GSM Radio Network Planning

GSM Radio Network Planning and Optimization Chapter 5 GSM Radio Network Planning Confideniality level

2006-01-05 All rights reserved Page 1 of 121

Table of Contents

Chapter 5 GSM Radio Network Planning ...................................................................................... 3

5.1 Overview ............................................................................................................................. 3

5.2 Planning Foundation ........................................................................................................... 5

5.2.1 Coverage and Capacity Target Confirmation ............................................................ 5

5.2.2 Performance Target Confirmation ............................................................................. 6

5.3 Coverage Analysis .............................................................................................................. 7

5.3.1 Area Division ............................................................................................................ 7

5.3.2 Radio Environment Survey ..................................................................................... 10

5.4 Network Structure Analysis ............................................................................................... 11

5.4.1 Middle-Layer Station ............................................................................................... 11

5.4.2 High-Layer Station .................................................................................................. 12

5.4.3 Low-Layer Station ................................................................................................... 13

5.5 Traffic Analysis .................................................................................................................. 14

5.5.1 Traffic Prediction and Cell Splitting ......................................................................... 14

5.5.2 Voice Channel Allocation ........................................................................................ 17

5.5.3 Control Channel Allocation ..................................................................................... 20

5.6 Base Station Number Decision ......................................................................................... 23

5.6.1 Characteristics of 3-sector base stations in urban areas ........................................ 23

5.6.2 References for Design of Base Station Parameters ................................................ 25

5.6.3 Uplink and Downlink Balance ................................................................................. 27

5.6.4 Cell Coverage Estimation ....................................................................................... 34

5.6.5 Base Station Address Planning .............................................................................. 37

5.6.6 Coverage Prediction ............................................................................................... 39

5.7 Design of Base Station Address........................................................................................ 39

5.7.1 Address design ....................................................................................................... 39

5.7.2 Project Parameter Decision .................................................................................... 42

5.8 Location Area Design ........................................................................................................ 58

5.8.1 Definition of Location Area ...................................................................................... 58

5.8.2 Division of location areas ........................................................................................ 58

5.8.3 Others ..................................................................................................................... 63

5.9 Dual-Band Network Design ............................................................................................... 64

5.9.1 Necessity for Constructing Dual-Band Network ...................................................... 64

5.9.2 GSM 1800MHz Coverage Solutions ....................................................................... 65

5.9.3 Location Area Division for Dual-Band Network ................................................... 6867

5.9.4 Traffic Guidance and Control Strategies of Dual-Band Network ............................. 69

5.9.5 Dual-Band Networking Engineering Implementation ........................................... 7271

5.10 Design of Indoor Coverage System ................................................................................ 75

5.10.1 Characteristics of Indoor coverage ....................................................................... 75

5.10.2 Indoor Antenna System Design ............................................................................ 76

5.10.3 Capacity Analysis and Design .............................................................................. 83



5.10.4 Frequency Planning .............................................................................................. 85

5.10.5 Traffic Control ................................................................................................... 8685

5.11 Tunnel Coverage ............................................................................................................ 86

5.11.1 Characteristic of Tunnel Coverage ....................................................................... 86

5.11.2 Tunnel Coverage Solution ................................................................................ 8887

5.11.3 Tunnel Coverage Based on Coaxial distributed antenna system .......................... 89

5.11.4 Tunnel Coverage Based on Leaky Cable System ................................................. 92

5.11.5 Coverage Solutions to Tunnels in Different Length ............................................... 99

5.12 Repeater Planning ........................................................................................................ 101

5.12.1 Application Background ...................................................................................... 101

5.12.2 Working Principles of Repeater .......................................................................... 106

5.12.3 Repeater Network Planning ................................................................................ 108

5.13 Conclusion .................................................................................................................... 120



Chapter 5 GSM Radio Network Planning

5.1 Overview

The design of radio network planning (RNP) is the basis of the construction of a

wireless mobile network. The design level of network planning decides the future

layout of a network.

During network planning, the documents concerning base station distribution,

channel assignment, and cell data must be outputted. And the major tasks

involved are as follows:

1) Analyze carriers requirements on network coverage, capacity and quality.

2) Analyze the coverage and capacity features of the candidate mobile

communication systems and bands, and then analyze the investment

feasibility through estimating the network scale.

3) Decide the network structure and base station type based on further

analysis.

First analyze whether to construct a layering network according to user

distribution, propagation conditions, city development plan and existed

network conditions, and then analyze the sites within this area to decide

whether to use omni antennas or directional antennas to meet the

requirements on coverage and capacity.

4) Estimate the number of base stations

Before estimating the number of base stations, estimate the coverage

distance of base stations of various types in various coverage areas. The

factors deciding the effective coverage area of a base station include:

Valid transmit power of the base station

Working bands to be used (900 MHz or 1800 MHz)

Antenna type and installation position

Power budget

Radio propagation environment

Carriers indexes on coverage

Then through calculating the coverage distance and dividing the coverage

areas, you can obtain a rough number of base stations for various coverage

areas.

5) Plan an ideal base station address according to cellular structures.

According to geographic maps or administrative maps and with the help of

on-the-spot surveys, you can have a full understanding of the areas to be

planed, and then mark the area where the number of users is large as a

target address. After that, mark the addresses of other base stations

according to the ideal cellular structure and the result of link budget.

6) Calculate the number of channels of the cells of each base station



Estimate the traffic of a base station according to its ideal location, and then

obtain the number of carriers and channels needed by each base station by

checking Erl table according to the indexes of call loss rate.

Decide the frequency reuse mode according to band width, network quality

requirement, and equipment supportability.

Estimate the maximum base station configuration type according to the

frequency bandwidth and reuse mode provided by the construction carriers.

If the system capacity in some areas cannot be met, you need to add more

base stations or cells to the system according to cell splitting principles and

actual conditions. After that, reselect an ideal base station address on the

map and re-estimate the number of channels required by the base station.

7) Predict the coverage area and decide the project data, namely, perform the

preliminary emulation. The specific tasks are as follows:

Select the design indexes

Select the minimum received power and the penetration ratio index at the

coverage area edge.

Select the design parameters, which includes:

Antenna height (above the ground), antenna azimuth angle, antenna gain,

antenna tilt angle, base station height above sea level, base station type,

feeder length, antenna feeder system loss, combining and distribution

modes, transmitter output power, receiver sensitivity, base station diversity

reception, and diversity gains.

Predict the coverage area of each cell according to the propagation models

in different areas, and then give the opinions on adjusting the base station

address, antenna direction, antenna tilt angle, and antenna height in the

areas where dead zones may be present and signals are poor. Finally,

provide the project data.

8) Select actual base station address and decide base station type:

Perform filed examination according to the ideal base station addresses,

and then record the possible addresses according to various construction

conditions (including power supply, transmission, electromagnetic

background, and land taken over). Finally, recommend a suitable address

based on integrated consideration of the deviation from the ideal base

station address, the effect on future cell splitting, economic benefits, and

coverage prediction.

After the base station address is selected, decide the actual base station

type according to the number of base station channels.

After the base station type is decided, you need to make a scheme for

antenna configuration. For moving a network, if you intend to provide a best

combination scheme for the antenna feeders, you must fully investigate the

combination of the antenna feeders of the original carriers, plan the future



expansion of the base station, and design the combination of the antenna

feeders supported by current equipments.

9) Plan frequency and adjacent cell

Decide the frequency and adjacent planning according to the actual base

station distribution and type.

10) Make cell data

To ensure that the network runs stably, you must design the parameters

relative to performance for each cell. These parameters include system

information parameters, handover parameters, power control algorithm

parameters, and so on.

