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Page 1: WCDMA Radio Network Coverage Planning

WCDMA Radio Network Coverage Planning

Huawei Technologies Co., Ltd.

All rights reserved

Page 2: WCDMA Radio Network Coverage Planning

WCDMA Radio Network Coverage Planning Confidentiality level: Customer

Mexico Training Center Confidential information of Huawei. Page 2/50

Page 3: WCDMA Radio Network Coverage Planning

WCDMA Radio Network Coverage Planning Confidentiality level: Customer

Mexico Training Center Confidential information of Huawei. Page 3/50

Revision Record

Date Version Change description Author

30-06-2007 1A Victor Toledo

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Table of Contents

1 Process of WCDMA Network Planning ............................................................. 9

Overview of Radio Network Planing .............................................................. 9

Huawei concept of Network Planing ............................................................ 11

Process of Wireless Network Planning ........................................................ 13

Process of Radio Network Planning ........................................................... 14

Radio Network Dimensioning ...................................................................... 15

Radio Network Pre-planing ......................................................................... 16

Radio Network Cell Planing ........................................................................ 18

Radio Network Cell Planing-Site Survey ..................................................... 20

Radio Network Cell Planing-System simulation .......................................... 20

2 Uplink Budget ................................................................................................... 27

Capacity-Coverage-Quality.......................................................................... 27

Fundamental Principle ................................................................................. 28

Algorithm Introduction.................................................................................. 28

Elements of WCDMA Uplink Budget............................................................ 29

3 Down link Budget.............................................................................................. 42

Fundamental Principle ................................................................................. 42

Elements of WCDMA Uplink Budget ............................................................ 43

4 Coverage Enhancement Technologies ........................................................... 46

Tower mounted Amplifier ............................................................................. 46

Academic calculation About TMA ................................................................ 47

4 Antennas Reception Diversity .................................................................. 48

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Objectives

Upon completion of this module, you will be able to:

� Know the contents and process of network planning.

� Understand the uplink budget and its elements.

� Understand the downlink budget and its elements.

� Familiarize the coverage enhancement technologies.

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1 Process of WCDMA Network Planning

Overview of Radio Network Planning

� Definition:

� Network planning means that proper network elements (NEs) are

selected according to the network target, network evolution requirement,

and cost, and then the quality, configuration, and connection mode of the

NEs are determined to facilitate engineering implementation.

� Categories:

� Planning of core network

� Planning of radio network

� Planning of transmission network

Importance of Radio Network Planning in 3G

� The construction cost of the mobile communications network mainly

lies in the equipment investment.

� Among the three parts of the 3G network (radio access network,

transmission network, and core network), the radio access network

occupies more than 70% investment.

� The investment in the radio access network depends on the number

and configuration of the BSs.

The investment in the radio access network depends on the number and

configuration of the BSs, which are determined by the radio network planning.

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Figure 1.- Comparison between WCDMA Network Planning and GSM.

The WCDMA system uses 1×1 frequency multiplexing. It distinguishes cells and

subscribers through scrambling and OVSF codes. The capacity and coverage of the

WCDMA system are affected by the network interference. The network planner needs to

consider how to reduce the interference. The GSM system uses the TDMA technology. It

distinguishes subscribers through frequency and timeslot. Therefore, the capacity of the

GSM system is mainly affected by the frequency resource and the frequency

multiplexing technology.

The WCDMA system is an interference-limited system. Its coverage depends on the

maximum transmit power and system load. The higher the system load, the higher the

noise, and the smaller the system coverage, and vice versa. However, if the frequency is

well planned and there is no external interference, the coverage of the GSM network is

only related to the maximum transmit power, and its capacity is only related to the

number of available channels. The capacity is not related to the coverage. Therefore, in

designing the WCDMA system, the relationship between capacity and coverage shall be

considered to ensure the required system KPI.

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In the WCDMA system, the power resource is limited. Therefore, the goal of either

power control or RRM algorithm is to save network resources and minimize the transmit

power of the service channels as well as ensuring the communication quality. These

factors shall be considered in configuring cell parameters. In the WCDMA system, pilot

pollution greatly affects the network performance. In the GSM system, because the

BCCH frequency is loosely used (for example, 5×3) and well planned, pilot pollution

rarely occurs.

Huawei Concept of Wireless Network Planning

� Optimal coverage for profitable services

� The 3G network is a multi-service network, so the network resources

need be distributed among different services. The cell radius and coverage

scheme should be determined after the profitable services and their

coverage quality are determined. At the early stage of the 3G network, if

the planning focuses on high-speed data service, it will result in waste of

the BSs because there are not enough services.

