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ESG
Engineering Services Group


WCDMA Network Planning and
Optimization




80-W0853-1

Revision B

May, 2006




























QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92121-1714
U.S.A.
This technology is controlled by the United States Government.
Diversion contrary to U.S. law prohibited.
WCDMA Network planning and optimization
80-W0853-1
Revision B
May, 2006
Copyright © 2006 QUALCOMM Incorporated.

All rights reserved

ii

80-W0853-1 Rev B



T A B L E O F C O N T E N T S
1
Introduction.................................................................................................. 1
2
WCDMA Network Planning......................................................................... 3
3
WCDMA/UMTS optimization methodology ............................................. 11
4
Conclusion ................................................................................................. 17
5
References ................................................................................................. 19

80-W0853-1 Rev B


iii




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80-W0853-1 Rev B



1 Introduction
The Engineering Service Group at QUALCOMM is working with operators
throughout the world to find solutions to the same four challenges that are
faced repeatedly: 1) sub-optimal RF optimization, 2) difficulty to tune all the
parameters, 3) increasing the reliability of inter-system transition, and 4)
providing better in-building coverage.

These are complex issues, but solving them can be simplified if a proper
deployment process is followed as illustrated in Figure 1, [1], [5]. This
process follows a “divide and conquer” approach, focusing on a selected
variable at each step.

Network Planning
Verify coverage
Define network
Select (re-use)
Deploy all
and capacity
objectives
sites
network nodes
objectives
Initial Optimization
Service
Service
Pre-optimization
RF optimization
Optimization
optimization
verification
(AMR)
(PS and CS)
Continuous Optimization
Commercial
Continuous
launch
optimization

Figure 1: Summary of Network Deployment Steps

From the different phases of network deployment, Radio (RF) network
planning and RF optimization are seen as critical as having long term impacts
on both performance and capacity [6]. Proper RF configuration is so
important that it even impact the coverage continuity (i.e., inter-system
change to GSM [7]) and network evolution, notably with the introduction of
High Speed Downlink Packet Access (HSDPA) [4].
80-W0853-1 Rev B


1




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2

80-W0853-1 Rev B


2 WCDMA Network Planning
Ensuring that the RF coverage is sufficient within the network should start
naturally with a good RF network plan [2]. Network planning is, may be even
more for existing operator, an area that is too often overseen. Greenfield
operator have the advantage of starting from a clean plate while incumbent
operator already have a set of site that they are compelled to use even if these
sites were originally acquire to fit in a network with different coverage and
capacity limitation.

So what is a good RF network plan?

A good network plan should address the coverage and capacity requirement of
the area considered, but also be sufficiently flexible to allow network
expansion without major change of the existing sites.

In WCDMA, the coverage and capacity requirement cannot be considered
independently, but should be planned at the same time with proper guidelines.
This relation between coverage and capacity is often referred to as the
“breathing effect” of WCDMA. Comparing with TDMA/FDMA
technologies, such as GSM, the coverage of a WCDMA network cannot be
planned independently of the load on the network. The load on the network
will impact the coverage in mainly two different ways, depending on which
link (Uplink or Downlink) is considered. On the uplink, as more users are
added to the network, higher noise would be detected at the node Bs. This
increase in noise, called rise over thermal, requires each of the phones or data
cards (UE) to increase its transmit power to overcome this noise increase:
effectively the uplink coverage is reduced by this required increase in transmit
power. This effect has been documented and can be summarized by the rise-
over-thermal versus load curve illustrated in Figure 2: as an example, when
the load is 50% of the pole capacity, the coverage is reduced by a factor of 3
dB.

On the downlink, the breathing effect cannot be quantified so easily as
coverage is impacted by the maximum transmit power assigned to traffic
channels and the current load on the network rather than by a quantifiable
formula.

80-W0853-1 Rev B

3




14.0
] 12.0
B
d
l
[
10.0
rma
e

8.0
h
T
r-

6.0
e
v
-O

4.0
e
i
s
R

2.0
0.0
0%
20%
40%
60%
80%
100%
120%
Loading [% of pole capacity]

Figure 2: Impact of uplink loading on coverage express by the Rise-Over-Thermal, a.k.a.
Interference Margin.


