PLANNING AND DESIGN OF 3G RADIO NETWORK

M. HEMANTH

T. MOUNISH KUMAR

T. RISHITHA REDDY

Department of Electronics and Communication Engineering

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY (Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad 500 075

2014

PLANNING AND DESIGN OF 3G RADIO NETWORK

PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

BY

M. HEMANTH (10261A0438)

T.MOUNISH KUMAR (10261A0454)

T.RISHITHA REDDY (10261A0455)

Department of Electronics and Communication Engineering

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY

(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad 500 075

2014

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY (Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad-500 075

Department of Electronics and Communication Engineering

CERTIFICATE

Date:

This is to certify that the project work entitled Planning and Design of 3G

Radio Network is a bonafide work carried out by

M. Hemanth (10261A0438)

T.Mounish kumar (10261A0454)

T. Rishitha Reddy (10261A0455)

in partial fulfillment of the requirements for the degree of BACHELOR OF

TECHNOLOGY in ELECTRONICS & COMMUNICATION

ENGINEERING by the Jawaharlal Nehru Technological University, Hyderabad

during the academic year 2013-14.

The results embodied in this report have not been submitted to any other

University or Institution for the award of any degree or diploma.

(Signature) (Signature)

-------------------------- -------------------

Mr. K. Bala Prasad , Asst. Professor Dr. SP Singh

Advisor/Liaison Professor & Head

ACKNOWLEDGEMENT

We express our deep sense of gratitude to our Faculty Liaison

Mr.P.Naresh,Sr. Engineer, RTTC, BSNL, Hyderabad, for his invaluable guidance and

encouragement in carrying out our Project.

We are highly indebted to our Faculty Liaison Mr. K. Bala Prasad ,

Assistant Professor, Electronics and Communication Engineering Department, who

has given us all the necessary technical guidance in carrying out this Project.

We wish to express our sincere thanks to Dr. S.P Singh, Head of the

Department of Electronics and Communication Engineering, M.G.I.T., for permitting

us to pursue our Project in BSNL and encouraging us throughout the Project.

Finally, we thank all the people who have directly or indirectly helped us

throughout the course of our Project.

M. Hemanth

T. Mounish Kumar

T. Rishitha Reddy

(ii)

ABSTRACT

The emergence of the Third Generation Mobile Technology (Commonly

known as 3G) has been the latest innovation in the field of communication. The first

generation included Analog mobile phones [e.g., Total Access Communications

Systems(TACS), Nordic Mobile Telephone (NMT), and Advanced Mobile Phone

Service (AMPS)], and the second generation (2G) included digital mobile phones

[e.g., global system for mobile communications (GSM), personal digital cellular

(PDC), and digital AMPS (D-AMPS)]. The 3G brings digital multimedia handsets

with high data transmission rates, capable of providing much more than basic voice

calls.After initial teething troubles, the technology is finally taking shape. The

architecture and the specification are in place. The products and the network rollouts

have started and customer base is growing. This can give the customers Internet

access at 2Mbps, while he/she is on the move. Although practically, the bit rate is

likely to be lower at least in the initial phase.

In WCDMA (access technology of 3G), the coverage and capacity

requirement cannot be considered independently but should be planned at the same

time with proper guidelines. This relation between coverage and capacity is often

referred to as the breathing effect of WCDMA. Comparing with TDMA/FDMA

technologies, such as GSM, the coverage of a WCDMA network cannot be planned

independently of the load on the network. Hence planning of this 3g network takes

into account many considerations.

This project involves the basic study of GSM and CDMA architecture

along with planning and design of a 3G radio network in a particular area using Atoll

Rf planning software. In this mini project, we successfully planned the UMTS radio

network for Gachibowli region with around thirty UMTS Node-Bs or base stations.

(iii)

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Table of contents

CERTIFICATE FROM ECE DEPARTMENT (i)

CERTIFICATE FROM BSNL i (a)

ACKNOWLEDGEMENTS (ii)

ABSTRACT (iii)

LIST OF FIGURES (iv)

LIST OF TABLES (v)

CHAPTER 1. OVERVIEW

1.1 Introduction 1

1.2 Aim of the project 2

1.3 Methodology 2

1.4 Significance and applications 3

CHAPTER 2. LITERATURE REVIEW ON THE PLANNING OF UMTS

NETWORKS

2.1 Evolution of cellular networks 4

2.1.1 1G cellular networks 4

2.1.2 The second generation & phase 2+ systems (digital) 6

2.1.3 The third-generation (WCDMA in UMTS,CDMA 2000 8

& TC-SCDMA)

2.2 Spread spectrum techniques 11

2.2.1 DS-CDMA 12

2.2.2 Frequency-Hopping CDMA 12

2.2.3 Time-Hopping CDMA 13

2.2.4 Multicarrier CDMA 14

2.3 Approaches to planning problems 14

2.3.1 Sequential Approach 14

2.3.2 Global Approach 24

2.3.3 Sectional Remarks 25

CHAPTER 3. CODE PLANNING & NETWORK PLANNING OF 3G UMTS

MOBILE NETWORKS

3.1 Introduction 27

3.2 Radio network planning 27

3.2.1 Dimensioning 28

3.2.2 Capacity and coverage planning 31

3.3 WCDMA/UMTS Optimization methodology 33

3.4 Importance of Network Planning 37

3.5 Network Planning Process 37

3.6 Issues to be considered in Network Planning of WCDMA 39

3.6.1 Pilot Pollution 39

3.6.2 SHO Parameters 39

3.6.3 HO Problems 39

3.6.4 Hierarchical Cells 40

3.7 Other Issues 40

3.7.1 Link Budgets 40

3.8 Planning tool which we used in our project (ATOLL software.) 42

CHAPTER 4. RESULTS AND CONCLUSIONS

4.1 Results obtained by using Atoll RF Software Planning tool 46

4.2Conclusion and future scope of the project 47

REFERENCES 48

LIST OF FIGURES

1.1 Block Diagram..3

2.1.1 Graph .......5

2.1.2 Next Generation Mobile Communication.11

2.2.1 DS-CDMA............................................................................12

2.2.2 FH-CDMA ...13

2.2.3 TH-CDMA .. 13

2.2.4 MC-CDMA.,,14

2.3 Sequential Steps..15

3.1 Optimization in basic steps.. ..34

3.2 Simplified Network.........36

3.3 Workflow in Atoll45

4.1 Result 1................................... 46

4.2 Result 2.47

(iv)

LIST OF TABLES

3.7 Standard Deviation ..41

(v)

CHAPTER 1. OVERVIEW

1.1 Introduction

All cellular phone networks worldwide use a portion of the radio frequency spectrum

designated as ultra high frequency, or UHF,for the transmission and reception of

their signals. Radio frequencies used by 3g are 1920MHz-2170MHz, referred as

UMTS (Universal Mobile Telephone System) frequency bands. UMTS specifies a

complete network system, which includes the geographical coverage area of UMTS

network (UTRAN) and core network (CN) and the authentication of users via SIM

(Subscriber Identity Module) cards.

In India, the Department of Telecommunications (DoT) conducts auctions of

licenses for electromagnetic spectrum,In 2010 3G and 4G telecom spectrum were

auctioned in a highly competitive bidding in which the winner was tataindicom.

Hence Tataindicom was the first private operator to launch 3G services in India. Once

the operators get spectrum through auction process, they must build entirely new

networks and license entirely new frequencies, especially to achieve high data

transmission rates.3G UMTS networks are very popular in the world.3G cellular

systems are very flexible,but more complex and costly compared to older systems

which make the design and planning of such networks very challenging.In this

context the competitive market of cellular networks mandates operators to capitalize

on efficient design tools.Planning tools are used to optimize networks and keep both

operators and users satisfied

Hence, in this paper, evolution of 3g,planning 3g network and its design is studied

which provides an optimum topology for the network with which both the network

provider who aspires to have high number of users,capacity,quality with low capital

expenditure and users who expect to have high quality services at affordable prices

are both satisfied.This can be achieved by using proper planning tools.One of the

popular planning tool Atoll used for UMTS network design is studied under this

project.