Note:

For the selection of handover bands, the handover algorithms to be enabled,

and whether to use frequency hopping, power control, and DTX, they must

be decided in coverage prediction and frequency planning, because the

related parameters will be used in emulation.

In addition, sections 5.9 and that later introduce the solutions to the planning of

dual-band network and the planning in special occasions.

5.2 Planning Foundation

5.2.1 Coverage and Capacity Target Confirmation

Before planning a network, you must confirm the network coverage and capacity

target and relative specifications from carriers. They are specified as follows:

Definition of coverage areas

Specific division of the service quality in coverage areas

Grade of service (GoS) at Um interface

Prediction of network capacity and subscriber growth rate

Available bands and restrictions on using bands

Restrictions on base station address and the number of carriers

Penetration loss in cars or indoor environment

Performance and sensitivity of base stations

Rules on base station naming and numbering

Information of the base stations in the existing network

Engineers perform the network planning and guide the subsequent construction

work according to the previous technical specifications. Because any change of

these specifications will affect network construction, you must discuss these

specifications with carriers and get their confirmation.



5.2.2 Performance Target Confirmation

Carriers emphasize much on the future network quality. Therefore, network

planning engineers must judge the indexes concerning network performance

according to construction difficulty and experience, and then cooperate with

carriers to design a reasonable solution.

Generally, the performance of voice services can be judged according to KPI

indexes, which are specified in Table 5-1Table 5-1

Table 5-1 Descriptions of KPI indexes

Number KPI index Meaning Test method Reference

value

1 TCH congestion

ratio

TCH seizure

failures/attempted

TCH seizures 100%

OMC < 2%

2 SDCCH congestion

ratio

SDCCH seizures and

all busy

times/SDCCH seizure

requests 100%

OMC < 1%

3 Call drop ratio

TCH call drop

times/TCH

occupation success

times 100%

OMC < 2%

4 Handover success

ratio

Handover success

times/handover

attempted times

100%

OMC > 92%

5 Call setup time Average call setup

times Drive test < 10s

6 Coverage

probability

The percentage of the

received level greater

than -90 dBm

Drive test > 90%

7

FTP average

download rate

(kbps)

Applied to GPRS Drive test = 16

8 FTP average

upload rate (kbps) Applied to GPRS Drive test = 3.2

9 Forward/reverse

transmission delay Applied to GPRS Drive test < 20s

10 Ping success ratio Applied to GPRS Drive test = 90%

11 Ping average delay Applied to GPRS Drive test < 3.5s



12

Mean opinion score

(MOS)

The voice quality is

divided into fiver

levels from excellent

to bad.

Drive test = 3

Note:

The KPI indexes vary slightly with carriers.

The mean opinion score (MOS) in the previous table is divided into five levels,

which are specified in Table 5-2Table 5-2.

Table 5-2 Mean opinion score (MOS)

Quality level Quality evaluation standard

5 Excellent

4 Good

3 Fair

2 Poor

1 Bad

Note:

The call whose quality is above level 3 can access the mobile

communication network.

The call whose quality is above level 4 can access the public network.

5.3 Coverage Analysis

5.3.1 Area Division

I. Types of coverage area

The signal propagation models are applied in accordance with the propagation

environments in areas of different types. The signal propagation models decide

the design principles, network structures, grade of services and frequency reuse

modes for the radio networks in coverage areas. In order to decide the cell

coverage area, you can the radio coverage areas into the following four types:

Big city

Middle-sized city

Small town

Countryside



Error! Reference source not found. lists the divisions.

Table 5-3 Coverage area division

Area type Description

Big city

Dense population

Developed economy

Large traffic

Dense high buildings and mansions distributed in

center areas

Flourishing shopping centers

Middle-sized city

Relatively dense population

Relatively developed economy

Relatively large traffic

Dense buildings distributed in center areas

Active and promising shopping centers

Small town

Relative large population

Promising economic development

Moderate traffic

Relative dense buildings distributed in center areas

A certain scale of shopping centers but with great

potentiality

Countryside

Scattered population

Developing economy

Low traffic

In addition, you must consider the coverage of the areas at the intersections and

various transport arteries, including:

Express way

National high way

Provincial highway

Railway

Sea-route

Roads in mountain areas

Generally, it is recommended to apply omni base stations in the countries plains

and the areas with restricted landforms. In big cities, middle-sized cities, and

along expressways, it is recommended to apply directional base stations.

II. Define the field strength at coverage area edges

When defining the field strength of the uplink edges of a service area, you must

consider the factors listed in Table 5-4Table 5-4.



Table 5-4 Typical factors concerning the definition for the filed strength at

coverage area edges

Factor Value

Mobile station sensitivity -102 dBm

Fast fading protection 4 dB (3 dB for countryside)

Slow fading protection 8 dB (6 dB for countryside)

Noise (environmental noise and

interfering noise) protection 5 dB

Remark:

To ensure the indoor coverage in big and middle-sized cities, you can

consider 15dB for the average penetration loss between buildings and

consider adding 5dB to the protection margin.

Generally, the propagation loss of GSM 1800MHz signals is 8 dB greater

than that of the GSM 900MHz signals in average.

Radio links have two directions, namely, uplink direction and downlink

direction, and the coverage area is defined by the direction in which the

signals are poor, so you must consider the uplink and downlink balance.

Therefore, if you intend to plan an ideal network, you must make a good

power control budget so that the uplink and downlink can be as balance as

possible.

III. Define coverage probability

The definition of coverage probability varies with the coverage areas, and the

coverage probability is gradually improved along with the construction of the

network.

In China, the coverage probability can be defined according to Table 5-5Table

5-5.

Table 5-5 Definition of coverage probability at different stages and in different

areas

Construction

stage Areas Coverage target

Early stage

Significant national tourism areas,

expressways, national highways,

and the areas along busy railways.

Full coverage.



Other major roads, railways and

sea-routes

The coverage probability

must be greater than

90%.

Development

stage

Key areas, such as government

offices, press centers, airport

lounges, waiting rooms of train

stations, subways, commercial

office buildings of high ranks,

entertainment centers, and large

shopping malls.

With the development of

the network

construction, the number

of users grows larger

and they require

services of higher grade,

so the quality of indoor

coverage of the areas in

the left column must be

greatly enhanced.

Remarks:

Generally, a call must be ensured to access the network at 90% of the places

and 99% of the time within the coverage area.

For the outdoor environment in big cities, the two ratios must be greater.

For the areas in countryside, the two ratios can be lower.

For transport arteries, different standards are applied, and the coverage

probability can be defined in accordance with the types of the arteries.

5.3.2 Radio Environment Survey

Through surveying radio propagation environments, you can get familiar with the

overall landforms, estimate the rough antenna height, and select the proper radio

propagation model, among which the radio propagation model helps you estimate

the number of base station when predicting the coverage. If necessary, you must

adjust the propagation model.

For GSM 900MHz, the formulas estimating radio path loss in different areas are

simplified in Table 5-6Table 5-6.

Table 5-6 Formulas estimating radio path loss in different areas

Formula Application

area

Propagation model

adopted

Example



PLDU = 147.2 +

8d + 40.5lgd

Densely

populated

urban areas

Walfish-Ikegami If carrier frequency = 925

MHz, hBTS < hobstacle, and d <

0.5km, hBTS = 25mhobstacle =

30m, street width = 25m,

building width = 50m

PLU = 128.73 +

38lgd

Common

urban areas

Walfish-Ikegami If carrier frequency =

925MHz and hBTS > hobstacle,

hBTS = 25m, hobstacle = 20m,

street width = 25m, building

width = 50m

PLSU = 126 +

35lgd

Suburban

areas

Okumura-Hata If carrier frequency =

925MHz, hBTS = 30m

PLRU = 116 +

35lgd

Countryside

areas

Okumura-Hata If carrier frequency =

925MHz, hBTS = 30m

Note:

The four formulas provided in this section are applicable to simple estimation

during project survey only. For later planning, you must adopt the precise

propagation models. If necessary, you must further adjust the propagation models

through CW measurement.

