMS on the system according to an SMS traffic model.

Assume that the SMS service is three SMS/subscriber/day, the resend proportion is 30% and the centralized index in busy hour is 0.12. Take 100,000 subscribers in an LA as an example, SMS pagings in busy hour of an LA is:

100000 x 3 x 0.12 x (1 + 30%) = 46800 (pagings/h)From the result, we can see that paging caused by SMS is large and has effect on the system.

In addition, SMS features in burst. In peak hours such as holidays, the burst factor reaches 3-8. That is, in peak hours, SMS in holidays are 3-8 multiples more than normal. At this time, pagings caused by SMS is:

100000 x 3 x 0.12 x 8 x (1 + 30%) = 374400 (pagings/h)This value is very tremendous and peak hours of SMS accompany peak hours of traffic. These two peaks lead to very big paging and attack the system greatly. In this case, flow control protection is required. For example, do not resend the SMS, delay sending SMS in peak hours, and decrease the maximum pagings. This meets the requirements of SMS and traffic in peak hours.

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