How to Do Rf Planning

Chapter 1 Introduction

CHAPTER 1

INTRODUCTION

1.1 Introduction

The world has seen phenomenal changes in the telecommunication industry during the last

decades. Communication that was wired formerly is now performed wirelessly or in other

words by radio means. Thus, the wireless communication, which uncouples the telephone

from its wires, has exploded.

In 1985 the governing body of the European Postal Telephone and telegraph (PTT) and

CEPT set up a committee known as Group Special Mobile, later changed to Global System

for Mobile Communications (GSM). The advantages of GSM over the previous technologies

were, improved spectrum efficiency, international roaming, low cost mobile sets and base

stations (BSS), support for new services, high quality speech, compatibility with Integrated

Services Digital Network (ISDN) and other telephone companies [1].

The early years of the GSM were devoted mainly to the selection of the radio interface and

techniques for network access. Thus, since the very beginning radio access network is of

prime importance. The radio access network is the part that includes the base station

(BTS), the mobile station (MS) and the interface between them. The combination of

Frequency Division Multiple Access (FDMA) and Time Division Multiple access (TDMA)

technique is used in GSM networks and it can operate in frequency bands of 400MHz,

900MHz, 1800MHz and 2100MHz. The allocated operating band is divided into 200 KHz

channels called ARFCNs (Absolute Radio Frequency Channel Numbers) which are also

referred as physical channels. There are also logical channels in the GSM network that

carry user data (Traffic channels) and control information (Control channels). As the

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frequency is considered as limited resource, so for spectrum efficient utilization the concept

of frequency reuse is used. The basic construction block of the network is a “cell”. In a

cellular system like GSM, the coverage area is divided into hexagonal cells also called as

sector.

The designing of Radio Access Network (RAN) is a multidiscipline task that needs

balancing of competing requirements. Several objectives need to be achieved while

designing a RAN which are mainly classified as optimum radio coverage, sufficient network

capacity and quality of service.

In this project, the radio access network is to be designed for the given area or terrain

taking under consideration the specifications, allocated resources and requirements given

by Huawei, one of the world’s leading telecommunication vendor. The total cost for the

radio access network cost is given as: 2 Million $, one Base Transmission Station (BTS)

cost is 0.2 Million $, operating frequency bands are 900MHz and 1800MHz with 27

ARFCNs allocated, the number of users that are to be provided with services are 140,000

with GoS or blocking probability of 2%.

For sake of estimation and prediction, post processing RF tools are used. Here, such a tool

namely TEMS, Mapinfo and our own developed software Quick online Budget is used.

TEMS and Mapinfo are comprehensive planning tool to assist in fulfilling the requirements

of network designing and optimization. These tools were provided by Huawei and are

relatively new to us, so its exploration is the foremost task.

The process of RAN designing consists of two phases that are, pre-planning and system

growth phase. The phase one of preplanning can be accomplished in four discrete steps.

First step is of Coverage and traffic analysis, the objective is to provide optimum coverage

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and enable the network to have a capacity of at least 7,000 users. The aspect of network’s

coverage includes defining the clutter profile of the given terrain and the related signal

strength. The clutters are made for the sake of resource dimensioning. Dimensioning of the

resource means finding answers to two fundamental questions: How many traffic channels

(TCH) does a sector can handle and how many TCH are actually required in the area it is

covering? The result of the first step is the number of BTS per clutter needed to provide

required capacity and best possible coverage.

The second step is the nominal cell planning, which leads to a layout of cell pattern on the

given map. The propagation, frequency reuse and interferences are catered in second step.

A prediction model namely “Okumura-Hata” is used to estimate the propagation losses,

gains and received signal power. The frequency reuse pattern is chosen and two types of

interferences that are Co-channel (C/I) and adjacent channel (C/A) are decreased to

minimum possible level.

The step three consists of two major tasks that are, “Surveys of proposed Sites” and

“Tuning of prediction model”. The aspects like exact location, space for the equipment and

antenna types etc are checked in site survey which leads to the approval for physical

installment of BTS. The model tuning is done to enhance the accuracy of predictions model

applied in post processing tool. A transmitter is mounted on the proposed Site location and

the changes of one variable (losses) at different time interval are taken. Then each change

is analyzed to determine the modification factor for the model.

The final step for RAN designing is dimensioning of Base Control Stations (BSC) .So, at the

end of this fourth step the final design of radio access network is ready to be deployed.

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Chapter 2 Radio Access Network

CHAPTER 2

RADIO ACCESS NETWORK OVERVIEW

2.1 Introduction

The radio access network is between the mobile stations and the fixed infrastructure. It is

the most important part of the GSM system, being the key element to enable mobility and

wireless access. One of the main objectives of GSM is roaming. Therefore, in order to

obtain a complete compatibility between mobile stations and networks of different

operators, the radio interface must be completely defined.

In this chapter the Base Station Subsystem (BSS) is illustrated, giving the clear picture of

equipment used; its integration and respective working. The second part consisting of the

Radio interface gives a comprehensible idea of “which access technology is used and how

the mobile station gets connected to the GSM network.”

2.1.1 Base Station Subsystem

The Base Station subsystem (BSS) provides connection between MS and Network

Switching Subsystem (NSS) though Air interface. The BSS provides radio coverage on

prescribed geographical areas, known as the cells. The BSS consists of following parts:

1. Base Station Controller (BSC)

2. Base Transceiver station (BTS)

3. Transcoding Rate and Adaptation Unit (TRAU)

2.1.1.1 Base Station Controller (BSC)

The Base Station Controller (BSC) provides the connectivity of BTS to Mobile Switching

Center through E1 or microwave links. A group of BTSs are connected to a particular BSC

which manages the radio resources for them. Today's intelligent BTSs have taken over

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many tasks that were previously handled by the BSCs. The primary function of the BSC is

call maintenance. The mobile stations normally send a report of their received signal

strength to the BSC every 480ms. With this information the BSC decides to initiate

handovers to other cells, control the BTS transmitter power, etc.

2.1.1.2 Base Transceiver station (BTS)

The BTS is the radio transmission equipment and covers each cell. BTS is also referred as

SITE. BTS can be divided into three parts,

i.) Radio Base Station (RBS)

a. Combiner Distribution Unit (CDU) - Multiplexing and de-multiplexing of signal.

b. Transceiver unit (TRX) - Used to provide communication path between mobile

station and Mobile Station Center when dedicated channel is assigned .Each TRX

has eight time slots.

c. Power Supply Unit (PSU) - Converts AC power to DC power (220 AC to 48 dc).

d. Control Module (CM) - Controls the micro wave link of the site that provides the

connectivity between BTS and BSC.

ii.) Transmission Module (TRM)

iii.) Power unit

Figure 2.1 shows the block diagram of RBS-900 illustrating the different elements of RBS.

Empty slots are left for future expansion.

Figure 2.1: Block diagram of RBS 900

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2.1.1.3 Transcoding Rate and Adaptation Unit (TRAU)

The transcoder multiplexes four 16 Kbps speech or data (at 300, 600, and 1,200 bps)

channels. The 13 Kbps voice is brought up to a 16 Kbps level by inserting additional

synchronizing data. Then, four 16 Kbps channels are multiplexed onto a DS0 (64 Kbps)

channel.

There are two spots in GSM network where TRAU is placed,

1. At BTS in order to connect with BSC.

2. At BSC in order to connect with Mobile Switching Center (MSC).

2.1.2 GSM Radio Interface

The spectrum efficiency depends on the radio interface and the transmission of signals,

particularly in aspects such as the capacity of the system, techniques used in order to

decrease the interference and to improve the frequency reuse scheme. The specification of

the radio interface has an important influence on the spectrum efficiency.

2.1.2.1 Operating frequency bands

The operating frequency band is divided into uplink and downlink channels with a guard

band in between them. The uplink channel or reverse channel is from MS to BTS. The

downlink channel or forward channel is from BTS to MS. This table lists the specification of

the GSM–900, GSM–1800 and GSM–1900 system. For this project GSM-900 band is used.

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Table 2.1: Specifications of GSM System

2.1.2.2 Multiple Access

A combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple

Access (TDMA), combined with frequency hopping, has been adopted as the multiple

access schemes for GSM.

The 200 KHz carrier spacing is required to provide the necessary bit rate per carrier

frequency. The 200 kHz carrier spacing yields 125 carriers from the 25MHz spectrum

allocation. Because some of the energy in a GMSK modulated signal lies outside the

nominal 200KHz band, GSM recommends that carriers 1 and 124 will be used (guard band

of 200 KHz) in order to protect services using adjacent spectrum bands as shown in figure

2.2. These 124 possible carriers are defined for the uplink (Fu) and downlink (Fd) as

follows:

Fu (n) = 890.2 MHz + 0.2(n-1) MHz (0<n <125)

Fd (n)

= 925.2 MHz + 0.2(n-1) MHz (0<n <125)

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Figure 2.2: FDMA/TDMA based radio channel concept

2.1.2.3 Channel types

There are two types of channels in GSM networks, the physical and the logical channels.

Physical channel: It is defined by specifying both, a carrier frequency

and a TDMA timeslot number. It is important to note that the frame

structure used on each physical channel is independent of those on the

other channels, most notably those with the same carrier frequency

assignment but different timeslot designations.

Logical channel: They are multiplexed into the physical channels.

Logical channels are, so to speak, laid over the grid of physical channels.

Each logic channel performs a specific task. Consequently the data of a

logical channel is transmitted in the corresponding timeslots of the

physical channel. During this process, logical channels can occupy a part

of the physical channel or even the entire channel.

There are two different types of logical channel within the GSM system:

i. Traffic channels (TCHs).

ii. Control channels (CCHs).

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i. Traffic channels

Traffic channels carry user information such as encoded speech or user data. Traffic

channels are defined by using a 26-frame multi-frame structure. Two general forms are

defined:

a. Full rate traffic channels (TCH/F), at a gross bit rate of 22.8 kbps.

b. Half rate traffic channels (TCH/H), at a gross bit rate of 11.4 kbps.

ii. Control channels

Control channels carry system signalling and synchronisation data for control procedures

such as location registration, mobile station synchronisation, paging, random access etc.

between base station and mobile station. Three categories of control channel are defined:

a. Broadcast

b. Common

c. Dedicated

Table 2.2: Types and Functions of Control Channels

Channel Abbreviation Function/ ApplicationAccess Grant Channel - (DL) AGCH Resource allocation to MSBroadcast Common Control Channel – (DL)

BCCH Dissemination of general information

Cell Broadcast channel – (DL) CBCH Transmit cell broadcast messages

Fast Associated Control Channel – ( UL / DL)

FACCH For user network signalling

Paging Channel – ( DL ) PCH Paging for a mobile terminalRandom Access Channel – (UL) RACH Resource request made by

mobile terminalSlow Associated Control Channel (UL/DL) SACCH Used for transport of radio

layer parametersStand alone dedicated control (UL/DL) SDCCH For user network signallingSynchronization Channel (DL) SCH Synchronization of mobile

terminal

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2.1.2.4 Interfaces

The following are the interfaces between different network entities of GSM. Figure 2.3

shows the placement of each interface.

Um or Air interface- it is between MS and BTS. It has gross data rate of

22.8kps (voice + data) and net data rate of 13kbps (voice).

Abis interface- it is between BTS and BSC. The interface comprises of

traffic and control channels. It has data rate of 16kbps.

A interface- it is between BSC and MCS. It has data rate of 64kps.

B interface- it is between MSC and VLR

C interface- it is between MSC and HLR

D interface- it is between HLR and VLR

E interface- it is between MSC and MSC

F interface- it is between MSC and EIR

G interface-it is between VLR and other MSC VLR

Figure 2.3: Interfaces of GSM network

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2.1.2.5 Control Signalling on the GSM Radio Interface

Any flow of data in a network requires some additional information that helps the data to

reach the destination in the desired fashion. This additional information is known as

signalling. Signalling in GSM is required at all the interfaces, but radio network planners

deal mostly with the signalling between the mobile station and base station [2].