� Competitive core service

� Core service refers to the service that has a long-term effect on the

network development. It is possible that the core service is not profitable in

a short period, but is the attraction of the subscriber increase and service

development, for example, high-speed data service. Therefore, the quality

of the core service should be guaranteed in order to show the service and

performance advantages of the 3G network and promote the operator's

brand.

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For an operator, the ultimate goal of network construction lies in profit. In the

preliminary planning, the future capacity expansion as well as the cost of network

construction should be considered. If the overall network performance is ensured, the

cost shall be as low as possible. The cost includes network construction cost and

operating cost. The cost goes with the lifecycle of the network. In the planning, the focus

should be on the network construction cost, and the scheme requiring lowest cost shall

be selected. For example, in the urban area, the cost of site increases gradually.

Therefore, the inter-site distance should be reasonable in order to avoid frequent site

addition for capacity expansion, thus effectively reducing network construction cost.

Compared with the 2G network, the 3G network provides much more services.

Some high-speed services are attractive to subscribers, but they require many resources,

so that they may be not profitable. So far, most of the profit of the operator derives from

voice service. In network construction, the coverage and quality of profitable services

should be guaranteed.

� Highest capacity based on limited resources

� The capacity of the 3G network is mainly affected by interference.

Reasonable parameter planning may help to reduce intra-cell and inter-cell

interference, improve the cell capacity, and make full use of the limited

resources.

It is hard to ensure highest capacity based on limited resources. In the 3G network,

the network capacity is closely related to coverage and quality. If the coverage and

quality are balanced, the key is to control interference effectively through different means.

Huawei provides reliable and effective power control and radio resource

management algorithm by using abundant test data and advanced simulation means.

They are proved in many customers of Huawei around the world. Huawei has drawn rich

related experience.

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� Lowest overall cost of network construction

� The construction of the radio network goes through the lifecycle of

the network. In the planning, further development shall be considered, in

order to reduce the total cost of network construction.

Core service is different from profitable service. Core service refers to the

characteristic service that is most attractive to the subscribers and is profitable to the

operators. It is possible that the core service is not profitable in a short period. The

quality of the core service should be guaranteed, in order to promote the network brand.

Process of Wireless Network Planning

� Radio Network Dimensioning (RND)

At the early stage of the project planning, the future network is preliminarily planned,

and the configuration and the number of RAN NEs are output for preliminary project

negotiation and for cost estimation in contract signing.

RND is rough.

� Pre-planning of radio network

At the mid stage of project planning, based on the dimensioning output, the future

network is planned in detail, and the accurate network scale and theoretical site location

are determined. A pre-planning report will be output for mid-stage project and cost

estimation in contract signing.

Pre-planning is detailed.

� Cell planning of radio network

At the later stage of project planning, based on the pre-planning output, each

selected site is surveyed, and the related cell parameters are determined. If the result is

quite different from the planning, the cell parameters and planning effect should be

checked through simulation, and the output report would be the final radio network

planning scheme that can guide the project implementation.

Cell planning is precise.

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Process of Radio Network Planning

Figure 2.- Radio Network Planning Process.

According to the above figure, the output result of the budget stage serves as the

input condition of the pre-planning, and the pre-planning is based on the network

dimensioning and also checks the network dimensioning. The site quantity can be

adjusted according to the pre-planning result in order to obtain the theoretically

reasonable sites. If the existing sites are considered in the selection of theoretical sites

during the pre-planning, the pre-planning result will be more practical, thus facilitating the

cell planning.

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Radio Network Dimensioning

� Radio network dimensioning is a simplified analysis of the future network.

� Objective:

To obtain the network scale (Approximate BS quantity and configuration),

to obtain the construction period, and to obtain information such as

electronical cost and human resource cost.

� Method:

Select a proper propagation model, and subscriber mobility, distribution,

and traffic models, and then estimate the site quantity, cell quantity,

coverage size and capacity.

Requirement of RND parameters

� Information of coverage area

� The engineers of RNP should know exact information about

coverage area ,for example :

− Area , economy, population

− Distribution of cluster

− The information of mobile communication market

� Target of network

� The target of network should include several factors:

− Service

− Coverage area & Coverage quality

− Network Capacity

− Target load of cell

� Limited by network scale & Building plan in different phase

� Base on commercial contract

� Base on RND result if there is no commercial contract

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� Information of available site

� For a new operator who doesn’t have abundant 2G mobile

communication network sites, the RNP engineer should collect exact

information about available site.

Radio Network dimensioning

Figure 3.- Inputs and Outputs of the Radio Network Dimensioning.

Radio Network Pre-planning

� Based on radio network dimensioning, the network pre-planning intends to

determine the initial layout and theoretical location of the BSs and select

engineering parameters (BS location, network hierarchy, transmit power, antenna

layout/type/direction/tilt angle, and so on) and some cell parameters (common

channel, transmit power of traffic channel, orthogonal factor, cell scrambling code,

and so on) .

