Wray Castle - Cell Planning for UMTS Networks

Cell Planning for UMTS Networks Course Code: MB2005

Duration: 2 days

Technical Level: 3

Radio Principles and Planning courses include:          

Radio Principles

Principles of Radio Site Engineering

Digital Radio and Microwave Link Planning Cell Planning for GSM Networks

2G/3G Indoor Coverage Planning 3G Indoor Coverage Planning

Introduction to GSM Optimization

Drive-Test Data Capture and Analysis Cell Planning for UMTS Networks

Introduction to UMTS Optimization

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Cell Planning for UMTS Networks

CELL PLANNING FOR UMTS NETWORKS

First published 2001 Last updated May 2004 by WRAY CASTLE LIMITED BRIDGE MILLS STRAMONGATE KENDAL CUMBRIA LA9 4UB UK

Yours to have and to hold but not to copy The manual you are reading is protected by copyright law. This means that Wray Castle Limited could take you and your employer to court and claim heavy legal damages. Apart from fair dealing for the purposes of research or private study, as permitted under the Copyright, Designs and Patents Act 1988, this manual may only be reproduced or transmitted in any form or by any means with the prior permission in writing of Wray Castle Limited.

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CELL PLANNING FOR UMTS NETWORKS

CONTENTS Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8

UMTS Planning Philosophy Review of UMTS Structure UMTS Air Interface Considerations for CDMA Traffic Analysis Coverage Predictions UMTS Network Planning UMTS Cell Structures

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SECTION 1

UMTS PLANNING PHILOSOPHY

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SECTION CONTENTS 1

The Conventional Cell Planning Loop 1.1 Introduction 1.2 The Loop 1.3 Requirements and Targets for the Plan

1.1 1.1 1.1 1.3

2

Coverage 2.1 Coverage Requirements 2.2 Coverage Definition

1.5 1.5 1.5

3

Capacity 3.1 Traffic Factors 3.2 Traffic Types

1.7 1.7 1.7

4

The Link Between Capacity and Coverage 4.1 The Coverage Loop

1.9 1.9

5

Cost

1.11

6

Planning Constraints

1.13

7

Section 1 Questions

1.15

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OBJECTIVES At the end of this section you will be able to: • • •

describe how conventional planning philosophy has to be modified for application to the Universal Mobile Telecommunications System (UMTS) describe how planning constraints such as capacity, coverage and quality are interrelated for UMTS justify the use of an iterative approach in the planning process for UMTS

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1

THE CONVENTIONAL CELL PLANNING LOOP

1.1

Introduction

The term cell planning refers to a collective series of processes designed to produce a network plan that will meet a predefined set of cost and performance targets. It would, however, be wrong to think of planning as a finite process which ends at some point when a particular target is met. It is iterative, and each additional step may result in a re-evaluation of the existing plan.

1.2

The Loop

The planning process is probably best considered as a loop. The loop involves target setting, initial planning, assessment and re-evaluation at all stages. This is an important concept, which can be applied both to individual planning processes and to the system plan as a whole. Figure 1 shows a loop which would be considered typical when applied to a secondgeneration system. A key feature of this is that the initial plan is an estimate which can be refined once the network has been built and has become live. Thirdgeneration systems are much more sensitive to errors in the planning process, this making subsequent optimization more difficult. There is a heightened need to plan effectively prior to network build and operation.

1.1

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Analyze the Requirements for the Network Plan

Produce an Initial Plan

Tests and Surveys

Improve/Modify the Network Plan

Build the Network

Testing, Monitoring and Analysis of Network Performance

Re-evaluate and Optimize the Plan

Figure 1 The Conventional Planning Loop MB2005/S1/v6.2

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1.3

Requirements and Targets for the Plan

Before any plan can be started, a set of design criteria must be set out. These will define where and how the completed system should operate. In general, the criteria will describe five factors: • coverage – initial wide area coverage is unlikely • capacity – determining traffic capacity will be more difficult to analyze and predict • Quality of Service (QoS) – will impact both coverage and capacity • timescale – may be dictated by the licence conditions or finance • cost – there will be a strict budget to work to Each of these factors will consist of a series of individual requirements, some of which may be essential and some simply desirable. The requirements of each factor will probably need to be balanced against those of others. An example of an essential requirement may be that the terms of the licence dictate that 80% of a country’s population is covered within five years. The desired requirement may be to meet that target within four years.

1.3

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Capacity Quality of Service

Coverage

Requirements for Network Plan Desired

Essential

xxxxxxxxxxx xxxxxxx xxxxxxxxx xx xxxxxxx xxxxxxxx

xxx xxxxxxxxxx xxxxxx xxxxxx xxxxxxxxxx xxxx xxxxxxxx xxxxxxxxx

Timescale

Cost

Figure 2 Network Plan Requirements MB2005/S1/v6.2

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COVERAGE

2.1

Coverage Requirements

The driving force for coverage will usually be competitive advantage, but in many cases the licence agreement will itself stipulate a coverage requirement within a given timeframe. It is important that any coverage requirements set should be realistic, i.e. 100% coverage will be impossible. Because of the nature of a Code Division Multiple Access (CDMA) radio interface, it would be impossible to predict and to guarantee with absolute certainty any given figure for coverage. As a result of this, coverage requirements can only be expressed as desirable with percentage reliability.

2.2

Coverage Definition

Percentage population coverage is probably the most important driver as it is likely to be one of the terms of the licence. There is perhaps little point striving for blanket geographical coverage when there is already GSM coverage, which may be used for backup. The power budget will impact on coverage and this will need to be carefully planned taking into account that signal strength requirements will vary from service to service and the effect of cell loading will cause cell breathing. Path loss at 2 GHz will be greater than at 900 MHz resulting in much smaller cell sizes and a greater cell density than for a traditional 900 MHz network. Cell densities will be more in line with traditional 1800 MHz networks, though this will depend upon service types. Small macro cells and micro cells are most likely to be employed in built-up environments, with pico cells being used in hotspot areas where high-bit-rate services are needed. Voice traffic will be the most dominant along roads and motorways, but high-bit-rate data services may be popular along railways, for business commuters and entertainment. High-bit-rate data services may be required in buildings as well as meeting special requirement needs such as providing video links at a motor racing event.

1.5

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Signal Strength Power Budget

Path Loss

% Geographical

Coverage Requirements % Population

Licence Agreement

Area/Clutter Types

Special Requirements

Railways Roads/Motorways In-building Coverage

Figure 3 Coverage Requirements for Each Traffic Type MB2005/S1/v6.2

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CAPACITY

3.1

Traffic Factors

The specification of traffic capacity requirements for the network cannot be exact. The traffic requirement itself will only be an estimate and may not accurately reflect the traffic that occurs on the completed network. Traffic load and distribution is likely to vary a great deal in the completed network, but the network is planned on the basis of an estimated snapshot. This should be taken into account when setting realistic targets within the planning criteria. Any large variations from this which show up once the network begins operation should result in re-evaluation and optimization.

3.2

Traffic Types

To plan a multimedia network it is important to know the total volume of traffic expected. This can then be broken down into the different traffic types. These types will include voice traffic, which has been the most dominant traffic type in 2G networks. This could be handled by an existing GSM infrastructure, leaving the 3G network to support the high-bit-rate data services. Data services will be divided into circuit-switched services offering constant bit rates desirable for real-time applications such as videoconferencing, and packet-switched services offering high-bit-rate non-real-time applications. This is seen as the most important traffic type and it is important to identify QoS levels and ensure they are met. Message services will also be an important traffic type and will include text, voice and video. There will also be a need to support messaging for Supplementary Service (SS) activities. Many of the new services will be based on lifestyle, so it is important to define user profiles, detailing the behaviour of subscribers and incorporating demographic information. The available spectrum will have an impact upon capacity. The number of carriers an operator has may vary from one to three Frequency Division Duplex (FDD) carriers and possibly one Time Division Duplex (TDD) carrier. Finally, a decision about the percentage blocking level for circuit-switched connections must be made and will impact traffic capacity. For packet operation delay criteria will influence the QoS targets.

1.7

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Data PS/CS Voice Video Telephony

Total Volume

SMS/SS Messaging

Capacity

% Blocking

User Profiles

Demographics

Spectrum

Figure 4 Traffic Factors MB2005/S1/v6.2

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THE LINK BETWEEN CAPACITY AND COVERAGE

Conventional planning practices deal with capacity and coverage as fundamental but independent processes. This approach is not applicable for a CDMA-based system. UMTS is both CDMA based and it provides multimedia support, hence capacity calculations cannot be separated: any tool used to simulate and plan a UMTS network must link these calculations.

4.1

The Coverage Loop

The link budget is a normal starting point for any coverage estimate. However, in a CDMA-based system the link budget must account for interference levels. The interference level for a cell can be calculated if the capacity of a cell is known. If traffic distribution and traffic types are known, then cell capacity can be calculated for a given coverage. In order to calculate cell coverage it is necessary to calculate a link budget. To establish an initial entry point to this loop, an assumed capacity is used, allowing an iterative process to begin. This will ultimately converge on a solution.

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Coverage

Link Budget

Capacity

Figure 5 The Coverage Loop MB2005/S1/v6.2

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COST

Almost every aspect of the planning process will have an impact upon cost. In most cases, cost will be the main constraint in the design process. The aim will always be to provide the best overall performance at the least cost. Careful planning, particularly at the roll-out stage of a network, can make a big difference in this respect.

1.11

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Licence Fee Radio Access Hardware

Masts/Antennas

Costs

Network Infrastructure and Switching

Ground Rent

Transmission Equipment/ Leasing

Optimal Features

Figure 6 Cost Factors MB2005/S1/v6.2

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PLANNING CONSTRAINTS

It is impossible to produce a plan which will fully satisfy all requirements all of the time; there has to be a compromise between conflicting requirements. A decision will need to be made about how best to balance these conflicting requirements and which, if any, are higher priorities. For example, almost all requirements will need to be balanced against the initial cost of the rollout. However, if strict adherence to budget results in poor coverage or capacity, then there will be a long-term reduction in revenue from the network. This brings us back to the concept of the planning loop. Any major and unresolvable conflicts between requirements should result in re-evaluation before planning even begins. The aim should be to make targets ambitious, but realistic.

1.13

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Service Requirements

? Cost

Licence

Quality of Service

Capacity

Figure 7 Overall Constraints on the Network Plan MB2005/S1/v6.2

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SECTION 1 QUESTIONS

1

In conventional planning, after the production of an initial plan, in which order would the follow up activities be carried out in relation to the planning loop? a b c d

2

Conventionally, when considering the traffic capacity requirements, which of the following should be taken into account? a b c d

3

UMTS is both CS and PS oriented UMTS uses CDMA UMTS operates at higher frequencies than GSM Interference levels are very low

Which of the following do you consider not to be a major constraint when planning a UMTS network? a b c d

1.15

Volume of SMS traffic In-building coverage Licence agreement Area/clutter types

In UMTS, both capacity and coverage together are part of the planning process. This is because: a b c d

5

PS and CS data requirements Cell size and numbers User profiles % blocking

Conventionally, when taking into account the coverage requirements, which of the following should be considered? a b c d

4

Re-evaluate and optimize then build the network Build the network then improve/modify the plan Perform tests and surveys and then build the network Perform tests and surveys and modify the plan

Cost Licence Capacity Transmit frequency

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SECTION 2

REVIEW OF UMTS STRUCTURE

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SECTION CONTENTS 1

The Third Generation (3G) Concept 1.1 The Movement Towards Third Generation Mobile 1.2 The UMTS Vision 1.3 Service Aims for UMTS 1.4 UMTS Data Rates

2.1 2.1 2.3 2.5 2.7

2

Spectrum Allocation 2.1 International Spectrum Allocations

2.9 2.9

3

Air Interface Technologies 3.1 Major Technology Options – ETSI Activity

2.11 2.11

4

Radio Network Architecture 4.1 The UMTS Radio Environment 4.2 Network Hierarchy

2.15 2.15 2.15

5

UTRAN Architecture 5.1 Key Components of the UTRAN 5.2 Node B 5.3 Radio Network Controller (RNC) 5.4 Radio Network Subsystem (RNS)

2.17 2.17 2.17 2.17 2.17

6

UTRAN Interfaces 6.1 Required Connections 6.2 Interface Protocols

2.19 2.19 2.19

7

Section 2 Questions

2.21

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OBJECTIVES At the end of this section you will be able to: • • • • • • •

describe the origins of UMTS technology name the two physical layer types defined for the UMTS air interface, FDD and TDD state the general aims for UMTS performance and service provision state the spectral requirements for UMTS radio carriers and the UMTS operational bands characterize macro, micro and picocellular architectures in respect of UMTS describe the functional elements within the UMTS Terrestrial Radio Access Network (UTRAN) state the general functions of the Radio Network Controller (RNC) and the Node B

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THE THIRD GENERATION (3G) CONCEPT

1.1

The Movement Towards Third Generation Mobile

Mobile telephone networks first began to enter commercial service in the early 1980s, initially in America and Scandinavia. They spread rapidly across the remainder of Europe and the rest of the developed world. The first generation of systems was based on an analogue air interface, hence they were only suitable for voice and very low-speed data. The number of additional services was limited, and security was poor. Second generation (2G) systems began to appear during the early 1990s. Several 2G systems have evolved, most of them either Japanese or American, but two standards have dominated the market: the European Global System for Mobile communications (GSM), and the American National Standards Institute (ANSI)-based IS-95, known as cdmaOne™. 2G systems are still predominantly based upon voice and low data-rate services, although these services are a significant improvement upon the first generation. More importantly, security was greatly improved; indeed, such has been the success of the GSM security system that many of its principles are being directly migrated to UMTS. The current generation of mobile phone technology, known as Generation 2.5, or 2.5G, has seen the introduction of packet data services and increased data rates, with the development of High Speed Circuit Switched Data (HSCSD), the General Packet Radio Service (GPRS), and Enhanced Data-rates for Global Evolution (EDGE) technology. While 3G systems are designed to be compatible with 2G, they offer a major step forward in service offerings. Much higher user data rates (up to 2.048 Mbit/s peak) may be offered, together with full support for multimedia services. The system is data-optimized and will ultimately transfer all information as packet data. Also, for the first time in mobile communication, bandwidth-on-demand is supported. Nonetheless, the third generation – known in Europe as the UMTS – has a complex evolution path, as Figure 1 shows.