Signalling on all the interfaces except for the air-interface is done at 64 kbps. On the air-

interface the signalling can be done either by using the slow associated control channels

(SAACH), or by using the main channel itself wherein the signalling channel is sent instead

of sending the data – this is known as fast associated control channel (FAACH) signalling.

Fig 2.4 illustrate physical layer signalling protocol between entire network entities.

Figure 2.4: Physical layer Signalling protocol between network entities

The processing of protocols happen at different network entities, for example the

processing of Communication management (CM) is at MSC not on the BSC or BTS. The

functions of some important protocols are as follow [3].

Communication Management (CM) - Controls User Information

Mobility Management (MM) - Manages DB for Mobile location

Radio Resource (RR) - Provide communication link (MS to MSC)

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Figure 2.5: 3 layer Signalling protocols between network entities

Figure 2.5 elaborates GSM specific signalling protocols of OSI layers on the radio interface.

Layer 2 signalling employs a modified version of the ISDN layer 2 signalling protocol, LAPD,

that is called LAPDm (m for modified). Layer 3 signalling on the GSM radio interface

contains control message exchanges between a numbers of protocol control processes.

These processes are Call Control (CC), Mobility Management (MM), Radio Resource

management (RR) [4].

2.2 Fundamentals of system design

The system design fundamentals include cellular concept and concept of frequency reuse.

GSM architecture is a cellular architecture. The region is divided into cells of hexagon

geometry. Hexagon are chosen because it covers largest area as compared to other

shapes of geometry like square or circle and it covers the region without leaving gap

between them.

2.2.1 Cell

A cell is defined as the area covered by one sector, i.e. one antenna system. The

hexagonal nature of the cell is an artificial shape (Figure 2.6). This shape is being closest to

circular, which represents the ideal coverage of the power transmitted by the base station

antenna. The circular shapes are themselves inconvenient as they have overlapping areas

of coverage; but, in reality, their shapes look like the one shown in the ‘practical’ view in

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Figure 2.6. A practical network will have cells of non geometric shapes, with some areas not

having the required signal strength for various reasons.

Figure 2.6: Hexagonal Shape of Cell.

There are two main types of cell:

Omni directional cell - An omni-directional cell is defined as a BTS with an antenna

which transmits power equally in all directions (360 degrees) as shown in fig 2.7

Sector cell - A sector cell is the area of coverage from an antenna, which transmits

in a given direction only. The coverage area may be equal to 120˚ or 180˚.

Commonly BTS uses 3 sector cell with each antenna covering an area of 120˚ as

shown in fig 2.7 [5].

Figure 2.7: Omni Directional and Sector Cells

2.2.2 Site

A site is the position where the tower and antennas are located. Normally, a site has TRXs,

power supplies, radio base station units (RBS) etc. A site may serve an omni-cell or two or

more sector cells. In the first case the site is called an omni site, in the latter case a sector

site.

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2.2.3 Cell Splitting

Cell splitting is a process of subdividing a congested cell into smaller cells each with its own

base station and a corresponding reduction in antenna height and transmitted power as

shown in fig 2.8. Cell splitting increase the capacity of cellular system since it increase the

number of times the channels are used.

Figure 2.8: Cell Splitting2.2.4 Cell Sectoring

It is the process of dividing a cell into three cells .Cell Sectoring keeps the cell radius

unchanged and seek methods to increase coverage and capacity. Sectoring increases

signal to noise ratio so that the cluster size may be reduced. Signal to noise ratio is

improved using directional antennas then capacity improvement is achieved by reducing the

number of cells in a cluster, thus increasing the frequency reuse [3]. The interference in

cellular system may be decreased by replacing a single omni directional antenna at the

base station by several directional antennas each radiating within specified sector as shown

in figure 2.9.

Figure 2.9: Cell Sectoring

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2.2.5 Frequency Re–use

Frequency re-use means that two radio channels within the same network can use exactly

the same pair of frequencies, provided that there is a sufficient geographical distance (the

frequency re-use distance) between them so they will not interfere with each other. The

tighter frequency re-use plan, the greater the capacity potential of the network. Based on

the traffic calculations, the cell pattern and frequency re-use plan are worked out not only

for the initial network, but also for the future demands.

In [6], Groups of frequencies can be placed together into patterns of cells called clusters. A

cluster is a group of cells in which all available frequencies have been used once and only

once. Since the same frequencies can be used in neighboring clusters, interference may

become a problem. Therefore, the frequency reuse distance must be kept as large as

possible. However, to maximize capacity the frequency re-use distance should be kept as

low as possible.

The re-use patterns recommended for GSM are the 4/12 and the 3/9 pattern. 4/12 means

that there are four three-sector sites supporting twelve cells using twelve frequency groups.

The 3/9 cell pattern is use in the project as shown in figure 2.10.

.Figure 2.10: Frequency Reuse

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2.2.6 Resource Dimensioning

In Radio Access Network, resource dimensioning is an important step of architecture

design. The architects study the system performance requirements and come up with an

architecture that meet or exceed the requirements in a cost effective fashion. Resources

mean any hardware or software entity needed to perform transactions initiated by users.

Resources are outgoing digital trunks, timeslots etc.

2.2.6.1 Busy Hour

The load handled by a system varies based on the time of day and day of the week. Most

systems are heavily loaded for a few hours in a day. The main objective of resource

dimensioning is to make sure that the system performs well during these busy hours. This

will make sure that the system has adequate resources to handle peak as well as off-peak

traffic.

2.2.6.2 Erlang

Erlang, a dimensionless unit is used in telephony as a statistical measure of the volume of

telecommunications traffic. It is named after the Danish telephone engineer A. K. Erlang,

the originator of traffic engineering and queuing theory. Traffic of one Erlang refers to a

single resource being in continuous use, or two channels being at fifty percent use. Erlang

can be calculated as:

A = λh 2.1

Where A = Traffic in Erlangs

λ = Arrival of new call per unit time.

h = Call holding time.

Alternatively it can be calculated as:

Erlang = (Average time for all resources / Total Time ) 2.2

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http://en.wikipedia.org/wiki/Channel_(communications)

http://en.wikipedia.org/wiki/Queueing_theory

http://en.wikipedia.org/wiki/Teletraffic_engineering

http://en.wikipedia.org/wiki/Agner_Krarup_Erlang

http://en.wikipedia.org/wiki/Engineer

http://en.wikipedia.org/wiki/Denmark

http://en.wikipedia.org/wiki/Traffic

http://en.wikipedia.org/wiki/Telecommunication

http://en.wikipedia.org/wiki/Telephony

http://en.wikipedia.org/wiki/Dimensionless_unit


Erlang calculation is used to determine whether the system is over provisioned or under

provisioned (too many or too few resource allocated). The traffic calculation is also used to

calculate E1 to determine how many voice lines are likely to be used during the busiest

hours.There are a range of different Erlang formulae to calculate these, including Erlang B

and Erlang C.

2.2.6.3 Blocking Probability

The blocking probability defines the chance that a user will be denied service due to lack of

resources. For example, a blocking probability of 0.01 means that 1% of the users will be

denied service. Blocking probability calculations refer to the busy hour only. Blocking

probability during the busy hour can be decreased by:

i. Increasing the resources in the system

ii. Offering incentives and discounts to encourage usage during off-peak

hours

2.2.6.4 Grade of Service

Grade of service is directly related to the blocking probability. A higher grade of service

guarantee to the user means ensuring a low blocking probability during the busy hours.

Providing a higher grade of service requires increasing the number of resources in the

system. Conversely, reducing number of resources; lower the system cost, but at the

expense of grade of service [6].

2.2.6.5 Erlang Calculations

There is a tradeoff between resource dimensioning and grade of service. The choice of

using the Erlang-B and Erlang-C formulas is dependent upon the handling of users when all

resources are busy.

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Erlang-B is used when failure to get a free resource results in the user being denied

service. The users request is rejected as no free resources are available.

Erlang-C is used when failure to get a free resource results in the user being added into a

queue. The users stay in the queue until a free resource can be found.

The formulas of Erlang B and Erlang C works under the following conditions:

The number of customers is much larger than the number of resources available. In

general, the formula gives acceptable results if the number of customers is at least

10 times the total number of resources.

Requests from customers are independent of each other.

Customer requests are blocked/ queued only when no resources are available to

service them.

The resource is allocated exclusively to one customer for the specified period.

2.2.7 Clutter

Clutter is defined as the man-made and natural features that may impair radio frequency

propagation by reflection, diffraction, absorption, or scattering of the transmission waves.

There are various sources of clutter (morphological) data. The more current the clutter data,

the more accurate the propagation predictions will be. The benefits of updated clutter data

are:

Enhance coverage and reduce dropped calls

Predict the performance of wireless services

Optimize transmission site locations and reduce infrastructure costs

Some Clutter and Terrain Descriptions are:

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2.2.7.1 Dense Urban:

Consist of densely built areas with mainly high buildings. Typically there is small number of

trees and vegetation within this area due to the density of buildings.

2.2.7.2 Urban:

Consist of metropolitan regions, industrial areas and closely spaced residential homes and

multi-storied apartments. Building density is high but may be interspersed with trees and

other vegetation.

2.2.7.3 Suburban:

Consist mainly of single family homes, shopping malls and office parks. Significant

vegetation, trees and parking lots are intermixed with buildings. Most buildings are 1 to 3

stories but significant exceptions do occur. Significant areas within small and medium cities

along with suburban communities surrounding major cities are examples of this

environment.

2.2.7.4 Rural/Quasi-Open:

Consist of open space with few buildings or residences. Major interconnecting highways,

farms, and barren land are found within rural areas. The largest variations in cell coverage

area are found in rural areas due to differences in vegetation and terrain.

2.2.7.5 Terrain:

Terrain descriptions focus on the land mass. Examples of terrain description are:

mountainous, desert, water (ocean, lake, and stream), etc. Types of terrains are

i. Forest: Foliage descriptions focus on the tree density and tree height.

ii. Roads: Roads are normally described in terms of their capacity to carry traffic. For

example, highways are described as being primary if they are heavily traveled multi-

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lane roads (such as toll roads and inter-state highways). Smaller roads in and

around the city or town would be described as secondary roads.

2.2.8 Propagation Models:

The design of a new radio communication system starts with determination of a proper

location of the base station and determination of the frequency plan, both of which depend

highly on the propagation loss. By determining a model for the transmission of the

information through the channel, these two characteristics can be accurately determined.

In general the propagation model can be made in three steps. In the first step information

for the environment has to be considered. The second step includes the definition of

mathematical approximations of the physical propagation mechanisms, and the third step is

the formalization of the results of the previous two steps. These steps are described in

details in the following sections [7].

2.2.8.1 Influence of the Environment

The environments, where mobile radio systems are intended to be installed, are ranging

from in-door up to large rural areas. Wave propagation prediction methods are required

covering the whole range of macro-, micro, and pico –cells. In order to be described

accurately, different data is considered for the different types of environment. While for the

prediction of macro-cells terrain height information and land usage data is taken into

account for urban environment. Table 2.3 illustrate cell type definition

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Table 2.3 Definition of types of cell

Cell type Cell radius Typical position of Base Station Antenna

Macro cell (large cell, terrain)

1km to 30 km Outdoor, mounted above rooftop level, heights of all surrounding buildings are below base station antenna height

Mini cell (small cell, suburban)

0.5 km to 3 km Outdoor, mounted above medium rooftop level, heights of some surrounding buildings are below base station antenna height

Micro cell (small cell, urban)

Up to 1 km Outdoor, mounted below medium rooftop-level, heights of all surrounding buildings are above base station antenna height

Pico Cell (indoor) Up to 500 m Indoor or outdoor mounted below roof top level.