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Figure 4.- Initial layout of NodeBs from pre-planning process.

Wireless network dimensioning intends to obtain the approximate BS scale. Based

on the network dimensioning, geography and traffic distribution, the network is pre-

planned in detail by using planning software and digital map. The engineering

parameters (BS location, network hierarchy, transmit power, antenna

layout/type/direction/tilt angle, and so on) and some cell parameters (common channel,

transmit power of traffic channel, orthogonal factor, cell scrambling code, and so on) are

determined.

Based on the network dimensioning and site information, the initially selected

WCDMA BS is imported into the planning software, and coverage is estimated by setting

the cell parameters and engineering parameters. Then an analysis is made to check

whether the coverage of the system meet the requirements. Then the system capacity is

analyzed to check whether it meets the requirement. If necessary, the height and tilt

angle of the antenna and the BS quality are adjusted to optimize the coverage.

� Based on the result of RND, theoretical location of site, parameters of

project, parameters of cell, We should carry out coverage simulation.

� We should carry out more detailed adjustment (for example amount of

NodeB, configuration of NodeB, antenna altitude, antenna azimuth) after

analyzing the results of coverage simulation.

� Finally, we should get perfect coverage result.

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Figure 5.- Pilot Ec/Io and Best server by pilot from simulation tool.

� Radio Network Pre-planning report

� We should output Radio Network Pre-planning report after finishing

previous jobs. Radio Network Pre-planning report should include following

factors:

− Introduce of project background

− Information of planning area :area, population, cluster

− Project of radio network pre-planning: site distribution map,

site list ( include site name, latitude ,longitude, parameters)

− Performance of project :based on the simulation result

− Appendix: statistical diagram about performance

Radio Network Cell Planning

Figure 6.- Flowchart of cell planning.

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Based on the pre-planning scheme of radio network, sites are selected/surveyed. In

selecting BS site, it is necessary to cooperate with the engineering designer in

considering the feasibility of the construction of equipment room, tower and rooftop as

well as in considering the effect of the antenna height, isolation, and direction on the

network quality.

Based on the site selection/survey, the location of all the sites and the site quantity

are determined. Then the cell parameters are configured to ensure the reliable running of

the network. The network planning parameters include engineering parameters and cell

parameters. All the engineering parameters are determined in the site survey.

Reasonable cell parameters ensure the normal running of the network.

The cell parameters involved in the radio network planning include the following:

system parameters (for example, cell selection and reselection parameters) , basic

channel configuration parameters (for example, power configuration of pilot/common

channel/ dedicated channel and scramble planning) and RRM algorithm configuration

parameters (for example, power control parameters and handover parameter).

The cell parameters directly affect the KPI of the network. In parameter planning, the

basic channel configuration parameters mainly derive from the radio network pre-

planning scheme, including power and scrambling code of different channels, and so on.

The system message parameters mainly derive from the research results of network

planning. The principles for configuring system message parameters in different situation

may be obtained by analyzing the typical network structure and typical coverage

environment. The RRM algorithm parameters are mainly used for control the connected

subscribers. They directly affect the quality and performance of the network.

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Radio Network Cell Planning – site survey

� In fact, perfect site position could not be acquired. We must select some

backup site. But how can we select the backup site?

� Based on experience, backup site is selected in SEARCH RING scope ,

SEARCH RING =1/4*R, at the same time ,we still consider its height.

� We still pay attention to some other factors when we select the backup

sites :

� Radio propagation

− Site position

− Site height

− Surrounding

� Job implementation

− Space of room

− Antenna installation

− Transmission

− Power

� Commercial factor

− Rent

Radio Network Cell Planning – System Simulation

� System Simulation class

� Static simulation

− Static simulation would gain the performance of radio network

based on “snapshot”

� Dynamic simulation

− Dynamic simulation would gain the performance of radio

network based on analysis of mobile subscribers.

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� At present, Static simulation is in common use. Monte Carlo simulation is

one type of static simulations.

Figure 7.- The example of Monte Carlo simulation.

Static simulation focuses on user behavior such as browsing Internet call.

Dynamic simulation focus on detail of user behavior such as duration and data rate

of browsing, and it requires higher precision of e-map.

Figure 8.- Access ratio for static simulation.

Now, we will present some results from simulation tools:

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Distribution of NodeBs

Figure 9.- Distribution of NodeBs.

Simulation diagram – pilot coverage intensity

Figure 10.- Pilot coverage Intensity.

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Simulation diagram – pilot coverage quality (Ec/Io)

Figure 11.- Pilot coverage quality.

Coverage probability of 12.2k voice service

Figure 12.- Coverage probability of 12.2 kbps voice service.

