wcdma radio network coverage planning
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WCDMA Radio Network Coverage PlanningTRANSCRIPT
WCDMA Radio Network Coverage Planning
Huawei Technologies Co., Ltd.
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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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1
1
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
N
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n nj
T
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N
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P
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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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