5.4 Network Structure Analysis

When considering the layout of base stations, you must deeply analyze network

structure. Generally, according to network layers, a network can be divided into

middle-layer, high-layer, and low-layer. The base stations at the middle-layer bear

the greatest traffic in a network

5.4.1 Middle-Layer Station

I. Definition and application

A middle-layer station in big and middle-sized cities is defined as follows:

The antenna is installed on building tops.

The antenna height ranges from 25 to 30 meters, which is greater than the

average height of the buildings.

It covers several blocks.



In small towns and countryside areas, except the high-layer stations are designed

for controlling traffic flow or for landform reasons, most of the base stations are

middle-layer stations.

II. Advantages

Compared with high-layer stations, middle-layer stations can utilize frequency

resources more efficiently. Compared with low-layer stations, middle-layer

stations can absorb traffic more efficiently. Therefore, the middle-layer stations

bear the greatest traffic in a network.

III. Distance between stations

The average distance between most middle-layer stations range from 0.6 to 5 km

except in countryside areas. In big cities, the distance between some

middle-layer stations is shorter than 0.6 km. However, it is suggested that the

distance between middle-layer stations in big cities cannot be shorter than 0.4 km.

If this distance is too short, the buildings will produce strong interference against

the signals of the base stations. In this case, to control the coverage area is quite

demanding.

IV. Challenges

Because no suitable ground objective is available, to ensure the quality of service

of a network is quite demanding. According to the experience on project

construction and maintenance, great challenge is present in the selection of base

station address, station design, project construction, network maintenance, and

network quality.

5.4.2 High-Layer Station


A high-layer station in big and middle-sized cities is defined as follows:

The antenna height ranges from 10 to 50 meters, which is far greater than

the average height of the buildings.

Its coverage areas contain the areas covered by multiple middle-layer

stations.

Because the high-layer stations make poor use of the frequency resources, they

are mainly applied to the traffic networks where people move fast in big and

middle-sized cities.

In addition, to control construction cost and meet coverage requirements, you can

install some high-layer stations in suburban areas, highroads, small towns, and

countryside areas.



II. Functions

The high-layer stations must be as fewer as possible but be as effective as

possible. They mainly provide services to the fast-moving subscribers in cities.

Note:

The coverage of high buildings is realized by indoor distribution systems.

5.4.3 Low-Layer Station


A low-layer station is defined as follows:

The antenna height is shorter than 20 meters, which is shorter than the

average height of the buildings.

The antenna can be installed on the outer walls of the lower floors of a

building, on the top of lower roofs, or in the rooms of a building.

Generally, at the early stage of the network construction, signal network design is

applied, so most of the base stations are middle-layer stations. After the basic

network is established, you must adjust the base stations and add new base

stations according to traffic and coverage requirements.

For populated commercial areas where the traffic is heavy, you can use low-layer

stations, which are constructed with micro cell layer and distributed antenna

system. In this case, not only the requirements on indoor coverage are met, but

also the interference and difficulties of base station selection caused by short

distance between stations are avoided. With the development of the network, the

low-layer stations will develop into the layering network structure.

II. Other considerations

The coverage area of a low-layer station is small, so it can fully use frequency

resources but cannot absorb the traffic efficiently. As a result, ideal traffic cannot

be ensured if the base station deviates far away from the areas where the traffic is

heavy.

Therefore, when constructing a low-layer station, you must consider whether the

base station is used to make up coverage or solve the problem of heavy traffic,

because the construction purpose is directly related to the selection of the

address and type of the base station.

Note:

A layering network cost much frequency resource, so it is not recommended for

the networks where the frequency resource is inadequate.



5.5 Traffic Analysis

5.5.1 Traffic Prediction and Cell Splitting

I. Traffic prediction

The network construction requires the consideration of economic feasibility and

rationality. Therefore, a reasonable investment decision must be based on the

prediction of the network capacity of the early and late stage.

When predicting network capacity, you must consider the following factors:

Population distribution

Family income

Subscription ratio of fixed telephone

Development of national economy

City construction

Consumption policy

After predicting the total network capacity, you must predict the density of

subscriber distribution. Generally, base stations are constructed in urban areas,

suburban areas, and transport arteries. Therefore, you can use the percentage of

prediction method.

At the early stage of construction, the subscribers in cities account for a larger

percentage of the total predicted subscribers. With the development of the

network construction, the percentage of the subscribers in suburban areas and

transport arteries grows. The traffic of each subscriber is 0.025 Erl in urban areas

and 0.020 Erl in suburban areas.

The formula calculating traffic is:

A = (n T) / 3600

Here,

n is the call times in busy hour

T is the duration of each call, in the unit of second.

In this way, the number of voice channels needed for a base station can be

obtained through predicting the traffic.

Note:

When estimating the number of voice channels needed for a base station in the

future, you must consider the effect caused by cell splitting.

In a GSM system, you can use Erl model to calculate the traffic density that the

network can bear. The call loss can be 2% or 5% depending on actual conditions.



Because restrictions on cell coverage area and the width of the available

frequencies are present, you must plan the cell capacity reasonably. If good voice

quality is ensured, you must enhance the channel utilization ratio as much as

possible.

In actual networking, if the network quality is ensured at a certain level, two

capacity solutions are available, namely, a few stations with high-level

configuration and multiple stations with low-level configuration. Both the

advantages and disadvantages of the two solutions are apparent, so which one

should be used depending on the actual conditions of an area.

For network construction, you can expand the capacity either through adding

base stations or through expanding the base station capacity. The expansion

strategies adopted must be in accordance with the traffic density in an area. For

example, the strategies such as adding 1800 MHz base stations, expanding

sector capacity, adding micro cells, or improving indoor coverage can be used to

expand network capacity.

II. Cell splitting

Cell splitting is quite effective for the expansion of network capacity. An omni base

station can split into multiple sectors, and a sector can split into multiple smaller

cells. In other word, you must plan cell radius in accordance with the traffic

density of an area.

Cell splitting means more base station and greater cost are needed. Therefore,

when planning a network, you must consider the following factors:

The rules and diagrams of frequency reuse are repeatable.

The original base stations can still work.

The transition cells must be reduced or avoided.

The cell can split without effect.

Cell splitting is quite important in a network. The followings further describe the

cell splitting based on 1-to-4 splitting.

Cell splitting is used to split a congested cell into multiple smaller cells. Through

setting the new cells whose radiuses are smaller than the original cells and

placing them among the original cells, you can increase the number of channels

in a unit area, thus increasing channel reuse times. In this case, system capacity

is expanded.

Through adjusting the project parameters relative to antenna feeders and

reducing transmitter power, you can narrow the coverage area of a cell. Error!

Reference source not found. shows that a cell splits into four smaller cells by

half of its radius.



Figure 5-1 Schematic diagram of cell splitting (1-to-4)

As shown in Figure 5-1Figure 5-1, smaller cells are added without changing the

frequency reuse mode. They are split proportional to the shape of the original cell

clusters.

In this case, the coverage of a service area depends on the smaller cells, which

are 4 times outnumber of the original cells. To be more specifically, you can take a

circle with the radius R as an example, the coverage area of the circle with the

radius R is 4 times that of a circle with the radius R/2.

According to Figure 5-1Figure 5-1, after cell splitting, the number of cell clusters

in the coverage area increases. Thus the number of channels in this coverage

area increases and the system capacity is expanded accordingly.