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1.2 Aim Of The Project:

To study in detail the evolution of 3g, planning of the 3g networks, difficulties

that arise in planning process, methods to overcome them and designing 3g network

that provides optimum topology with which both the network provider who aspires to

have high number of users, capacity, quality with low capital expenditure and users

who expect to have high quality services at affordable prices are both satisfied. This

can be achieved by using proper planning tools. One of the popular planning tool

Atoll is used for UMTS network design in this project to achieve our purpose.

1.3 Methodology

The radio network planning process can be divided into different phases. At the

beginning is the Preplanning phase. In this phase, the basic general properties of the

future network are investigated, for example, what kind of mobile services will be

offered by the network, what kind of requirements the different services impose on

the network, the basic network configuration parameters and so on.

The second phase is the main phase. A site survey is done about the to-be-covered

area, and the possible sites to set up the base stations are investigated. All the data

related to the geographical properties and the estimated traffic volumes at different

points of the area will be incorporated into a digital map, which consists of different

pixels, each of which records all the information about this point. Based on the

propagation model, the link budget is calculated, which will help to define the cell

range and coverage threshold. There are some important parameters which greatly

influence the link budget, for example, the sensitivity and antenna gain of the mobile

equipment and the base station, the cable loss, the fade margin etc. Based on the

digital map and the link budget, computer simulations will evaluate the different

possibilities to build up the radio network part by using some optimization algorithms.

The goal is to achieve as much coverage as possible with the optimal capacity, while

reducing the costs also as much as possible. The coverage and the capacity planning

2

are of essential importance in the whole radio network planning. The coverage

planning determines the service range, and the capacity planning determines the

number of to-be-used base stations and their respective capacities.

In the third phase, constant adjustment will be made to improve the network planning.

Through driving tests the simulated results will be examined and refined until the best

compromise between all of the facts is achieved. Then the final radio plan is ready to

be deployed in the area to be covered and served. The whole process is illustrated as

the figure below:

Figure 1.1

1.4 Significance Of Project

Wireless cellular networks have unbelievably spread across the globe during the

last two decades and currently, 3rd Generation (3G) Universal Mobile Telecommuni-

cation System (UMTS) networks are very popular in the world. 3G cellular systems

are very flexible, but more complex and costly compared to the older systems which

make the design and planning of such networks very challenging. In this context, the

competitive market of cellular networks mandates operators to capitalize on efficient

design tools. Planning tools are used to optimize networks and keep both operators

and users satisfied. On one side, users expect to have seamless access to different high

quality services with affordable prices. On the other side, operators expect to have

an always-operational network with high number of users, capacity and quality with

low Capital Expenditure (CAPEX) and Operational Expenditure (OPEX).Thus this

project mainly concentrates on the design and planning aspects of 3g networks which

is of the atmost importance in this communication era.

3

Begin Site Survey Network

Planning End

Pre-planning

Phase

CHAPTER 2. LITERATURE REVIEW ON THE

PLANNING OF UMTS NETWORKS

2.1 Evolution of Cellular Networks

History of mobile telephony dates back to the 1920s with the use of radiotelephony by

the police department in United States. The initial equipment were bulky and phones

were not dealing well with obstacles and buildings. Introducing Frequency

Modulation (FM) in 1930s made some progress and helped radio communications in

battlefield during World War II. The first mobile telephony was introduced in 1940s

with limited capacity and manoeuvre. Mobile communications development

continued for years to become commercial as we have it today.Terminology of

generation is used to differentiate the significant technology improvement in cellular

networks which in turn, resulted in major changes in the wireless industry. The first

generation (1G) of cellular networks was introduced in late 1970s,which was

followed by the second generation (2G) in early 1990s, the third generation (3G) in

early 2000 and the fourth generation (4G) nowadays. Changes from analog to digital

technology, implementing new multiplexing and access techniques, employing new

codes and frequencies, introducing IP as a substitution for legacy transmission

methods and many other innovations resulted in networks with more services, higher

capacity, speed and security. In the following sub-sections, we explain different

generations of cellular networks and discuss their specifications.

4

Narrow Wide band Era Broadband Era1Gbps

Multimedia band

2.4kbps 64kbps 2Mbps

Voice

1980 1990 2000 2010 year..

Figure 2.1.1 Graph

2.1.1 1G Cellular Networks (Analog)

In 1980 the mobile cellular era had started, and since then mobile communications

have undergone significant changes and experienced enormous growth. First-

generation mobile systems used analog transmission for speech services. In 1979, the

first cellular system in the world became operational by Nippon Telephone and

Telegraph (NTT) in Tokyo, Japan. Two years later, the cellular epoch reached

Europe. The two most popular analog systems were Nordic Mobile Telephones

(NMT) and Total Access Communication Systems (TACS). Other than NMT and

TACS, some other analog systems were also introduced in 1980s across the Europe.

All of these systems offered handover and roaming capabilities but the cellular

networks were unable to interoperate between countries. This was one of the

inevitable disadvantages of first-generation mobile networks.

In the United States, the Advanced Mobile Phone System (AMPS) was launched in

1982. The system was allocated a 40-MHz bandwidth within the 800 to 900 MHz

frequency range by the Federal Communications Commission (FCC) for AMPS. In

1988, an additional 10 MHz bandwidth, called Expanded Spectrum (ES) was

allocated to AMPS. It was first deployed in Chicago, with a service area of 2100

square miles. AMPS offered 832 channels, with a data rate of 10 kbps. Although

5

1G

2G

3G

4G

Omni directional antennas were used in the earlier AMPS implementation, it was

realized that using directional antennas would yield better cell reuse. In fact, the

smallest reuse factor that would fulfill the 18db signal-to-interference ratio (SIR)

using 120-degree directional antennas was found to be 7. Hence, a 7-cell reuse pattern

was adopted for AMPS. Transmissions from the base stations to mobiles occur over

the forward channel using frequencies between 869-894 MHz. The reverse channel is

used for transmissions from mobiles to base station, using frequencies between 824-

849 MHz.AMPS and TACS use the frequency modulation (FM) technique for radio

transmission. Traffic is multiplexed onto an FDMA (frequency division multiple

access) system.

2.1.2 The Second-generation & Phase 2+ Systems (Digital)

Second-generation (2G) mobile systems were introduced in the end of 1980s. Low bit

rate data services were supported as well as the traditional speech service. Compared

to first-generation systems, second-generation (2G) systems use digital multiple

access technology, such as TDMA (time division multiple access) and CDMA (code

division multiple access). Consequently, compared with first-generation systems,

higher spectrum efficiency, better data services, and more advanced roaming were

offered by 2G systems. In Europe, the Global System for Mobile Communications

(GSM) was deployed to provide a single unified standard. This enabled seamless

services through out Europe by means of international roaming. Global System for

Mobile Communications, or GSM, uses TDMA technology to support multiple users

During development over more than 20 years, GSM technology has been

continuously improved to offer better services in the market. New technologies have

been developed based on the original GSM system, leading to some more advanced

systems known as 2.5 Generation (2.5G) systems.In the United States, there were

three lines of development in second-generation digital cellular systems. The first

digital system, introduced in 1991, was the IS-54 (North America TDMA Digital

Cellular), of which a new version supporting additional services (IS-136) was

introduced in 1996. Meanwhile, IS-95 (CDMA One) was deployed in 1993. The US

Federal Communications Commission (FCC) also auctioned a new block of spectrum

in the 1900 MHz band (PCS), allowing GSM1900 to enter the US market. In Japan,

6

the Personal Digital Cellular (PDC) system, originally known as JDC (Japanese

Digital Cellular) was initially defined in 1990 .Since the first networks appeared at the

beginning of the 1991, GSM gradually evolved to meet the requirements of data

traffic and many more services than the original networks. GSM (Global System for