2.1

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digital data-optimized CS + PS high data rates bandwidth on demand full multimedia support enhanced security

GPRS

HSCSD

EDGE

UMTS

CDMA2000™

EDGE

Third Generation 2001+

higher data rates packet data support possible multimedia support

2.5 Generation 2000+

Second Generation 1990s TDMA GSM

cdmaOne™

PDC

First Generation 1980s AMPS

TACS

NMT

digital voice-optimized low-speed data better security

analogue voice-optimized data via modem poor security

Figure 1 UMTS Evolution Path MB2005/S2/v6.2

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1.2

The UMTS Vision

The International Telecommunication Union’s (ITU) vision of UMTS was that of a third generation of mobile telecommunications technology which would: • become an international standard, adopted by all ITU member countries • be a catalyst for the convergence of fixed and mobile telephony • support wideband and multimedia services, up to 2 Mbit/s • support network-independent innovative devices Following the allocation of the 3G spectrum (at around 2 GHz) by the World Radio Conference (WRC) in 1992, the ITU Radiocommunications Sector (ITU-R) began defining a standard for third-generation technologies known as International Mobile Telecommunications 2000 (IMT-2000). The initial aim was to achieve a single, international standard which would be endorsed by the ITU. To this end, several candidate technologies were submitted to the ITU for consideration. This took place before the end of June 1998. Unfortunately, however, political and commercial constraints have prevented a single standard from becoming a reality. IMT-2000 now represents several different but harmonized standards based upon 2.5G and 3G technologies. UMTS is being developed and specified under the auspices of the 3rd Generation Partnership Project (3GPP). Standards will be deployed largely upon areas of political influence, but it is hoped that handset technologies will evolve far enough and quickly enough to support all of the recognized standards. More spectrum was identified for 3G operation at the World Radio Conference of 2000 (WRC2000). This spectrum encompasses existing 800, 900 and 1800 MHz segments currently in use for 1G, 2G and 2.5G systems. It also identifies new spectrum around 2500 MHz.

2.3

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ETSI

TIA

EDGE (2.5G)

CDMA2000™

(GSM based)

(cdmaOne™ based)

ETSI

ARIB

UMTS

WCDMA

3GPP UMTS

3G Family

Figure 2 Radio Access Technology (RAT) Convergence MB2005/S2/v6.2

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1.3

Service Aims for UMTS

UMTS has been designed to offer true mobile multimedia for the mass market, with an air interface that will support wideband and multimedia services. Voice has been the dominant traffic type in second-generation technology. However, because of the high-data-rate capability of the air interface (data rates of up to 2 Mbit/s are proposed), new services are expected to be developed. These services should be innovative and network-independent. They could include: • Internet access • remote file transfer • database access • e-mail • Web browsing • high-quality audio • video telephony • multimedia • customized supplementary services Specifications for services and the methods of carrying these applications over the network have been kept flexible, allowing operators to differentiate their services from those of their competitors. As many different service classes will be developed for UMTS, an increased emphasis on careful service and user interface design and service availability is needed. Most applications, especially multimedia, will require very careful network design with a particular emphasis upon QoS parameters.

2.5

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Designed for multimedia applications Voice is the dominant traffic in the second generation

Internet Search:

http//www.

X XXxxxX XXXXXX

XXxxxXX XXXXXX XX X XXXxXX

XXX XXX XXX

XXXXXX XXXXXX XX xxXX XXXXxxx

XXX XXX

XXX XXX XxXX X XXX XXX

XXX XXX

Service specifications are loosely defined

Increased emphasis upon QoS parameters

XXX

1 4 7

3

2 5 8

6 9

0

Many new services will be innovative and network independent

2.6

Messaging Internet access Remote file transfer e-mail Web browsing Video telephony Games Multimedia Database access High-quality audio Customized supplementary services

Cell Planning for UMTS Networks

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Figure 3 Service Aims for UMTS

r

tle Browse

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1.4

UMTS Data Rates

UMTS aims to offer the user a range of data rates that will depend upon the service requirements at any time. The ability to support any given data rate is determined by a number of environmental factors, including: • location • speed • cell usage (Eb/No) • cell capacity 3GPP has specified three maximum theoretical rates as network rollout targets. Up to 144 kbit/s, in a (rural) outdoor environment with a maximum speed of 500 km/h; up to 384 kbit/s, in a (suburban) outdoor environment with a maximum speed of 120 km/h; and up to 2 Mbit/s in an indoor environment (or low-range outdoor) with a maximum speed of 10 km/h. Each of the peak bit rates has associated Bit Error Rate (BER) and delay requirements.

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Operating Environment

Bit Rate

User Speed

Rural Outdoor

144 kbit/s

500 km/h

Urban/suburban outdoor

384 kbit/s

120 km/h

Indoor/low range outdoor

2048 kbit/s

10 km/h

Figure 4 WCDMA Data Rates MB2005/S2/v6.2

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SPECTRUM ALLOCATION

2.1

International Spectrum Allocations

2.1.1

World Radio Conference (WRC)

The WRC proposed international spectrum allocations for all three ITU regions during 1992. A uniform spectrum allocation was designed to simplify mobility and the coordination of spectrum between the satellite and terrestrial elements of IMT-2000. Unfortunately, it is not possible to implement a global plan because of existing spectrum allocations and the logistic and financial difficulties of spectrum refarming. In 2000, the WRC reached general agreement on three new bands for thirdgeneration operation: • 806–960 MHz • 1710–1885 MHz • 2500–2690 MHz

2.1.2

Region 1 – Europe

This is probably the least troubled region. The only major issue here is the spectrum that is allocated to Digital Enhanced Cordless Telephony (DECT), from 1880–1900 MHz. However, because of the DECT radio interface and service capabilities, it is probable that DECT and a future IMT-2000 system could coexist.

2.1.3

Region 2 – USA

This region has by far the most troublesome issues. The recently-allocated PCS1900 bands in North America completely overlap the lower part of the IMT-2000 spectrum. This problem can only be solved if the technology chosen for IMT-2000 is compatible to the extent that it can coexist with the current second-generation Personal Communication Systems (PCS).

2.1.4

Region 3 – Japan

The potential problems in this region are similar to those of Region 1.

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1750

1800

1850

1900

2000

1950

Satellite Uplink

GSM 1800 Uplink

GSM 1800 Downlink

D E C T

Licensed Uplink

PHS

2050

2100

2150

2200 Satellite

WRC-92

Downlink

EUROPE Licensed Satellite Downlink Uplink JAPAN

USA

Reserved

Satellite Downlink

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Figure 5 Current Spectrum Usage in the ITU World Regions

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AIR INTERFACE TECHNOLOGIES

3.1

Major Technology Options – ETSI Activity

The European Telecommunications Standard Institute (ETSI) working group SMG5 selected two Radio Access Technologies (RAT) for the UTRAN: Wideband CDMA (WCDMA) and Time Division CDMA (TD-CDMA). WCDMA, operating in FDD mode, will be used in the paired spectrum, primarily for wide area coverage; TD-CDMA, operating in TDD mode, will be utilized in the unpaired spectrum, principally for lowmobility indoor applications.

3.1.1

UMTS Terrestrial Radio Access (UTRA)/FDD

UTRA/FDD is designed to operate in either of three paired bands, as illustrated in Figure 6a. Bands I and III are intended for use in ITU Region 2. Twelve additional channels are specified and may be offset 100 kHz to the normal 200 kHz raster. The 200 kHz raster runs across the entire UMTS spectrum and acts as marker points for the channels. Each channel is identified by a UMTS Absolute Radio Frequency Channel Number (UARFCN). These are illustrated in Figure 6b. The nominal channel band spacing is taken to be 5 MHz. Duplex separation must be flexible, but Figure 6c shows the typical duplex distances applicable to the three bands.

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a) UTRA/FDD Frequency Bands Operating Band I II III

UL Frequencies 1920–1980 MHz 1850–1910 MHz 1710–1785 MHz

DL Frequencies 2110–2170 MHz 1930–1990 MHz 1805–1880 MHz

Uplink 9612 to 9888 9262 to 9538 and 12, 37, 62, 87, 112, 137, 162, 187, 212, 237, 262, 287 8562 to 8913

Downlink 10562 to 10838 9662 to 9938 and 412, 437, 462, 487, 512, 537, 562, 587, 612, 637, 662, 687 9037 to 9388

b) UARFCNs Operating Band I II

III

UARFCN = DL Freq or UL Freq in MHz x 5

c) Duplex Distance Operating Band I II III

TX-RX Frequency Separation 190 MHz 80 MHz 95 MHz Figure 6 UTRA/FDD

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3.1.2

UTRA/TDD

UTRA/TDD is intended to operate in one of five unpaired frequency bands as illustrated in Figure 7a. Bands b and c are intended for use in Region 2. The same 200 kHz raster applies to the TDD spectrum as for FDD and acts as marker points for the channels. Each channel will be identified by its UARFCN, as illustrated in Figure 7b. Channel spacing will be 5 MHz if the system chip rate is 3.84 Mcps, but in the case where the chip rate is 1.28 Mcps channel spacing will be 1.6 MHz.

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a) UTRA/TDD Frequency Bands Region 1 2

Frequency Bands 1900–1920 MHz 2010–2020 MHz 1850–1910 MHz 1930–1990 MHz 1910–1930 MHz

b) UTRA/TDD ARFCNs Region 1 2

Frequency Range 1900–1920 MHz 2010–2025 MHz 1850–1910 MHz 1930–1990 MHz 1910–1930 MHz

UARFCN 9512 to 9588 10062 to 10113 9262 to 9538 9662 to 9938 9562 to 9638

UARFCN = 3.84 Mcps TDD

Region 1 2

Frequency Range 1900–1920 MHz 2010–2025 MHz 1850–1910 MHz 1930–1990 MHz 1910–1930 MHz

UARFCN 9504 to 9596 10054 to 10121 9254 to 9546 9654 to 9946 9554 to 9646

UARFCN = 1.28 Mcps TDD

Figure 7 UTRA/TDD MB2005/S2/v6.2

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4

RADIO NETWORK ARCHITECTURE

4.1

The UMTS Radio Environment

The UMTS environment is deemed to comprise a number of individual domains: • macrocellular • microcellular • picocellular Macro cells give public wide-area coverage and support rapidly moving terminals. Micro cells give localized coverage, providing higher bit rates to slower terminals in areas where traffic density is likely. Pico cells can be either publicly or privately operated systems, serving homes and offices and other commercial areas.

4.2

Network Hierarchy

The domains need to combine to form a very strictly defined network hierarchy, which will be split between: • public wide area networks • public microcellular networks • public/private picocellular networks The defined interaction between these network domains is a critical part of the network design process. The importance of this is particularly applicable when considering demographics and traffic modelling.