You can adjust the coverage area of the new cells through reducing the transmit

power. For the transmit power of the new cells whose radiuses are half of that of

the original cell, you can check the power Pr received at the new cell edge and

at the original cell edge, and make them equal. However, you must ensure that

the frequency reuse scheme of the new micro cells is the same as that of the

original cell. As for Figure 5-1Figure 5-1,

Pr [at the edge of the original cell] = Pt1R-n, and,

Pr [at the edge of the new cell] = Pt2 (R/2)-n

Here,

Pt1 and Pt2 are the transmit power of the base stations of the original cell and the

new cell, and n is path fading exponent. If make n = 4, make the received power at

the edge of the new and original cell equal, the following equation can be

obtained:

Pt2 = Pt1/16



That is to say, if the micro cells are used to cover the original coverage area and

the requirement of S/I is met, the transmit power must be reduced by 12 dB.

Not all cells need splitting. In fact, it is quite demanding for carriers to find out a

perfect cell splitting scheme. Therefore, many cells of different scales exist in a

network simultaneously. As a result, the minimum distance among intra-frequency

cells must be maintained, which further complicate frequency allocation.

In addition, you must pay attention to the handover because success handover

ensure the all subscribers to enjoy good quality of service regardless of moving

speed.

As shown in Figure 5-1Figure 5-1, when two layers of cells are present within an

area but their coverage scale is different, according to the formula Pt2 = Pt1/16,

neither all new cells can simply apply the original transmit power, nor all original

cells can simply apply the new transmit power.

If all cells apply great transmit power, the channels used by smaller cells cannot

be separated from the intra-frequency cells. If all cells apply lower transmit power,

however, some big cells will be exclusive from the service areas.

For the previous reason, the channels in the original cells can be divided into two

groups. One group meets the reuse requirement of the smaller cells, and the

other group meets the reuse requirement of the bigger cells. The bigger cells are

applied to the communication of fast-moving subscribers, which requires a fewer

handover times.

The power of the two channel groups decides the progress of cell splitting. At the

early stage of cell splitting, the channels in the low-power group are fewer. As the

requirement grows, more channels are needed in low-power group. The cell

splitting does not stop until all channels within this area are applied in the

low-power group. In this case, all cells in this area have split into multiple smaller

cells, and the radius of each cell is quite small.

Note:

Commonly, you can restrict cell coverage area through adjusting the project

parameters of the base station.

5.5.2 Voice Channel Allocation

I. Voice channel decision

The base station capacity refers to the number of channels that must be

configured for a base station or a cell. The calculation of the base station capacity

is divided into the calculation of the number of radio voice channels and the

calculation of the number of radio control channels.



According to the information of base stations and cells and the density distribution

of subscribers, you can calculate the total number of the subscribers. Then

according to the radio channel call loss ratio and traffic, you can obtain the

number of voice channels that must be configured by checking Erl B table.

Generally, you can decide the number of voice channels as follows:

1) According to the bandwidth and the reuse mode allowed by current GSM

networks within the areas to be planned, you can obtain the maximum

number of carriers that can be configured for a base station.

2) Each carrier has 8 channels. You can obtain the maximum number of voice

channel numbers that can be configured for a base station by detracting the

control channels from the 8 channels.

3) According to the number of voice channels and call loss ratio (generally 2%

dense traffic areas and 5% for other areas), you can obtain the maximum

traffic (Erl number) that the base station can bear through checking Erl B

table.

4) Through dividing the Erl number by the average busy-hour traffic of

subscribers, you can obtain the maximum number of subscribers that the

base station can accommodate.

5) According to the data of subscriber density, you can obtain the coverage

area of the base station.

6) After the areas are specified based on the subscriber density, according to

the area of an area and the actual coverage area of the base station, you

can calculate the number of needed base stations.

7) For important areas, you must consider back up stations and the cooperation

between carriers. For example, an important county needs at least two base

stations and three important carriers.

8) For the areas where burst traffic is possible, such as the play ground and

seasonal tourism spots, you must prepare the equipments (such as carriers

and micro cells) and frequency resources for future use.

9) The dynamic factors, such as roaming ratio, subscriber mobility, service

development, industry competition, charging rate change, one-way charge,

and economic growth, must be considered.

10) To configure a base station, you must consider the transmission at the Abis

interface so that the capacity can be met while saving transmission. For

example, the application and concatenation of the Abis interface 15:1 and

12:1 should be considered.

11) For indoor coverage and capacity, you can use micro cells and distributed

antenna systems. For the coverage in countryside areas and highroads, you

can use economical micro base stations. For the transmission in countryside

areas and highroads, you can use HDSL because it is cost effective.

12) Prepare the some carriers, micro cells, and micro base stations for new

coverage areas and future optimization.



13) In some special areas, you can use the base stations consisting of omni and

directional cells, but you must consider the isolation between omni antennas

and directional antennas. For traffic control, you can use the algorithm in

terms of network layers.

14) For some highroads which require a little traffic by large coverage, you can

use the two networking modes. They are:

(A micro base station with single carrier) + (0.5 + 0.5 cell with two set of

directional antennas)

A micro base station with single carrier + 8-shaped antenna

II. Relationship between carrier number and bearable traffic

Erl traffic model can calculate the traffic that a network can bear. The call loss

ratio can be 2% or 5% according to actual conditions. Table 5-7Table 5-7

describes the relationship between the number of carriers and the traffic that a

network can bear according to Erl B table.

Table 5-7 Relationship between the number of carriers and the traffic that a

network can bear

Number of carriers in

each cell

Number of

TCHs Traffic (Erl)

2% 5%

1 6 2.27 2.96

2 14 8.2 9.73

3 21 14.03 16.18

4 29 21.03 23.82

5 36 27.33 30.65

6 44 34.68 38.55

7 52 42.1 46.53

8 59 48.7 53.55

9 67 56.25 61.63

10 75 63.9 69.73

According to this table, the larger the number of carriers and the call loss ratio are,

the greater the traffic that each TCH bear, and the greater the TCH utilization ratio

is (the channel utilization ratio is an important indicator of the quality of network



planning and design). If the number of subscribers of a base station is small, you

can consider delaying the construction.

Because restrictions on the coverage area of a cell and the bandwidth of the

available frequencies, you must plan a reasonable capacity for the cell. If good

voice quality is ensured, you must take measures to enhance the channel

utilization ratio as much as possible.

For the construction of the dual-band network, you can use the frequencies with

wider bands to enhance channel utilization ratio, which is helpful for traffic

sharing.

In actual applications, when the traffic on each TCH accounts for 80-90% of total

given by Erl B table (the call loss ratio is 2%), the congestion ratio in this cell rise

greatly. Therefore, we generally calculate the traffic that a network can bear by

taking the 85% of the traffic given by Erl B table as a reference.

III. Example

The capacity of a local network needs to be expanded. According to the service

development, population growth and mobile popularity, the subscribers in this

area are expected to reach 100,000 in 2 years.

If only the followings are considered:

Roaming factor (according to the development trend of traffic statistics) =

10%.

Mobile factor (the subscriber moves slightly within the local network instead

of roaming) = 10%.

Dynamic factor (with burst traffic considered) = 15%.

The network capacity = 100000 * (1 + 10% + 10% + 15%) = 135,000.

However, because the congestion is present, we generally calculate the traffic

that a network can bear by taking the 85% of the traffic given by Erl B table as a

reference. As a result, the network capacity must be designed as follows:

The network capacity = 135, 000/85% = 158,800, about 160,000.

5.5.3 Control Channel Allocation

I. SDCCH allocation

Stand-alone dedicated channel (SDCCH) is an important channel in a GSM

network. Mobile station activities, such as location update, attach and detach, call

setup and short message, are performed on SDCCH. The SDCCH is used to

transmit signaling and data.