Mobile Communication): The main element of this system are the BSS (Base Station

Subsystem), in which there are BTS (Base Transceiver Station) and BSC (Base

Station Controllers); and the NSS (Network Switching Subsystem), in which there is

the MSC (Mobile Switching Centre); VLR (Visitor Location Register); HLR (Home

Location Register); AC (Authentication Centre) and EIR (Equipment Identity

Register). This network is capable of providing all the basic services up to 9.6kbps,

fax, etc. This GSM network also has an extension to the fixed telephony network. A

new design was introduced into the mobile switching center of second-generation

systems. In particular, the use of base station controllers (BSCs) lightens the load

placed on the MSC (mobile switching center) found in first generation systems. This

design allows the interface between the MSC and BSC to be standardized. Hence,

considerable attention was devoted to interoperability and standardization in second-

generation systems so that carrier could employ different manufacturers for the MSC

and BSCs. In addition to enhancements in MSC design, the mobile-assisted handoff

mechanism was introduced. By sensing signals received from adjacent base stations, a

mobile unit can trigger a handoff by performing explicit signaling with the network.

GSM and VAS (Value Added Services): The next advancement in the GSM system

was the addition of two platforms, called Voice Mail Service (VMS) and the Short

Message Service Centre (SMSC). The SMSC proved to be incredibly commercially

successful, so much so that in some networks the SMS traffic constitutes a major part

of the total traffic. Along with VAS, IN (Intelligent services) also made its mark in

the GSM system, with its advantage of giving the operators the chance to create a

whole range of new services. Fraud management and prepaid services are the result

of the IN service.

GSM and GPRS (General Packet Radio Services): As requirement for sending data

on the air-interface increased, new elements such as SGSN (Servicing GPRS) and

GGSN (Gateway GPRS) were added to the existing GSM system. These elements

made it possible to send packet data on the air-interface. This part of the network

7

handling the packet data is also called the packet core network. In addition to the

SGSN and GGSN, it also contains the IP routers, firewall servers and DNS (Domain

Name Servers). This enables wireless access to the internet and bit rate reaching to

150 kbps in optimum conditions. The move into the 2.5G world began with General

Packet Radio Service (GPRS). GPRS is a radio technology for GSM networks that

adds packet-switching protocols, shorter setup time for ISP connections, and the

possibility to charge by the amount of data sent, rather than connection time. Packet

switching is a technique whereby the information (voice or data) to be sent is broken

up into packets, of at most a few Kbytes each, which are then routed by the network

between different destinations based on addressing data within each packet. Use of

network resources is optimized as the resources are needed only during the handling

of each packet. GPRS supports flexible data transmission rates as well as continuous

connection to the network. GPRS is the most significant step towards 3G.

GSM and EDGE (Enhanced Data rates in GSM Environment):

With both voice and data traffic moving on the system, the need was felt to increase

the data rate. This was done by using more sophisticated coding methods over the

internet and thus increasing the data rate up to 384 kbps. Implementing EDGE was

relatively painless and required relatively small changes to network hardware and

software as it uses the same TDMA (Time Division Multiple Access) frame structure,

logic channel and 200 kHz carrier bandwidth as today's GSM networks. As EDGE

progresses to coexistence with 3G WCDMA, data rates of up to ATM-like speeds of 2

Mbps could be available. Nowadays, second-generation digital cellular systems still

dominate the mobile industry throughout the whole world. However, third generation

(3G) systems have been introduced in the market, but their penetration is quite limited

because of several techno-economic reasons.

8

2.1.3 The Third-generation (WCDMA in UMTS, CDMA2000 & TD-SCDMA)

In EDGE, high-volume movement of data was possible, but still the packet transfer on

the air-interface behaves like a circuit switch call. Thus part of this packet connection

efficiency is lost in the circuit switch environment. Moreover, the standards for

developing the networks were different for different parts of the world. Hence, it was

decided to have a network which provides services independent of the technology

platform and whose network design standards are same globally. Thus, 3G was born

The International Telecommunication Union (ITU) defined the demands for 3G

mobile networks with the IMT-2000standard. An organization called 3rd Generation

Partnership Project (3GPP) has continued that work by defining a mobile system that

fulfills the IMT-2000 standard. In Europe it was called UMTS (Universal Terrestrial

Mobile System), which is ETSI-driven. IMT2000 is the ITU-T name for the third

generation system, while cdma2000 is the name of the American 3G variant.

WCDMA is the air-interface technology for the UMTS. The main components

includes BS (Base Station) or nodeB, RNC (Radio Network Controller), apart from

WMSC (Wideband CDMA Mobile Switching Centre) and SGSN/GGSN. 3G

networks enable network operators to offer users a wider range of more advanced

services while achieving greater network capacity through improved spectral

efficiency. Services include wide-area wireless voice telephony, video calls, and

broadband wireless data, all in a mobile environment. Additional features also include

HSPA (High Speed Packet Access) data transmission capabilities able to deliver

speeds up to 14.4 Mbps on the downlink and 5.8 Mbps on the uplink. The first

commercial 3G network was launched by NTT DoCoMoin Japan branded FOMA,

based on W-CDMA technology on October 1, 2001. The second network to go

commercially live was by SK Telecom in South Korea on the 1xEV-DO (Evolution

Data Optimized) technology in January 2002 followed by another South Korean 3G

network was by KTF on EV-DO in May 2002. In Europe, the mass market

commercial 3G services were introduced starting in March 2003 by 3 (Part of

Hutchison Whampoa) in the UK and Italy. This was based on the W-CDMA

technology. The first commercial United States 3G network was by Monet Mobile

Networks, on CDMA2000 1x EV-DO technology and the second 3G network

operator in the USA was Verizon Wireless in October 2003 also on CDMA2000 1x

9

acerHighlight

EVDO. The first commercial 3G network in southern hemisphere was launched by

Hutchison Telecommunications branded as Three using UMTS in April 2003. The

first commercial launch of 3G in Africa was by EMTEL in Mauritius on the W-

CDMA standard. In North Africa (Morocco), a 3G service was provided by the new

company Wana in late March 2006. Roll-out of 3G networks was delayed in some

countries by the enormous costs of additional spectrum licensing fees. In many

countries, 3G networks do not use the same radio frequencies as 2G, so mobile

operators must build entirely new networks and license entirely new frequencies; an

exception is the United States where carriers operate 3G service in the same

frequencies as other services. The license fees in some European countries were

particularly high, bolstered by government auctions of a limited number of licenses

and sealed bid auctions, and initial excitement over 3G's potential. Other delays were

due to the expenses of upgrading equipment for the new systems. Still several major

countries such as Indonesia have not awarded 3G licenses and customers await 3G

services. China delayed its decisions on 3G for many years. In January 2009, China

launched 3G but interestingly three major companies in China got license to operate

the 3G network on different standards, China Mobile for TD-SCDMA, China Unicom

for WCDMA and China Telecom for CDMA2000

2.1.4 Fourth Generation (All-IP)

The emergence of new technologies in the mobile communication systems and also

the ever increasing growth of user demand have triggered researchers and industries

to come up with a comprehensive manifestation of the up-coming fourth generation

(4G) mobile communication system . In contrast to 3G, the new 4G framework to be

established will try to accomplish new levels of user experience and multi-service

capacity by also integrating all the mobile technologies that exist (e.g. GSM - Global

System for Mobile Communications, GPRS - General Packet Radio Service, IMT-

2000 - International Mobile Communications, Wi-Fi - Wireless Fidelity, Bluetooth)

The fundamental reason for the transition to the All-IP is to have a common platform

for all the technologies that have been developed so far, and to harmonize with user

expectations of the many services to be provided. The fundamental difference

10

between the GSM/3G and All-IP is that the functionality of the RNC and BSC is now

distributed to the BTS and a set of servers and gateways. This means that this network

will be less expensive and data transfer will be much faster . 4G will make sure - The

user has freedom and flexibility to select any desired service with reasonable QoS and

affordable price, anytime, anywhere. 4G mobile communication services started in

2010 but will become mass market in about 2014-15.