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Coverage probability of 64k video phone service

Figure 13.- Coverage probability of 64 kbps video phone service.

Coverage probability of 144k Net Meeting service

Figure 14.- Coverage probability of 144k Net Meeting service

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Coverage probability of 384k HTTP service

Figure 15.- Coverage probability of 384k HTTP service.

Simulation result about pilot pollution

Figure 16.- Simulation result about pilot pollution.

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Summary of the Section

This Section covered the following:

� Categories of radio network planning

� Huawei concept of radio network planning

� Differences between GSM network planning and WCDMA network

planning

� Process of radio network planning

� Input and output requirements of the radio network pre-planning

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2 Uplink Budget

Capacity–Coverage–Quality

� Relation between capacity, coverage, and quality of the WCDMA system

� The WCDMA system is a self-interference system, and its capacity,

coverage, and quality closely related to each other.

� Capacity–coverage (e.g. cell breath)

− If the load increases, the capacity and interference also

interference and the coverage shrink.

� Capacity–quality (e.g. outer loop power control)

− The system capacity may increase by lowering the quality of

some connections.

� Coverage–quality (e.g. AMRC)

− The coverage may increase by lowering the quality of some

connections.

Process of Coverage Budget

Figure 17.- The process of Coverage Budget.

In the coverage dimensioning, the link is estimated according to elements such as

planned area, network capacity, and equipment performance in order to obtain the

allowed maximum path loss. The maximum cell radius is obtained according to the radio

propagation model of the planned area, and then the site coverage area is calculated.

Finally, the site quantity is calculated. Of course, the site quality is only for the ideal cell

status, and some additional sites will be needed in actual terrain environment.

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Fundamental Principle

Figure 18.- Fundamental principle for link budget.

Link dimensioning intends to estimate the system coverage by analyzing the factors

of the propagation channels of the forward signal and reverse signal. It is the link

analysis model. If the parameters such as transmit signal power, gain and loss of the

transmitter and receiver, interference power, and quality threshold of received signal are

known or estimated, the allowed maximum path loss used for ensuring the quality of

received signal can be calculated. The allowed maximum coverage radius can also be

obtained based on the propagation model. The BS quantity and cell quantity can be

estimated by comparing the area of the planned area and the coverage area of a single

cell.

Algorithm Introduction

Uplink (reverse)

� PL_UL=Pout_UE +Ga_BS+Ga_UE –Lf_BS+Ga_SHO –Mpc– Mf– MI – Lp – Lb –

S_BS

− PL_UL: Maximum propagation loss of the Uplink

− Pout_UE: Maximum transmit power of the traffic channel of the UE

− Lf_BS: Cable loss

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− Ga_BS: Antenna gain of the BS; Ga_UE: Antenna gain of the MS

− Ga_SHO: Gain of soft handover

− Mpc: Margin for fast power control

− Mf: Slow fading margin (related to the propagation environment)

− MI: Interference margin (related to the designed system capacity)

− Lp: Penetration loss of a building (used if indoor coverage is required)

− Lb: Body loss

− S_BS: Sensitivity of BS receiver (related to factors such as service and multi-path

condition)

According to the signal propagation channel from the transmitter to the receiver, the

uplink budget involves these basic elements: Pout_UE (maximum transmit power of the

traffic channel of the BS), Lf_BS (cable loss), Ga_BS (antenna gain of the BS), Ga_UE:

(antenna gain of the MS), Ga_SHO (Gain of soft handover), Mpc (margin for fast power

control), Mf (slow fading margin, related to the propagation environment), MI

(interference margin, related to the designed system capacity), Lp (penetration loss of a

building, used if indoor coverage is required), Lb (body loss), and S_BS (sensitivity of BS

receiver, related to factors such as service and multi-path condition).

Elements of WCDMA Uplink Budget

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Now, we will explain the 20 link budget elements one by one.

� 1.Max Power of TCH (dBm)

� For a UE, the maximum power of each traffic channel is usually the

nominal total transmit power. There are many types of UE in a commercial network, so

these parameters should be reasonably set in the link budget according to the

specifications of a mainstream commercial cell phone and the requirement of the

operator.

Table I.- Types of UEs.

In Version 3.30, the default value is the lowest power grade, and the UE capacity is

21 dBm.

In network planning, the value should be set according to the UE capacity with

lowest power grade in the commercial network of the operator.

Note that it is possible that a UE supporting high-speed uplink data service (higher

than 64kbps) has a higher power grade than a UE supporting only voice and low-speed

data services, for example, power grade 3dBm ~ 24dBm.

125mW~21dBm

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� 2. Body Loss (dB)

� For voice service, the body loss is 3 dB.