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Macro cell

Micro cell

Pico cell

Macro

Micro

Pico

High Mobility Wide Area Voice Low Data 5 MHz e.g. 5.2 MHz Operator A

< 5 MHz e.g. 4.8 MHz Operator B

Figure 15 ACLR Requirements and Guard Channels MB2005/S4/v6.2

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3.6

Cell Breathing

3.6.1

Eb/No Requirements

Eb/No is defined as the energy per bit, divided by the noise density. Where Eb = S/R, signal power divided by bit rate and No = KT, Boltzmanns Constant multiplied by absolute temperature. The Eb/No ratio in simple terms is equivalent to the SNR in analogue systems. The Eb/No ratio is usually quoted with reference to a required BER. So to provide a service with a required QoS the ratio interface must be engineered to give the correct Eb/No ratio. In practical terms, because the No value is constant the only parameter which may be engineered is the signal power for a given bit rate. In a CDMA system, because all mobiles are transmitting on the same frequency the SNR is more accurately expressed at Eb/No + Io where Io represents the noise power contributed by the other mobiles. As more mobiles become active in the cell the background noise will increase, a phenomenon known as noise rise. This will degrade the performance of the system.

3.6.2

UL Cell Breathing

As the number of active mobiles in a cell increases the load on the cell is said to increase. The interference will grow to the extent that distant mobiles will be dropped due to the poor signal-to-noise ratio, effectively causing the cell to shrink. As mobile connections are terminated the interference reduces and the cell size increases. This is known as cell breathing.

3.6.3

DL Cell Breathing

Downlink cell breathing also occurs as the cell becomes loaded. However, this is caused by the fact that the base station employs a linear power amplifier. As more connections are established in the cell each mobile will be given proportionally less power, causing the range of the cell to reduce. With fewer connections each mobile may be apportioned more power, effectively increasing the cell range.

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Small Cell Load

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Figure 16 Cell Breathing MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.7

Example Cell Breathing Simulation

3.7.1

Jersey Sites

Figure 17 shows a small system comprising 26 sectorized sites. All sites are on 25 m masts using three 85° antennas with 2° downtilt. The area in view is about 20 km by 12 km.

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Cell Planning for UMTS Networks

Figure 17 Jersey – Site Locations MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.7.2

Radio Coverage

All sites have an Effective Isotropic Radiated Power (EIRP) of 50 dBm and the propagation model is adapted from one used for GSM 1800 in open areas. Coverage is indicated in areas with a predicted signal level above –98 dBm. Given a suitable link budget this could be considered a reasonable prediction of coverage for a GSM system.

4.35

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Figure 18 Jersey – Radio Coverage MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.7.3

CDMA Coverage with Heavy Traffic

Figure 19 shows a simulation for the system taking into account inter- and intra-cell interference. In this case traffic was used at 12.2 kbit/s with around 70 users per cell. A Monte Carlo simulation ran and 10,000 drops were used to produce the image. The dark areas near the Node Bs show coverage likelihood above 80%.

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Figure 19 Jersey – 3G Coverage Heavy Traffic MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.7.4

CDMA Coverage with Light Traffic

Figure 20 shows the same system simulated under light traffic conditions. In this case, load was reduced to around ten users per cell. Coverage above 80% is not contiguous but patches can be seen at much greater ranges from the Node Bs.

4.39

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Figure 20 Jersey – 3G Coverage Light Traffic MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.8

Cell Dead Spots

In order to maximize cell capacity the power control algorithm must balance the interference contribution from all UEs in a cell. It is therefore important that dynamic range for power adjustment at the UE is sufficient to account for the range of path loss variations in a cell. If this is not the case, dead spots can occur near to a cell. This happens when traffic load is high and UEs near to a cell are asked to reduce power such that UEs nearer the cell edge can be retained. A UE which does not have enough dynamic range to reduce power sufficiently may be refused access by admission control at the cell. Thus a mobile near to the cell may not receive service because it is not capable of transmitting a low enough power. This results in a similar effect to cell breathing, except that it works from the cell site outwards.

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Figure 21 Dead Spots MB2005/S4/v6.2

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Cell Planning for UMTS Networks

3.9

Multi-Service Coverage

The UMTS air interface, unlike GSM, has been designed to carry different types of services and data rates simultaneously. These different services will be characterized by: • user bit rate • activity factor (in UL and DL) • traffic model • radio quality requirements (UL and DL) in terms of Eb/No • maximum mobile transmit power per service class Each one of these factors has an impact on cell size; higher data rates result in a lower spreading factor, therefore a greater Eb/No requirement, hence reduced cell size. In practice this means that each service type has a different cell radius, despite being transmitted from the same base station. It may, therefore, be desirable to plan coverage on a service-by-service basis.

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Medium Data Rate Voice and Low Data Rate

High Data Rate

Figure 22 Multi-Service Coverage MB2005/S4/v6.2

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Cell Planning for UMTS Networks

4

HANDOVER

4.1

Soft Handover

When a mobile is in an area of overlapping coverage from two or more cells it may be placed in a state of soft handover. In soft handover the mobile will be communicating with a number of Node Bs simultaneously. In the downlink direction this is made possible by using individual rake fingers to despread traffic from a number of cells, aided by the fact each cell has its own scrambling code. In the uplink direction, traffic from the mobile will be received by a number of Node Bs, which can then be combined. Figure 23a shows a mobile in soft handover between two Node Bs connected to the same RNC. Traffic will be carried over two Iub interfaces to the RNC where it will be combined. In Figure 23b a mobile is in soft handover between two Node Bs attached to two separate RNCs. Once again, traffic will be carried over two Iub interfaces, but the drift RNC will relay the traffic over the Iur interface to the serving RNC, where it will be combined. It can be seen that mobiles engaged in soft handover will demand extra capacity on the backhaul circuits. From IS-95 experience 30 to 40% of mobiles may be involved in soft handover at any one time. One of the benefits of soft handover is that the parallel communication channels give an improvement in receive performance. This is known as soft handover gain. This can be as much as 4 dB and may be included in the link budget calculation.

4.1.1

Softer Handover

Figure 23c shows a mobile in soft handover between two cells controlled by the same Node B. Here the traffic will be combined locally in the Node B. No extra backhaul capacity will be required and the combining process in the Node B will provide a slightly greater soft handover gain of 5 dB. This process is commonly called ‘softer handover’. From IS-95 experience 5 to 15% of mobiles may be engaged in a softer handover. Both soft handovers and softer handovers are also known as Diversity Handovers (DHO).

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a) Soft Handover, two Node Bs, one RNC

SRNC

RNC Iub

b) Soft Handover, two Node Bs, two RNCs

Iub

Node B

DRNC

Iub

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Figure 23 Soft Handover MB2005/S4/v6.2

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Cell Planning for UMTS Networks

4.2

Hard Handover

When a mobile is in soft handover it will be power-controlled by all Node Bs involved in the handover. This is imperative to control the interference in a CDMA system. However, when a mobile is in coverage by two cells on different frequencies it may be desirable to perform a hard handover. But before the handover is executed a mobile may contribute adjacent channel interference to the neighbouring cell. Consider Figure 24. Mobile UE1, though nearer to base station B2 than to B1, is still power-controlled by B1. Similarly, UE2 is controlled by B2. For simplicity, also assume that the condition for a mobile to be correctly received by a base station is that the SIR received by this base station is greater than unity. Then, B1 does not receive UE1 correctly, since the interference that B1 receives from UE2 is greater than the signal received from UE1. Therefore, B1 asks UE1 to raise its transmission power. But this increases the interference seen by B2 and, as a consequence, B2 asks UE2 for an increase of transmission power. Clearly, we have a regenerative effect that ends only when the two mobiles have reached their maximum transmission power.

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Figure 24 Hard Handover MB2005/S4/v6.2

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Cell Planning for UMTS Networks

4.3

Example of a Soft Handover

The example is simplified for clarity and involves a UE monitoring three Node Bs. The diagram shows the relative quality levels of the Node Bs’ CPICHs as the UE moves through the system. Over the period of time shown on the diagram, the UE starts with an active set containing only cell A. In this case it is assumed that the active set is limited to two cells. 1

At this point, the quality measurement for cell B has reached the additional threshold for macro diversity. This is reported to the RNC and, subject to the requirements of access control and the expiry of a wait timer, the UE is sent a handover command. This message instructs the UE to add cell B to the active list and includes the required code and timing information.

2

At this point, the difference between the quality of cell A and cell C has fallen below the replacement hysteresis threshold. This is reported to the RNC and, subject to the requirements of access control and the expiry of a wait timer, the UE is sent a handover command. This time the handover command instructs the UE to remove cell A from the active list and replace it with cell C.

3

At this point, the quality measurement for cell C has fallen below the removal threshold for macro diversity. This is reported to the RNC and if this situation is maintained beyond the expiry of the appropriate timer, a handover command is sent to the UE. This message instructs the UE to remove cell C from the active set, leaving only cell B.

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Quality

Timer

Cell A Timer

Macro Add Threshold

Timer

Macro Replacement Threshold

Cell B

Cell C

Time 1.

2.

3.

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Cell Planning for UMTS Networks

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Figure 25 Example of a Soft Handover

Macro Remove Threshold

Cell Planning for UMTS Networks

5

HANDOVER MEASUREMENTS

RRC procedures relating to measurements are used by the UTRAN to set up the measurement process, and by the UE to provide requested measurements.

5.1

Measurement Process

The purpose of this procedure is to set up, modify or release one or more measurements that are being, or will be, performed by a UE. It is applicable for a UE in any of the RRC-connected mode states. The UTRAN transmits the Measurement Control message to the UE using the established RRC connection. This message will contain a number of parameters. Included in this message are the following. Measurement Type This indicates to the UE the type of quantity which is to be measured. Measurement Identity Number This is used by the UTRAN to identify the measurement, should it need to be modified subsequently. Measurement Command This is used to set up, modify or release. Measurement Objects This is neighbour cell information. Measurement Quantity These are specific details on the indicated quantities to be measured. Reporting Quantities These are the quantities to be reported. Measurement Reporting Criterion This is the criterion that will trigger a report generation. Reporting Mode This is the acknowledged or unacknowledged mode for RLC.

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RRC

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Figure 26 Measurement Control MB2005/S4/v6.2

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Cell Planning for UMTS Networks

5.2

Measurement Types

There are seven categories for measurement types. The UTRAN will indicate to the UE which types are to be included in its measurement process, and specific details relating to that type. The types are: • intra-frequency measurements • inter-frequency measurements • inter-system measurements • uplink traffic volume measurements • downlink quality measurements • UE internal measurements • measurements for location services

5.3

Modes for Measurements

The measurement process is applicable for UEs in all modes of operation, and they therefore require instruction from the UTRAN on the measurements to be made. The Measurement Control message is only used for UEs in the CELL_DCH state. For UEs in idle mode or in one of the other connected states, the instructions for measurements to be made are included in the System Information Blocks (SIBs) being broadcast on the BCCH.

5.4

Reporting of Measurement Results

Reporting of measurement results is only performed by UEs in the CELL_DCH state. The UTRAN instructs the UE about its reporting requirements. Reporting is normally performed using the Measurement Report message. However, the UTRAN may instruct a UE to append radio link related measurements to other uplink messages including RRC Connection Request, Direct Transfer and Cell Update.

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GSM BTS

Intersystem

Node B Micro

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Interfrequency

Downlink Quality RLC Buffer

Intra-frequency

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Internal – TX Power – RSSI Location Measurement Figure 27 UE Measurements MB2005/S4/v6.2

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6

SECTION 4 QUESTIONS

1

From an operator’s point of view, which of the following would not be regarded as an advantage of using CDMA? a b c d

2

The number of downlink scrambling codes available is: a b c d

3

Slurred speech Slanted antennas and slant polarization The whole system falling down The need for power control

When using closed loop power control the power level can be adjusted how many times per second? a b c d

4.55

AICH PICH DPCH FACH

The Cocktail Party Effect results in which of the following? a b c d

5

384 16 512 sets of 16 512

Which of the following indicates to the UE that access to the network is available? a b c d

4

It allows for multimedia features It has an increased spectral efficiency It is suitable for applications with advanced features It requires a greater number of cell sites than 2G systems

384 1500 77 200

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Cell Planning for UMTS Networks

SECTION 5

TRAFFIC ANALYSIS

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ii

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SECTION CONTENTS 1

Traffic Characteristics 1.1 High-Level Call Characteristics 1.2 Detailed Call Characteristics 1.3 Quality of Service (QoS) 1.4 QoS – Human Factors

5.1 5.1 5.1 5.3 5.5

2

Data Usage 2.1 UMTS Call Characteristics 2.2 User Profiles 2.3 Data Symmetry

5.7 5.7 5.9 5.11

3

Traffic Modelling 3.1 Traditional Methods 3.2 Packet Data Modelling

5.13 5.13 5.15

4

Section 5 Questions

5.19

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OBJECTIVES At the end of this section you will be able to: • • • • • •

relate QoS to UMTS service capabilities state the general UMTS service aims in respect of the radio environment describe traffic types likely to be available in a UMTS system and relate them to QoS discuss possible UMTS user profiles and relate these to demographic distribution discuss appropriate traffic modelling for UMTS systems describe the impact on capacity and coverage of the operation of contentionbased physical channels in the UL direction and shared channels in the DL direction

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Cell Planning for UMTS Networks

1

TRAFFIC CHARACTERISTICS

1.1

High-Level Call Characteristics

Primarily, UMTS will provide customers with two different types of service: Circuit Switched (CS) and Packet Switched (PS).