Figure 2.1.2 The next generation mobile communication system features

2.2 SPREAD SPECTRUM TECHNIQUES

Spreading Technique

There are several techniques employed for spreading the information signal. The most

important ones are discussed below, although these are by no means the only ones,

and these techniques can be combined to form hybrid techniques. UTRAN uses the

direct-sequence CDMA (DS-CDMA) modulation technique.

11

Seaml

ess

acces

4G Quality of service

personalization

IP

based

2.2.1 DS-CDMA

In DS-CDMA, the original signal is multiplied directly by a faster-

rate spreading code (Figure 4.1). The resulting signal then modulates the digital

wideband carrier. The chip rate of the code signal must be much higher than the bit

rate of the information signal. The receiver despreads the signal using the same code.

It has to be able to synchronize the received signal with the locally generated code;

otherwise, the original signal cannot be recovered

2.2.2 Frequency-Hopping CDMA

In frequency-hopping CDMA (FH-CDMA), the carrier frequency at

which the signal is transmitted is changed rapidly according to the spreading code.

Frequency-hopping (FH) systems use only a small part of the bandwidth at a time, but

the location of this part changes according to the spreading code (Figure 2.2.2). The

receiver uses the same code to convert the received signal back to the original. FH-

CDMA systems can be further divided into slow- and fast-hopping systems. In a

slow-hopping system, several symbols are transmitted on the same frequency,

whereas in fast-hopping systems, the frequency changes several times during the

transmission of one symbol. The GSM system is an example of a slow FH system

because the transmitters carrier frequency changes only with the time slot rate217

hops per secondwhich is much slower than the symbol rate. Fast FH systems are

very expensive with current technologies and are not at all common.

Figure 2.2.1 DS-CDMA principle.

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Figure 2.2.2 FH-CDMA principle

2.2.3 Time-Hopping CDMA

In time-hopping CDMA (TH-CDMA), the used spreading code

modulates the transmission time of the signal. The transmission is not continuous, but

the signal is sent in short bursts. The transmission time is determined by the code.

Thus, the transmission uses the whole available bandwidth, but only for short periods

at a time (see Figure 2.2.3).

Figure 2.2.3 TH-CDMA principle.

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2.2.4 Multicarrier CDMA

In multicarrier CDMA (MC-CDMA), each data symbol is transmitted

simultaneously over N relatively narrowband subcarriers. Each subcarrier is encoded

with a constant phase offset. Multiple access is achieved with different users

transmitting at the same set of subcarriers, but with spreading codes that are

orthogonal to the codes of the other users. These codes are a set of frequency offsets

in each subcarrier. It is unlikely that all of the subcarriers will be located in a deep

fade and, consequently, frequency diversity is achieved (see Figure 2.2.4).

Figure 2.2.4 MC-CDMA principle.

2.3 Approaches to planning problems

2.3.1 Sequential Approach

In a sequential (or decomposition) approach, the planning problem of UMTS network

is divided in three sub-problems :

a. The cell planning sub-problem;

b. The access network planning sub-problem;

c. The core network planning sub-problem.

Beside the input of each sub-problem, the output of the previous sub-problem is

also used as input for the next sub-problem. As shown in Figure , the output of

the cell planning is used as input for the access network sub-problem. In a similar

way, the output of the access network sub-problem is given as input for core network

sub-problem. The final solution is a topology which satisfies all three sub-problems.

14

Each sub-problem has been widely explored from different perspective. In the

following sub-sections, each sub-problem is explained and the major works in solving

them are presented.

input input input

Figure 2.3 Sequential steps

a.The Cell Planning Sub-Problem

Cell planning is the process of connecting all mobile users to the Node Bs in a

specific geographical area. Cell planning in 3G UMTS networks is different form that

in 2G networks. Cell planning in 2G networks (like GSM) is divided in two steps:

coverage and capacity planning. During the coverage planning phase, different

propagation techniques are used to place BSs in locations where the maximum

number of users can receive an acceptable level of signal power. Signal to Interface

Ratio (SIR) is a signal quality factor which should be greater than a predefined

threshold in 2G systems. Capacity planning, also known as frequency planning, is the

process of channel (frequency) assignment to the BSs in order to minimize the

interference in the network while being able to re-use those frequencies in other cells.

Unlike 2G networks, coverage and capacity planning in UMTS network should be

done concurrently . Using WCDMA technology in the air interface, mobile users in

UMTS network share the whole spectrum, therefore no frequency planning is strictly

required , but the capacity planning remains a valid and complex task. The main

differences between GSM and UMTS radio network are explained by Neubauer and

Toeltsch and Ramzi .

Cell Planning Objectives

The objective of the cell planning sub-problem depends on the interests of network

planners. The following objectives may be the target for a cell planning sub-problem:

1. Minimize network cost;

2. Maximize capacity;

15

Cell

planning

subproblem

Access

Network

planning

subproblem

Core network

planning

subproblem

Final

solution

3. Maximize coverage;

4. Maximize signal quality;

5. Minimize electromagnetic field level.

Some of the above objectives are conflicting with each other. For example,

maximizing the coverage and capacity requires deploying more Node Bs, which in

turn, increases the network cost. Another example of contradiction happens when the

signal power is increased for maximizing signal quality, but that results in higher

electromagnetic field level. If more than one criterion is considered during the cell

planning, then multi-objective functions are defined. A multi-objective function can

be produced in either linear and/or weighted combinations of the single objectives.

Cell Planning Inputs and Outputs

As stated earlier inputs are required to solve the cell planning sub-problem. Usually,

the following inputs must be known :

1. The potential locations where Node Bs can be installed. Some geographical

constraints are applied to restrict the location selection;

2. The types (or models) of Node Bs, which includes, but not restricted to,

the cost and capacity (e.g. power, sensitivity, switch fabric capacity, interfaces, etc.);

3. The user distributions and their required amount of traffic (e.g. voice and data);

4. The coverage and propagation prediction.

Various planning algorithms are used to solve cell planning sub-problem. Each

algorithm may consider one or more of the objectives mentioned previously. The goal

of the cell planning sub-problem is to provide one or more of the following as output:

1. The optimal number of Node Bs;

2. The best locations to install Node Bs;

3. The types of Node Bs;

4. The configuration (height, sector orientation, tilt, power, etc.) of Node Bs;

5. The assignment of mobile users to Node Bs.

For the modeling of the cell planning sub-problem, it is required to know how to

represent users (or traffic) in the model. In the following sub-section traffic modeling

and related issues are discussed.

16

Traffic Modeling of Mobile Users

UMTS networks provide voice and data services for mobile users. It is important to

decide how to represent mobile users in the cell planning sub-problem. A basic model

could be to represent a user with a point in the cell. For unknown traffic distribution,

a regular point grid can be used. Dealing with practical cases, as the number of users

is high, a clustering or agglomeration technique is required to reduce the complexity.

The cluster of users is often called traffic node or test point . A traffic node

or test point represents several mobile users.

It is also important to consider the traffic (link) direction. Traffic direction can be

uplink (from user to Node B) or downlink (from Node B to user). Uplink direction

is used when planners deal with symmetric traffic like voice services. However, if the

network is designed to provide data services, downlink direction is more appropriate

because downlink is highly utilized for services like web browsing and Internet

downloads. The type of area which is aimed to be planned is also required to be

known. The area can be rural, urban, sub urban, dense urban and so on. Each of these

areas has specific characteristics which need to be taken in account during cell

planning assignment.