� Because the data service mainly involves reading and video, so the

UE is relatively far from body, and the body loss is 0 dB.

� 3. Gain of UE Tx Antenna (dBi)

� In general, assume that the receiver gain and transmitter gain of the

UE antenna are both 0 dBi.

� 4. EIRP(dBm)

� UE EIRP (dBm)

= UE Tx Power (dBm) - Body Loss (dB) + Gain of UE Tx Antenna (dBi)

Body loss occurs at the UE side, and the value is related to the habit of the

subscribers. In the current version of link budget tool, the assumed default body loss is

as following: UE 3 dB for voice service; because the data service mainly includes read

and video, so the UE is relatively far from body, and the body loss is 0 dB.

EIRP refers to the sum of the transmit power output, loss of the transmitter system,

and the antenna gain of the transmitter of each traffic channel in the direction with

maximum radiation.

EIRP: Equivalent Isotropic Radiated Power

� 5. Gain of BS Rx Antenna (dBi)

Figure 19.- Antenna specifications.

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Antenna gain: It refers to the ratio of the square of the actual field of an antenna at a

point in the space to the square of the field of an ideal radiation unit at the same point in

the space, namely power ratio. It is the gain in the main transmits direction. In general,

the gain is related to the antenna pattern. If the central lobe is narrow and the back lobe

and side lobe are small, the gain is high. If the transmit direction is centralized, the

antenna gain is high. For an Omni directional antenna, the gain in all the directions is the

same.

Front-to-back ratio: It refers to the ratio of the maximum gain in the principal

direction to the gain in the reverse direction. It describes the directing feature. If it is high,

the directed receive performance of the antenna is high.

Beam width: It refers to the separation angle between the main transmit direction of

the power and the point with 3 dB of transmit power reduced, and the area is called an

antenna lobe. Tilt: It refers to the tilt angle of a directional plate antennal. It is used to

control interference and improve coverage.

Polarization: The vector direction of the electrical field in the direction with the

highest radiation. A dual polarized antenna can provide diversity over a single antenna,

thus saving one antenna.

In general, there are two or more lobes in an antenna pattern. The largest lobe is the

central lobe, and others are side lobes. The separation angle between the two half-

power points of the central lobe is the lobe width of the antenna pattern, namely, half-

power (angle) lobe width. If the central lobe is narrow, the directivity is high, and the anti-

interference capability is high.

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� 6. Cable Loss (dB)

� It includes the loss of the feeders and connectors between the

cabinet top and the antenna connector.

− Lower jumper

− Connector

− Feeder

− Upper jumper

− Etc.

� Except for the feeder, the loss is relatively constant. Assume that the

connecter loss is 0.8 dB.

− 7/8-inch feeder: 6.1 dB / 100m for 2GHz

− 5/4-inch feeder: 4.5 dB / 100m for 2GHz

Figure 20.- Components of the antenna system.

Feeder is used to connect the BS and the antenna. In calculating the feeder loss, it

is necessary to consider the loss such as the connectors on both sides of the antenna. In

3G, the feeder is similar to that used in 2G. However, the loss is related to the signal

frequency, so the unit loss of a 3G feeder is slightly higher than that of a 2G feeder.

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� 7. Noise Figure (dB)

� Noise figure (NF): It is used to measure the noise performance of an

amplifier. It refers to the ratio of the input SNR to the output SNR of the

antenna.

� Thermal noise of receiver (unit bandwidth):

− PN = K×T×BW×NF

= -174 (dBm/Hz) + 10lg(3.84MHz / 1Hz) + NF(dB)

= -108 (dBm/3.84MHz) + NF (dB)

If no tower mounted amplifier (TMA) is used, the equivalent noise figure of the

connector on the tower top is equal to the sum of the feeder loss and the noise figure of

the antenna on the cabinet top. Therefore, if no TMA is used, the equivalent noise figure

of the connector on the tower top= NF_BS + feeder loss. If a TMA is used, it is

necessary to consider the noise figure of the TMA.

� 8. Eb/No Required (dB)

� It is obtained through link simulation. It is related to the following:

− Configuration of receiver diversity

− Multi-path channel condition

− Bearer type

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� 9. Sensitivity of BS Receiver (dBm)

� Sensitivity of Receiver (dBm)

= -174 (dBm/Hz) + NF (dB) + 10lg(3.84MHz/1Hz) + required Eb/No (dB) -

10log[3.84MHz/Rb(kHz)]

= -174 (dBm/Hz) + NF (dB) + 10lg[1000 * Rb (kHz)] + Eb/No (dB)

Configuration of receiver diversity (no receiver diversity/two-antenna receiver

diversity/four-antenna receiver diversity)

Multi-path channel condition (TU3/TU50/TU120/HT120/RA120/RA250)

Bearer type (AMR12.2k/LCD64/LCD144/LCD384/UDD64/…)

Sensitivity of BS receiver refers to the signal level required at the input end of the

receiver that can offer the required Eb/(No+Io). It is closely related to the BS noise figure,

channel rate, and demodulation threshold.