2.2.8.2 Propagation phenomena and propagation loss

Calculation of the path loss is called prediction. Exact prediction is possible only for simpler

cases, such as the free space propagation or the flat-earth model. For practical cases the

path loss is calculated using a variety of approximations.

The propagation in free space can be characterized with the following formula:

L = 32.44 + 20log (f) + 20log (d) 2.3

Where f (MHz) is the operating frequency and d (km) is the distance between the

transmitter and the receiver.

The receiving power in free space is decreasing proportionally with the square root of the

distance, and additionally it is influenced by the following propagation mechanisms in the

mobile radio channel (fig. 2.11): shadowing, reflection, refraction, scattering, and diffraction.

Figure 2.11: Shadowing, Reflection, Refraction, Scattering, and Diffraction.

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2.2.8.3 Modeling approaches

Three types of approaches have been used in order to find solutions for the problem of

channel planning.

Statistical methods (also called stochastic or empirical) are based on measured

and averaged losses along typical classes of radio channels.

Deterministic methods are based on the physical laws of wave propagation.

These methods produce more accurate and reliable predictions of the path loss

than the empirical methods; however, they are significantly more expensive in

computational effort and depend on the detailed and accurate description of all

objects in the propagation space, such as buildings, roofs, windows, doors, and

walls. The value of losses was provided for simulation purposes.

Semi-deterministic - combines the two methods described above.

2.2.8.4 Types of Propagation Model

The aim of propagation model is “to predict signal strength at a particular receiving point or

in a in a specific location area”. The propagation models are usually divided into:

i. Large-scale propagation models

ii. Small-scale propagation models

i. Large-scale propagation models

The large scale models normally are used to predict the mean signal strength for

transmitter-receiver separation distances (d) of several hundred meters apart. In general

when d > (5 * wavelength) the large scale model is applied.

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ii. Small scale propagation models

Small scale model or fading models, describe rapid fluctuations of the received signal

strength over very short T-R separation distances (d) or short time durations. In general

small scale model is applied when d < (5 * wavelength).

2.2.9 Outdoor Propagation Model

Some of the outdoor propagation models are:

1. Longley-Rice Model

2. Durkin’s Model

3. Okumura Model

4. Hata Model

A proper system design requires accurate and reliable radio channel models, among which

the selection of prediction models are most important. Investigation of different existing

models and extensive measurements of mathematical equations; Okumura-Hata model is

selected. Okumura-Hata model is suitable in GSM 900 MHz network for macro - micro cells

and has better accuracy in dense urban areas especially for pico cells.

2.2.9.1 Okumura-Hata model

The Okumura-Hata model is a simple empirical approach for prediction. This model is

based on Japanese measurements done by Okumura, while the mathematical formulation

of the model is done by Hata.

The equations derived from the measurement data require only the four parameters;

therefore this model features very short computation time.

1. f is the frequency in MHz,

2. hbs is the base station antenna height above ground in m,

3. hms is the mobile station antenna height above ground in m,

4. d is the distance between BS and MS in km,

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Figure 2.12: BTS and MS height for Okumura and Hata Model

Because of the calibration with measurement data the model is restricted to the following

ranges for the different parameters:

The operating frequency is between 150 MHz and 1500 MHz.

Height of the transmitter – 30 to 200m.

Height of the receiver – 1 to 10m.

Distance between transmitter and receiver – 1 to 10 km.

The basic transmission loss in dense urban areas is computed according to the formula:

2.4

Where hms is a correction factor with following values:

For Open Area, Suburbs, Medium city

) 2.5

For Large cities

2.6

2.7

In addition to the main formula for the dense urban case, there are some modifications for

rural (village, sub urban) and open areas.

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2.8

2.9

These formulas describe the model in flat way, because they describe the wave

propagation without taking into account the local effects around the receiver, like reflection

or shadowing.

2.2.10 Problems and Solutions of Air Interface

Radio interface is the most vulnerable part of GSM connection. The air interface has to

cope with problems, such as variable signal strength due to presence of obstacles along the

way, radio frequencies reflecting from buildings, interference from other radio sources etc.

This section briefly discuss some of the problems occur during transmission of radio signals

and some solutions. Some of the most common problems are described below.

2.2.10.1 Problems

i. Shadowing

Shadowing occurs when there are physical obstacles including buildings between the BTS

and the MS (fig 2.13). Instead of reflecting the signal, these obstacles attenuate signal

strength. When the MS moves, the signal strength fluctuates depending on the obstacles

between the MS and BTS. Drop in strength are called fading dips.

Figure 2.13: Shadowing

25


Shadowing is generally a problem in the uplink direction; because BTS transmits

information at a much higher power compared that from MS. The solution to over come this

problem is known as Adaptive Power Control. Based on quality and strength of the received

signal, BTS informs MS to increase or decrease power as required.

ii. Multi-path Propagation

Multi path fading occurs when there is more than one transmission path to the MS or BTS,

and therefore more than one signal is arriving at the receiver. This may be due to buildings

either close to or far from the receiving device. Rayleigh fading and time dispersion are

forms of multi path fading.

Figure 2.14: Multi-path Propagation

In figure 2.14, the received signal is the sum of identical signals that differ only in phase

(and to some extent amplitude). A reflected signal that has traveled some distance causes

“Inter Symbol Interference” where as near reflection causes “Frequency Dips”.

iii. Time Alignment

Each MS on a call is allocated a time slot on a TDMA frame. This is an amount of time

during which the MS transmits information to the BTS. The information must also arrive at

the BTS within that time slot. The time alignment problem occurs when part of the

information transmitted by an MS does not arrive within the allocated time slot. Instead, that

part may arrive during the next time slot, and may interfere with information from another

26


MS using that other time slot. A large distance between the MS and the BTS causes time

alignment. Effectively, the signal cannot travel over the large distance within the given time.

Figure 2.15: Time alignment problem

In figure 2.15, an MS is assigned time slot 1 initially. During the call MS moves from position

A to position B. As distance increases, answer from MS arrives late at the BTS. The delay

becomes so long that the transmission from the MS in time slot 1 overlaps with the

information which the BTS receives in time slot 2 [3].

2.2.10.2 Solution to Problems

There are number of solutions to overcome these problems.

Channel Coding

Interleaving

Frequency hopping

Antenna Diversity

Time Advance

i. Channel Coding

Channel coding is normally used for overcome the problems caused by fading dips. In

channel coding, user data is coded using standard algorithms. This coding is not for

encryption, but for error detection and correction purposes

ii. Inter-leaving

Inter-leaving is the spreading of the coded speech into many bursts. By spreading the

information into many bursts, it is easy to recover the data even if one burst is lost.

27


Figure 2.16: Inter-Leaving of data

As shown in Figure 2.16, the bits of each block are sent in a non-consecutive manner. If

one block is lost in transmission, it is still manageable to recover the data [2].

iii. Frequency Hopping

In frequency hopping, the frequency on which the information is transmitted is changed for

every burst. In GSM there are 64 patterns of frequency hopping; one of them is a simple

cyclic or sequential pattern. The remaining 63 are known as pseudo-random patterns,

which an operator can choose from. Generally it does not significantly improve the

performance if there are less than four frequencies in the cell. The reasons of using

Frequency Hopping are:

Decreasing the probability of interference

Suppressing the effect of Rayleigh fading

iv. Antenna Diversity

Antenna diversity increases the received signal strength by taking advantage of the natural

properties of radio waves. Increased received signal strength at the BTS is achieved by

mounting two receiver antennae instead of one. Two Rx antennas are physically separated;

the probability that both of them are affected by a deep fading dip at the same time is low as

shown in figure 2.17. There are two primary diversity methods: space diversity and

polarization diversity.

28


Figure 2.17: Antenna Diversity

v. Timing advance

Solution to counteract the problem of time alignment. It works by instructing the misaligned

MS to transmit its burst earlier or later than it normally would. In GSM, the timing advance

information relates to bit-times. An MS is instructed to do its transmission by a certain

number of bit-times earlier or later related to previous position, to reach its timeslot at the

BTS in right time. Maximum 63 bit-times can be used in GSM systems. This limits GSM

normal cell size to 35km radius.

Figure 2.18: Timing Advance

As shown in figure 2.18 , BTS instruct MS to start sending information at TS-4 so that it

reaches at BTS on its allocated TS i.e. at TS-5.

2.2.11 Interference

The signal at the receiving antenna can be weak by virtue of interference from other

signals. These signals may be from the same network or may be due to man-made objects.

Interference is the major limiting factor in the performance of cellular radio systems.

Sources of interference include mobile in the same cell, a call in progress in a neighboring

cell, another base station operating in the same frequency band. Interference is a major

bottleneck in increasing capacity.

29


2.2.11.1 Co-channel Interference (C/I)

Co-channel interference is caused by the use of a same frequency close to another cell.

The former will interfere with the latter, leading to the terms interfering frequency (I) and

carrier frequency (C).The GSM specification recommends that the carrier-to-interference

(C/I) ratio is greater than 9 decibels (dB). However, its recommended that 12 dB be used as

planning criterion. This C/I ratio is influenced by the following factors:

i. The location of the MS

ii. Local geography and type of local scatters

iii. BTS antenna type, site elevation and position

Figure 2.19: Co-channel interference

2.2.11.2 Adjacent channel interference (C/A)

Adjacent frequencies (A), that is frequencies shifted 200 kHz from the carrier frequency (C),

must be avoided in the same cell and preferably in neighboring cells also. Although

adjacent frequencies are at different frequencies to the carrier frequency they can still

cause interference and quality problems. The GSM specification states that the carrier-to-

adjacent ratio (C/A) must be larger than -9dB. It is recommended that higher than 3 dB be

used as planning criterion.

30


Figure 2.20: Adjacent channel interference

By planning frequency re-use in accordance with well established cell patterns, neither co-

channel interference nor adjacent channel interference will cause problems. In reality cells

vary in size depending on the amount of traffic they are expected to carry. Therefore, real

cell plans must be verified by means of predictions to ensure that interference does not

become a problem. Nevertheless, the first cell plan based on hexagons, the nominal cell

plan, provides a good picture of system planning.

2.2.12 Handover

As a mobile station moves away from its serving BTS towards the coverage area of

neighboring BTSs, the mobile station measurement reports will show a gradual decrease in

signal strength from its serving BTS while showing an increase in measured signal strength

from one or more neighboring BTSs. It is the responsibility of the serving BSC to analyze

the measurement reports from the mobile station and to decide when a handover should be

performed.

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Figure 2.21: The handover process

Figure 2.21 shows that as MS moves from cell ‘a’ to cell ‘b’, RSL of MS decreases

gradually. When RSL drop down to minimal RSL level (i.e. less than -100dBm) it hand over

to neighboring BTS.

2.2.12.1 Handover types

The type of handover procedure executed depends on what level of switching must be

performed in order to move the call from the serving BTS to the new candidate BTS.There

are basically four types of handovers:

i. Internal or intra-BSS handover, which can be:

Intra-cell handover

Inter-cell handover.

ii. External or inter-BSS handover, which can be:

Intra-MSC handover

Inter-MSC handover.

If the serving and candidate BTSs reside within the same BSS, the BSC for the BSS can

perform the handover without the involvement of the MSC; thus termed internal or intra-

BSS handover. This type of handover can also be sub-divided into intra-cell and inter-cell

32


handovers. An intra-cell handover is an intra-BSS handover within the same BTS. An inter-

cell handover is a handover between different BTSs.

If the serving and candidate BTSs do not reside within the same BSS, then an inter-BSS

handover is performed, which requires the MSC to coordinate and switch facilities

(handover the call) between the serving BTS and the candidate BTS. This type of handover

can also be divided into intra-MSC and inter-MSC handovers.

2.2.13 Power control

Power Control enables the mobile station and/or the BTS to increase or decrease the

transmission power on a radio link. Power Control is separately performed for the uplink

and downlink. In both cases the BSC is responsible for initiating Power Control. The mobile

station and the BTS adopt transmit power according to the BSC power control commands.