Air Interface Power Control

The coverage and capacity planning of UMTS network should be done mutually. The

capacity of each cell is based on the actual interference level which depends on the

emitted power . In UMTS networks, the power of the Node B is shared among all

the cell users and the allocated power to a given user depends on its distance from

the Node B. The cell size is not fixed and depends on the number of users, level of

interference and their distance form the Node B. Air interface in UMTS systems is

self-interference, meaning that cell interference level is increased as it is overloaded

by users. With an increase in interference level, users located at the edge of the cell

are detached from the parent Node B and this in turn, results in decrease of cell

size. Such users will be covered by neighbor cells. On the other hand, when calldrops

occur, interference decreases for the remaining users and cell is expanded. This

phenomenon is called cell breathing. Cell breathing is the result of constant changes

in the coverage area with respect to amount of traffic.

It is important to keep the transmission power of Node Bs and users at the minimum

17

acerHighlight

levels to minimize interference and guarantee adequate quality at the receiver. SIR in

UMTS networks is highly affected by the traffic distribution in the whole area and

unlike 2G networks, SIR should be equal to a given threshold.

In summary, the cell capacity and coverage depends on number of users and their

distribution, as well as Power Control (PC) mechanisms. The PC mechanisms are

based on either the received power or estimated SIR .

b.The Access Network Planning Sub-Problem

The main elements of the access network are the Node Bs and the RNCs. In order to

plan a good access network, the following inputs are usually needed:

1. The physical location of Node Bs (either given or obtained from the cell planning

sub-problem);

2. The traffic demand passing through each Node B (either given or obtained from

the cell planning sub-problem);

3. The set of potential locations to install RNCs;

4. The different types of RNCs;

5. The different types of links to connect Node Bs to RNCs;

6. The handover frequency between adjacent cells.

Depending on the planners decision, the Node Bs might connect internally to

each other based on some interconnection policies. This is also true for the RNCs.

By so doing, the access network sub-problem is more extended and will include the

trunks among Node Bs with themselves, as well as RNCs with themselves. In a tree

interconnection, the Node Bs are either directly connected to RNCs or cascaded.

Other types of topologies are star, ring and mesh. The interested reader on access

network topologies can find more information in reference. Given the above

inputs and the type of topology, the access network planning sub-problem aims to

find one or more of the following as output:

1. The optimal number of RNCs;

2. The best location to install RNCs;

3. The type of RNCs;

4. The link topology and type between Node Bs;

5. The link topology and type between RNCs;

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acerHighlight

6. The link topology and type between Node Bs and RNCs;

7. The traffic (volume and type) passing through each RNC.

The objective function is usually cost minimization, but other objectives such as

reliability or combination of cost and reliability could be considered.

Cost-effective Access Networks

The cost of the access network includes the cost of RNCs, interconnection links and

interfaces. Depending on the access network topology, the cost might vary. As a

result, it is important to evaluate the cost subject to the topology. Harmatos et al.

propose an algorithmic network topology optimization method to simultaneously find

the optimum number of location of RNCs, as well as the transmission network

between BSs and RNCs. In order to solve the NP-hard sub-problem, their method

uses a combination of SA and greedy algorithm to minimize the cost. They also

consider a degree constraint on the number of BSs that can be supported by one RNC.

In a second paper, Harmatos et al. found the bottleneck in their previous algorithm

, which was the tree topology of the access network based on simple greedy

algorithm. Because of the greedy principle, in many cases, the algorithm was not able

to build the access tree correctly, causing a significant rise in cost. They modified

their algorithm to provide more cost-effective access network topology for one RNC.

The objective is to find the cost-optimal interconnection of BSs to their dedicated

RNC, considering topological limitations, constraints and the originating traffic of

BSs. The authors state that, although their optimization model and process is working

for UMTS network, it is also applicable to any multi-constrained capacitated tree

optimization problem with non-linear cost function.

Lauther et al approach the access planning sub-problem as a clustering problem.

They try to find the optimal number and size of clusters for a set of BSs to

minimize the cost. Given the location of BSs, they present two clustering procedures

based on proximity graph. The first method is based on tree generation and cutting.

The idea is to build a tree in the first step. In the second step, the tree is cut

into sub-trees (clusters). The first step is based on an algorithm like Prim or

Kruskal , while the second step is based on the generation of sub-trees starting

form the leaves. Initially, each Node B forms its own cluster. Then, two clusters are

merged per iteration if the cost of the access network is reduced. Another clustering

19

approach is also presented in a paper by Godor and Magyar . They aggregate

the user traffic in multi-level tree-like fashion using some intermediate concentrator

nodes. Considering several constraints, the NP-hard problem is solved by heuristic

algorithms to minimize the cost.

Krendzel et al consider the problem of physical links ring configuration between

BSs in 4G network. Considering planning constraints and using dynamic

programming,they try to minimize the cost of the ring configuration. In another paper,

Juttner et al propose two network design methods to find the cost-optimal

number and location of RNCs and their connection to BSs in tree topology, while

respecting a number of constraints. First, a global algorithm combines a metaheuristic

technique with the solution of a specific b-matching problem. Then, the tree

structure made by the first method is improved by the second method, which uses a

combination of Lagrangian lower bound with branch-and-bound. They demonstrate

the effectiveness of their algorithms in reducing the cost by a number of test cases.

Constraint-based optimization of the access network sub-problem was considered

by Wu and Pierre, they propose a model to optimally find the number and

location of RNCs and solve the assignment of Node Bs to selected RNCs. Constraints

like number of Node Bs supported by one RNC, number of interfaces on the RNC,

the amount of traffic supported by one RNC, as well as handover volume between

adjacent cells are taken into consideration. Greedy heuristic algorithms, TS and SA,

are explored in the proposed model to minimize the cost. Wu and Pierre, used a three-

staged hybrid constraint-based approach. In the first step, good feasible solutions are

found and then improved by local search in the second step. Such solutions are

considered as the upper bound. In the last step, the solution is refined by constraint

optimization technique. They state that the obtained solutions can beused as initial

solutions for heuristics.Minimizing handover cost has been investigated in a series of

cell-to-switch papers. The idea is to reduce the number of handovers between two

adjacent cells by linking both cells to the same RNC.

Bu et al. investigate the access planning problem from a different perspective.

Usually, Point to Point (P2P) transmission links (E1 and/or T1) used in 3G access

network are not optimal in case of asymmetric and bursty traffic. The authors propose

to use a 802.16 (WiMAX) based radio access networks to transmit data from Node

Bs to RNCs. They design the access network with minimum number of 802.16 links

20

upon position of BSs and RNCs. Charnsripinyo considers the design problem of

3G access network while maintaining an acceptable level of quality of service. The

problem was formulated as a Mixed Integer Programming (MIP) model to minimize

the cost.

Reliable Access Networks

Network reliability (also known also as survivability) describes the ability of the

network to function and not to disturb the services during and after a failure. The need

for seamless connectivity has been a motivation for many researchers to explore new

techniques for network reliability. Tripper et al.introduce a framework to study

wireless access network survivability, restoration techniques and metrics for

quantifying network survivability. Cellular networks are very vulnerable to failure.

Failure can happen either on node level (BSs, RNC, MSS, etc.) or link level.

Simulation results on different types of failure scenarios in a GSM network shows

that after a failure, mobility of users worsens network performance. For example, in

the case of a BS failure, users will try to connect to the adjacent BS and that degrades

the overall network performance.