Sensitivity: Minimum power of received signal required by demodulation.

� 10. Background Noise Level (dBm)

� External electromagnetic interference sources:

− Wireless transmitters (GSM, microwave, radar, television station,

and so)

− Automobile ignition

− Lightning

− …

� For the planning for a specific area, it is recommended to estimate

the local interference through noise test.

Because of the complexity of the radio environment, if possible, it is recommended

to make a noise test in order to know the local radio environment. The WCDMA system

is a self-interference system, and the interference in the radio environment also affects

the network performance.

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� 11. Penetration Loss (dB)

� Indoor penetration loss refers to the difference between the average

signal strength outside the building and the average signal strength of one

layer of the building.

� The penetration loss is related to building type, arrive angle of the

radio wave, and so on. In the link budget, assume that the penetration loss

is subject to the lognormal distribution. The penetration loss is indicated by

average penetration loss and standard deviation.

� It is uneconomical to provide better indoor coverage through an

outdoor BS. The indoor coverage shall be provided through a reasonable

indoor coverage solution.

� In the actual construction of a commercial network, the penetration

loss margin is usually specified by the operator in order to compare the

planning results of different manufacturers.

� 12. Fast Fading Margin (dB)

� In the link budget, the demodulation performance of the used

receiver is the simulation result based on the assumed ideal power control.

In an actual system, because of the limited transmit power of the

transmitter, non-ideal factors are introduced in the closed loop power

control.

� Effect of power control margin on the uplink demodulation

performance:

− The simulation shows the following: When the Headroom is

large, the target Eb/No set in the outer loop power control is

appropriate to the simulation result under the ideal power control. As

the power margin decreases, the Eb/No gradually increases (if the

power margin decreases by 1 dB, the required Eb/No increases by

about 1 dB). If power control performance is almost not available,

the BER/BLER cannot be ensured.

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� 13. Edge coverage Probability

� When the transmit power of a UE hits the threshold, but the path

loss does not meet the requirements for the lowest receive level, the link

will be disconnected.

� For a UE at a distance of d, the link disconnection probability is as

follows:

� ρ(d) = Pmax_UE – S_min – 10γlg(d),It refers to the difference

between the average loss of the paths at a distance of d and the allowed

maximum path loss for ensuring the connection.

� The average fading component is 0, and the standard variation is σ

Sometimes, the operator needs a coverage probability. In this case, the edge

coverage probability can be obtained through surface integral.

� 14. Slow Fading Margin (dB)

� Key point: Property of normal distribution.

Figure 21.- Normal distribution.

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� Slow Fading Margin (dB) = required edge coverage Probability×Std.

dev. of Slow Fading (dB)

If an RF path is blocked by a building or a natural object, the signal may change

much, which is known as fading. Fading may result in scattering of the signal received at

a fixed distance from the BS. The propagation model is used to estimate the average

signal strength only, which depends on the accuracy and precision of the algorithm.

The signal strength is fluctuant, even though the fast fading is not considered. This

is not embodied in the propagation model.

The deviation (dB) between the local (measured) mean values and the predicted

mean is in an approximately lognormal distribution. The deviation is called log-normal

fading. The possibility for the actual signal strength at the cell border to exceed the

required signal is 50%. Log-normal fading margin is introduced in order to provide a

coverage probability of higher than 50%.

� 15. Uplink Cell Load

� Uplink cell load is used to measure the uplink load of a cell.

� The higher the uplink cell load, the higher the uplink interference.

� If the uplink load is about 100%, the uplink interference becomes

infinite, and the corresponding capacity is the limit capacity.

The theoretical spectrum efficiency of the WCDMA is indicated by a load expression.

( ) ( )( )

∑∑ ⋅+=⋅+=N

jjjN

jULW

vREbvsNoiLi

11

11η

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� 16. Uplink Interference Margin (dB)

Figure 22.- Noise Raise against Load Factor graphic.

In the network design, if the uplink interference margin is high, the network can

support a high load. In case of limited coverage, a low interference margin is

recommended to increase the coverage. In case of limited capacity, a high interference

margin is recommended to increase capacity.

� 17. SHO Gain over Fast Fading (dB)

� The soft handover gain includes two parts:

− Multiple related soft handover branches lower the required

margin for fading, which results in multi-cell gain.

− Gain for the link demodulation of the soft handover –marco

diversity combining gain.

� The SHO Gain over Fast Fading refer to the macro diversity

combination gain.

� This value is obtained through simulation. The typical value is 1.5 dB.