1.1.1

Circuit Switched (CS)

A specific data rate is chosen at the start of the call, based upon user requirements and service category. This rate may be renegotiated during the call. The allocated resources are solely for the use of that customer. Charging is generally based on the type of service selected and the duration of use. CS communications are needed for applications which are sensitive to delay, such as voice and videoconferencing.

1.1.2

Packet Switched (PS)

With PS communications there is no permanently established end-to-end connection. Network resources are allocated to users in bursts to deliver packets as they are generated. The network is a shared resource, so at one instant a user may be using the whole channel capacity and at the next none at all. Packets may be delivered with a required QoS that may influence delay. Charging is generally based on volume rather than time. Typical packet-based applications include e-mail, file transfer and WWW page download. These applications are delay tolerant.

1.2

Detailed Call Characteristics

Within the general terms of packet- and circuit-switched traffic, a number of traffic types, each with their own agreed set of characteristics, can be described in terms of: • data rate • symmetry (whether more data is transferred in one direction than another) • typical usage (duration in terms of switched call, average data transfer volume for packet services) • delay as perceived by the user.

5.1

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Fixed data rate, set at start of call

Circuit switched

Dedicated resource for call duration Type of service Charging is generally based upon: Duration Delay-sensitive applications

High-level call characteristics

No permanent connection Resources allocated in bursts Packet switched

Shared resources Charge based upon volume

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Call characteristics

Delay-tolerant applications

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Figure 1 Call Characteristics MB2005/S5/v6.2

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Cell Planning for UMTS Networks

1.3

Quality of Service (QoS)

Services are generally defined as being either circuit switched or packet switched. Currently, in terms of QoS, these may be treated differently. For CS systems, QoS is consistent and guaranteed. On packet networks, however, congestion leads to increased delays and therefore reduced (and variable) QoS. Longer term it may be more appropriate to view all services as being delivered by a packet-based network. In this case it must be assumed that adequate QoS guarantees and resource reservations are built into packet-based transmission protocols. To help identify suitable levels of QoS, three factors must be considered for each service type: data rates, average usage and delay.

1.3.1

Data Rates

For CS data, the data rate offered to a user is fixed unless renegotiated during the call. In the packet data context, a guaranteed data rate will need to be offered; this could be a fixed percentage of the maximum nominal rate of data transfer. In this case, the user would subscribe to a minimum guaranteed QoS that must be maintained during periods of congestion. However, under lighter traffic conditions better performance would be expected.

1.3.2

Average Usage

To determine a circuit or network Grade of Service (GoS), it is necessary to know the average usage for each type of customer/service. For CS services, average call duration is needed, whereas for the packet-based services the average file size is needed, which must take into account overheads incurred by the radio interface or protocol headers. The distribution of these inputs also needs to be known or assumed, i.e. a standard Poisson distribution.

1.3.3

Delay

It is reasonable to assume that customers will be increasingly sensitive to delay, and that QoS demands will increase. For packet-based services, delay targets should be achieved for a percentage of customers. Delay is not just service-sensitive, but UEsensitive also. For example, Internet radio stations do not deliver a complete file before audio playback begins; sufficient buffering on the terminal device will enable playback of the file as soon as enough of the file has been received to satisfy these QoS demands. 5.3

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QoS

Data Rate CS fixed rate may be negotiated

Delay CS none

PS guaranteed rate nominal rate rate may be exceeded

PS service sensitive UE sensitive delay ranges for percentage of customers

Average Usage CS average call duration

PS average file size and protocol overhead

Figure 2 QoS MB2005/S5/v6.2

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5.4

Cell Planning for UMTS Networks

1.4

QoS – Human Factors

1.4.1

Data Services

Internet-based services currently provide a best-effort QoS. For applications such as file access, file download and WWW browsing, users require a QoS that they deem to be acceptable. Perceived quality in this situation, where applications are not highly sensitive of QoS, is subjective. It is possible to define recommended and maximum response times for a number of applications and services that will suit the majority of users. Given that the amount of data to be transferred in a given time is known, the required bandwidth can be calculated. However, in some situations it may not be necessary for all the data to be transferred in order for the user to perceive a satisfactory response, for example where later parts of a WWW page continue to be downloaded while the user is reading the page.

1.4.2

Voice Services

As with data, there is a wide range of acceptable delays for voice-based services. Perceived quality depends not only on the actual delay in the network, but also whether echo cancellation techniques are used. The ITU makes recommendations for one-way transmission delays where echo is controlled; these values concern international links, which may be appropriate in the UMTS global context.

5.5

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Example

Recommended

Maximum

Simple service

Select page from menu, select hyperlink

0.5 seconds

2 seconds

Complex service

Send message, process data, return, e.g. WWW-based database enquiry

< 5 seconds

5 seconds

Loading data

Loading of programs and data, < 15 seconds e.g. file download for use with helper application, Java Applet

60 seconds

The ITU recommendations for one way transmission delay where echo is controlled: 0–150 ms delay acceptable for most applications 150–400 ms provided that degradation in quality is acceptable (applies to international links with a satellite component) over 400 ms is unacceptable but may be necessary under some circumstances, e.g. multiple satellite hops

Figure 3 QoS – Human Factors MB2005/S5/v6.2

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5.6

Cell Planning for UMTS Networks

2

DATA USAGE

2.1

UMTS Call Characteristics

Prior to understanding usage patterns, service types and their associated characteristics need to be defined. Seven service types are characterized: • voice • fax • interactive • high-quality interactive • messaging • medium multimedia • high multimedia Clearly, there are many sub-categorizations below this top level.

5.7

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Service

Data Rate

Symm

AV Use

Delay (2005)

Delay (2010)

Grade of Comments Service

Voice

7.8 kbit/s

50% Stream

2 min.

< 30 ms < 20 ms

1%

Depends on distance and echo cancellation

Fax 50% 28.8 kbit/s (Low-speed data) Stream

3 min.

200 ms

n/a

2%

Superseded by 2010

64 kbit/s 50% 25 min. 200 ms (wide area) Stream

100 ms

5%

80% of total interactive traffic 2005, 70% 2010

High-Quality Interactive

384 k (wide area) 50% 2 Mbit/s Stream 40 min. 200 ms (in pico cell)

100 ms

5%

20% of total interactive traffic 2005, 30% 2010

Best Effort

Best Effort

n/a

No attachments

< 2 sec

< 1 sec

n/a

LAN access, WWW, e-mail with attachments

80% 1 kbyte Packet

Messaging Medium Multimedia (small file) High Multimedia (large file)

64 k

90% Packet

100 kbyte

200 k guaranteed 90% 2 Mbyte < 2 sec minimum Packet in busy hour

< 1 sec

n/a

Requires buffering on terminal for streamed video and audio

5.8

Cell Planning for UMTS Networks

Figure 4 UMTS Call Characteristics

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Interactive

Cell Planning for UMTS Networks

2.2

User Profiles

2.2.1

Usage Patterns and Traffic Statistics

In order to develop realistic assumptions for user profiles, these should include: • call holding times • typical data volumes • data rates • types of service • time of day when services are used • locations where services are used Data from a number of sources needs to be investigated. This can then be used to compare traffic levels seen today with proposed traffic characteristics for UMTS.

2.2.2

Circuit Switched (CS)

It may be possible to estimate future demand for UMTS streaming-based services by analyzing current demand for CS services on PSTN and ISDN networks. Data on analogue modem and ISDN traffic is available from a wide range of sources.

2.2.3

Packet Switched (PS)

It is far more difficult to find information on Internet usage patterns since, historically, traffic profiles are generally recorded on a per-network basis. There is little regard given to the amount of traffic generated per user. This makes it difficult to validate the assumed average and maximum file sizes for UMTS.

5.9

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Percentage of calls 20 18 16 14 12 10 8 6 4 2 0

1

30

60

Holding time (minutes)

Application

Mean duration (minutes)

Videoconferencing Private circuit back-up

42 29

Remote LAN access Desktop conferencing

26 25

Internet access High-quality audio

23 22

Complex file transfer LAN interconnection Database access Security/surveillance Voice Short file transfer Fax Card verification

21 20 17 15 6 5 3 0.3

Holding time (minutes) Figure 5 User Profiles MB2005/S5/v6.2

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5.10

Cell Planning for UMTS Networks

2.3

Data Symmetry

The development of UMTS is based on a number of environments, ranging from those found in the Central Business District (CBD) of a town or city through to those found in rural areas. For any defined UMTS service group the degree of asymmetry in the traffic being generated will vary. This is because the service people require varies in different environments. For example, for high multimedia, in the CBD some business/professional users may want to upload large files (especially images from remote information gathering) just as often as they want to download files (database, intranet, etc.). However, in the suburban and rural areas, people in their leisure activities may generally be seeking to download Internet pages, hobby-related data or educational information. The trends in transactional and therefore net asymmetry will vary depending on the market environment. This could have an impact on the net asymmetry in spectrum requirements between the UMTS macro cell and micro cell layers, and/or between urban, suburban and rural macro cells.

5.11

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Cell Planning for UMTS Networks

DL Tra

ffic

wray castle Brow

ser

w.

Internet Search: http//ww

xxxXX XXXXXXXX X XXXxXXXX XXXX XXXXXXXX XX XX XXXXxxxxx XXX XxXX XXX X XXX XXX

UL Tra

Node B

ffic

UE

Voice

Symmetric

50:50

Video Telephony

Symmetric

50:50

Messaging

Asymmetric

60:40

Audio/Video streaming

Asymmetric

Heavy DL

Web Browsing

Asymmetric

Heavy DL

E-mail

Asymmetric

60:40

Figure 6 Data Symmetry MB2005/S5/v6.2

© wray castle limited

5.12

Cell Planning for UMTS Networks

3

TRAFFIC MODELLING

3.1

Traditional Methods

First- and second-generation systems have relied on traditional traffic modelling techniques, which were developed for fixed telephony networks. There are several reasons why these models are not really suited to a mobile environment, although they are generally considered to be close enough to be usable.

3.1.1

Inclusion of Data

Second-generation systems have seen the introduction of data and messaging. Even with these in place, a simple Erlang B model can still be applied. Data is largely circuit switched and can thus be modelled as a telephone call with modified characteristics, i.e. call rate and call duration. Similarly, SMS can be treated as a telephone call of very short duration.

5.13

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Cell Planning for UMTS Networks

Voice ser wray castle Brow

C

h Switc t i u c r i int-t MS Po

w.

Internet Search: http//ww

xxxXX XXXXXXXX X XXXxXXXX XXXX XXXXXXXX XX XX XXXXxxxxx

c

Traffi

ed Da

ta

nt

o-Poi

S

BTS

XXX XxXX XXX X XXX XXX

MS

Erlang B

Average Call Duration Average Call Arrival Rate

Figure 7 Traditional Traffic Modelling MB2005/S5/v6.2

© wray castle limited

5.14

Cell Planning for UMTS Networks

3.2

Packet Data Modelling

The modelling of packet data involves a far greater level of complexity than that of circuit-switched data. It must take into account packet size, throughput rate, retransmission rate and packet activity. The wide range of services that are likely to rely on packet data will probably require a range of different packet traffic types to be defined, each with unique characteristics. The chosen modelling tool must be able to accommodate and combine these varied traffic types.

3.2.1

Characterizing Packet Traffic

Figure 8 illustrates an example of packet data traffic and represents what may happen whilst web browsing. The following parameters characterize the packet data traffic. A session is a period of time that a user is accessing resources via a packet connection, i.e. web browsing. A session can be divided into a number of calls with perhaps five calls per session. Each call would be initiated by a user selecting a hyperlink or menu option. The number of packets in a call will depend upon content and packet size. The average packet size is typically 500 bytes with 25 packets in a call. The inter-arrival time of packets in a call is typically 2 ms. There is usually a longer interval between calls, known as the call interval. This is taken as being the time a user reads the downloaded content before selecting another option. This so-called reading time is often taken to be about 400 seconds. This information will be needed for each packet-based service and may be different in the uplink and downlink directions. Knowing the bit rate for the defined service, the packet characteristics and assuming a Poisson packet arrival distribution for all users it is possible to determine the capacity and load placed on a cell.