Reasons for Power Control - While a mobile station is active on a call, it has the

responsibility of providing measurement report about the performance of the air-interface

periodically to its serving BTS so that the serving BSC can decide if a power control should

be performed. Reason of power control is to save mobile station battery power. The main

reason for power control is improving the carrier-to-interference ratio within the cellular

network.

2.3 Radio Access Network Design

GSM system network planning undergoes extensive modification so as to fulfill the ever-

increasing demand from operators and mobile users with issues related to capacity and

coverage. In order to meet the requirements of the mobile services, the radio network must

offer sufficient coverage and capacity while maintaining the lowest possible deployment

costs. The designing of Radio Access Network (RAN) consists of mainly three stages that

are:

33


Fig 2.22: Stages of RAN Design

The Radio Access Network designing begins with traffic and coverage analysis. The

analysis should produce information about the geographical area and the expected capacity

(traffic load). The types of data collected are:

Cost of network

Capacity & Coverage of Network

Grade Of Service (GOS)

Available frequencies

Speech quality

System growth capability

The simplified radio network planning process is shown in Figure 2.23:

Figure 2.23: Radio network planning process

2.3.1 Coverage Planning

Coverage in a cell is dependent upon the area covered by the signal. The distance traveled

by the signal is dependent upon radio propagation characteristics in the given area, since it

is important for the interference management to correctly estimate the situation of the

propagation from the base station. Radio propagation varies from region to region so

predictions are different for both coverage and capacity. The radio wave propagation loss

varies greatly depending on the incidence of buildings and the population density in the

34


area. The propagation loss can be estimated either by statistical or deterministic

techniques. The prime requirement is that the network design should cover 100% of the

area. Fulfilling this requirement is usually impossible, so efforts are made design a network

that covers all the regions with no ‘holes’. The whole land area is divided into five major

classes – dense urban, suburban, industrial, residential and rural – based on human-made

structures and natural terrains. The cells (sites) that are constructed in these areas can be

classified as outdoor and indoor cells. Outdoor cells can be further classified as macro-

cellular, micro-cellular or pico-cellular (see Table 2.3).

2.3.2 Capacity Planning

Capacity can be understood in simplest terms as the number of mobile subscribers a BTS

can cater for at a given time. The greater the capacity, the more mobile subscribers can be

connected to the BTS at a given time, thereby reducing the amount of base stations in a

given network. This reduction would lead to an increase in the operation efficiency and

thereby profits for the network operator. Capacity planning is a very important process in

the network rollout. Capacity plans are made in the preplanning phase for initial estimations,

as well as later in a detailed manner. The number of base stations required in an area

comes from the coverage planning, and the number of transceivers required is derived from

capacity planning as it is directly associated with the frequency re-use factor. The minimum

frequency re-use factor calculation is based on the C/I ratio. As soon as the C/I ratio

decreases, the signal strength starts deteriorating, thereby reducing the frequency re-use

factor.

Another factor is the antenna height at the base station. If the antenna height is too high

then the signal has to travel a greater distance, so the probability that the signal causes

interference becomes greater. The average antenna height should be such that the number

of base stations (fully utilized in terms of their individual capacities) is enough for the

needed capacity of the network. There are three essential parameters required for capacity

35


planning: estimated traffic, average antenna height, erlang calculations, busy hour and

frequency usage.

Average Antenna Height - The average antenna height is the basis of the

cellular environment (i.e. whether it is macro-cellular or micro-cellular). If the

average antenna height is low, then the covered area is small in an urban

environment. This will lead to the creation of more cells, and hence increase the

number of times the same frequency can be re-allocated. Exactly the opposite is the

case in a macro-cellular environment. Here the coverage area would be more, so

the same frequency can be reallocated fewer times. All these calculations are based

on the interference analysis of the system as well as the topography and

propagation conditions.

Frequency Usage and Re-use - Frequency usage is an important concept

related to both coverage and capacity usage. Frequency re-use basically means

how often a frequency can be re-used in the network. If the average number of the

transceivers and the total number of frequencies are known, the frequency re-use

factor can be calculated. Example :If there are 3 TRX that are used per base station

and the total number of frequencies available is 27, then the total number of

frequencies available for re-use is 27/3 = 9.

2.3.3 Frequency Planning

In the radio planning process, the maximum utilization of the available frequencies is known

as frequency planning. Capacity and frequency planning go hand-in-hand. A good

frequency plan ensures that frequency channels are used in such a way that the capacity

and coverage criteria are met without any interference. This is because the total capacity in

a radio network in terms of the number of sites is dependent upon two factors: transmission

power and interference. Frequency plan must ensure that C/I > 12 dB and C/A > -12 dB

36


(GSM recommendation).The re-use of the BCCH TRX (which contains the signalling time

slots) should be greater than that of the TCHs, since it should be the most interference-free.

2.3.4 Quality

The quality of the radio network is dependent on its coverage, capacity and frequency

allocation. The quality of the network is dependent upon the parameter settings. Most of

these are implemented during the rollout of the network and are based on measurements.

Once there are measurements available from the initial launch of the network, these

parameters then can be fine-tuned. This process becomes a part of the optimization of the

radio network. Most of the severe problems in a radio network are attributed by signal

interference. When interference exists in the network; the source needs to be found. The

entire frequency plan is checked again to determine whether the source is internal or

external. The problems may be caused by flaws in the frequency plan, in the configuration

plans (e.g. antenna tilts), inaccurate correction factors used in propagation models, etc.

2.4 Cell Planning

2.4.1 Introduction

The Cell Planning process consists of three phases, preliminary tasks, design and

implementation. This section describes these activities and the links between them.

The first phase’s main objective is to gather hypotheses (antenna heights and technical

data such as terrain database, link budget calculation, traffic dimensioning, and propagation

model) in order to start the cell planning design.

The second phase objective is cell planning (target site locations, frequency planning, TRX

planning, and propagation modeling).

37


The third phase covers the cell planning implementation (final site locations, coverage

concession, frequency planning, TRX planning, network engineering support, radio

acceptance support).

These phases are named as preliminary tasks, design and implementation and are

described below in detail.

2.4.2 Preliminary Tasks

Before starting this project several assumptions were made. The objective of preliminary

tasks is to summarize the required inputs for the design activities into the cell planning. This

phase is further divided into several parts which are shown below.

Figure 2.24: Preliminary Tasks of Cell Planning process

2.4.2.1 Hypotheses Gathering

Most of assumptions are derived from the RFQ (Request for Quotation), from meetings with

the customer or from vendor decisions (products used). Hypotheses gathering consist of

collecting data from various sources that are required for cell planning (coverage target,

BTS equipment information, site constraints, existing sites, traffic information, frequency

information). This information was provided for this project.

38


2.4.2.2 Terrain Database Selection and Improvement

Digital Terrain Map (DTM) is a mandatory input for cell planning. Purchase of a terrain

database is a deal between cost, delay and accuracy. Then, it is required to perform several

checks on the terrain database data (heights, clutters, and vectors, geographical continuity)

to validate it. The objective of DTM with appropriate accuracy in regards to cost and delay is

to check the database consistency and updating using results of RF survey.

2.4.2.3 Link Budget

The link budget calculation specifies for each type of environment (urban, suburban, rural

and other clutters), each type of product (indoor BTS, outdoor BTS, coupling system,

antennas type) and RF design assumptions, a maximum cell radius based on the Quality of

Service requirements (quality of coverage). These radius are used to produce cell counts

that give an idea of the number of sites required to meet requirements.

2.4.2.4 Traffic Dimensioning

The objective for this activity is to identify area where traffic is more constraining than

coverage, like in urban areas; and to determine BTS maximum configuration to be used for

each traffic area.

2.4.2.5 Cell Count

This activity consists of calculation of the number of cell sites required to both fulfill traffic

and coverage requirement, in relation with choice of equipment. The cell count may be

performed before design phase, to work out the number of cell sites that will be positioned.

For this project cells which were required to fulfill the requirement was found to be above 70

cells.

39


2.4.2.6 Model Design

This activity includes the choice of a propagation model, its calibration to focus on the major

cell planning requirements linked to a contract. The propagation modeling process assumes

that the terrain database is validated. The propagation model is specific to a terrain

database. Propagation model which is used in this project is Okumara - Hata.

2.4.3 Design

The main task of design is Site determination activity. Model tuning, frequency planning and

TRX planning may be part of this phase but not necessarily. Pictorial illustration for this

phase is shown in the figure

.

Figure 2.25: Design phase of Cell Planning

2.4.3.1 Site Determination

This activity consists in determination of each site position and characteristics to achieve

compliance with coverage and traffic requirement. Coverage maps are used to represent

the result of this design step. The objective for this is to evaluate the number of sites and

40


their potential locations and to predict the service area. This prediction shows and distinct

the number of sites deployed in different clutters.

2.4.3.2 Model Tuning

This activity is not mandatory but may occur during the design or the implementation phase.

The model tuning might be required if the level of confidence in the terrain database or in

the model is not high enough. The objective for this activity is to check the validity of radio

measurements; and to verify consistency between existing propagation model and radio

measurements.

2.4.3.3 TRX Planning

Based on the contract subscriber profiles and contract products, the traffic planning

specifies the TRX configuration for each site. If the required capacity cannot be provided by

a site location then cell splits may be necessary. A new site determination step might have

to be done. The main objective for this is to determine (or confirm) the number of TRXs per

cell needed to satisfy the customer's traffic requirements.

2.4.3.4 Frequency Planning

Assign frequencies according to the available RF channels in order to minimize the

interference. A C/I (Carrier to Interference) map is created to determine the levels of

interference. These two activities (frequency allocation and C/I analysis) are repeated until

the frequency plan is acceptable.

Once the cells have been positioned and the number of TRXs per cell has been set (or

confirmed by the TRX Plan), frequencies must be allocated to each cell in a way which

minimizes interference using tilts and azimuths. The ARFCN which have been allotted for

this project are 27 which make the total bandwidth of 5.4MHz

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2.4.4 Implementation

The last phase for cell processing is of implementation. Objective of the project is planning

of access part not implementation. Last phase is included to give an overview of complete

Cell planning process.

Theoretical site locations specified during the site determination activity represent target.

SAQ (Site Acquisition) tries to find real locations which are the best matching with site

location criteria. The figure 2.26 illustrates the implementation phase.

Figure 2.26: Implementation phase

2.4.4.1 Site Selection

The purpose for this activity is described below:

Choose a single real location per theoretical site, this location is supposed to be the

best among the proposed ones.

Share data (site location, antennae height, azimuths, and tilts) between cell

planning, site acquisition, and transmission teams.

Maintain the cellular planning tool site database up to date.

2.4.4.2 Coverage Concessions

The purpose for this activity is to:

Keep track of coverage problems.

Propose solutions to solve coverage holes.

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Maintain an accurate communication link with customer project management to

deal with cell planning problems.

2.4.4.3 Radio Data fill

Radio data fill is an iterative process which defines the radio parameters (TRX plan,

frequency plan). It has an objective to:

Provide updated values for TRX plan, frequency plan, and BSIC plan.

Provide neighboring cell definition.

Provide initial LAC definition

43

Chapter 3 BSS Planning

CHAPTER 3

BSS Planning

3.1 Introduction

The main aim of radio network designing is to provide a cost-effective solution for the radio

network in terms of coverage, capacity and quality. The network design criteria vary from

region to region depending upon the dominating factor or priority, which could be capacity

or coverage. Our task was to completely plan the site using 27 ARFCN when its generally

done with the help of 37 ARFCN.

This chapter illustrates the procedure followed for designing the radio access network for

the given area taking under consideration all the parameters, resources allocated and

standards mentioned by HUAWEI.

3.2 Steps of Designing Process

The approach adopted to accomplish designing of radio access network is broken down in

different steps as shown in figure 3.1. According to project design, fig 3.1, planning steps

are divided in two phases which are initial planning and System growth.