Because of the macro diversity combination, the soft handover reduces the required

Eb/No by a single radio link, which results in additional macro diversity gain. In general,

the soft handover gain is 2 dB~3 dB.

UL

N

jN

TOT

LP

INoiseRise

η−=

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1

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� 18.SHO Gain over Slow Fading (dB)

� As mentioned above, the soft handover gain includes two parts:

− Multiple irrelevant soft handover branches lower the required

margin for fading, which results in multi-cell gain.

− Gain for the link demodulation of the soft handover

− Macro diversity combination gain.

� The SHO Gain over Fast Fading refers to the macro diversity

combining gain.

� This value is obtained through simulation.

Some slow fading between the BSs is irrelevant, and an MS can select a better BS

through soft handover. Therefore, soft handover reduces the lognormal fading and brings

in an anti-fading gain.

� 19. Minimum Signal Strength Required (dBm)

� After the interference factors and the factors degrading the

performance are considered, the signal strength required by the

correct demodulation is receiver sensitivity in the network.

� Minimum Signal Strength Required

= Sensitivity of Receiver (dBm) - Gain of Antenna (dBi) + Body Loss

(dB) + Interference Margin (dB) + Margin for Background Noise (dB)

- SHO Gain over fast fading (dB) + Fast Fading Margin (dB)

If factors such as antenna gain, soft handover link gain, margin for fast power

control are considered based on the static receiver sensitivity, the minimum receive

signal strength for ensuring the link quality can be calculated.

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� Summary: Cell edge path loss

� Based on the maximum path loss allowed by the link, the path loss

at the cell edge can be calculated if the fading margin and soft handover

gain for providing the required edge/area coverage probability and the

penetration loss of indoor coverage are considered.

� Path Loss (dB) = [ EiRP (dBm) - Minimum Signal Strength Required

(dBm) ]- Penetration Loss (dB) - Slow Fading Margin (dB) + SHO Gain over

Slow Fading (dB)

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3 Downlink Budget

Fundamental Principle

Figure 23.- Fundamental Principle of Downlink Budget.

Link budget intends to estimate the system coverage by analyzing the factors of the

propagation channels of the forward signal and reverse signal. It is the link analysis

model. If the parameters such as transmit signal power, gain and loss of the transmitter

and receiver, interference power, and quality threshold of received signal are known or

estimated, the allowed maximum path loss used for ensuring the quality of received

signal can be calculated. The allowed maximum coverage radius can also be obtained

based on the propagation model. The BS quantity and cell quantity can be estimated by

comparing the area of the planned area and the coverage area of a single cell.

Algorithm

Downlink (forward)

� PL_DL=Pout_BS – Lf_BS+Ga_BS+Ga_UE +Ga_SHO –Mpc– Mf – MI – Lp – Lb –

S_UE

− PL_DL: Maximum propagation loss of the downlink

− Pout_UE: Maximum transmit power of the traffic channel of the BS

− Lf_BS: Cable loss

− Ga_BS: Antenna gain of the BS; Ga_UE: Antenna gain of the MS

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− Ga_SHO: Gain of soft handover

− Mpc: Margin for fast power control

− Mf: Slow fading margin (related to the propagation environment)

− MI: Interference margin (related to the designed system capacity)

− Lp: Penetration loss of a building (used if indoor coverage is required)

− Lb: Body loss

− S_UE: Sensitivity of UE receiver (related to factors such as service and

multi-path condition)

According to the signal propagation channel from the transmitter to the receiver, the

downlink budget involves these basic elements: Pout_UE (maximum transmit power of

the traffic channel of the BS), Lf_BS (cable loss), Ga_BS (antenna gain of the BS),

Ga_UE: (antenna gain of the MS), Ga_SHO (Gain of soft handover), Mpc (margin for

fast power control), Mf (slow fading margin, related to the propagation environment), MI

(interference margin, related to the designed system capacity), Lp (penetration loss of a

building, used if indoor coverage is required), Lb (body loss), and S_UE (sensitivity of UE

receiver, related to factors such as service and multi-path condition).

Elements of WCDMA Downlink Budget

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� 1. Downlink Cell Load

Downlink cell load factor is defined in two ways:

� Downlink cell load at the receiver:

� This definition is similar to that of the uplink cell load:

− The higher the downlink cell load, the higher the cell transmit

power, and the higher the receiver interference.

− When the downlink cell load is 100% , the corresponding

capacity is the limit capacity of the downlink.

� Downlink cell load at the receiver: The ratio of the current cell

transmit power to the maximum BS transmit power. Characteristics:

− The higher the downlink cell load, the higher the cell transmit

power. The downlink cell load is related to service type, UE receiver

performance, cell size, and BS capability.