5.15

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Cell Planning for UMTS Networks

Packet interval

Packet size

Call interval

Packets in call Total number of calls in session

call and session arrival assumed to follow a Poisson process

Figure 8 Packet Characterization MB2005/S5/v6.2

© wray castle limited

5.16

Cell Planning for UMTS Networks

3.2.2

Transport for Packet Data

For successful system simulation, the model should ideally account for the different mechanisms for packet data transfer on the UMTS air interface. In particular, account needs to be taken of the inclusion (or otherwise) of fast power control in the used channel. A channel without power control will represent more interference contribution. In addition, the support of soft handover must be accounted for since this will also impact on interference and capacity. These effects must be modelled accurately for reliable predictions to be obtained.

5.17

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Cell Planning for UMTS Networks

RACH FACH CPCH

ser wray castle Brow w.

DSCH

Internet Search: http//ww

xxxXX XXXXXXXX X XXXxXXXX XXXX XXXXXXXX XX XX XXXXxxxxx XXX XxXX XXX X XXX XXX

Node B

DCH

UE

Transport Channel

Advantage

Disadvantage

RACH/FACH

Rapid set-up Small amounts Bursty applications

Few RACH/FACH pairs No fast power control No soft H/O Generates more noise

CPCH/FACH

Share channel High or low bit rates Multiple CPCH/cell Fast power control Small/medium amounts of data

No soft H/O

DSCH

Sharing OVSF codes Fast power control Medium/large amounts of data Soft H/O

DCH

Fast power control Soft H/O Less interference High bit rates High data volumes

Not suited to bursty traffic Slower set-up time

Figure 9 Packet Transport MB2005/S5/v6.2

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5.18

Cell Planning for UMTS Networks

4

SECTION 5 QUESTIONS

1

Cell breathing has which of the following effects? a b c d

2

Which of the following is a feature of a packet-switched call? a b c d

3

Voice Messaging Web browsing E-mail

When modelling for packet data, which of the following may be ignored? a b c d

5.19

Call holding time Class of UE in use Time when service is used Locations where services are used

When assessing data symmetry, which of the following would be regarded as symmetric? a b c d

5

No permanent connection Uses a dedicated resource Is suitable for delay-sensitive applications Charging is based upon call duration

Which of the following would not be regarded as a user profile? a b c d

4

It allows more users into the cell coverage area It removes the need for open loop power control It results in the cell varying in size It prevents high capacity users accessing the Node B

Packet size Throughput Retransmission rate SMS traffic

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MB2005/S5/v6.2

Cell Planning for UMTS Networks

SECTION 6

COVERAGE PREDICTIONS

© wray castle limited

i

Cell Planning for UMTS Networks

ii

© wray castle limited

Cell Planning for UMTS Networks

SECTION CONTENTS 1

Propagation Modelling 1.1 Introduction 1.2 Current Models 1.3 Frequency Change for UMTS 1.4 Emphasis on Microcellular Models 1.5 UMTS Wideband Channel 1.6 Lack of UL and DL Correlation

6.1 6.1 6.1 6.3 6.3 6.7 6.7

2

Link Budget 2.1 Load Factor (Lj) 2.2 Noise Rise 2.3 Interference Margin

6.9 6.9 6.9 6.11

3

Calculation of Load Factor 3.1 Individual UL Load Factor 3.2 UL Cell Load Factor (ηUL) 3.3 DL Load Factor (ηDL) 3.4 Load Factor and Noise Rise

6.13 6.13 6.15 6.17 6.19

4

Link Budget Examples 4.1 Introduction 4.2 Ul 12.2. kbit/s Speech 4.3 144 kbit/s Data 4.4 384 kbit/s Data 4.5 Translating Pathloss to Range

6.21 6.21 6.21 6.23 6.25 6.27

5

Handover Regions and Cell Breathing 5.1 Soft Handover Regions 5.2 Consideration of Cell Breathing

6.29 6.29 6.31

6

Section 6 Questions

6.33

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iii

Cell Planning for UMTS Networks

iv

© wray castle limited

Cell Planning for UMTS Networks

OBJECTIVES At the end of this section you will be able to: • • • • • • •

state typical radio parameters applicable to coverage prediction in UMTS suggest appropriate propagation models and prediction techniques for UMTS coverage planning describe multipath effects and receiver characteristics in respect of CDMA operation discuss link budgets for different traffic types and loads to allow for cell breathing state the significance of noise rise and load factor relate traffic characteristics to a typical UMTS link budget estimate approximate range from link budget

© wray castle limited

v

Cell Planning for UMTS Networks

1

PROPAGATION MODELLING

1.1

Introduction

Although UMTS introduces a very different air interface structure to that of GSM, it may not need a fundamental change in radio propagation prediction. However, there are several points that may require consideration: • shift in frequency • emphasis on microcellular not macrocellular models • wideband channel • lack of UL and DL correlation

1.2

Current Models

Research into propagation models has been extensive since the introduction of second-generation systems. Most are based on an empirical format and range from a basic Okumura Hata model to more complex offerings resulting from COST 231. Most of these models are more suited to the macrocellular environment and are supplemented by diffraction loss and clutter loss weightings. Some of the more advanced models may need very little adaptation for UMTS. There are some microcellular and picocellular models in use, both empirical and ray tracing based. It is likely that more effort will be required in this area to develop models better suited to UMTS channel characteristics.

6.1

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

shift in frequency microcellular rather than macrocellular wideband channel lack of UL and DL correlation

Figure 1 Considerations for UMTS Propagation Models MB2005/S6/v6.2

© wray castle limited

6.2

Cell Planning for UMTS Networks

1.3

Frequency Change for UMTS

The degree to which the change to a new frequency band for UMTS affects propagation modelling may depend on the operator in question. A GSM 900 operator may see the introduction of new propagation models. It is likely that a GSM 1800 operator will only initially need to modify existing models. In either case, most models used for GSM 900 and GSM 1800 could be adapted for use with UMTS. Models could be recalibrated for UMTS using measurement information gathered from the UE. Additionally, drive test logging could also be used.

1.4

Emphasis on Microcellular Models

Many factors suggest a much smaller cell size than has been the case for secondgeneration systems. There is already a trend to reduce cell size for increased capacity and this continues for UMTS. Thus there will be a great deal of interest in microcellular models. There are two modelling approaches of interest, a statistical model and a deterministic model.

1.4.1

Statistical Models

Statistical models are based on mathematical analysis of a statistically significant set of field measurements. The precise approach varies, but often takes the form of a power law model with modifications for the local environment. Figure 2 shows a general form for such a model.

6.3

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

The general form of a Power Law model:

Lp(d) = L(do) + 10n Log10 (d/do) + x

dB

Lp(d) = path loss in dB L(do) = free space path loss at 1m reference point (38.5 dB at 2 GHz) n = path loss exponent x = location-specific factors of fade margins

Figure 2 Power Law Micro Cell Model MB2005/S6/v6.2

© wray castle limited

6.4

Cell Planning for UMTS Networks

1.4.2

Deterministic Models

A deterministic model attempts to predict propagation through the application of the first principles of physics and detailed knowledge of the local environment. The most well-known technique is Ray Tracing. This is an attempt to predict the precise path from transmitter to receiver. A detailed knowledge of buildings and terrain is required, and, as a result, this type of model is very limited in its application.

6.5

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Cell Planning for UMTS Networks

Node B

wray castle Brow

ser

w.

Internet Search: http//ww

xxxXX XXXXXXXX X XXXxXXXX XXXX XXXXXXXX XX XX XXXXxxxxx XXX XxXX XXX X XXX XXX

Figure 3 Ray Tracing MB2005/S6/v6.2

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6.6

Cell Planning for UMTS Networks

1.5

UMTS Wideband Channel

A UMTS propagation model may need to account for the wideband nature of air interface transmission. The 5 MHz bandwidth means an uncorrelated channel. In some respects, this is an advantage of CDMA systems. However, it may mean that predictions made on the basis of a spot frequency will lack validity. This is caused by selective fading of frequency components in a wideband channel, as opposed to the flat fading assumed in simple second-generation modelling.

1.6

Lack of UL and DL Correlation

There will be an even greater lack of correlation between UL and DL radio channels. The assumption of reciprocity typical in second-generation systems may not be applicable in UMTS. In GSM, the duplex separation of 45 MHz in the 900 MHz band corresponds to a 5% frequency difference between uplink and downlink. However, in UMTS, the 190 MHz duplex separation for FDD mode represents at least a 10% frequency difference between uplink and downlink. This greater difference needs accounting for within the propagation modelling. In TDD mode, however, UL and DL radio paths will correlate, simplifying issues such as power control.

6.7

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

5 MHz

5 MHz

190 MHz

Non-correlated channel Non-correlated UL and DL

Figure 4 Effects of the Wideband Channel MB2005/S6/v6.2

© wray castle limited

6.8

Cell Planning for UMTS Networks

2

LINK BUDGET

A link budget would normally be a function of accounting for link losses and requirements in order to ascertain an acceptable path loss. For CDMA-based systems, the power budget must also take account of the interference level and QoS requirements. These in turn will be a function of system load.

2.1

Load Factor (Lj)

The load factor is an indicator of how close a link is operating in respect of its theoretical maximum capacity. Given that loading will reduce coverage, it is undesirable to plan a system for a very high load factor. Ideally, the system should be dimensioned such that cells operate with a load factor allowing a margin of safety.

2.2

Noise Rise

The noise rise is a measure of the increase in noise caused by the interference level in the cell. The interference in question includes both intra-cell and inter-cell sources. The noise rise can be calculated from serving and neighbour cell operating load factors. Thus a higher load factor results in a higher noise rise.

6.9

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

Radio Parameters

Link Budget

Interference Margin

Load Factor

Noise Rise

Figure 5 Link Budget Inputs MB2005/S6/v6.2

© wray castle limited

6.10

Cell Planning for UMTS Networks

2.3

Interference Margin

The interference margin is a factor in the link budget that is used to account for predicted noise rise. As part of the planning process an assessment of operating load factor will indicate a noise rise. The interference margin should be set such that the link budget is valid for the required noise rise. However, in setting interference margin, hence link budget, the cell size is determined. This in turn will affect the predicted load factor, leading to a reassessment. Thus an iterative process is required to arrive at suitable parameters for system planning and simulations.

6.11

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Cell Planning for UMTS Networks

Offered Traffic

Load Factor

Noise Rise

Interference Margin

Link Budget

Radio Parameters

Coverage

Figure 6 Setting Interference Margin MB2005/S6/v6.2

© wray castle limited

6.12

Cell Planning for UMTS Networks

3

CALCULATION OF LOAD FACTOR

The total load factor for a cell is simply the sum of all the individual load factors (Lj) for all UEs which have influence in a cell. A typical way to find this is to calculate Lj for all UEs in a single cell and then allow a weighting for neighbour cells.

3.1

Individual UL Load Factor

Refer to Figure 7.

6.13

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Cell Planning for UMTS Networks

The load factor for an individual UE (Lj) is the ratio of wanted signal power (Pj) against total interference power (Itotal) for that UE. Pj

Lj =

Itotal

Pj is a function of required Eb/No, processing gain, activity factor (νi) and the ratio signal power to total power in the channel. Starting from an expression for Eb/No for user j, (Eb/No)j: (Signal power)j

(Eb/No)j = (Processing gain)j

(Eb/No)j =

Total receive power excluding that of user j

W

Pj

νj Rj

Itotal – Pj

where: W is the chip rate Rj is the bit rate for user j. Solving this for Pj gives: 1

Pj = 1+

Itotal

W (Eb/No)j . Rj . νj

Substituting for Pj in the expression for Lj gives: 1

Lj = 1+

W (Eb/No)j . Rj . νj

Figure 7 Individual UL Load Factor MB2005/S6/v6.2

© wray castle limited

6.14

Cell Planning for UMTS Networks

3.2

UL Cell Load Factor (ηUL)

The load factor for the cell (ηUL) is the sum of all the individual load factors (Lj) of the UEs in the cell. It is then necessary to add a weighting for UEs in neighbour cells. This can be expressed as: neighbour cell weighting i =

neighbour cell interference serving cell interference

The load factor for a cell serving N users can be expressed as: N

η

UL

= (1+ i )

∑

Lj

j=1

substituting for Lj N

η

UL

= (1+ i )

∑ j=1

6.15

1+

1 W

(Eb /No )j R j νj

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Cell Planning for UMTS Networks

N

η

UL

= (1+ i )

∑ j=1

η

UL

1+

1 W

(Eb /No )j R j νj

= UL load factor

i = neighbour cell interference factor j = an individual UE N = number of UEs in the cell W = chip rate Eb = energy per bit No = noise spectral density Rj = bit rate for UEj νj = activity factor for UEj

Figure 8 UL Load Factor MB2005/S6/v6.2

© wray castle limited

6.16

Cell Planning for UMTS Networks

3.3

DL Load Factor (ηDL)

A similar process can be used to arrive at an expression for DL load factor. However, there are two important differences. Firstly, the UL has multiple transmit sources and one receiver, whereas the DL has one (main) transmitter with secondary interference sources and receivers in multiple locations. The result is that the effect of neighbour cell interference must be considered independently for each UE, i.e. the factor i becomes ij. Secondly a new factor, α j , is introduced to account for DL orthogonal code performance in a multipath channel. In theory this should be independently set for each UE, but in practice it may be set for the cell and based on its environment. Typically this may lie between 0.4 and 0.8. N

η

DL

=

∑ j=1

6.17

1+

1 W

((1− αj )+ ij )

(Eb /No )j R j νj

© wray castle limited

MB2005/S6/v6.2

Cell Planning for UMTS Networks

N

η

DL

=

∑ j=1

η

DL

1+

1 W

((1− αj )+ ij )

(Eb /No )j R j ν j

= DL load factor

N = number of UEs in the cell j = an individual UE W = chip rate Eb = energy per bit No = noise spectral density Rj = bit rate for UEj νj = activity factor for UEj αj = orthogonality factor ij = neighbour cell interference factor

Figure 9 DL Load Factor MB2005/S6/v6.2

© wray castle limited

6.18

Cell Planning for UMTS Networks

3.4

Load Factor and Noise Rise

The load factors (η) in either the UL or DL directions are related to noise rise in the following way: Noise rise =

1 1–η

Noise rise (dB) = –10 log10 (1 – η) An important consequence of this is that as the load factor approaches unity, the noise rise tends to infinity. It can be seen that attempts to dimension a system with very high load factors will result in the requirement for an impossibly large interference margin. Since such a margin would be impractical, the resulting system plan would give very poor coverage.