Figure 3.1: Project Design

44


The phase of initial or pre-planning starts from first step of “traffic and coverage analysis”

goes till “System design”. The specifications and targets given by HUAWEI are:

Network cost: 10 Million $ ARFCNS: 27

Cost per BTS: 0.2 Million $ Number of users: 7,000

GoS : 2%

3.2.1 STEP 1: Traffic and Coverage Analysis

The aspect of network’s coverage includes defining the coverage areas,

terrain profile and related signal strength. In this project the area allocated is

“Super Highway”, the signal strength of -70dBm is the outdoor acceptance

level required by the HUAWEI.

It is mandatory to calculate number of sites required to fulfill the coverage and capacity

requirement. As per budget for this project, maximum sites that can be placed are 80.

These sites have to be placed in such a way to give an optimum coverage and capacity.

There are coverage-driven areas and capacity-driven areas in a given network region. The

average cell capacity requirement per service area is estimated for each phase of network

design, to identify the cut-over phase where network design will change from a coverage-

driven to a capacity-driven process. While the objective of coverage planning in the

coverage-driven areas is to find the minimum number of sites for producing the required

coverage. It is necessary to experiment with both coverage and capacity, as due to the

capacity requirements the number of sites may have to be increased resulting in a more

effective frequency usage with minimal interference.

The definition of capacity include the number of subscribers and traffic profile in the region,

information on the radio access system and the antenna system performance associated

with it. Traffic is classified in two types

45


Offered Traffic: It is defined as traffic which user attempt to originate .

Carried Traffic: It is the traffic actually successfully handled by the system.

There are basically two approaches to perform the calculation of network’s capacity and

required equipment.

1. Theoretical approach

2. Practical approach

3.2.1.1 Theoretical Approach

The theoretical approach is the empirical method to perform the capacity calculations. The

steps involved during the capacity calculations using the data and assumptions are

mentioned below:

i. Choose sectorization that satisfies the desired Signal-to-Noise ratio.

ii. Calculate number of voice channels for the given area

iii. Calculate traffic density

iv. Find the traffic per sector using Erlang B chart

v. Cell area and number of cell.

i. Sectorization

Sectorization scheme is chosen first for pre-planning. The standard Signal-to- Noise ratio is

12dB. Following formulas are used to calculate Signal to Noise ratio.

For Omni

3.1

For Sector

3.2

Where γ = path loss value in dB q =√3N

46


ii. Voice channels (m)

The number of voice channels for city and highways are calculated using eq 3.3. Voice

channels are used to estimate the number of TRX required in particular area.

3.3

Where;

BW = Total bandwidth ; Channels BW=200 kHzSpeech/RF = voice channels ; N = reuse factor

iii. Traffic density (TD)

Traffic density of the city is calculated using eq 3.4. TD has unit of Erlang/km².

3.4

Where;

E = Traffic per subscriber ; Pop = PopulationPene = Market penetration ; ROT = Roll out time/yearShare = Market share ; Growth = Annual Population growth

iv. Traffic per sector (TS)

For a given GoS of 2%, traffic on each sector is calculated using Erlang-B chart for six

different terrains.

v. Number of cells

Area of a single cell is calculated using eq 3.5. Cell area has unit of ‘km²’ and it is

used to calculate minimum number of cells required to cover given area

Cell Area = TS × Sector TD

3.5

Number of Cells = Total Area Cell Area

3.6

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3.2.1.2 Calculations:

Area Radio Planning(A case to Study)

Given Data:

Site specifications system scenario:

Signal Strength = -70dBmSite Configuration = S333Out door HighwayFrequency band = 900MHzEnviroment = rural area (semi-open)

Financial Specifications:

Cost per BTS = 0.2 Million $Network Cost = 2 Million $

Technical Limitations:

Total BW = 5.4MHzChannel BW = 200 kHzPath loss = -156 dBGoS = 2%

Statistical Analysis:

Traffic per subscriber = [25mEr occupy the resource/channel for 90 seconds (standard)]Penetration (pene) = 7% [Next year 7% of the net population will be added to network]Roll out time/year = 15 days Annual population growth = 20%Number of Users (PoP) = 16000Market share = 90% [How much share our network (N) will hold in total telecom market]Number of Interference Cell (j) = for Omni: j = 1, for Sector: j = 3 Total area = 100 x 7 km2

*If X operators in sum carry Y% of total population, our market share will be = (N/X) * Y

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Capacity Planning:

Number of sites:

It is mandatory to calculate number of sites required to fulfill the coverage and capacity

requirement. As per budget for this project, maximum sites that can be placed are 10.

These sites have to be placed in such a way to give an optimum coverage and capacity.

2 Million $ = 10 sites (Maximum)

0.2

That means we can install up to 10 sites to provide coverage.

Busy-hour traffic: A is the maximum traffic on the busiest hour of system or line. A= a * b * t. .a = is everyday call times (originating and terminating) per user . b = is busy-hour to day ratio( busy-hour traffic divided by daytime traffic. t = is average call duration

Area Topographic features

DenseUrban

Average height of surrounding buildings is more than 30 metres (over 10 storey) and average distance between buildings is 10-20 metres. Usually the buildings are crowded around the site with the height of 10-20 stories and the ambient roads are not considerablly wide.

Urban

Average height of surrounding buildings is about 15-30 metres (5-9 storey) and average distance between buildings is 10-20 metres. The buildings are evenly distributed around the site. Mostly are below 9 stories and some are over 9 stories and the ambient roads are not considerably wide.

suburb

Average height of surrounding buildings is about 10-15 metres (3-5 storey) and average distance between buildings is 30-50 metres. The buildings are evenly distributed around the site. Mostly are 3-4 stories and some are over 4 stories. Roads around are wide.

ruralAverage height of surrounding buildings is below 10 metres. They are dispersed and mainly are 1-2 storey high. There are spacious space between.

49


a) Theoretical Approach:

(i) Sectorization:

Where q =√3N and γ = path loss value in dB = -156 dB q = 3N = 3

Therefore SIR = -886.3 dB for sector

(ii) Voice Channels (m)

Where;

BW = Total bandwidth ; Channels BW=200 kHz Speech/RF = voice channels

N = reuse factor = no. of channels x no. of sites 27 x 9 = 3 Total no. of TRX 81Since

Total BW = 5.4MHzSpeech/Rf = 8 (since full rate) [Note: At Half rate Speech/Rf is taken 16]Channels BW = 200 kHzN = 3

Therefore, m = 23

Total available Channels = Total BW divide by Channel BW = 5.4 MHz/ 200kHz = 27 ARFCN

Since

m = 23Therefore, 27-23 = 4 controls channels

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(iii) Traffic Density (TD):

OR Where;

E = Traffic per subscriber = 25m ; Pop = Population = 16000Pene = Market penetration = 0.07 ; ROT = Roll out time/year = 15Share = Market share = 0.14 ; Growth = Annual Population growth = 0.2

TD = 25m x 16000 x 0.07 x (1 + 0.2)15 x 0.90 = 0.97 Er/ km2 100 x 7 km2

(iv) Traffic per sector (TS):

One site has 3 sectors. Each sector has 3 Radios and each radio has 8 channels/slots so we have 24 slots per sector, 3 slots per sector are used for other purposes like signaling, broadcast, and data traffic so we are left with 21 slots per sector.

Our GOS is 2 %. Now using ErlangB table we can find out how much traffic one sector of a site can carry it turns out to be 14.03 Erlangs, Total trafic a site can carry is 42.09 Erlangs

Total traffic for that area is 0.9 Er/kmsq x 400 kmsq = 360 Erlangs

Total sites required = Total traffic = 360 = 8.5 (app 9 sites) Traffic per site 42.09

(v) Number of Cells:

Cell area has unit of ‘km²’ and it is used to calculate minimum number of cells required to

cover given area

Cell Area = TS × Sector TD

Cell Area = 14.03 × 3 = 46.76 m2 0.9

Number of Cells = Total Area Cell Area

Number of Cells = 400 = 8.5 sites (app 9 sites) 46.7

TD = 25m x Population x market share Area

51


b) Practical Method:

The maximum configuration stated by customer for this project is S333. It means that each

of the three sectors has 3 TRX in it. From the Erlang B table the traffic carried by this

configuration is 14.03 Erlang/ sector.

Site traffic it calculated as:

Traffic Carried by Site = Traffic carried by a cell × number of cell in that Site

= 14.03* 3 = 42.09 Erlang/ Site.

Total Erlang which is offered by the target population can be found as:

Total offered traffic in Erlang = Number of total users * traffic offered by a user

= 16000 * 25mErlang

= 400 Erlang

No. of sites = 16000 * 25mErlang = 8 sites (approx 24 sectors)

(14.03*3)

Comparison between Theoretical and practical approachesNumber of sites in Theoretical = 9

Number of sites in Practical = 8

Frequency hopping and Frequency Reuse – Frequency hopping and tighter reuse plan

also helped in accommodating capacity requirements. This approach allows more

transceivers to be deployed in the network, gradually enhancing traffic capacity.

Fractional Load Guide

□ For 1 x 1 schemeFractional Load = 16 %

■ For 1 x 3 schemeFractional Load = 50 %

Fractional Load = No of hopping radios = 50 % (Since we are using 1 x 3 scheme) 2x

Where 2x = No. of frequencies in each MAL list Therefore, x = 2 if we want 50 % OR 2x = 4

(In other words, 4 frequencies will be assign to each MAL list)

52


Duplex Sub bands of width = 25 MHz – Duplex Spacing 45 MHzUplink Sub band = 890 – 915 MHzDownlink Sub band = 935 – 960 MHzFrequency Spacing between carriers = 200 kHz (0.2 MHz)

One acrrier is used for guard band, giving:

Total number of carriers (ARFCN) = (25 – 0.2)/0.2 = 124

Uplink frequencies: Fu(n) = 890 + 0.2n MHz where 1 < n < 124Downlink Frequencies: Fd(n) = Fu(n) + 45 MHz

53


Frequency allocation Data Sheet:

NCC: 2, 3BCC: 0-7BSIC combinations: 20, 21, 22, 23, 24, 25, 26, 27, 30, 31, 32, 33, 34, 35, 36, 37MAL frequencies for sector A 1, 4, 7, 10MAL frequencies for sector B 2, 5, 8, 11MAL frequencies for sector C 3, 6, 9, 12MAIO for sector A: 0, 2MAIO for sector B: 1, 3MAIO for sector C: 0, 2Guard frequency = 20BCCH = 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26Guard Frequency for Next operator = 27HSN: 0-63

SD Calculation:

SITE VIEW:13/4 BCCH distribution scheme

400 kilo meter

1517

21

16

19

14

23

19

25

24

26

18

54


Since no. of slots per sector = 21 and GoS = 2%, From ErlangB TS = 14.03

Therefore ¼ * 14.03 = 3.5 (app 4) SD Time Slots i.e 32 channels

Total no. of subscribers per sector = TCH traffic per sector = 14.03 Traffic per subscriber 25m

= 561 subscribers

Actual traffic = Total – SDCCH usageSDCCH traffic = no.of subscribers per sector *no.of sectors*SD traffic/sub SDCCH traffic on each site = (561 *3) x 3.56 m erlang = 5.9 erlangSo actual traffic = 42.09 – 5.9 = 36.09 erlang

We can also refer to the standard table for SD traffic per sector

CGI:

Where MCC (Mobile country code) = 092, MNC (Mobile network code) = 01 LAC (Location area code) = 1234CI = Cell Id (given to each cell)

E1 Calculations:

Our one site contains data = 16 kbps x 8 time slots x 9 TRX = 1.152 Mbps

However one E1 carries = 32 slots x 64 kbps

= 2.048 Mbps (which is greater than 1.152 Mbps)