Table 5-8Table 5-8 describes SDCCH configuration.



Table 5-8 SDCCH configuration principles

No cell broadcast channel (CBCH)

TRX

number

SDCCH configuration

General cell Internal cell Edge cell

1 SDCCH/4 SDCCH/4 SDCCH/4


3 SDCCH/4+SDCCH/8 SDCCH/4+SDCCH/8 SDCCH/4+SDCCH/8

4 2*SDCCH/8 SDCCH/4+SDCCH/8 2*SDCCH/8

5 2*SDCCH/8 2*SDCCH/8 2*SDCCH/8

6 SDCCH/4+2*SDCCH/8

2*SDCCH/8 SDCCH/4+2*SDCCH/8

7 SDCCH/4+2*SDCCH/8

SDCCH/4+2*SDCCH/8

3*SDCCH/8


Cell broadcast channel (CBCH) is present

TRX

number

SDCCH configuration

General cell Internal cell Edge cell


2 SDCCH/8 SDCCH/8 SDCCH/8+SDCCH/4

3 SDCCH/4+SDCCH/8 SDCCH/4+SDCCH/8 SDCCH/4+SDCCH/8


5 2*SDCCH/8 2*SDCCH/8 2*SDCCH/8+SDCCH/4

6 SDCCH/4+2*SDCCH/8

SDCCH/4+2*SDCCH/8

SDCCH/4+2*SDCCH/8

7 3*SDCCH/8 SDCCH/4+2*SDCCH/8

3*SDCCH/8

8 3*SDCCH/8 3*SDCCH/8 3*SDCCH/8+SDCCH/4

It is difficult to induce a traffic model for the SDCCH; especially it even becomes

impossible after the large-scale application of layering networks and short

messages. Moreover, the equipments of some carriers support SDCCH dynamic

allocation function. As a result, the traffic model for SDCCH must be adjusted

according to actual conditions.



The advantages of the SDCCH dynamic function are as follows:

Adjusting SDCCH capacity dynamically

Reducing SDCCH congestion ratio

Reducing the effect of initial SDCCH configuration against system

performance

Making SDCCH and TCH configuration more adaptive to the characteristics

of cell traffic

Optimizing the performance of the systems under the same carrier

configuration.

In conclusion, the SDCCH dynamic allocation function is divided into two types,

namely,

Dynamic allocation from SDCCH to TCH

Dynamic recovery from SDCCH to TCH

II. CCCH allocation

Common control channels (CCCH) contain access grant channel (AGCH), paging

channel (PCH) and random access channel (RACH). The function of a CCCH is

sending access grant message (immediate assignment message) and paging

message.

All traffic channels in each cell share the CCCH. The CCC can share a physical

channel (a timeslot) with SDCCH, or it can solely occupy a physical channel. The

parameters relative to the CCCH include CCCH Configure, BS AG BLKS PES,

and BS PA MFRMS.

Here,

CCCH Configure designates the type of CCCH configuration, namely,

whether the CCCH shares one physical channel with the SDCCH. If there

are 1 or 2 TRX in a cell, it is recommended that the CCCH occupies a

physical channel and share it with the SDCCH. If there are 3 or 4 TRXs, it is

recommended that the CCCH solely occupies a physical channel. If there

are more than 4 TRX, it is recommended to calculate the capacity of the

paging channels in the CCCH according to actual conditions first, and then

you can perform the configuration.

BS AG BLKS PES indicates that the number of CCCH message blocks

reserved to the AGCH. After CCCH configuration is done, this parameter, in

fact, decides allocates the ratio of AGCH and PCH in CCCH. Some carriers

can set sending priority for the access grant message and paging

message. When the former message set to be prior to the later one, the BS

AG BLKS PES can be set to 0.

BS PA MFRMS indicates the number of multi-frames that can be taken as a

cycle of paging sub-channels. In fact, this parameter decides the number of

paging sub-channels that a cell can be divided into.



Note:

In CCCH configuration, the location area planning, paging modes and system

flow control must be considered.

5.6 Base Station Number Decision

After traffic and coverage analysis, according to the selected base station

equipments and parameters, you can obtain the coverage areas of various base

stations through link budget. The coverage area helps you calculate the number

of base stations required by each area. Then you decide the base station

configuration according to traffic distribution. Finally, you must perform emulation

using relative planning software so that coverage, capacity, carrier-to-interference

ratio can be assured and interference can be avoided.

5.6.1 Characteristics of 3-sector base stations in urban areas

Cellular communication is named because the coverage areas of base stations

are extruded through small cellular-shaped blocks. In urban areas, for the

purpose of capacity expansion and radio frequency optimization, mainly 3-sector

base stations are used. This section explains some basic concepts of a 3-sector

base station.

For the concept of the cell radius, see Figure 5-2Figure 5-2.

Figure 5-2 3-sector cellular layout

This is a standard 3-sector cellular layout. According to Figure 5-2Figure 5-2, the

distance between two 3-sector base stations is R + r, here R = 2r. However, R is

mainly used in cell radius estimation because the direction along R is the



direction of the major lobe of the directional antenna. In the design for cellular

layout, however, r indicates the cell radius.

In a cellular cell, if the included angle between a direction and the direction of the

major lobe of the antenna, the coverage distance along this direction is r = R/2,

and the path loss along this direction is about 10dB less than that along the

direction of the major lobe of the antenna (for the deduction, it is introduced in the

following), namely, the equivalent isotropic radiated power (EIRP) along this

direction can be about 10dB less than that along the major lobe.

According to this feature, in the cellular layout of this kind, you can adopt the

directional antenna whose azimuth beam width ranges from 60 to 65 degrees

because their horizontal lobe gain diagram also meets this feature.

If R is the cell radius, the cell area is S = 0.6495 R R. Sometimes the r is

used as cell radius, so the cell area is S = 2 5981rr. Therefore, when

calculating the cell area, you must make clear whether r or R is used.

Figure 5-3Figure 5-3 shows the relationship between R and r.

Figure 5-3 Relationship between R and r

The followings deduce the EIRP required along R direction and r direction.

As shown in Figure 5-3Figure 5-3, the coverage distance along r direction is half

of that along R direction, namely, r = R/2. To keep even coverage, you must

make the field intensity at the edges of the cell equal, namely, RxlvelB =

RxlevelC.

Suppose that the EIPR transmitted from cell A is EIRPR and EIRPr along R

direction and r direction respectively, and the city HATA mode is used for path

loss, the path loss from point A and B is expressed as equation (1) :

EIRPR RXLEVB = 69.55 + 21.66lgf - 13.82lgh1 + (44.9 - 6.55lgh1) lgR (1)

And the path loss from pint A to point C is expressed as equation (2):

EIRPr- RXLEVc = 69.55 + 21.66lgf - 13.82lgh1 = (44.9 - 6.55lgh1) lgr (2)

Subtract (2) from (1), the equation (3) is expressed as follows:

EIRPR - EIRPr =(44.9 - 6.55lgh1)(lgR lgr) =(44.9 - 6.55lgh1) lg (R/r) (3)

Introduce R = 2r, the equation (4) is obtained as follows:

EIRPR - EIRPr = 0.3 (44.9 - 6.55lgh1) (4)



Figure 5-4Figure 5-4 shows the relationship between antenna height and values

of (EIRPR - EIRPr).

Figure 5-4 Relationship between antenna height and values of (EIRPR - EIRPr)

As shown in Figure 5-4Figure 5-4, when the antenna height h1 increases from

5m to 100m, the values of (EIRPR - EIRPr) decrease from 12 to 9.5, which can be

roughly treated as 10dB.