6.19

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Cell Planning for UMTS Networks

Noise Rise

1

Load Factor (η)

1

Figure 10 Noise Rise and Load Factor MB2005/S6/v6.2

© wray castle limited

6.20

Cell Planning for UMTS Networks

4

LINK BUDGET EXAMPLES

4.1

Introduction

The key radio parameters in a UMTS link budget are as they would be for a secondgeneration system. Thus transmit and receive powers, antenna gains, feeder losses, equipment noise figures and fade margins are still relevant. The new factors for UMTS are processing gain and interference margin. Another change for UMTS is the need to perform multiple link budgets reflecting the range of different services that may need to be supported.

4.2

UL 12.2 kbit/s Speech

Figure 11 shows a possible link budget for the Adaptive Multi-Rate (AMR) voice service. The margins allowed are suitable for an in-car user travelling at up to 120 km/h. The interference margin of 3 dB relates to expected noise rise.

The processing gain is: 10 log

3.84 x 106 12.2 x 103

= 25 dB

The log-normal fade margin provides the required probability of coverage.

6.21

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Cell Planning for UMTS Networks

Mobile (TX) Maximum Transmit Power

dBm

21

A

Antenna Gain

dBi

0

B

Body Loss

dB

3

C

dBm

18

D=A–C

Thermal Noise Density

dBm/Hz

–174

E

Receiver Noise Figure

dB

5

F

dBm

–102.2

dB

3

dBm

–99.2

Processing Gain

dB

25

J

Required Eb/No

dB

5

K

Receiver Sensitivity

dBm

–119.2

Antenna Gain

dBi

18

M

Feeder Loss

dB

2

N

Fast Fade Margin

dB

0

O

Log Normal Fade Margin

dB

7.3

P

Soft Handover Gain

dB

3

Q

In-Car Loss

dB

8

R

Maximum Path Loss

dB

140.9

EIRP Node B (RX)

Receiver Noise Power over 4.8 MHz Interference Margin Effective Noise and Interference

G = E + F + 10 log 4.8 x 10 6 H I=G+H

L=I–J+K

S=D+M–N–O–P+Q–R–L

Figure 11 UL 12.2 kbit/s Speech MB2005/S6/v6.2

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6.22

Cell Planning for UMTS Networks

4.3

144 kbit/s Data

This budget assumes a low-mobility user in an indoor environment. Soft handover is supported. The antenna gain of 2 dB and absence of body could indicate the use of a PC data card. The processing gain is 10 log

3.84 x 106

= 14.3 dB

1.44 x 103

6.23

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Cell Planning for UMTS Networks

Mobile (TX) Maximum Transmit Power

dBm

24

A

Antenna Gain

dBi

2

B

Body Loss

dB

0

C

dBm

26

D=A–C

Thermal Noise Density

dBm/Hz

–174

E

Receiver Noise Figure

dB

5

F

dBm

–102.2

dB

3

dBm

–99.2

I=G+H

Processing Gain

dB

14.3

J

Required Eb/No

dB

1.5

K

Receiver Sensitivity

dBm

–112

Antenna Gain

dBi

18

M

Feeder Loss

dB

2

N

Fast Fade Margin

dB

4

O

Log Normal Fade Margin

dB

4.2

P

Soft Handover Gain

dB

2

Q

Indoor Loss

dB

15

R

Maximum Path Loss

dB

132.8

EIRP Node B (RX)

Receiver Noise Power over 4.8 MHz Interference Margin Effective Noise and Interference

G = E + F + 10 log 4.8 x 10 6 H

L=I–J+K

S=D+M–N–O–P+Q–R–L

Figure 12 UL 144 kbit/s Data MB2005/S6/v6.2

© wray castle limited

6.24

Cell Planning for UMTS Networks

4.4

384 kbit/s Data

This budget assumes a low-mobility user in an urban outdoor environment. Soft handover is not supported. Once again, the 2 dB antenna gain and absence of body loss suggest a PC card or stand-alone data terminal. The processing gain is 10 log

3.84 x 106 3.84 x

6.25

= 10 dB

103

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

Mobile (TX) Maximum Transmit Power

dBm

24

A

Antenna Gain

dBi

2

B

Body Loss

dB

0

C

dBm

26

D=A+B

Thermal Noise Density

dBm/Hz

–174

E

Receiver Noise Figure

dB

5

F

dBm

–102.2

dB

3

dBm

–99.2

Processing Gain

dB

10

J

Required Eb/No

dB

1

K

Receiver Sensitivity

dBm

–108.2

Antenna Gain

dBi

18

M

Feeder Loss

dB

2

N

Fast Fade Margin

dB

4

O

Log Normal Fade Margin

dB

7.3

P

Soft Handover Gain

dB

0

Q

Indoor Loss

dB

0

R

Maximum Path Loss

dB

138.9

EIRP Node B (RX)

Receiver Noise Power over 4.8 MHz Interference Margin Effective Noise and Interference

G = E + F + 10 log 4.8 x 10 6 H I=G+H

L=I–J+K

S=D+M–N–O–P+Q–R–L

Figure 13 UL 384 kbit/s Data MB2005/S6/v6.2

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6.26

Cell Planning for UMTS Networks

4.5

Translating Pathloss to Range

Pathloss can be translated to range using an appropriate pathloss model. As yet, no pathloss model has been formally identified for UMTS but the COST-231 Hata model (originally developed for GSM1800/1900) is often used. For a base station antenna height of 15 m and operating frequency of 2000 MHz, these models can be simplified to: Pathloss (Metropolitan Area)

= 144.95 + 37.2 log d

Pathloss (Urban Area)

= 141.95 + 37.2 log d

Pathloss (Suburban Area)

= 129.68 + 37.2 log d

Pathloss (Quasi-open Area)

= 114.44 + 37.2 log d

Pathloss (Open Area)

= 109.44 + 37.2 log d

in each case, d = range in km. For example, for a 12.2 kbit/s speech service in a metropolitan area the range can be estimated as follows: Pathloss (Metropolitan Area)

= 144.95 + 37.2 log d

140.9 = 144.95 + 37.2 log d 37.2 log d = 140.9 – 144.95

log d =

140.9 – 144.95 37.2

d

d

6.27

= antilog

(

140.9 – 144.95 37.2

)

= 0.778 km

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MB2005/S6/v6.2

Cell Planning for UMTS Networks

Open Area

Quasi-open Surburban Area Area

Urban Area

Metropolitan Area

12.2 kbit/s high mobility

7 km

5.14 km

2 km

940 m

780 m

144 kbit/s indoor

4.25 km

3.12 km

1.2 km

570 m

470 m

384 kbit/s outdoor, low mobility

6.19 km

4.54 km

1.77 km

830 m

690 m

Figure 14 Estimated Ranges MB2005/S6/v6.2

© wray castle limited

6.28

Cell Planning for UMTS Networks

5

HANDOVER REGIONS AND CELL BREATHING

5.1

Soft Handover Regions

The soft handover region represents the area in which a UE would be involved in either a soft or a softer handover. It is the responsibility of the planner to ensure appropriate handover parameter setting for optimal soft handover regions. It is suggested that an ideal figure for soft handover region would be between 30% and 40% of coverage area. If the soft handover region is too large it will become an excessive burden on system capacity. If the soft handover region is too small it may affect quality and, in turn, coverage. However, it is important to bear in mind the effects of mixed traffic types and cell breathing.

5.1.1

Mixed Traffic in Soft Handover

Different traffic types will have differing coverage footprints for any given cell. Thus, even in static traffic load conditions, there will be a number of different soft handover regions for different traffic types. If the planner optimizes soft handover region for one particular traffic type to the exclusion of all others, the resulting soft handover regions will be non-optimal for other traffic types. Setting of parameters will need to be a compromise weighted towards key traffic types. In addition, different sets of parameters may be applied to UEs in different traffic states.

6.29

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Soft handover region for high-rate data Soft handover region for voice

Figure 15 Soft Handover Regions MB2005/S6/v6.2

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Cell Planning for UMTS Networks

5.2

Consideration of Cell Breathing

As cell capacity increases, the coverage footprint of the cell will shrink. If this is not taken into account when setting coverage overlap between cells, the cell breathing effect could result in coverage holes at periods of high traffic demand. This is most likely to occur in high-priority coverage areas since these will be the areas most likely to present high traffic demand. Again, a compromise must be found between the general need to control soft handover regions and the need to prevent the occurrence of coverage holes. A simple way to achieve this is to ensure larger overlap between adjacent cell cover areas. At times this will mean the soft handover regions could be very large, but this will only occur when traffic load is light. At such times the inefficiency resulting from large soft handover regions is tolerable. When traffic load increases, the effect of cell breathing will reduce cell overlap and increase capacity efficiency.

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Light Traffic

Heavy Traffic

Figure 16 Consideration of Cell Breathing MB2005/S6/v6.2

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6

SECTION 6 QUESTIONS

1

The load factor indicates which of the following? a b c d

2

The interference margin used in the link budget is used to: a b c d

3

Transmit power Antenna gain Interference margin Feeder loss

Which of the following is a function performed by the Node B? a b c d

6.33

The ratio of the wanted signal power to the total interference power The ratio of the wanted signal power to interference from neighbour cells The ratio of the wanted signal power to interference from within the cell Not dependent upon the power transmitted by other UEs

When determining the UMTS link budget, which UMTS specific parameter should be considered? a b c d

5

Determine the amount of open loop power control required Determine the rate at which closed loop power control should be applied Account for the expected noise rise as more users load the network Determine QoS parameters

The load factor of a UE is: a b c d

4

How close a link is operating to its theoretical maximum capacity How many users can operate simultaneously The minimum number of users The maximum number of users allowed before discernible cell breathing occurs

Radio resource control Handover control Channel allocation Closed loop power control

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SECTION 7

UMTS NETWORK PLANNING

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ii

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SECTION CONTENTS 1

The UMTS Radio Planning Process 1.1 Introduction

7.1 7.1

2

Coverage Requirements 2.1 Coverage Scenarios

7.3 7.5

3

Capacity Requirements 3.1 Capacity Issues

7.7 7.9

4

QoS Requirements 4.1 Call Set-up Quality 4.2 Call Quality

7.13 7.15 7.17

5

Planning Constraints 5.1 Spectrum Availability 5.2 Emission Limits 5.3 Site Locations 5.4 Antennas 5.5 Radio Link Budget 5.6 Costs

7.19 7.19 7.19 7.19 7.19 7.21 7.21

6

Forming the Overall Radio Network Plan

7.23

7

Design Process in Detail 7.1 Monte Carlo Simulation 7.2 Simulation Process

7.25 7.25 7.27

8

Border Regions 8.1 Border Region Problem 8.2 Border Strategies

7.29 7.29 7.31

9

Section 7 Questions

7.33

Annex: Cell Dimensioning for Full and Concentric Coverage Scenarios

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Cell Planning for UMTS Networks

iv

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OBJECTIVES At the end of this section you will be able to: • • • • • • • • • • •

state the key factors required as inputs to the UMTS planning process explain the cyclical nature of UMTS planning describe the link between planning constraints and the system architecture discuss QoS and coverage target-setting for application to UMTS systems discuss the importance of usage patterns for UMTS users and services explain the significance and derivation of traffic type and load distribution relate coverage requirements, QoS and traffic within the planning loop outline the consideration for UMTS system dimensioning relate traffic, coverage and QoS requirements along with UL and DL power budgets to derive coverage estimates in a UMTS system consider how coverage may be described for a UMTS system characterize considerations for control of coverage and coordination of handovers in border regions

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1

THE UMTS RADIO PLANNING PROCESS

1.1

Introduction

The UMTS radio planning process can be divided into three broad areas comprising Input Requirements, Dimensioning and Output Results. The Input Requirements will detail coverage requirements in terms of percentage of population or geographical area, the choice of macro, micro, pico or hierarchical cell structures; capacity requirements based on the types of traffic and services with subscriber growth information; QoS detailing area location probability, blocking probability and service availability. The Dimensioning deals with the capacity and coverage calculations and radio network dimensioning and will take into account a number of constraints that may be forced upon the planning process. The Output Results will give an operator the basic facts to begin building a UMTS radio network in terms of the number of sites, locations, configurations, cell-specific parameters, number of RNCs, capacity and coverage analysis and QoS analysis. For an existing GSM operator existing sites are likely to be used for UMTS. This may not always be an ideal solution, but offers considerable cost savings as well as minimizing the site acquisition process. Data from the existing GSM network can be used, including traffic density information which may identify traffic hot spots. GSM may be used to extend coverage in outlying districts leaving UMTS to target high-bitrate services in areas where they are needed. However, co-siting GSM with UMTS may constrain the network plan. A new operator will have the advantage of starting with a clean slate but will be disadvantaged because rollout of a new network will include radio network planning, transmission planning, site acquisition, CN planning, construction work, commissioning and integration. It may be possible for a new entrant to use the services of third parties for such tasks as site acquisition.