Therefore, only one E1 will be enough for communication between HUB site and BTS

MNC CILACMCC

55


BCCH

14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,

26

SD = 2 time slots

BCCH

14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,

26

SD = 2 time slots

TRX Radio#1

BCCH

14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,

26

SD = 2 time slots

TRX Radio#1

TRX Radio#1

Hopping

14710

MAIO (0)

Hopping

14710

MAIO (2)

TRX Radio#3

TRX Radio#2

Hopping

25811

MAIO (1)

Hopping

25811

MAIO (3)

TRX Radio#3

TRX Radio#2

Hopping

36912

MAIO (0)

Hopping

36912

MAIO (2)

TRX Radio#3

TRX Radio#2

S333 Sector A

S333 Sector B

S333 Sector C

56


Site 1

Site Name = HihfrmALongitude = 67.27448Latitude = 24.97918CI = 123BSIC = 27HSN = 59MAL = 1, 4, 7, 10BCCH = 16

Site 2:

Site Name = GothoreA Longitude = 67.37873Latitude = 25.02176CI = 113BSIC = 35HSN = 16MAL = 1, 4, 7, 10BCCH = 15

Site 3:

Site Name = Taj_GothA Longitude = 67.5621Latitude = 25.0731CI = 116BSIC = 23HSN = 50MAL = 1, 4, 7, 10BCCH = 23

Site 4:

Site Name = BismillahA Longitude = 67.61521Latitude = 25.12002CI = 119BSIC = 31HSN = 31MAL = 1, 4, 7, 10BCCH = 24

Site 5

Site Name = HihfrmB Longitude = 67.27448Latitude = 24.97918CI = 111BSIC = 27HSN = 59MAL = 2, 5, 8, 11BCCH = 19

Site Name = HihfrmCLongitude = 67.27448Latitude = 24.97918CI = 112BSIC = 27HSN = 59MAL = 3, 6, 9, 12BCCH = 14

Site Name = GothoreBLongitude = 67.37873Latitude = 25.02176CI = 114BSIC = 35HSN = 16MAL = 2, 5, 8, 11BCCH = 17

Site Name = BismillahB Longitude = 67.61521Latitude = 25.12002CI = 120BSIC = 31HSN = 31MAL = 2, 5, 8, 11BCCH = 18

Site Name = Taj_GothB Longitude = 67.5621Latitude = 25.0731CI = 117BSIC = 23HSN = 50MAL = 2, 5, 8, 11BCCH = 19

Site Name = Taj_GothC Longitude = 67.5621Latitude = 25.0731CI = 118BSIC = 23HSN = 50MAL = 3, 6, 9, 12BCCH = 25

Site Name = BismillahC Longitude = 67.61521Latitude = 25.12002CI = 121BSIC = 31HSN = 31MAL = 3, 6, 9, 12BCCH = 26

Site Name = GothoreC Longitude = 67.37873Latitude = 25.02176CI = 115BSIC = 35HSN = 16MAL = 3, 6, 9, 12BCCH = 21

Site Name = NoriabadB Longitude = 67.68612Latitude = 25.16189CI = 123BSIC = 24HSN = 9MAL = 2, 5, 8, 11BCCH = 19

Site Name = NoriabadC Longitude = 67.68612Latitude = 25.16189CI = 124BSIC = 24HSN = 9MAL = 3, 6, 9, 12BCCH = 14

57


Site Name = NoriabadA Longitude = 67.68612Latitude = 25.16189CI = 122BSIC = 24HSN = 9MAL = 1, 4, 7, 10BCCH = 16

Site 6

Site Name = FayyakunA Longitude = 67.8019Latitude = 25.1433CI = 125BSIC = 30HSN = 2 MAL = 1, 4, 7, 10BCCH = 15

Site 7

Site Name = AlAhmedALongitude = 67.79743Latitude = 25.15303CI = 128BSIC = 26 HSN = 21MAL = 1, 4, 7, 10BCCH = 23

Site 8

Site Name = HajeramA Longitude = 67.79402Latitude = 25.1672CI = 131BSIC = 32HSN = 5MAL = 1, 4, 7, 10BCCH = 24

3.2.1.3 General Problems and their Remedies:

Site Name = HajeramC Longitude = 67.79402Latitude = 25.1672CI = 133BSIC = 32HSN = 5MAL = 3, 6, 9, 12BCCH = 26

Site Name = AlAhmedB Longitude = 67.79743Latitude = 25.15303CI = 129BSIC = 26HSN = 21MAL = 2, 5, 8, 11BCCH = 19

Site Name = AlAhmedC Longitude = 67.79743Latitude = 25.15303CI = 130BSIC = 26HSN = 21MAL = 3, 6, 9, 12BCCH = 25

Site Name = HajeramB Longitude = 67.79402Latitude = 25.1672CI = 132BSIC = 32HSN = 5MAL = 2, 5, 8, 11BCCH = 18

Site Name = FayyakunB Longitude = 67.8019Latitude = 25.1433CI = 126BSIC =30HSN = 2MAL = 2, 5, 8, 11BCCH = 17

Site Name = FayyakunCLongitude = 67.8019Latitude = 25.1433CI = 127BSIC = 30HSN = 2MAL = 3, 6, 9, 12BCCH = 21

58


i) Coverage Problems:

The terrain configuration and human-made structures are different on different locations

resulting in different area-area predictions. The measurements made in dense urban areas

are different from those made in urban, sub-urban and other areas. During coverage

planning optimum level of RSL (i.e. -65dBm) was not achieved at distinct locations due to

propagation losses. Following approaches are used at cell site to increase the coverage.

Increasing the Transmitted Power - Increasing the transmitted power of each affected cell

results in coverage of a large area. When power level is doubled, gain increases by 3dB.

Increasing Cell-Site Antenna Height – To fill the coverage holes, cell-site antenna’s

height is increased. The effective antenna height is dependent on the location of Site and

MS. Sometimes, doubling the actual antenna height results in a gain increase of less than

6dB and sometimes more.

High-Gain Antennas at Site – The high gain antennas are also used to increases the

coverage especially in dense urban areas, because coverage is generally found to be less

at farthest part of the network

Selecting Cell-Site Location – Coverage area is also increased by selecting proper site

location for actual antenna height and transmitted power. For better coverage purposes,

high site is selected for minimizing the impact of interference.

Antenna Pattern - Problem is solved by immediate scrutiny of the deployed antennas

pattern and tilts. Such problems are usually sorted out by moving the antenna positions and

altering the tilting of the antennas.

59


ii) Capacity Problems:

Efficient designing of Radio Access Network is all about building high-capacity networks in

the most economical way, and therefore, GSM radio network capacity solutions are

becoming increasingly important. Following techniques are used to cater the allocated

number of users.

Small Cell Size – Controlling the radiation pattern results in reduction of cell size and

increases the traffic capacity. This approach is based on the assumption that all mobile

units are identical.

Increasing the Number of Radio Channels in Each Cell – Requirement of capacity is

met by increasing the number of radio channels in each cell. This is done by increasing

number of TRX at each site resulting in increase of TS.

Frequency hopping and Frequency Reuse – Frequency hopping and tighter reuse plan

also helped in accommodating capacity requirements. This approach allows more

transceivers to be deployed in the network, gradually enhancing traffic capacity.

iii) Performance Aspects:

Apart from achieving capacity and coverage, the two main parameters that are considered

when building a network are monetary cost and time—the actual cost of each solution is

market-dependent, since the costs associated with cell sites (site acquisition, site

preparation, rental costs) and transmission vary from market to market. Over dimensioning

of the network causes too much cost, traffic revenue gets too low to support cost of

network, very poor economic efficiency. Similarly, under dimensioning of the network

causes blocking probability to increase, has poor technical performance (in other words

interference), capacity for billable revenue become low, revenue gets lower due to poor

quality and very poor economic efficiency

60


Remedy – The solution to above mention problem is to deploy more transceiver on a cell

site or tighter frequency reuse plan. A third option is to introduce micro cells as it is easier

and less expensive to acquire sites for them. While designing trade off should be made

between resources and requirements to avoid both over and under dimensioning.

3.2.2 STEP2: Nominal cell planning

A nominal cell plan is produced from the data compiled from traffic and coverage analysis.

The nominal cell plan is a graphical representation of the network and looks like a cell

pattern on a map. First cell plan is laid which formed the basis for further planning. The

nominal plan is made by taking under consideration the following parameters and methods

which help to predict the path losses, make efficient use of available frequency band and

cater the interference.

i. Radio propagation

ii. Frequency reuse

iii. Interference

i. Radio propagation

To predict the signal strength and path losses of the radio wave or transmitted signal many

propagation models are analyzed. The Okumura-Hata model is chosen as the prediction

model .The radio propagation is highly dependent on clutter profile and the terrain assigned

for planning. The Okumura - Hata model is best suited for its loss predictions. Losses due

to clutter profile, shadowing, multi-path fading and vertical diffraction losses are catered

(see figure 5.4 and table 5.3).

ii. Frequency reuse

61


Based on the traffic calculations, the cell pattern and frequency re-use plan are worked out

not only for the initial network, but also for future demands.

The re-use patterns recommended for GSM are the 4/12 and the 3/9 pattern. Selected

reuse pattern is 3/9.

iii. Interference

Co-channel Interference (C/I) - Cellular networks are more often limited by problems

caused by interference rather than by signal strength problems.

The criteria of C/I used for designing the radio network is as follow:

C/I >= 12dB

Where, C is carrier frequency

I is interfering frequency

Adjacent channel interference (C/A) - The main focus is made to mitigate C/A in the

same cell during the planning. The C/A in neighboring cell is given the second priority as it

does not affect the communication. Here, the criteria of C/A used for designing the radio

network is as follow:

C/A>= 3db

Where, C is carrier frequency

A is adjacent frequency

These criterions are chosen after consultations with experienced personals and vendors. As

GSM standards are C/I greater then 9db and C/A greater than -9db, these criterions taken

here are well above the acceptance levels.

3.2.3 STEP3: Surveys

62


When the pre-planning phase is completed, the site search process starts. Based on the

coverage plans, prospective sites location is identified for specific areas. The process of site

selection, from identifying the site to site acquisition, is very long and slow therefore it is

worked out in conjunction with transmission planners, installation engineers and civil

engineers to make this process faster. A good site is a place that does not have high

obstacles around it and has a clear view for the main beam. The responsibilities of site

acquisition, civil works and engineering teams are discussed below:

Site Acquisition

The Site Acquisition process is performed in close co-operation with the Civil Works. It

consists of the following activities:

Searching for sites and gaining a site appraisal.

Outlining the site design and evaluating the cost.

Negotiating and signing leasing contracts.

Handling permits and arranging the hand-over to the Engineering personnel.

Civil Works

The Civil Works process consists of the following activities:

Preparing a detailed civil works design of the site.

Updating the costs for the site construction.

Arranging the site construction.

Engineering

The Engineering process begins when the Site Acquisition process and ends when Civil

Works process are complete. It consists of the following activities:

Measuring and collecting information about the sites.

Designing the antenna and radio configuration and producing cable drawings.

63


Making drawings showing the position of antenna and RBS equipment.

“Radio measurements” are performed to adjust the parameters used in the planning tool to

match the real situations. That is, adjustments are made to meet the specific site climate

and terrain requirements. A test transmitter is mounted on a vehicle, and signal strength is

measured while driving around the site area. Afterwards, the results from these

measurements can be compared to the values the planning tool produces when simulating

the same type of transmitter. The planning parameters can then be adjusted to match the

actual measurements.

Model Tuning Process

In these steps model tuning of Okumra - Hata model is described.

1. The model tuning starts by selection of the propagation model, Okumura-Hata

model is selected for signal loss prediction. The equation is;

L=A + Blog(f) – 13.82log(hbts) – a(hms) + (C – 6.55log(hbts))logd

Where,

A,B,C =Constant

d = distance

hbts = Effective height of BTS

hms = Effective height of MS

2. The measurement reports are prepared. The amount of measurements depend on

a.) Resolution of digital map provided

64


b.) The size of target area

3. The results of model tuning measurement report are imported in “the planning

system software and alignment with the digital map of the given area is made. This

alignment is made to minimize the GPS-SA effect or inaccuracies in coordinate

conversion parameters.