5.6.2 References for Design of Base Station Parameters

When estimating the number of base stations, you must perform uplink and

downlink budget. Based on the coverage division and propagation environment

survey, you can obtain some project parameters and apply them to link budget.

Table 5-9Table 5-9 lists some recommended base station parameters

Table 5-9 References for base station parameters

Coverage target

Big and middle-sized

cities Small cities Highroads

Network type GSM 900MHz GSM 900MHz GSM 900MHz

Antenna gain (dBi) 15 17 18

Coverage target

Big and middle-sized

cities Small cities Highroads

Network type GSM 900MHz GSM 900MHz GSM 900MHz

Antenna

height

Densely

populated

urban areas

25



Other urban

areas 30 30

Suburban

areas 35 35 35

Countryside

areas 45 45 45

Antenna

diversity gain

(dB)

Densely

populated

urban areas

4

Other urban

areas 4 4

Suburban

areas 3 3 3

Countryside

areas 3 3 3

Building

penetration

loss (dB)

Densely

populated

urban areas

25

Other urban

areas 20 20

Suburban

areas 15 15

Countryside

areas 15 15

Car penetration loss (dB) 10 10 10

Slow fading

margin (dB)

Densely

populated

urban areas

8

Other urban

areas 8 8

Suburban

areas 8 8 8

Countryside

areas 8 8 8



Note:

The more densely the base station addresses, the lower the antenna height is.

The building penetration loss in northern cities is greater than that in southern cities.

5.6.3 Uplink and Downlink Balance

After base station parameters are specified, you can perform link budget to

estimate the coverage area of the base station. In addition, you must consider the

sensitivity of the base station equipments at this time.

In a mobile communication system, radio links are divided into two directions,

namely, uplink and downlink. For an excellent system, you must perform a good

power budget so that the balance is present between uplink signals and downlink

signals. Otherwise, the conversation quality is good for one party but bad for the

other party at the edges of the cell. If uplink signals are too bad, the mobile station

cannot start a call even if signals are present.

However, the because the fading for uplink channels and downlink channels is

not totally the same and the other factors such as the difference of the

performances of receivers are present, the calculated uplink and downlink are not

absolute, but the there a fluctuation of 2 to 3 dB.

The measurement report on uplinks and downlinks at the Abis interface can tell

whether the uplink and downlink reach a balance. In addition, dialing tests in

actual network can also tell whether the balance between uplinks and downlinks

are reached. If the conversation quality on downlinks uplinks becomes poor

simultaneously, it means that the downlinks and uplinks are balance.

Note:

Some carriers provide the traffic statistics on uplink and downlink measurement,

which can also tell whether the balance between uplinks and downlinks are

reached.

I. Link budget model

Figure 5-5Figure 5-5 shows the link budget model.



Figure 5-5 Link budget model

When calculating uplink and downlink balance, you must consider the functions of

the tower amplifier first. In a base station receiving system, the thermal movement

of the active parts and radio frequency (RF) conductors cause thermal noise,

which reduces the signal-to-noise ratio of the receiving system. In this case, the

receiving sensitivity of the base station is restricted and the conversation quality is

reduced. To improve the receiving performance of the base station, you can add a

low-noise amplifier under the receiving antenna. And this is the principle of the

tower amplifier.

The contributions of the tower amplifier to uplinks and downlinks are judged

according to the performance of its low-noise amplifier and gain. In fact, it is the

tower amplifier that reduces the noise coefficient of the base station receiving

system. The power amplifier can improve the coefficients for the uplink receiving

system (start from the output end of the receiving antenna). However, if the

functions of the tower amplifier are quantified by this, the uplink improved value

can be represented by the NFDelta (it is the reduced value of the noise coefficient

of the receiving system) after a tower amplifier is added to the system.

(1) No tower amplifier

When there is no tower amplifier, the sensitivity of the equipments at the duplexer

input interface at the top of the base station cabinet are taken as a reference.

For downlink signals, if,

Mobile station receiver output power = Poutm

Base station diversity received gain = Gdb

Base station receiving level = Pinb

Base station side noise deterioration = Pbn

Antenna receiving gain = antenna transmitting gain (according to reciprocity

theorem)

The following equation can be obtained:



Pinb + Mf = Poutm + Gam Ld + Gab + Gdb Lfb Pbn

Generally, Pmn is almost equal to Pbn, so the following equation can be

obtained:

Poutb = Poutm + Gdb + (Pinm Pinb) + Lcb

(2) With tower amplifier

If a tower amplifier is present, the improved value of the noise coefficients of the

uplink receiving system can be represented by NFDelta, so the equation Poutb =

Poutm + Gdb + (Pinm Pinb) + Lcb can be developed into the following equation:

Poutb = Poutm + Gdb + (Pinm - Pinb) + Lcb + NFDelta

The two equations, Poutb = Poutm + Gdb + (Pinm Pinb) + Lcb and Poutb =

Poutm + Gdb + (Pinm - Pinb) + Lcb + NFDelta are used to calculate base station

transmit power when the uplinks and downlinks are balance. Here,

Pinb is the base station receiving sensitivity

Pinm is the mobile station receiving sensitivity

Gdb (antenna diversity receiving gain) is 3.5dB

According to the requirements in protocols GSM05.05, the mobile station transmit

power and the reference receiving sensitivity of the mobile station and base

station are specified in Table 5-10Table 5-10. At present, however, the

sensitivities in actual systems are greater than the reference values listed in the

following table.

Table 5-10 Base station transmit power and reference receiving sensitivity of

mobile station and base station

Network type Mobile station

transmit power

Reference

receiving sensitivity

of mobile station

(dBm)

Reference receiving

sensitivity of base

station (dBm)

GSM 900MHz 2W (33dBm) -102 -104

GSM

1800MHz

1W (30dBm) -100 -104

Note:

From September, 1999 on, the reference receiving sensitivity of mobile station

is -102 dBm as required in GSM protocols. Considering the compatibility of the

previous mobile stations, we adopt -100dBm as the receiving sensibility of the

1800 MHz mobile stations.



II. Bass station sensitivity

This section further introduces the base station sensitivity and the functions of the

tower amplifier.

Receiver sensitivity refers to the minimum signal level needed to by the input end

of the receiver when the certain bit error rate (BER) is met. The receiver

sensitivity detects the performances of the following components:

Receiver analog RF circuit

Intermediate frequency circuit and demodulation

Decoder circuit

Three parameters are used to measure the receiver bit error performance. They

are frame expurgation rate (FER), residual bit error rate (RBER), and bit error rate

(BER). When a fault is detected in a frame, this frame is defined as deleted one.

Here,

FER indicates the ratio of the deleted frames to the total received frames.

For full rate voice channels, the FER is present when the 3-bit cyclic

redundancy check (CRC) detects errors or bad error indication (BFI) is

caused. For signaling channels, the FER is present when the fire code (FIRE)

or other packet codes detect errors. The FER is not defined in data services.

FBER indicates the BER that are not announced as deleted frames, namely,

it is the ratio of the bit errors in the frame detected as good to the total

number of bits transmitted in good frames.

BER indicates the ratio of the received error bits to all transmitted bits.

Because BER occurs at random, the statistical measurement is mainly applied to

measure receiver error rate. That is, sample multiple measuring points on each

channel and when the number of measuring points is certain, if the BER of each

measurement is within the required limit, the BER of this channel meets the BER

as required.

However, the number of sampled measured points and the limit value of the BER

must meet the following conditions:

For each independent sampled measuring point, the times for it to pass a

bad unit must be as fewer as possible, that is, the probability must be

smaller than 2%.

For each independent sampled measuring point, the times for it to pass a

good unit must be as more as possible, that is, the probability must be

greater than 99.7%.