7.1

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Input

Output

Requirements coverage capacity QoS Dimensioning

Constraints

site selection number of sites configuration of sites cell-specific parameters number of RNCs capacity and coverage analysis QoS analysis

Figure 1 UMTS Radio Planning Process MB2005/S7/v6.2

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Cell Planning for UMTS Networks

2

COVERAGE REQUIREMENTS

An operator may aim to provide 99% coverage for a populated area while maximizing geographical coverage. However, a 3G licence may dictate that only 80% of the population is covered within five years of launch. Even 80% coverage may not be necessary in the first years of operation, so an operator may plan to launch with 50% coverage. So, starting in the areas of major population an operator may roll out a network in three stages: 50%, 80% and finally 99%. An existing GSM operator will already have potential subscriber density information allowing coverage planning to be focused on areas of existing subscriber density. A new entrant may not have that luxury, and will therefore have to rely on population density information and potential market penetration figures to identify key areas of radio coverage. Figure 2a shows the relationship between percentage population and percentage geographical area. 50% of the population is likely to be located in 10% of the landmass. To provide 80% coverage, only 30% of the land mass needs radio coverage. 99% coverage equates to 84% of the landmass. Using morphology distribution information as illustrated in Figure 2b, it is possible to identify what percentage of landmass is covered by different clutter types such as dense urban, urban, commercial/industrial, suburban, forest and open. These proportions will aid in estimating the number of sites. This type of information is also available for radio planning tools in the form of clutter data. Such data overlaid onto terrain height data will quickly allow potential sites to be located. When planning coverage using a radio planning tool, information will be required concerning power levels in different environments; dense urban, suburban, etc. The power levels chosen will depend upon the service being planned for and the path loss and penetration losses that can be expected. With this information the planning tool can then statistically analyze and display whether the target signal level has been achieved.

7.3

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a) Population Distribution

Area % (Total: 244100 km2 incl lakes)

100 90 80 70 60 50 40 30 20 10 0 0

10

20

30

40

50 %

60

70

80

90

100

b) Morphology Distribution Coverage Area

50% pop

80% pop

Dense Urban

0.07

0.06

Urban

0.25

0.15

Commercial/Industrial

2.59

2.00

Suburban

10.20

10.00

Open

57.00

60.00

Figures are for illustrative purposes only Figure 2 Coverage Requirements MB2005/S7/v6.2

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Cell Planning for UMTS Networks

2.1

Coverage Scenarios

Design philosophy for CDMA can be based on two scenarios for coverage.

2.1.1

Full Coverage Scenario

In this case it is assumed that the aim is to provide the same coverage for all services within a given target area. This implies that services using higher bit rates must operate at higher power because of their lower spreading factor.

2.1.2

Concentric Coverage Scenario

This scenario assumes only one service is offered across the whole cell area (in general the lowest data rate service), whereas the remaining services are only offered across a reduced area nearer to the base station. It can be assumed that the area of the service with the lowest data rate corresponds to the cell area. The coverage radii of all other services, with higher data rates, are smaller. This results in a series of concentric service areas. Potential users of the higher-data-rate service will not be served in the outer zones of the cell. Since the coverage is not homogeneous for all services throughout the system, user distribution has to be determined for each service. Mobile transmit power is then assumed to be set to maximum for each service.

7.5

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Range for all services

Full Coverage Scenario

Range for lowest data rate service

Concentric Coverage Scenario High data rate service

Medium data rate service

Figure 3 Coverage Scenarios MB2005/S7/v6.2

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Cell Planning for UMTS Networks

3

CAPACITY REQUIREMENTS

Capacity and coverage are strongly interlinked and cannot be planned separately as with 2G networks. What will be required is a good long term plan from the start, which means predicting traffic levels five years hence. It is difficult to say what the uptake of 3G services will be, or what services may become available, but it may be possible to predict the potential number of subscribers from a number of growth forecast assumptions. Figure 4 illustrates subscriber growth over a 14-year period for 2G networks supporting speech only and 3G networks supporting a mix of speech and data. The table assumes that 3G services are launched in Year 3. After that date there would be a steady decline in the number of subscribers using voice only services on 2G networks. After launch of 3G voice and data services it is anticipated there will be an initial surge in the number of subscribers but after 5 years this will level out at a steady growth. The figures are not representative of any particular network but illustrate potential subscriber growth.

7.7

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Subscribers (millions) Year

Year 1

Year 2

Year 3

Year 4

Year 5

Year 6

Year 7

0.75

1.0

1.209

0.6

0.4

0.3

0.2

0

0

0.3

0.7

1.0

1.2

1.4

Total

0.75

1.0

1.2

1.3

1.4

1.5

1.6

Year

Year 8

2G voice 3G voice + data

2G voice 3G voice + data Total

Year 9 Year 10 Year 11 Year 12 Year 13 Year 14

0.15

0.1

0.05

0.05

0

0

0

1.5

1.6

1.7

1.75

1.75

1.8

1.85

1.65

1.7

1.75

1.8

1.75

1.8

1.85

Figure 4 Subscriber Growth MB2005/S7/v6.2

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Cell Planning for UMTS Networks

3.1

Capacity Issues

In order to quantify capacity requirements it is important to identify key demographics and usage patterns.

3.1.1

Demographics

Accurate demographic information is critical to 3G planning. Many of the advanced services to be offered are targeted on the basis of lifestyle. This means simple data on population density is insufficient on its own, it must include information on activity: • Where do people spend their leisure? • Where do people travel? • Where do people work? • Where do people live?

7.9

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Where do people spend their leisure?

Where do people travel?

Where do people work?

Where do people live?

Figure 5 Demographics MB2005/S7/v6.2

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Cell Planning for UMTS Networks

3.1.2

Usage Patterns

The way subscribers will use their UMTS terminals can only be guessed at today. Operators will almost certainly target one or more market segments. Their understanding of their subscribers’ usage patterns will be essential, not only for maintenance of the network, but also during the network design process. Usage patterns can be defined in terms of: Usage High data/high voice High data/low voice Low data/high voice Low data/low voice Time Call durations Time of usage Location High-rise Dense city Town Residential Journeys Mobility High mobility Low mobility Fixed line replacement From these categorizations, it is possible to build up standard usage tables to help plan radio network capacity.

7.11

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usage

time

location

mobility

Figure 6 Usage Patterns MB2005/S7/v6.2

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Cell Planning for UMTS Networks

4

QoS REQUIREMENTS

QoS cannot be treated in isolation because it is closely interlinked with coverage and capacity. With a UMTS network it will no longer be a case of ‘Is the coverage good enough in this location?’ but of ‘Is the quality good enough?’. But coverage will have a huge impact on quality. It may be desirable to identify location probabilities in different environments for the various types of service to be supported. See Figure 7. The UMTS QoS guidelines offer the operator the ability to set up a wide variety of QoS levels. The levels are set by parameter values, which are wide ranging. Because it is the end user that will perceive the quality of the network it is important to identify factors affecting quality from the user’s point of view. These can be broadly divided into Call Set-up Quality and Call Quality.

7.13

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Cell Planning for UMTS Networks

Bearer Service Coverage Probabilities 64 kbit/s CS

144 kbit/s CS

64 kbit/s PS

144 kbit/s PS

384 kbit/s PS

Dense Urban

Indoor 95%

Indoor 95%

Indoor 95%

Indoor 95%

Indoor 95%

Urban

Indoor 95%

Indoor 95%

Indoor 95%

Indoor 95%

Indoor 95%

Industrial/ Commercial

Indoor 90%

Indoor 95%

Indoor 95%

Indoor 95%

Indoor 90%

Suburban

Indoor 90%

Indoor 90%

Indoor 90%

Indoor 90%

–

Open

In-car 90%

In-car 90%

In-car 90%

In-car 90%

–

Area

Figure 7 Coverage Probabilities MB2005/S7/v6.2

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Cell Planning for UMTS Networks

4.1

Call Set-up Quality

This is what the user sees when attempting to set up a call in a UMTS network. It can be characterized by Accessibility, Call Blocking Probability and Call Set-up Delay.

4.1.1

Accessibility

This defines how easy it is for a user to access services on the network and will be influenced by: • lack of coverage • cell barring • equipment failure • signalling failure In terms of network reliability, equipment failure rate should be less than 0.01%, which equates to less than ten seconds in any 24-hour period.

4.1.2

Call Blocking Probability

This is the probability of a call not being processed because of lack of resources on the air interface or on a transmission line. For circuit-switched traffic the blocking probability would typically be between 1–3%.

4.1.3

Call Set-up Delay

This is the end-to-end delay the user sees when accessing a service. This will depend on what that service is. Figure 8 illustrates suggested call set-up times for a variety of UMTS services.

7.15

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Call Type

Set-up Time

Switched Voice Call

< 3s

Circuit-Switched Video Call

< 3s

Voice Call IP Based

< 4s

Real-Time IP Streaming

< 10s

Interactive IP Web Browsing

< 4s

Background e.g. e-mail

N/A

Figure 8 Call Set-up Delay MB2005/S7/v6.2

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Cell Planning for UMTS Networks

4.2

Call Quality

Call quality can be defined in terms of the user’s perception once the call is established. It can be categorized by: • delay variation • service interruption • call drop probability

4.2.1

QoS Classes

The QoS will vary from service to service and need not be constant across the entire network. It may therefore be useful for an operator to create a number of QoS profiles as illustrated in Figure 9. There are four broad classes of profile; conversational, streaming, interactive and background. An example of a conversational service would be speech or video conferencing characterized by delays of less than one second. Streaming audio or video would have longer delays, but less than ten seconds. Interactive services include web browsing with delays of approximately one second. Background services would include email and fax transmission where delays may exceed ten seconds. Profiles, however, would also specify other QoS parameters as illustrated in Figure 9.

7.17

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QoS 99 Parameter Traffic Class

VoIP

Web Audio Streaming Browsing

E-mail

Conversational Streaming Interactive Background

Max UL Bit Rate

64 kbit/s

5 kbit/s

64 kbit/s

128 kbit/s

Max DL Bit Rate

64 kbit/s

64 kbit/s

64 kbit/s

128 kbit/s

Guaranteed UL Bit Rate

36.4 kbit/s

5 kbit/s

N/A

N/A

Guaranteed DL Bit Rate

36.4 kbit/s

64 kbit/s

N/A

N/A

Residual BER

10–4

10–4

10–6

10–6

Transfer Delay

200 ms

250 ms

N/A

N/A

Delivery Order

yes

yes

N/A

Yes

Figure 9 QoS Profiles MB2005/S7/v6.2

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Cell Planning for UMTS Networks

5

PLANNING CONSTRAINTS

There are a number of factors that must be taken into account in the planning process that are not adjustable. These parameters will constrain the network plan.

5.1

Spectrum Availability

Most UMTS licences are for three WCDMA carriers. In several countries, however, some operators have only been allocated two carriers. This places severe limitations on the design of the network architecture and may restrict capacity enhancement. A further complication is spectrum usage from adjacent operators, who can cause significant adjacent channel interference and thus create dead zones around an operator’s base station.