In any case, predicting coverage is easier, in the early stage of network
planning by considering only the pilot channel (CPICH). Once that necessary
step is completed, the coverage should be further verified for both links
(downlink from Node B to UE and Uplink from UE to Node B) and for all
services.

For the downlink, CPICH coverage should be verified by considering not only
if the received signal code power (RSCP) of the pilot channel (CPICH) is
sufficient once all the margins are included, but also by estimating the level of
interference generated by the other cells. Such interference is typically
quantified by the energy per chip to total received power (Ec/No) of the
CPICH. Such quantity effectively estimated how much of the received signal
can be used at a given location, or put it in other word, how clean is the signal
received.

The relation between RSPC and Ec/No is mainly impacted by the loading of
the system and the quality of the network plan. This is illustrated in Figure 3
showing the high range of Ec/No for a given RSCP value. It should be noted
that the quality of the network plan would be reflected by the number of cells
detected at a given location, or to word it differently, the cell overlap: a high
quality network plan would be one where a single cell is detected over the
majority of the cell area and transition between cells are done over clear
boundaries.
4

80-W0853-1 Rev B


0
-2
-4
-6
-8
-10
Ec/No [dB] -12
-14
-16
-18
-20
-120
-110
-100
-90
-80
-70
-60
-50
-40
RSCP [dBm]
Single cell, Low Load
3 Equal cells, High load

Figure 3: Relation between Ec/No and RSCP for different cell loading and
different network plan quality


When the loading of the system increases the Ec/No degrades but the RSCP
stays constant. Degrading Ec/No is an indication of increased other cell
interference which will also increase the need for downlink traffic power
(DPCH Ec/Ior, when expressed in relative terms). Power being a limited
resource, the higher required transmit power may not be available, thus the
coverage not being met in loaded condition: this represent the coverage and
capacity trade-off for the downlink in a WCDMA systems.

In a similar way, adding sites to provide deeper coverage indoor without
controlling the footprint of each of them will increase other cells interference
and impact service quality and capacity of the system.

It should be noted that the total received signal power (Received Signal
Strength Indicator – RSSI) is never considered in a WCDMA system as an
indication of coverage. It is mainly due to the inability to estimate the quality
by this value: 10 weak cells would result in a strong RSSI, but the lack of any
dominant server would yield poor system performance. This concept is
sometime called pilot pollution, where multiple servers contribute to a high
RSSI, but where the signal cannot be used due to lack of strong dominant
server.


To ensure that these issues will be minimized, several simple steps can be
taken as illustrated and detailed below.
80-W0853-1 Rev B

5




• Defining the network requirements (coverage area, coverage depth,
expected traffic, traffic models …) is necessary to dimension the
network both for coverage and capacity.
• Defining the number of site required for a given coverage depth: the
site configuration, antenna height and downtilt notably, should be
selected as a function of this number of site. Without selecting the site
configuration relative to the site-to-site distance, the risk is to have
either insufficient coverage or excessive downlink interference.

Unlike in GSM network planning where sub-optimal site configuration
can be compensate with frequency planning, the 1/1 frequency re-use
of WCDMA does not allow such flexibility.
• Defining up front the number of sites required for capacity over the
next few years: this number should be compare to the number of site
for coverage to ensure that coverage, short term, and long term
capacity needs are met. For capacity limited design, the site
configuration should match the higher site count. For capacity limited
design, the decision between adding sites and adding carrier should
consider the possible site configurations. In particular, adding sites
with limited flexibility on the antenna configuration may not always
add capacity: if the added sites increase the downlink interference, the
capacity of each of the sites will decrease.

Obtain
Network
Propagation
Requirements
Model Tuning
Project Setup
Nominal Design
Site Acquisition & Review
Design for
Design for
Capacity
Coverage
Network
Deployment
Initial Optimization

Figure 4 Simplified Network planning process

6

80-W0853-1 Rev B

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