The measurement has vivid statistical features.

The measuring time must be reduced to the minimum.

As a result, you can measure the receiver sensitivity through measuring whether

the receiver BER has reached the requirement while entering sensitivity level to

the receiver.



Enter the reference sensitivity level to the receiver according to Table 5-10Table

5-10 in various propagation environments. For the data produced after receiver

demodulation and channel decoding, the indexes for FER, RBER, and BER are

more favorable that that defined in Table 5-11Table 5-11.

Table 5-11 Requirements on static and multi-path reference sensitivity

Requirement on receiver

sensitivity

Propagation condition

Static TU50 TU50 RA250 HT100

Channel type Parameter

No

frequency

hopping

No

frequency

hopping

Frequency

hopping is

present

No

frequency

hopping

No

frequency

hopping

FACCH/H (FER) 0.1% 6.9% 6.9% 5.7% 10.0%

FACCH/F (FER) 0.1% 8.0% 3.8% 3.4% 6.3%

SDCCH (FER) 0.1% 13% 8% 8% 12%

RACH (FER) 0.5% 13% 13% 12% 13%

SCH (FER) 1% 16% 16% 15% 16%

TCH/F9.6&H4.8

(BER) 105 0.5% 0.4% 0.1% 0.7%

TCH/F4.8 (BER) 104 104 104 104

TCH/F2.4 (BER) 2 104 105 105 105

TCH/H2.4 (BER) 2 104 104 104 104

TCH/FS (FER) 0.1/a% 6a% 3a% 3a% 7a%

Class Ib.

(RBER) 0.4/a% 0.4/a% 0.3/a% 0.2/a% 0.5/a%

Class II

(RBER) 2% 8% 8% 7% 9%

Note:

The requirements on BCCH, AGCH, PCH, and SACCH are the same as that on SDCCH.

The value of a in this table depends on the channels. It is 1 for base stations, and 1 to

1.6 for mobile stations.

III. Contributions of tower amplifier to base staiton sensitivity

In terms of technical principles, the tower amplifier reduces the noise coefficients

of the base station receiving system, which is helpful for improving the sensitivity

of the base station receiving system.



In an actual system, to improve the receiving performance of the base station,

you can add a low-noise amplifier near the feeder of the receiving antenna.

In a mobile communication system, the receiver sensitivity = noise spectrum

intensity (dBm/Hz) + bandwidth (dBHz) + noise coefficient (dB) + C/I (dB).

Here the noise spectrum intensity, bandwidth, and noise coefficient are system

thermal noise. C/I is the signal-to-noise ratio required at the Um interface. In a

narrow band system, C/I indicates the modulation performance required by the

receiver baseband, and it is a positive number.

In a spreading communication system, because spread spectrum gain is present,

the value of C/I is far beyond the requirement of the modulation performance of

the receiver baseband, and it is a negative number.

When there are n* cascaded receivers, the equivalent noise coefficient is as

follows:

n

n

GGG

F

GG

F

G

FFF

2121

3

1

21

111

Here,

Gn indicates the receivers gain at each level (including the loss at each

level).

Fn indicates the noise coefficient of the receivers at each level.

The noise coefficient of the passive device is equal to its loss, and the gain of the

passive device is the reciprocal of the loss.

According to the previous equation, the noise coefficient of the cascading system

is determined by the receivers at the first level.

It must be pointed out that the linear values of the parameters must be applied in

the previous equation, so the F is a linear value, which must be converted into a

logarithm. Moreover, according to this equation, the noise the cascaded receivers

are determined by the noise coefficient (F1) of the receivers at the first level.

However, when the tower amplifier stops working, because the loss is present on

duplexer and bypass connectors, about 2dB of redundant loss is introduced on

reverse link.

According to the equation n

n

GGG

F

GG

F

G

FFF

2121

3

1

21

111

, the

following two assumptions conclude the regularity of the effect of tower amplifier

on the base station system.

(1) Assumption 1

Hereunder is a series of assumptions:

F1 = 2.5 dB (1.7783), noise coefficient of the tower amplifier



F2 = 4.5 dB (2.8184), noise coefficient of the base station

G = 2 (15.849) dB, tower amplifier gain

Loss of the feeder and other passive devices = 3 dB (2)

Gain of the feeder and other passive devices G0 = 3 dB (1/2)

Noise coefficient of the feeder and other passive devices F0 = 1/G0

When the tower amplifier is not added, the noise coefficient of the base station

receiving system with the antenna output end as reference point is as follows:

F = F0 + (F21)/G0 = 10*log (2 + (2.81841)/0.5) =7.5dB

When the tower amplifier is added, the noise coefficient of the base station


F = F1 + (F0 1)/G + (F2 1)/(G*G0) = 10*log(1.7783 + (2 1)/15.849 + (2.8184

1)/(15.849 0.5) = 3.2dB

At this time, the added tower amplifier improves the noise coefficient, and FDelta is

4.3dB, that is, the uplink is improved by 4.3 dB.

(2) Assumption 2

Hereunder is a series of assumptions:

F1 = 2.2 dB (1.6596), noise coefficient of the tower amplifier

F2 =2.3 dB (1.6982), noise coefficient of the base station

G = 12 (15.849) dB, tower amplifier gain

Loss of the feeder and other passive devices = 3 dB (2)

Gain of the feeder and other passive devices G0 = 3 dB (1/2)

Noise coefficient of the feeder and other passive devices F0 = 1/G0

When the tower amplifier is not added, the noise coefficient of the base station


F = F0 + (F2 1)/G0 = 10*log (2 + (1.6982 1)/0.5) = 5.3dB

When the tower amplifier is added, the noise coefficient of the base station


F = F1 + (F0 1)/G + (F2 1)/(G*G0) = 10*log(1.6596+(2 1)/15.849 + (1.6982

1)/(15.849 0.5)) = 2.6dB

At this time, the added tower amplifier improves the noise coefficient, and FDelta is

2.7 dB, that is, the uplink is improved by 2.7 dB.

According to the previous calculation, the following conclusions can be obtained:

The tower amplifier improves the noise coefficient of the base station

receiving system, thus improving the receiving sensitivity of the base station.

The tower amplifier improves uplink signals effectively, which is also helpful

for improving the receiving sensitivity of the base station.

The gain of the antenna amplifier reduces the effect of the components

installed behind the tower amplifier against noise coefficient.



When the feeder is long and the loss of the feeder is great, if the tower

amplifier is added, the noise coefficient of the base station receiving system

and the uplink signals will be greatly improved.

The smaller the noise coefficient of the tower amplifier is, if the tower

amplifier is added, the greater the noise coefficient of the base station

receiving system is improved. However, if the noise coefficient of the tower

amplifier is too great, it may cause the noise coefficient of the base station

receiving system to deteriorate.

When the receiving sensitivity of the base station is great and the feeder is

short, the tower amplifier makes a little improvement on the noise coefficient

of the base station.

If the tower amplifier improves the base station sensitivity, the base station is

more sensitive to outside interference.

5.6.4 Cell Coverage Estimation

In actual project planning, the effective coverage area of a base station largely

depends on the following factors:

Effective base station transmit power

Working band (900MHz or 1800MHz) to be used

Antenna type and location

Power budget

Radio propagation environment

Carriers; coverage requirements

Based on the indexes of QoS for the mobile network and the actual applications,

this section introduces the coverage area of the base station in different

environments theoretically.

Table 5-12Table 5-12 lists the assumptions of the minimum received level

required in various environments.

Table 5-12 Assumptions of the minimum received level required in various

environments

Application

environments

Minimum

received level

(dBm)

Other indexes



The mobile

station works as

the receiver.