Charnsripinyo and Tipper proposed an optimization based model for the design

of survivable 3G wireless access backhaul networks in a mesh topology. Using a

two-phase algorithm, the authors first design a network with a minimum cost,

considering Quality of Service (QoS) and then update the topology to satisfy

survivability constraints. They also propose a heuristic, based on the iterative

minimum cost routing to scale the design with real world networks. Increasing

reliability level imposes more cost to the network. There is a balance (best trade off)

between cost and reliability and in fact, higher level of reliability will obtrudes higher

cost to the network. Aiming to create a balance between reliability and cost,

Szlovencsak et al. introduce two algorithms. The first algorithm modifies

the cost-minimum tree as produced in [70, 71], while respecting reliability constraints

and retains the tree structure. In the second algorithm, different links are added to

the most vulnerable parts of the topology to have a more reliable network. Krendzel

et al. study cost and reliability of 4G RAN in a ring topology. They estimate

cost and reliability in different configurations and state that considering cost and

reliability, the most preferable topology for 4G RAN is a multi-ring.

21

Once the access planning sub-problem is solved and the number, type, location

and traffic of each RNC in known, the next step is to deal with the core planning

sub-problem.

c. The Core Network Planning Sub-Problem

The core network is the central part of UMTS network. The core network is

responsible for traffic switching, providing QoS, mobility management, network

security and billing. The core network consists of CS and PS domains. The key

elements of CS domain are MGW and MSS, responsible for switching and controlling

functions respectively. PS domains key elements are SGSN and GGSN which are

responsible for packet switching.

The core planning sub-problem supposes that the following inputs are known:

1. The physical location of RNCs (either given or obtained from the access planning

sub-problem);

2. The traffic demand (volume and type) passing through each RNC (either given

or obtained from the access planning sub-problem);

3. The potential location of core NEs;

4. The different types of core NEs;

5. The different types of links to connect RNCs to core NEs.

Depending on the network planner, the topology of the backbone network could

be a ring, a full mesh, a mesh or a layered structure format. In the ring topology,

each NE is directly attached to the backhaul ring. Full mesh topology provides point

to- point communication such that each NE is able to communicate to any other NE

directly. The mesh topology is a limited version of the full mesh, whereas due to some

restrictions, not every NE can communicate directly to another NE. For fast growing

networks, maintaining a mesh or full mesh topologies becomes an exhaustive task.

To solve this sub-problem, the layered structure was introduced. A layered structure

does not provide direct link between all NEs. A tandem layer, as the nucleus of the

layered structure is defined. The tandem layer is composed of a series of tandem

(transit) nodes, usually connected in full mesh. Then, all NEs in the core network are

connected to at least one of the tandem nodes. Ouyang and Fallah state that a

layered structure has many advantages compared to full mesh topology. Given that

22

the above inputs are available and the type of topology is decided, the core network

planning sub-problem aims to find one or more of the following as output:

1. The optimal number of core NEs;

2. The best location to install core NEs;

3. The type of core NEs;

4. The link topology and type between RNCs and core NEs;

5. The link topology and type between core NEs;

6. The traffic (volume and type) passing through core NEs.

The objective function is usually cost minimization, but other objectives like

reliability could be considered. Not many researches have been concentrated on the

core network planning sub-problem. The reason could be the similarity of this sub-

problem to the wired network planning problem.

Shalak et al present a model for UMTS network architecture and discuss the required

changes for upgrading core network from GSM to UMTS. They outline network

planning steps and compare the products of different vendors in packet switch

network.

Ricciato et al deal with the assignment of RNCs to SGSNs based on measured

data. The optimization goals are to balance the number of RNC among the available

SGSNs and minimize the inter-SGSN routing area updates. Required inputs are taken

from live network and the objective function is solved by linear integer programming

methods. While they focus on GPRS, they state that their approach can be applied

to UMTS networks. Harmatos et al deal with the interconnection of RNCs, placement

of MGWs and planning core network. They split the problem in two parts. The first

problem is interconnection of the RNCs which belong to the same UTRAN and the

placement and selection of a MGW to connect to core network. The second problem

is interconnection of MGWs together in backbone through IP or ATM network. The

objective is to design a fault-tolerant network with cost-optimal routing.

Remarks on Sequential approach

The sequential approach used to solve the design problem of UMTS networks has

many advantages, but some disadvantages. The sequential approach reduces the

complexity of the problem by splitting the problem into three smaller sub-problems.

By so doing, it is possible to include more details in each sub-problem for better

23

planning. On the contrary, solving each sub-problem independently from the other

sub-problems may result in local optimization, because interactions between sub

problems are not taken into account. Combining the result of sub-problems does not

guarantee a final optimal solution. There is no integration technique developed yet to

incorporate all partial solutions in order to obtain a global solution. Therefore, a

global view from the network is required to define a global problem.

2.3.2 Global Approach

As mentioned earlier, the sequential approach breaks down the UMTS planning

problem in three sub-problems and solves them solely. As shown in Figure 2.7, a

global (also called integrated) approach considers more than one sub-problem at a

time and solves them jointly. Since all interactions between the sub-problems are

taken into account, a global approach has the advantage of providing a solution close

to the global optimal, but at the expense of increasing problem complexity. The global

problem of UMTS networks which is composed of three NP-hard sub-problems is

also an NP-hard problem .The objective of the global approach is similar to the

objective of the sequential approach. Network cost minimization is the main concern,

while considering network performance. Researches on the global approach are

mainly divided into three directions:

i ) cell and access networks, ii ) access and core networks and iii ) the whole

network (i.e. cell, access and core).

Zhang et al proposed a global approach to solve the UTRAN planning problem.

Their model finds the number and location of Node Bs and RNCs, as well as

their interconnections in order to minimize the cost. Chamberland and Pierre

consider access and core network planning sub-problems. Given the BSs locations,

their model finds the location and types of BSCs and MSCs, types of links and topol-

ogy of the network. Since such sub-problem is NP-hard, the authors propose a TS

algorithm and compare the results with a proposed lower bound. While the model

is targeted to GSM networks, it can be also applied to UMTS networks with minor

modifications. In another paper, Chamberland investigates the update problem

in UMTS network. Considering an update in BSs subsystem, the expansion model

accommodates the new BSs into the network. The model determines the optimal

24

access and core networks and considers network performance issues like call and

handover blocking. The author proposes a mathematical formulation of the problem,

as well as a heuristic based on the TS principle.Recently St-Hilaire et al proposed a

global approach in which the three subproblems are considered simultaneously. The

authors developed a mathematical programming model to plan UMTS networks in the

uplink direction. Through a detailed example, they compared their integrated

approach with the sequential approach. They proposed two heuristics based on local

search and tabu search to solve the NPhard problem. Furthermore, St-Hilaire et al

proposed a global model for the expansion problem of UMTS networks as an

extension to their previous works. They state that this model can also be used for

green field networks. They also present numerical results based on branch and bound

implementation.

2.3.3 Section Remarks

The purpose of solving the design problem of UMTS networks is to find an optimum

topology for the network which satisfies all desired constraints like cost, reliability,

performance and so on. Such an optimum topology is favorable for operators, as it can

save money and attract more subscribers. The planning problem of UMTS networks

is complex and composed of three sub-problems: the cell planning sub-problem, the

access network sub-problem and the core network sub-problem.

There are two main approaches to solve planning problem of UMTS networks:

the sequential and the global. In the sequential approach, the three sub-problems are

tackled sequentially. Since each sub-problem is less complex than the initial problem,

more details can be considered in each sub-problem. As a result, solving sub-

problems is easier than solving the whole planning problem. However, since each

sub-problem is solved independently from other sub-problems, the combination of the

optimal solution of each sub-problem (if obtained), might not result in an optimal

solution for the whole network planning problem. A global approach deals with more

than one sub-problem simultaneously and considers all interactions between the sub-

problems. The global problem has the advantage of finding good solutions which are

closer to the global minimum. The global problem is NP-hard and is more complex

compared to three sub-problems. To find approximate solutions for global planning of

25

UMTS networks in a polynomial time, heuristics need to be defined. It has been

proven by scholars that different adaptations of heuristics are effectively able to solve

the planning problem of cellular networks. Altogether, it is expected that the planning

algorithm proposed in this paper would be useful for operators to plan real networks.