4. In Okumura-HATA model there are many unassailable parameters. At first the slope

of Okumura-Hata model is tuned by changing the factor “C”. In the equation of the

model. It can be seen that first three terms are independent of distance “d”. As

log(d) has the coefficient “C – 6.55log(h)”, by changing the factor “C” model has

been tuned. The values of this very factor depends on the clutter, which is

Lower for rural environment

Higher for Urban environment

The correction by factor “D” affects the effect of antenna height on prediction of losses. As

the Okumura- Hata model is suitable for cells that have antenna installed well above roof

tops ( in other words the lattice towers ). If the antenna is installed near the roof-top then

factor “D” in the equation is used for improving the accuracy of the predictions. The height if

mobile antenna is not considered for correction as the correction factor is 0db (given in

Okumura - Hata profile).

3.2.4 STEP 4: System Design

In system designing, dimensioning plays a vital role on cost of a network. Dimensioning is

used to identify the equipment and the network type required in order to cater for coverage

65


and quality requirement. Network must be planned that capacity needs are fulfilled for next

3-5 years. The inputs that are required for the dimensioning include:

The geographical area to be covered

The estimated traffic in each region

The minimum requirement of power in each region and blocking criteria

Path loss

The frequency band to be used and frequency re-use.

With above parameters, number of base stations is calculated for estimated number of

users (Table 3.2) in different clutters. Initially all sites deliver equal power (i.e. -43dBm).

Variation in power is dependent on level of interference.

3.2.5 STEP 5: System Implementation

Implementation and deployment completes the 2G-network design process by realizing the

projected site locations, service target requirements and time to service. It takes into

account the solution adopted for the network deployment, e.g. sharing sites with existing

base stations and evolution of core network elements or a complete new overlay network. It

will also take into account the hierarchy of the network, i.e. the macro- and micro layers

where applicable. When deploying in the macro-cell environment the implementation will

take into account the coverage dependency on the transmission rates and technology

availability in terms of antenna configuration and interference minimizing features. Thus, the

four steps outlined above do have an iterative process.

3.2.6 STEP 6: System Tuning

Networks need to operate at full efficiency with a minimal amount of maintenance; a high

degree of quality and with enough capacity according to the traffic demand. Once the

system has been installed, it is continuously monitored to determine how well it meets

66


demand. This is called system tuning. It involves checking whether the final cell plan was

implemented successfully, evaluating customer complaints, monitoring the network

performance, changing parameters accordingly and taking other signal measurements, if

necessary.

Drive testing is used for system tuning. It analyzes the current performance of network and

analysis measurable objectives in terms of quality, capacity and cost. TEMS, Test Mobile

System, is a tool for investigations and maintenance of Cellular networks: to ensure

coverage, quality or to pinpoint problem areas. Drive Tests are used to capture the

throughput at lower layers over the air interface, measure radio conditions, and monitors

signaling messages between the terminal and the network. Drive Testing assist in detecting

specific problems in the network and performing trouble shooting. This tool composes of

one mobile terminal with special firmware and software that collect information from the

radio interface. Typical information that is achieved from Drive Tests is:

Information about system serving cell: Cell Id, frequency, broadcast information,

etc.

Measurement of radio quality: Received power (RXLEV), signal to interference

ratio, RQUAL, Cell selection (C1) and Cell Re-selection (C2), TXPOWER, Call

Status, neighbor information, block error rate, etc.

Through put and delay on radio interface.

Signalling messages

Drive test tools also use GPS (Global Positioning System) in order to correlate the

measurement with different locations.

67

Chapter 4 Quick Budget

CHAPTER 4

Quick Budget

4.1 Introduction

The post processing RF tools enables the RF engineers to predict the effect of their

designed network or changes they make to the network will have on the perceived

coverage and quality. Thus expensive problems can be avoided and trouble spots can be

identified early and fixed quickly. These tools basically provide the visualizing the radio

access network for any specific terrain. The combination of the map, ground profiles and

the 3D view can save engineers visiting sites as a lot of information can be deduced by

viewing the database maintained by post processing tools.

This chapter provides a description of Quick Budget working and its back programming.

Quick Budget is a software application that is intended to lend a hand in designing,

operating and optimizing a cellular radio network. Its database is used to store all the

relevant information on sites, base stations and cell parameters, and from this Quick

Budget.

68

Chapter 4 Quick Budget

This is a screenshot of our link budgeting software that has been uploaded on the following

link www.fyp.awardspace.com. For further details, visit the above mentioned link.

69

http://www.fyp.awardspace.com./

Chapter 5 Optimization

Chapter 5

Optimization

5.1 Introduction

Every alive Network needs to be under continues control to maintain/improve the

performance. Optimization is basically the only way to keep track of the network by

looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye

on its growth and modifying it for the future capacity enhancements. It also helps

operation and maintenance for troubleshooting purposes.

Successful Optimization requires:

• Recognition and understanding of common reasons for call failure

• Capture of RF and digital parameters of the call prior to drop

• Analysis of call flow, checking messages on both forward and reverse

links to establish “what happened”, where, and why.

Optimization will be more effective and successful if you are aware of what you are

doing.

5.1.1. Purpose and Scope of Optimization

The optimization is to intend providing the best network quality using available

spectrum as efficiently as possible. The scope will consist all below;

• Finding and correcting any existing problems after site implementation and

integration.

• Meeting the network quality criteria agreed in the contract.

• Optimization will be continuous and iterative process of improving overall

network quality.

• Optimization can not reduce the performance of the rest of the network.

• Area of interest is divided in smaller areas called clusters to make optimization

and follow up processes easier to handle.

70


5.2. Optimization Process

Optimization process can be explained by below step by step description:

5.2.1. Problem Analysis

Analyzing performance retrieve tool reports and statistics for the worst performing BSCs

and/or Sites.

Viewing ARQ Reports for BSC/Site performance trends

Examining Planning tool Coverage predictions

Analyzing previous drive test data

Discussions with local engineers to prioritize problems

Checking Customer Complaints reported to local engineers

5.2.2. Checks Prior to Action

Cluster definitions by investigating BSC borders, main cities, freeways, major roads

Investigating customer distribution, customer habits (voice/data usage)

Running specific traces on Network to categorize problems

Checking trouble ticket history for previous problems

Checking any fault reports to limit possible hardware problems prior to Test

5.2.3. Drive Testing

Preparing Action Plan

Defining drive test routes

Collecting RSSI Log files

Scanning frequency spectrum for possible interference sources

Re–driving questionable data

5.2.4. Subjects to Investigate

71


Non–working sites/sectors or TRXs

In–active Radio network features like frequency hopping

Disabled GPRS

Overshooting sites – coverage overlaps

Coverage holes

C/I, C/A analysis

High Interference Spots

Drop Calls

Capacity Problems

Other Interference Sources

Missing Neighbors

One–way neighbors

Ping–Pong Handovers

Not happening handovers

Accessibility and Retainability of the Network

Equipment Performance

Faulty Installations

5.2.5. After the Test

Post processing of data

Plotting RX Level and Quality Information for overall picture of the driven

area

Initial Discussions on drive test with Local engineers

Reporting urgent problems for immediate action

Analyzing Network feature performance after new implementations

Transferring comments on parameter implementations after new changes

5.2.6. Recommendations

72


Defining missing neighbor relations

Proposing new sites or sector additions with Before & After coverage plots

Proposing antenna azimuth changes

Proposing antenna tilt changes

Proposing antenna type changes

BTS Equipment/Filter change

Re–tuning of interfered frequencies

BSIC changes

Adjusting Handover margins (Power Budget, Level, Quality, Umbrella

HOs)

Adjusting accessibility parameters (RX Lev Acc Min, etc..)

Changing power parameters

5.3 TEMS Software

Example of Bad FER

73


Example of FER is OK

Collusion of MA list causing low C/I

74


RX_Level

75


Late Handovers

Ping-Pong Handovers

76


Missing Neighboring relation

Drop call due to low signal level

77


Drop call due to bad RX_Quality

Call drop due to interference

78

Chapter 6 Results & Discussions

CHAPTER 6

RESULTS AND DISCUSSIONS

6.1 Introduction

The radio access network design being a complex process has been accomplished in eight

discrete steps. Each step has its separate problems, which can be tackled in a number of

ways. The choice of a solution depends on the scenario, priority and resources at hand. In

this chapter the final results of each step are stated and the solutions to mitigate the

problems faced during the designing process are discussed in adequate detail.

6.2 Results and Discussion

6.2.1 Step1: Traffic and coverage Analysis

The final coverage and capacity is as follow:

The phase of initial or pre-planning starts from first step of “traffic and coverage analysis”

goes till “System design”. The specifications and targets given by HUAWEI are:

Network cost: 2 Million $

ARFCNS: 27

Cost per BTS: 0.2 Million $

Number of users: 7,000

GoS: 2%

Radio network capacity solutions can be divided into three solution categories:

79


i) Cell capacity solutions - These solutions consist of methods and features that permit

more transceivers per cell. Factor that has the greatest influence on cell capacity is

frequency reuse. Cell capacity is thus determined by different methods and functions to

enhance frequency reuse. Two common methods are

• Multiple Reuse Pattern (MRP); and

• Fractional Load Planning (FLP).

The Multiple Reuse Pattern, which is based on base-band frequency hopping, yields the

best results for network composed mainly of filter combiners. The primary transceiver

carries the broadcast control channel (BCCH) and must therefore have a relatively loose

reuse pattern (explanation: a handset must listen to the information broadcast on the BCCH

before it can make calls in a cell). Where as; due to the frequency hopping gain, all

remaining transceivers in the network can have a successively tighter reuse pattern.

Compared to a non-hopping network, the MRP solution can be more than double cell

capacity. The requirements of MRP are that it requires

• Considerable spectrum (greater than 5 MHz)

• At least three transceivers per cell for good performance.

Fractional Load Planning is based on synthesized frequency hopping, which requires the

use of hybrid combiners. In FLP, the gain from frequency hopping is not dependent on the

number of transceivers in a cell, since each transceiver can hop on every frequency

allocated to the cell. Notwithstanding, due to the characteristics of synthesized frequency

hopping, the BCCH transceiver cannot hop frequencies.

80


ii) Network capacity solutions - These solutions focus on adding different kinds of cells

and make most of cell capacity by distributing traffic as efficiently as possible.

In addition to improving cell capacity, operators can introduce micro cells, since site

acquisition for micro cells is usually easier and less expensive than when adding regular

cells. Traffic management is an important issue in a network composed of cells of different

sizes. With multilayered hierarchical cell structures, cells can be divided in up to eight layers

and traffic can be prioritized and distributed between these layers. There are also numerous

add-on functions, such as

• Cell load sharing, which distributes traffic within layers.

• Assignment to another cell, which redirects traffic to other cells when

congestion occurs during call setup.

• Handling of fast-moving mobiles, which moves calls to higher layers when

there are too many handovers within a given interval. This function reduces

the number of handovers, thereby increasing voice quality.

iii) Channel capacity solutions - These solutions center on ways of using the available

throughput of the channels in the air in a more efficient manner, for example half-rate voice

channels and GPRS.

In the context of circuit-switched traffic, the channel capacity is about half-rate voice

channels and the way they are managed as shown in the figure 5.1. Since the half-rate

technique reduces the quality of voice, it has not been widely deployed. However, operators

are now beginning to use this technique more and more, since it can be allocated on a

dynamic basis during traffic peaks as shown in figure 5.1.