The first floor of

the high buildings

in big cities

-70

Mobile station sensitivity: -102 dBm

Fast fading protection: 3dB

Slow fading protection (indoor): 7dB

(the standard deviation is 7dB for

indoors and 8dB for outdoors, the pass

ratio is 90% in coverage areas)

Penetration loss: 18dB

Interference noise: 2dB

Environment noise protection: 2dB

The mobile

station is the

receiver.

In cars.

The first floor of

the general

buildings in urban

areas.

-80




Penetration loss: 10dB



Outdoors. -90






If the following assumptions are present:

The antenna height of GSM 900MHz and GSM 1800MHz base stations are

30 meters.

The sensitivities of the GSM900 MHz 2W (33 dBm) mobile station and GSM

1800MHz 1W (30 dBm) mobile station are -102 dBm and -100 dBm

respectively.

The mobile station height is 1.5 meters and the gain is 0 dB.

When the combiner and divider unit (CDU) is used, the sensitivities of the

900MHz base station and 1800MHz base station are -110dBm and -108dBm

respectively.

The CDU loss is 5.5dB, and the SCU loss is 6.8dB.

The gain of the 65-degree directional antenna is 13dBd for the 900 MHz

mobile station and 16dBd for the 1800MHz mobile station.

The feeder is 50m in length. For 900MHz signals, the feeder loss is

4.03dBm/100m. For 1800MHz signals, the feeder loss is 5.87dB/100m.

In general cities, select Okumura propagation model.

No tower amplifier and the downlinks are restricted according to the

calculation of the uplink and downlink balance.



According to the previous assumptions, the calculated results are as follows:

(1) Outdoor coverage radius of the 900 MHz base station in urban areas

The minimum received level of the mobile station Pmr minminmin 90

dBm. The

coverage radius is calculated according to the maximum TRX transmit power.

The maximum TRX transmit power for the 900 MHz base station Pbt 40

W (46

dBm).

The EIRP of the base station antenna is: EIRP Pbt Lcom Lbf Gab 46 5.5 2.01 13 2.15 53.65

(dBm) Here,

LCOM indicates the combiner loss

Lbf indicates the feeder loss

Gab indicates the antenna gain of the base station

And the allowed maximum propagation loss is:

Lp EIRP Pmr minminmin 53.65 ( 90) 143.65 (dB)

According to the Okumura propagation model introduces earlier,

Lp 69.55 26.16 lglg f 13.82 lglghb (44.90 6.55 lglghb ) lglgd Ahm

Here,

hb

indicates the antenna height of the base station.

hm

indicates the antenna height of the mobile station.

f = 900 MHz.

Ahm (1.1 lglg f 0.7)hm (1.56 lglg f 0.8) 0.01 (dB)

According to the previous known number, the outdoor coverage radius of the 900

MHz base station in urban areas can be obtained, that is, d = 2.8km.

(2) Coverage radius of the 900 MHz base station in urban buildings


(dBm).


Therefore, the coverage radius of the 900 MHz base station in urban buildings

can be obtained, that is, d = 0.75km.

If the previous assumptions are present, this indicates that the 900 MHz base

station can cover the outdoor areas 2.8 km away, but for the subscribers on the

first floor of the buildings 750 m away, the quality of the received signals is not

satisfying.

(3) Coverage radius of the 900 MHz base station in suburban areas


(dBm).


The Okumura propagation model in suburban areas must be modified as follows:



Lp 69.55 26.16 lglg f 13.82 lglghb (44.90 6.55 lglghb ) lglgd

Ahm 2[lglg(f/28)]2 5.4

Therefore, the coverage radius of the 900 MHz base station in urban areas can

be obtained, that is, d = 5.4km, so it is obvious that the coverage radius of the

base station with the same configuration is larger in suburban areas that in urban

areas.

(4) Outdoor coverage radius of the 1800 MHz base station in urban areas


(dBm). Because

the maximum transmit power of the 1800 MHz TRX is 40W (46dBm), the

coverage radius is calculated based on this maximum transit power.

EIRP Pbt Lcom Lbf Gab 46 5.5 2.93 16 2.15 55.73

(dBm)

Lp EIRP Pmr minminmin 145.73 (dB)

For the 1800 MHz base station, the Okumura propagation model is:

Lp 46.3 33.9 lglg f 13.82 lglghb (44.90 6.55 lglghb ) lglgd Ahm

In addition, f = 1800 MHz and Ahm (1.1 lglg f 0.7)hm (1.56 lglg f 0.8) 0.04 (dB).

According to the previous known number, the outdoor coverage radius of the

1800 MHz base station in urban areas can be obtained, that is, d = 1.7km.

(5) Coverage radius of the 1800 MHz base stations in urban buildings

The minimum received level of the mobile station Pmr minminmin 70 (dBm).


If the previous assumptions are present, this indicates that the 1800 MHz base

station can cover the outdoor areas 1.7km away, but for the subscribers on the

first floor of the buildings 500m away, the quality of the received signals is not

satisfying.

5.6.5 Base Station Address Planning

I. Overview

When planning base station addresses, first you must estimate the number of the

base stations needed in various coverage areas according to the coverage

distance and the divisions of the coverage areas. For the convenience of

prediction and emulation, you must plan an initial layout the base station

addresses with the help of maps and the estimated results.

II. Planning methods

The base station address can be planned based on standard girds, or it can be

planned from a specific area.

(1) Plan base station address based on standard grids



First you set the base stations in the coverage areas according to the distance of

the standard grids, and then adjust the address layout and project parameters

according to the estimated coverage results to meet the coverage requirement.

After that, continue the planning according to the following instructions:

If a satisfying address layout is obtained, you must analyze the capacity of

the base stations to be planned according to this layout, and determine the

reasonable number of base stations. When designing the capacity, you must

calculate the number of TRXs needs to be configured for each base station,

and then analyze and adjust the configuration of the base station according

to the number of the configured TRXs.

The adjustment of the configuration of the base station is determined by

subscriber distribution. If the number of base stations in some areas does

not meet capacity requirement, another base stations must be added.

(2) Plan base station address based on a specific area

According to this method, you are required to start the planning from the areas

where the subscribers are most densely distributed or the planning work is quite

hard to be performed. As a result, you must fully survey the subscriber distribution,

landforms, and ground objectives within the coverage area to position the key

coverage area where the center base stations should be planned. And these

center base stations function as ensuring the coverage and capacity in important

areas.

After the layout of these center base stations is determined, you can plan other

base station addresses according to coverage and capacity target. And this is

how the final layout of the base station addresses come from. After the overall

solution is determined, the subsequent steps are performed according to the first

planning method.

Note:

The difference of the traffic intensity and the abnormality of the landforms

and ground objectives result in irregularity of the radio coverage. Therefore,

the distance between base stations varies. Generally, this distance is smaller

in the areas where traffic intensity is great. In some hot areas, you can

ensure the system capacity by using micro cells and distributed antennas to

provide multi-layer coverage.

For restrictions from frequency resources are present, you must consider

avoiding interference while ensuring system capacity.

There is no standard available for the layout of the base station addresses. A

good planning solution is selected based on the integrated performance of

the network.



5.6.6 Coverage Prediction

The coverage prediction is to predict the coverage of the network to be

constructed according to the selected base station addresses, designed base

station types, suitable electronic maps, and network planning tools to judge

whether the coverage meet the requirements of the subscribers.

The coverage of a base station is determined by the following factors:

Indexes of QoS

Output power of transmitters

Available sensitivity of receivers

Direction and gain of antennas

Working bands

Propagation environment (such as landforms, city constructions)

Application of diversity reception

If the predicted results of the network coverage fail to meet the requirement

Date post:	19-Nov-2015
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GSM Radio Network Planning

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