26

CHAPTER 3. CODE PLANNING & NETWORK

PLANNING OF 3G UMTS MOBILE NETWORKS

3.1 Introduction:

WCDMA radio network planning includes..,

i)dimensioning,

ii)detailed capacity and coverage planning, and

iii) network optimization.

In the dimensioning phase an approximate number of base station sites, base stations

and their configurations and other network elements are estimated, based on the

operators requirements and the radio propagation in the area. The dimensioning must

fulfill the operators requirements for coverage, capacity and quality of service. The

planning and the optimization process can also be automated with intelligent tools and

network elements. 3G Americas is the company played significant role for evolution

of UMTS to Release5 (Rel5) of 3GPP in 2002 March. UMTS Rel5 offers higher

speed wireless data services with vastly improved spectral efficiencies through the

HSDPA feature. Addition to HSDPA, UMTS Rel5 introduces the IP Multimedia

System (IMS), UMTS Rel5 also introduces IP UTRAN concepts to realize n/w

efficiencies and to reduce the cost of delivering traffic and can provide wireless traffic

routing flexibility, performance and functionality advantages over the Rel99 and

Rel4 standards.

3.2 Radio Network Planning:

Achieving maximum capacity while maintaining an acceptable grade of service and

good speech quality is the main issue for the network planning. Planning an immature

network with a limited number of subscribers is not the real problem. The difficulty is

to plan a network that allows future growth and expansion. Wise re-use of site

27

location in the future network structure will save money for the operator.

Various steps in planning process:

Planning means building a network able to provide service to the customers wherever

they are. This work can be simplified and structured in certain steps. The steps are,

For a well-planned cell network planner should meet the following requirements,

Capacity Planning

Coverage Planning

Parameter Planning

Frequency Planning

Scrambling Code Planning

WCDMA Radio Network Planning:

WCDMA radio network planning, including dimensioning, detailed capacity and

coverage planning, and network optimisation. The dimensioning must fulfill the

operators requirements for coverage, capacity and quality of service.Capacity and

coverage are closely related in WCDMA networks, and therefore both must be

considered simultaneously in the dimensioning of such networks. Capacity and

coverage can be analysed for each cell after the detailed planning. The planning and

the optimization process can also be automated with intelligent tools and network

elements.

3.2.1 Dimensioning:

WCDMA radio network dimensioning is a process through which possible

configurations and the amount of network equipment are estimated, based on the

operators requirements related to the following.

Coverage:

- Coverage regions;

- Area type information;

- Propagation conditions.

28

Capacity:

- Spectrum available;

- Subscriber growth forecast;

- Traffic density information.

Quality of Service:

- Area location probability (coverage probability);

- Blocking probability;

- End user throughput.

Radio Link Budgets:

There are some WCDMA-specific parameters in the link budget that are not used in a

TDMA-based radio access system such as GSM.

- Interference margin: The interference margin is needed in the link budget because

the loading of the cell, the load factor, affects the coverage. The more loading is

allowed in the system, the larger is the interference margin needed in the uplink, and

the smaller is the coverage area.

- Fast fading margin: Some headroom is needed in the mobile station transmission

power for maintaining adequate closed loop fast power control. This applies

especially to slow-moving pedestrian mobiles where fast power control is able to

effectively compensate the fast fading.

- Soft handover gain: Handovers soft or hard give a gain against slow fading by

reducing the required log-normal fading margin. This is because the slow fading is

partly uncorrelated between the base stations, and by making a handover the mobile

can select a better base station. Soft handover gives an additional macro diversity gain

against fast fading by reducing the required Eb/N0 relative to a single radio link, due

to the effect of macro diversity combining.

b) Load Factors:

The second phase of dimensioning is estimating the amount of supported traffic per

base station site. When the frequency reuse of a WCDMA system is 1,the system is

typically interference-limited and the amount of interference and delivered cell

capacity must thus be estimated.

29

c) Capacity Upgrade Paths:

When the amount of traffic increases, the downlink capacity can be upgraded in a

number of different ways. The most typical upgrade options are:

----more power amplifiers if initially the power amplifier is split between sectors;

---two or more carriers if the operators frequency allocation permits;

---transmit diversity with a 2nd power amplifier per sector.The availability of these

capacity upgrade solutions depends on the base station manufacturer. All these

capacity upgrade options may not be available in all base station types.

These capacity upgrade solutions do not require any changes to the antenna

configurations, only upgrades within the base station cabinet are needed on the site.

The uplink coverage is not affected by these upgrades. The capacity can be improved

also by increasing the number of antenna sectors, for example, starting with Omni-

directional antennas and upgrading to 3-sector and finally to 6-sector antennas. The

drawback of increasing the number of sectors is that the antennas must be replaced

increased number of sectors also brings improved coverage through a higher antenna

gain.

d) Capacity per km2:

Providing high capacity will be challenging in urban areas where the offered amount

of traffic per km2 can be very high. In this section we evaluate the maximal capacity

that can be provided per km2 using macro and micro sites. For the micro cell layer we

assume a maximum site density of 30 sites per km2. Having an even higher site

density is challenging because the other-to-own cell interference tends to increase and

the capacity

per site decreases. Also, the site acquisition may be difficult if more sites are needed.

e) Soft Capacity:

Erlang Capacity: In the dimensioning the number of channels per cell was calculated.

Based on those figures, we can calculate the maximum traffic density that can be

supported with a given blocking probability. If the capacity is hard blocked, i.e.

limited by the amount of hardware, the Erlang capacity can be obtained from the

Erlang B model. If the maximum capacity is limited by the amount of interference in

the air interface, it is by definition a soft capacity, since there is no single fixed value

for the maximum capacity. The soft capacity can be explained as follows. The less

30

interference is coming from the neighbouring cells, the more channels are available in

the middle cell, With a low number of channels per cell, i.e. for high bit rate real time

data users, the average loading must be quite low to guarantee low blocking

probability.

f) Network Sharing:

The cost of the network deployment can be reduced by network sharing.If both

operators have their own core networks and share a common radio access network,

RAN, the solution offers cost savings in site acquisition, civil works, transmission,

RAN equipment costs and operation expenses. Both operators can still keep their full

independence in core network, services and have dedicated radio carrier frequencies.

When the amount of traffic increases in the future, the operators can exit the shared

RAN and continue with separate RANs.

3.2.2 Capacity and Coverage Planning and Optimisation:

a. Iterative Capacity and Coverage Prediction:

In this section, detailed capacity and coverage planning are presented. In the detailed

planning phase real propagation data from the planned area is needed, together with

the estimated user density and user traffic. Also, information about the existing base

station sites is needed in order to utilize the existing site investments. The output of

the detailed capacity and coverage planning are the base station locations,

configurations and parameters. Since, in WCDMA, all users are sharing the same

interference resources in the air interface, they cannot be analysed independently.

Each user is influencing the others and causing their transmission powers to change.

These changes themselves again cause changes, and so on. Therefore, the whole

prediction process has to be done iteratively until the transmission powers stabilize.

Also, the mobile speeds, multipath channel profiles, and bit rates and type of services

used play a more important role than in second generation TDMA/FDMA systems.