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Figure5.1: Dynamic half-rate allocation

6.2.1.1 Capacity Planning Approaches

For comparative analysis purpose capacity planning is done using two approaches.

i. Cell based approach

i) Cell based Approach

During the cell based capacity planning of the Global System for Mobile Communications

(GSM) network, traffic measurements are of significant importance. Because of false

predictions, the capacity planning of a cell may be done inaccurately. If the capacity of the

cell is not adequate to handle all of the busy-hour requests, the requests are not granted a

channel and users are blocked. Thus, when the blocking ratio is high, the cellular capacity

should be re-planned.

6.2.2 STEP2: Nominal cell planning

The result of nominal cell planning is shown in the figure 5.2 which is the cell pattern on

map. The densely polluted areas have cells with small radii and others have comparatively

larger radii. The small radius cells are enabling greater number of traffic channels in the

respective area, thus more users can be catered in densely polluted areas.

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The following results are achieved from the three under considered parameters while

making the nominal plan.

i) Radio propagation – The prediction model Okumura-Hata is selected. The

figure 5.3 shows the coverage prediction of a site by using Okumura- Hata.

Figure 6.3: Coverage Prediction by Okumura-Hata

ii) Interferences

Reduction of co channel interference in a cellular mobile system is always a

challenging problem. A number of methods are considered to overcome this

problem, such as

a) Increasing separation between two co channel cells

b) Using directional antennas at BTS

c) Lower antenna height at BTS

Method ‘a’ is not advisable because as number of frequency-reuse cells increases,

the system efficiency, which is directly proportional to the number of channels per

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cells increases, decreases. Method ‘c’ is not recommended either because such an

arrangement also weakens the RSL at mobile unit.

Method ‘b’ is a good approach, because the use of directional antennas in each cell

serves two purposes:

Further reduction of co channel interference when it is not eliminated by

a fixed separation of co channel cells

Increasing the channel capacity when traffic increases.

Initially the co-channel interference was 60%, which is reduced to 10% by using one

of the following methods:

Designing of Antenna Pattern - By designing an antenna that emit strong signals

in a particular direction and no signal in other direction, co channel interference can

be significantly reduced.

Tilting Antenna Pattern – Co-channel interference is minimized by confining the

energy within small area. This is achieved by downward tilting of directional

antenna.

Reducing Antenna Height – This method is used because minimal interference is

more important than radio coverage.

Reducing the Transmitted Power – In certain circumstances, reducing transmitted

power is more effective in eliminating interference than reducing height of antenna

Four conditions are used to compare the co channel interference results:

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If Carrier to interference ratio C/I is greater than 15 dB throughout the

network, system is properly designed for capacity.

If C/I is greater than 12 dB and Carrier to Noise ratio C/N is greater than

18dB in some areas, there is a co channel interference

If both C/N and C/I are greater than 3dB and C/N = C/I in a particular area,

there is a coverage problem

If both C/N and C/I are greater than 3 dB and C/N > C/I in particular area,

there is a coverage problem and co channel interference.

6.2.3 STEP3: Site surveys

The “site surveys” were conducted for all sites and following are the results of checked

parameters.

Exact location – Most of the site’s locations were mono pol. These sites are

displaced to acceptable location such that it doesn’t affect the coverage to

considerable level.

Space for the BTS equipment- The equipments used is HUAWEI BSC-6000.

The HUAWEI BSC-6000 belongs to the BSC family of HUAWEI. Its a 10

Transceiver (TRX) radio base station for outdoor applications. The HUAWEI

BSC-6000 is a high coverage base station and configured for three sectors

site.

Antennas – The 25dBi gain antennas are used, one for each sector. It has

zero electrical polarization and 4 to 5 degree mechanical down tilt where

ever there was requirement of more capacity.

The radio measurement is done to find the corrections in prediction model. The quality of a

network plan is dependent on the accuracy of the propagation model used to predict

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coverage pattern. The model tuning of Okumura-Hata resulted in modified area curves as

under.

Figure6.4: Okumura-Hata Correction curves

Due to the model tuning, the prediction gets better as in figure 5.3, which shows the

coverage pattern of same site as in figure 5.4. These graphs are being provided by external

advisor for calculation purposes

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Figure 6.5: Coverage prediction by Tuned Okumura-Hata

6.2.4 STEP4: System Design

Once the planning parameters have been adjusted to match the actual measurements,

dimensioning of the BSC is performed and the final cell plan produced. As the name

implies, this plan can then be used for system installation. New coverage and interference

predictions are run at this stage, resulting in Cell Design Data (CDD) documents containing

cell parameters for each cell. In [1], Dimensioning of BSC includes:

i. Calculation of number of E1 (trunk circuits) at each site.

ii. Total number of Erlang supported by BSC.

iii. Determination of the kinds of links.

iv. Distribution of microwave links.

v. Assigning the BTS sites to appropriate BSCs.

vi. Link Capacities calculations.

vii. Total num4ber of radio required.

viii. Bandwidths for radio links.

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i. Calculation of E1s

For calculations of E1s at each site it is mandatory to calculate the traffic carrying capacity

of each Site.

Data rate of 1 Time slot of E1 = 64 Kbps

Traffic channel on E1 = 30

Data rate of 1 Time slot of TRX = 16 Kbps.

Data rate of 1 TRX = 16 Kpbs × 8 = 128 Kbps.

Traffic carrying capacity of 1 cell = 3 × 128 Kpbs = 384 Kbps.

Traffic carrying capacity of 1 Site = 384 Kbps × 3 = 1152 Kbps

Required time slot for carrying traffic of S333 site = 1152 / 64 = 18 TS of E1s

Results show that one E1 is required by each site for supporting S333 configuration. So

total number of required E1 in the network is equal to total number of sites deployed. In total

79 E1 are required.

ii. Capacity of BSC :

Total number of Erlang supported by BSC is dependent on type and size of BSC. Here,

capacity of BSC is given to be 900 Erlangs.

iii. Determination of kind of link:

The determination of link is dependent on real site location and neighboring sites. This

parameter is calculated during installation and integration phase.

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iv. Assigning BTSs to BSCs :

The assignment of BTSs to a particular BSC is dependent on amount of traffic and location

of site. In this project, four BSCs have been deployed each is linked to 8 BTSs.

6.2.5 STEP5: System tuning

The system tuning is done by drive testing using TEMS.

Beside drive testing the system tuning also include:

a.) Eliminating equipment failures

b.) Improving network operation indicators, such as radio completion rate, call

drop rate, the worst cell, handover success rate and congestion rate, etc.

c.) Improving voice quality, such as balancing the traffic between the cells

inside the network.

d.) Network balancing, such as signalling load balancing, equipment load

balancing and link load balancing, etc.

e.) Adjusting the network resources reasonably, for example, improving

equipment and spectrum utilization and adjusting the traffic in each channel.

f.) Creating and maintaining a long term network optimization platform, and

creating and maintaining network optimization archives.

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CHAPTER 7

CONCLUSION

7.1 CONCLUSION

It can be concluded that radio access network designing requires a thorough

analysis of resources, geographical area and required standards. A fine line or trade

off is to be made at different stages, depending on the circumstances. This very

project provided an opportunity of grasping the concepts of RAN, understanding the

procedure of its designing, resolving different encountered problems and studying

diverse solutions. It also granted a juncture, to interact with professionals of the

telecommunication industry.

This project provides an individual with intrinsic details of BSS planning and radio

access network. The analysis made between the theoretical and practical

approaches is based on professional consultancy, theory mentoring and real

environment testing. Thus this project provides information about working in the

field. The radio access network is developed in four distinguished steps, which can

assist an individual in developing a clear idea of the complex process of designing of

RAN.

The proposed design is enabling an optimum service of 94%. The required stages of

coverage, capacity, and frequency planning are well accomplished in the designed

RAN and the frequency planning has been taken to the next level, called transceiver

planning for all the sites which contributes in mitigating the problem of interferences.

The coverage prediction and loss estimations are improved by model tuning and

drive testing. The outcome of model tuning is implemented. The surveys and site

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visits gave a clear idea of hardware requirements, its limitations and cost which

assisted in increasing the real environment realization of the designed RAN.

The designed RAN is a cost effective design, it can be said so as the cost of

network is 1.6 million$ (cost per site is 0.2 million $ and total sites are 8). The total

given budget for the network was 2 million$, thus 0.4 million$ have been saved. This

RAN also has the dispensation of easy implementation because of likeness between

sites of a clutter or defined traffic density.

Although the designed RAN is fulfilling the given target but it can be improved in a

number of ways. The shortcomings of few stages of designing are as follows. In the

stage of coverage planning, the loss and gain factors to cater open qausi terrain

could not be found due to clandestine company data. 100% service could not be

enabled in the given city. Thus, efforts can be made to further improve the tuning of

applied model. In the second stage of capacity planning, the concept of cell

hierarchy can be applied to improve the user catering, as it will classify the outdoor,

indoor, moving and stationary users.

The designed RAN in this project is for a 2G technology (GSM), as its currently

deployed all over Pakistan and license of 3G has not been provided by PTA. Yet 3G

is the future of mobile communication technology. The foremost and major

recommendation is to make this network for the 3G technologies (like WCDMA or

WIMAX); developing a RAN will provide an opportunity to be distinctive and gain

latest knowledge. The second recommendation is the application of quality planning

in the proposed design. This stage is not implemented as it was not a requirement of

HUAWEI but it can make the network resource utilization efficient. The quality

planning will also satisfy the customer’s needs more appropriately.

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GLOSSARY

ARFCN: Absolute Radio Frequency Channel Number

BSC: Base Station Controller

BSIC: Basic Station identity controller

BSS: Base Station Subsystem.

BSSMAP: BSS Management Application Part

BTS: Base Transceiver Station.

dTRX: double Transceiver Unit

CCH: Control Channel

CDD: Cell Design Data.

CDU: Combiner Distribution Unit.

CM: Control Module.

EIR: Equipment Identity Register

FDMA: Frequency Division Multiple Access.

FLP: Fractional Load Planning.

GoS: Grade of Service

GSM: Global System for Mobile communications.

HLR: Home Location Register

ISDN: Integrated Services Digital Network

LAC: Location Area code

LAPD: Link access Protocol on Data channel

LAPDm: Link access Protocol on Data modified channel

MAP: Mobile Application Part

MRP: Multiple Reuse Pattern

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MS: Mobile Station.

MSC: Mobile Switching Centre

MTP: Message Transfer Part

NSS: Network Switching Subsystem

PSU: Power Supply Unit

PTT: Postal Telephone and Telegraph

RAN: Radio Access Network

RBS: Radio Base Station.

RIL3: Radio Interface Layer 3

RSL: Received Signal level

RSM: Radio Subsystem Management

TRAU: Transcoding Rate and Adaptation Unit.

TRM: Transmission Module.

TRX: Transceiver Unit.

TDMA: Time Division Multiple Access.

TCH: Traffic Channel

TCAP: Transaction Capabilities Application Part

SAQ: Site acquisition

SCCP: Signaling Connection Control Part

Um: User mode

VLR: Visitor Location Register

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REFERENCES

[1] “Modern Approaches in Modeling of Mobile Radio Systems Propagation

Environment”,

http://www.comsoc.org/livepubs/surveys/public/3q00issue/neskovic.html;

access date: 18/06/07

[2] Wireless and cellular wireless communications, 3rd Edi by Willian C.Y.LEE

[3] atlas.cc.itu.edu.tr/~pazarci/WandelGoltermann_gsm.pdf

[4] “COST 231 Walfisch- Ikegami Model”

http://www.ee.bilkent.edu.tr/~microwave/programs/wireless/prop/costWI.htm; access

[5] Wireless Network by Jeffery Wheat

[6] End-to-End Quality of Service Over Cellular Networks: Data Services ...

By Gerardo Gomez, Rafael Sánchez

[7] Principles and Applications of GSM by Vijay k. Garg and Joseph E. Wilkey

[8] en.wikipedia.org/wiki/GSM

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How to Do Rf Planning

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