� 2. Downlink Interference Margin (dB)

� Downlink interference at UE receiver:

The downlink load factor is:

� The link budget tool uses the following typical values:

− Orthogonal factor : It is obtained through simulation. It is

related to environment type and cell radius.

− Cell edge adjacent-cell interference factor: 1.78

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N

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T

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N

total

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α

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The downlink interference includes three parts: thermal noise No of UE receiver,

local cell subscriber interference Isc, and adjacent-cell interference Ioc.

The following factors may cause nonorthogonality of the downlink: PSCH 1.Among

the downlink common channels, PSCH and SSCH directly send signature sequence and

is nonorthogonal to the channels (common/dedicated) using OVSF code for spreading

spectrum. The PSCH and SSCH transmits signal at the first timeslot of each frame, and

the power ratio is not high (for example, 5%), so the nonorthogonal factor does not have

much effect. 2. In case of multiple paths, because of the structure of the RAKE receiver,

the demodulation in a path is whitening due to the relative delay of other paths, thus

resulting nonorthogonal interference. This the major source of nonorthogonal factor in

case of multi-path environment. 3. Because of the non-ideal multi-path search

performance and timing accuracy, some energy of the signal of a path in demodulation

may also result in nonorthogonal interference. In the environment in which most of the

paths are direct, this may become the major source of the no orthogonal factor.

For different multi-path environment, the no orthogonal factor changes much. It is

related to the environment complexity and cell radius.

It is hard to analyze the adjacent-cell interference of a single subscriber, because it

is related to cell layout, subscriber location, fading, and so on. The adjacent-cell

interference in the worst environment is distinctly different from that in the common

environment. For the service with contiguous coverage, refer to the analysis conclusion

in "J.S. Lee 1998", where f(j) = 2.5 dB = 1.78 is used for the link budget of the worst case.

For the service with discontinuous coverage, the adjacent-cell interference

dramatically decreases as the distance between the subscriber and the serving cell

becomes short. For simplification, the adjacent-cell interference factor of such service is

considered to be 0.

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4 Coverage Enhancement Technologies

Tower Mounted Amplifier (TMA)

Figure 24.- The use of the Tower Mounted Amplifier.

• No TMA is used

Assume that the noise figure on the cabinet top is 2.92 dB, the feeder loss is 3

dB, the jumper loss is 0.8 dB, and the lightning arrester loss is 0.2 dB. If the

calculated noise figure on the cabinet top is 5.92 dB, the sensitivity is decreased

by 4 dB, which is the sum of the loss of the feeder, jumper, and lightning arrester.

• TMA is used

Assume that the TMA gain is 12 dB, the noise figure is 1.6 dB. Because the

TMA gain is introduced, the NDDL need to be adjusted to ensure a fixed gain of

RF channel. In this case, the noise figure on the cabinet top is 5.27 dB. The

calculated noise figure of the TMA is 2.82 dB. The loss of the feeder between the

antenna and the TMA is 0.3 dB, so the noise figure of the TMA is 3.12 dB.

Therefore, the sensitivity on the antenna top is increased by 2.8 dB.

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Academic calculation about TMA

Academic calculation about TMA improve the uplink receive sensitivity

Figure 25. - Academic calculation about TMA.

The example of academic calculation about TMA

� The example of academic calculation about TMA improve the uplink

receive sensitivity

Table II.- Noise Figures for TMA, cables, connectors and NodeB.

Gain 3.063dB for uplink when using TMA

Receiver Chain Noise Figure

Without TMA: 2.433+2.2 dB

With TMA: 1.57 dB

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4-antennas Reception Diversity

Figure 26.- 4 Rx Diversity.

� 4-Antenna reception diversity

� 4-Antenna reception diversity has two types

� Two Cross-polarization antennas

� Four antennas

� 4-Antenna reception diversity helps to improve the uplink reception

performance

� Improve the uplink coverage and capacity performance

� 4-Antenna reception diversity need equipment support

Figure 26.- Rx Eb/No Reduction with 4 Rx antenna.

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� 4RxDiv principle –diversity gain

� Resist fast fading

� Correlation combination

� Gain relates to multi-path ,service ,speed, antenna performance

� 2RxDiv-> 4RxDiv

� Reduce the requirement of Eb/No

Table III.- Eb/No Improvement with 4 Rx Diversity.

• 4 Compared with a double-antenna receive diversity, 4-antenna

reception diversity requires lower Eb/No. The gain can be embodied by

the uplink coverage or uplink coverage of the BS.

• If the uplink load is constant, the subscriber capacity is in inverse

proportion to Eb/No.

• Eb/No If the uplink load is constant, the improvement on Eb/No may

increase the maximum uplink path loss and ultimately affect the

coverage radius and area of the BS.

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