5.2

Emission Limits

Most countries have their own standard emission limits for radio base stations. These limits are usually broken into public exposure limits and occupational limits. In the United Kingdom, the National Radiological Protection Board (NRPB) has defined these limits. Throughout the European Union, new, tighter emission limits defined by the International Committee for Non-Ionizing Radiation Protection (ICNIRP) are being introduced. Maximum EIRP is also limited by the license terms.

5.3

Site Locations

Site acquisition is becoming increasingly difficult with most prime sites already taken for 2G installations. A 2G operator will be forced to use many of the existing sites because of cost. These sites may not always be the most suitable for 3G services. A new entrant may be forced into site sharing. Site location will therefore become a significant input into the planning process rather than an output, as would be ideal.

5.4

Antennas

In the early stages of UMTS roll-out similar antennas to those used in 2G networks will be utilized. Later, more capacity could be found by using beamforming or adaptive antennas. There are increasingly more multiband antennas entering the market. These fall into one of two categories: wideband and dual/triband antennas. Such antennas may be ideal for an operator co-siting GSM with UMTS because of their low visual impact, but may constrain the network plan.

7.19

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spectrum availability

emission limits

site locations

antennas

radio link budget

costs

Figure 10 Planning Constraints MB2005/S7/v6.2

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7.20

Cell Planning for UMTS Networks

5.5

Radio Link Budget

Different link budgets will be required for different traffic types. In a CDMA system, link budgets should be considered as dynamic rather than static.

5.6

Costs

Experience from many GSM networks would suggest that radio planning and economic planning are two separate functions that frequently clash. However, they must be considered as two inputs with a common goal if a quality network is to be built and to survive.

7.21

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spectrum availability

emission limits

site locations

antennas

radio link budget

costs

Figure 10 (repeated) Planning Constraints MB2005/S7/v6.2

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7.22

Cell Planning for UMTS Networks

6

FORMING THE OVERALL RADIO NETWORK PLAN

An effective overall plan requires coordinated consideration of coverage requirements, traffic density and QoS targets. Regarding these as three input layers, they must be geographically referenced onto a map to allow each geographic area to be associated with an architectural option suiting its needs. This will include coverage requirements on a service-by-service basis, QoS requirements on a service-by-service basis, spectrum usage and hierarchical layers. The resulting architectural output forms the basis of the radio network plan.

7.23

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Coverage Requirements

Traffic Density Mapping (Raster)

QoS Targets

Resulting Network Map/Architecture

Figure 11 Forming the Overall Radio Network Plan MB2005/S7/v6.2

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7.24

Cell Planning for UMTS Networks

7

DESIGN PROCESS IN DETAIL

A radio planning tool will be used to create a detailed plan on the UMTS network. The flow chart in Figure 12 illustrates the basic steps. To create a nominal cell plan the following information will be required: • carriers – for interference evaluation • services – to characterize bearers, e.g. packet or circuit switched, bit rates, required Eb/No values, QoS values • terminals – detailing transmit power levels and fast power control parameters • cells – locations in the area to be planned • cell parameters – antenna height, gains, transmit power, codes, channels • prediction model – macro cell model or micro cell model • traffic – detailing terminal density The nominal plan will allow the planner to see if there is adequate coverage in the areas of interest, for example that power levels are high enough to offer indoor coverage. Once satisfied with the nominal plan the next step is to simulate the behaviour of a WCDMA network

7.1

Monte Carlo Simulation

In first- and second-generation networks coverage was determined by the link budget with margins added to take into account fading problems. Fast fading has a Rayleigh distribution and slow fading a log-normal distribution allowing fading margins to be added to the link budget based upon statistical probabilities. This process was also done in early CDMA networks with gains added to the budget to account for soft handovers. However, this approach could not take into account intra- and inter-cell interference. From an uplink point of view, this would be caused by mobiles in the serving cell and neighbouring cells. The extent of this interference would depend upon the mobiles’ transmit powers and relative positions. Using statistics to derive a margin gives misleading results; what is required is some means of simulating the random behaviour of mobiles. Monte Carlo algorithms can be used to simulate this randomness and provide a good balance between accuracy and practicality. The mobile terminals are randomly distributed across the network and tested for probability of satisfactory service support. The terminals are redistributed randomly and tested again. This process is repeated over and over again and accounts for the random behaviour of the mobiles and radio environment. The snapshots are then used to obtain measurement information giving an indication of the network performance. If the design criteria are met a final plan may be produced, otherwise the initial plan needs to be reassessed.

7.25

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Start

Produce Nominal Cell Plan Adjust Inputs

Simulation

Analyze Problems

No

Design Criteria Met? Yes Produce Final Plan

Stop

Figure 12 Design Process Details MB2005/S7/v6.2

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7.26

Cell Planning for UMTS Networks

7.2

Simulation Process

Figure 13 details the Monte Carlo simulation process. Set Initial Conditions Firstly the mobile terminals are given a random priority level and will be tested in order of priority. This is to ensure there is no biasing of the results. The terminals are then placed in statistically determined positions before having their transmit powers initialized. The power levels are set to fulfil the Eb/No requirement at the base station taking into account the base station sensitivity, data rate and the path loss. These will be adjusted by considering the soft handover gain and activity factor. The base station power is also initialized in a similar way to ensure all mobiles receive an adequate signal level. By initializing the transmit powers in the cell, the initial noise rise can be determined. Creating a Snapshot The first terminal in the list is tested for satisfactory performance. If it fails it is placed to outage and the next terminal is chosen. If it does not fail then its transmit power and that of the base station are modified, simulating power control. Potential handover cells are tested for handover. If a handover is possible, mobile and base station powers are adjusted accordingly. Then the next terminal in the list is chosen. Once all of the terminals have been tested the simulator returns to the first terminal and repeats the process until there is little change in the noise rise. The results are then said to have converged. Typically only a few iterations are needed before convergence is reached and the results of the snapshot can be appended to the overall simulation. Redistribution The simulator will then redistribute the terminals to represent the random behaviour of terminals and the simulation is repeated. After many thousands of iterations, the results of the simulation can be analyzed. Arrays can then be created quantifying the probability of satisfactory performance.

7.27

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Cell Planning for UMTS Networks

Start

Randomly prioritize terminals Place terminals in statistically determined positions Initialize cell and mobile transmit powers

Assess Performance for all user terminals

Redistribute user terminals

No

Snapshot or drop

Have results stabilized (converged)

Yes Analyze results of simulation

Analyze problems, implement corrections and re-run simulation

No

Satisfactory performance ?

Yes

Produce final plan

Figure 13 Monte Carlo Simulation MB2005/S7/v6.2

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Cell Planning for UMTS Networks

8

BORDER REGIONS

8.1

Border Region Problem

In any cellular system where there has been international cooperation regarding spectrum allocation, there will be potential interference problems in border regions. This is because in these regions there will be neighbouring operators utilizing the same spectrum allocation. This is usually dealt with by common agreement for restricted spectrum use in these regions, i.e. each operator agrees to use different subsets of their total spectrum allocation. This limited amount of cooperation between operators is sufficient to prevent serious problems. In principle a similar approach could be taken in a CDMAbased system, particularly for second-generation systems. However for thirdgeneration systems, such as UMTS, the width of a radio channel results in limited scope for such spectral cooperation. An operator may have only two or three FDD carrier pairs, in some cases they may have only one. In addition, radio carrier centre frequencies are not fully standardized. The result is that spectral cooperation may not be sufficient to prevent serious interference problems in border regions.

7.29

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Cell Planning for UMTS Networks

F1

F1

F1

?

wray castle Brows er Interne

t Search

: http// www. XX XX XX XXxxx

XXX XXX XXX XXX XXX XXX XXX XXX

XX XXX XXX XXX xXX XXxxxX XX X X XXX XXX XXXXXX Xxx xxx XXX XX XX

XxX XXX X XXX XXX

X

1

XXX

2

4

3

5

7

8 0

6 9

F1

F1

F1 International Border Figure 14 Border Regions MB2005/S7/v6.2

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Cell Planning for UMTS Networks

8.2

Border Strategies

Although spectral cooperation may not be the whole solution, there is still some scope for its use. Where bordering operators have more than one radio carrier available and where their centre frequencies are the same, agreement could be reached on limited use. This would limit capacity in border regions, but in many cases these are not areas likely to present high traffic load and thus it may be an acceptable compromise. In some cases an operator may be able to absorb some of the loss in UMTS capacity by handing down to GSM/GPRS. However, there will be areas where a reduction in capacity will not be acceptable; in these areas a more radical solution is required.

8.2.1

Inter-System Handover

If operators cannot tolerate the loss in capacity that would be associated with spectral cooperation, co-channels will need to be allocated in neighbouring, or in extreme cases, co-sited cells. These cells would be separated by code, but in order to meet the stringent requirements for power control, soft handover must be provisioned between cells. Thus inter-system handover will be required between operators in border regions. The implications of this are considerable. Some are listed below: • interconnection of CN • interconnection of the UTRAN • cooperation on handover parameter setting • cooperation over service provision • cooperation over UL code allocation • cooperation over radio resource management • cooperation over admission control

7.31

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External Networks

Core Network Operator 1

UTRAN Operator 1

Inter-operator links

Inter-operator links

wray cas Internet Search:

Core Network Operator 2

UTRAN Operator 2

r

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Figure 15 Border Strategies MB2005/S7/v6.2

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7.32

Cell Planning for UMTS Networks

9

SECTION 7 QUESTIONS

1

In relation to an initial UMTS radio planning model, which of the following statements is incorrect? a b c d

2

Coordination of code usage is required at international boundaries Cell breathing does not affect soft handovers Link symmetry impacts on cell range Coverage is affected by the number of active users in a cell

In relation to a planning philosophy, which of the following statements is true? a QoS is not constant everywhere b Coverage, quality and capacity are not necessarily related c A planning model is considered as having three inputs: requirements, standard inputs and constraints d QoS is constant everywhere

3

When determining a subscriber’s profile which of the following may be disregarded? a b c d

4

When assessing possible usage patterns, which of the following can be ignored? a b c d

7.33

The user’s speed The user’s priority The user’s location The user’s antenna

A user’s mobility The time a user is likely to require network services A user’s location The user’s type of user equipment

© wray castle limited

MB2005/S7/v6.2

Cell Planning for UMTS Networks

MB2005/S7/v6.2

© wray castle limited

7.34

Cell Planning for UMTS Networks

7.35

© wray castle limited

MB2005/S7/v6.2

Cell Planning for UMTS Networks

ANNEX TO SECTION 7

CELL DIMENSIONING FOR FULL AND CONCENTRIC COVERAGE SCENARIOS

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7.36

Cell Planning for UMTS Networks

DETAILED PROCESS

1

The first step of the dimensioning process consists of fixing the cell loading assumption for the UL. The initial value of XUL is chosen arbitrarily according to the planner’s experience.

2

Calculate the mobile transmit powers for the full coverage scenario and the concentric coverage scenarios.

3

Calculate the pole (theoretical absolute maximum) capacities for both links.

4

When the cell loading has been fixed for the UL, the number (NkUL ) of mobiles using service k within the UL of one cell, for all services (k), can be derived, which is only valid for the assumed UL loading factor.

5

The DL loading factor XDL has to be modified in order to achieve the same number of users for service k in UL and DL. Since the loading factor of one link constitutes a percentage of its pole capacity, the ratio between the loading factors x = XUL/XDL leading to an equal number of users in both links is reciprocal to the ratio of the corresponding pole capacities.

6

The assumption of a UL cell load therefore directly implies a DL cell load. The ratio x = XUL/XDL between the UL and the DL loading has to remain constant in order to maintain the equilibrium on the links in terms of number of users for a given service k in one cell.

7

Calculate the receiver sensitivity and the Maximum Allowable Path Loss (MAPL) for the UL for the different services. In the full coverage scenario, the MAPL is the same for all the services, because the mobile transmitting powers have been fixed to fulfil the condition of same service radii for all services, which are directly related to the MAPL by the propagation model. In the concentric coverage scenario, there will be one MAPL for each service.

8

In order to balance UL and DL, the UL MAPL results are taken as input for the DL budget, adding a margin for the PCCPCH and the synchronization.

9

Fixing the MAPL derives the DL transmission power share Ti,k for each connection i of service k. Summing up all service power shares determines the total transmission power Ttotal. This sum of all output powers must not exceed the maximum DL transmission power. If this occurs, the system is DL-limited and the UL powers will have to be reduced accordingly.

7.37

© wray castle limited

MB2005/S7/v6.2

Cell Planning for UMTS Networks

Full Coverage Scenario

Choose Dimensioning Scenario

Concentric Coverage Scenario

1 2

Calculate Mobile Transmit Power values (includes ii0 calculation) Calculate Pole Capacities NULpole and NDLpole Calculate number of users Nk for all services k and Derive downlink cell load xDL Calculate the MAPLUL and the cell radius r

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8

Calculate number nkarea of users for each service k located within the cell area

with nkarea