Furthermore, in WCDMA fast power control in both uplink and downlink, soft/softer

handover and orthogonal downlink channels are included, which also impact on

system performance. The main difference between WCDMA and TDMA/FDMA

coverage prediction is that the interference estimation is already crucial in the

coverage prediction phase in WCDMA. In the current GSM coverage planning

31

processes the base station sensitivity is typically assumed to be constant and the

coverage threshold is the same for each base station. In the case of WCDMA the base

station sensitivity depends on the number of users and used bit rates in all cells, thus it

is cell- and service-specific. Note also that in third generation networks, the downlink

can be loaded higher than the uplink or vice versa.

b. Planning Tool:

In second generation systems, detailed planning concentrated strongly on coverage

planning. In third generation systems, a more detailed interference planning and

capacity analysis than simple coverage optimisation is needed. The tool should aid the

planner to optimise the base station configurations, the antenna selections and antenna

directions and even the site locations, in order to meet the quality of service and the

capacity and service requirements at minimum cost.

c. Network Optimisation:

Network optimisation is a process to improve the overall network quality as

experienced by the mobile subscribers and to ensure that network resources are used

efficiently. Optimisation includes:

1. Performance measurements.

2. Analysis of the measurement results.

3. Updates in the network configuration and parameters.

The measurements can be obtained from the test mobile and from the radio network

elements. The WCDMA mobile can provide relevant measurement data, e.g. uplink

transmission power, soft handover rate and probabilities, CPICH Ec/N0 and downlink

BLER. The network performance can be best observed when the network load is high.

With low load some of the problems may not be visible. Therefore, we need to

consider artificial load generation to emulate high loading in the network. A high

uplink load can be generated by increasing the Eb/N0 target of the outer loop power

control. In the normal operation the outer loop power control provides the required

quality with minimum Eb/N0. If we increase manually the Eb/N0 target, e.g. 10 dB

higher than the normal operation point, that uplink connection will cause 10 times

more interference and converts 32 kbps connection into 320 kbps high bit rate

connection from the interference point of view.

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3.3 WCDMA/UMTS Network Optimization Methodology

Network optimization can initially be seen as a very involving task as a large number

of variable are available for tuning impacting different aspect of the network

performance. To simplify this process a step by step procedure is adopted.This

approach divides the optimization in simpler steps, each step focusing on a limited set

of parameters:

RF optimization will focus mainly on RF configuration and in a lesser extend on

reselection parameters.

Voice optimization will focus on improving the call setup (Mobile Originated and

Mobile Terminated) and call reliability thus focusing mainly on access and handover

parameters.

Advance services optimization will rely extensively on the effort conducted for

voice. The initial part of the call setup are similar for all type of services and vendor

have not at this point defined different set of handover parameters for different

services. Consequently, optimizing these services will focus on a limited set of

parameters,

typically power assignment, quality target, and Radio Link Control (RLC) parameters.

Inter-system (also known as inter-RAT) change (both reselection and handover)

optimization is considered once the WCDMA layer is fully optimized. This approach

will ensure that inter-system parameters are set corresponding to finalize boundaries

rather than set to alleviate temporary issues due to sub-optimal optimization.

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Ensure system ready for optimization

Focus on RF coverage (RSCP and Ec/Io) and

RF configuration.

Limited system parameters

optimization: PSC

assignment, monitor list, reselection

parameters

Focus on Voice performance: Access (call

origination and termination) and retention

probability.

System parameter tuning: access

parameters, handover parameters

Limited tuning of RF configuration

Focus on quality and retention performance

of different services

Further system parameter tuning: RLC (PS

domain) and service specific parameters

Limited tuning of access, handover

parameters and RF configuration

Focus on improving the retention during

intersystemchange. WCDMA and GSM

system parameter tuning:Inter-system reselection

and handover parameters. Limited tuning of

intra-frequency parameters

Figure 3.1: Optimization process is simplified by isolating basics steps

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Pre -Optimization

task

RF Optimization

Voice service

optimization

CS and PS

service

optimization

Optionally

(Inter system

change

optimization)

Even after careful RF planning, the first step of optimization should concentrate on

RF. This is necessary as RF propagation is affected by so many factors (e.g.,

buildings, terrain, vegetation) that propagation models are never fully accurate. RF

optimization thus takes into account any difference between predicted and actual

coverage, both in terms of received signal (RSCP) and quality of the received signal

(Ec/No). In addition, the same qualitative metrics defined for planning should be

considered: cell overlap, cell transition, and coverage containment of each cell. At the

same time, assuming that a UE is used to measure the RF condition in parallel with a

pilot scanner, reselection parameters can be estimated considering the dynamics

introduced by the mobility testing: during network planning dynamics cannot be

considered, as network planning tools are static by nature, only simulating at one

given location at a time, irrespectively of the

surrounding. In addition, once the RF conditions are known, dynamic simulation can

be used to estimate the handover parameters, even before placing any calls on the

network.

Service optimization is needed to refine the parameter settings (reselection, access,

and handover). Because the same basic processes are used for all types of services, it

is best to set the parameters while performing the simpler and best understood of all

services: voice. This is fully justified when the call flow difference for the different

services are considered. Either for access or for handover, the main difference

between voice and other service is the resource availability. Testing with voice

service greatly simplifies the testing procedure and during analysis limits the number

of parameters, or variable, to tune. During this effort, parameter setting will be the

main effort. Different set of parameters are likely to be tried to achieve the best

possible trade-offs: coverage vs. capacity, call access (Mobile Originated and Mobile

Terminated) reliability vs. call setup latency, call retention vs. Active Set size... to

name only a few. The selection of the set of parameter to leave on the network will

directly depend on the achieved performance and the operator priority (coverage,

capacity, access performance, call retention performance)

Once the performance targets are reached for voice, optimizing advanced services

such as video-telephony and packet switched (PS) data service will concentrate on a

limited set of parameters: power assignment, quality target (BLER target), and any

35

bearer specific parameters (RLC or channel switching parameters for example).

During the optimization of PS data service the importance of good RF optimization

will be apparent when channel switching is considered. Channel switching is a

generic terms referring to the capability of the network to change the PS data bearer to

a different data rate (rate switching) or a different state (type switching). Channel

switching is intended to adapt the bearer to the user needs and to limit the resource

utilization. Saving resource will be achieved by reducing the data rate when the RF

conditions degrade. By reducing the data rate, the spreading gain increases, resulting

in lower required power to sustain the link.

Last once the basic services are optimized, i.e., the call delivery and call retention

performance targets are met, the optimization can focus on service continuity, through

inter-system changes, and application specific optimization. Inter-system changes,

either reselection or handover, should be optimized only once the basic WCDMA

optimization is completed to ensure that the WCDMA coverage boundary is stable.

Application optimization can be seen as a final touch of service optimization and is

typically limited to the PS domain. In this last effort, the system parameters are

optimized not to get the highest throughput or the lowest delay, but to increase the

subscriber experience while using a given application. A typical example would be

the image quality for video-streaming. The main issue for this application base

optimization might be that different applications may have conflicting requirements.

In such case, the different applications and their impacts on the network should be

prioritized. Irrespective of the application considered, the main controls available to

the optimization engineer are the RLC parameters, target quality and channel

switching parameters. The art in this process is to improve the end user perceived

quality, while improving the cell or system capacity.

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Figure 3.2 Simplified Network planning process

3.4 Importance of Network Planning

Network planning is a major task for operators. It is time

consuming, labor-intensive, and expensive. Moreover, it is a never-ending process,

which forces a new round of work with each step in the networks evolution and

growth. Sometimes extra capacity is needed temporarily in a certain place, especially

during telecommunications conferences, and network planning is needed to boost the

local capacity. Changes in the network are also needed with changes in the

environment: A large new building can change the multipath environment, and a new

shopping center can demand new cell sites, and a new highway can create new

hotspots.

The quality of the network-planning process has a direct

influence onthe operators profits. Poor planning results in a configuration in which

some places are awash in unused or underused capacity and some areas may suffer

from blocked calls because of the lack of adequate capacity. The income flow will be

smaller than it could be, some customers will be unhappy, and expensive equipment

will possibly be bought unnecessarily

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3.5 Network Planning Process

Network planning is not just frequency planning, but a much

broader process. The network planning process includes things like traffic esti