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Title3G Cluster Optimization by Drive Testing
TagsDatabase Index Mathematical Optimization Antenna (Radio) Radio Propagation Electromagnetic Interference
File Size1.7 MB
Total Pages43
Document Text Contents
Page 1

3G Cluster/City Pre-Optimization
Instructions for engineers







1. Introduction to RF Optimization (Pre-Optimization)

During RF (pre)optimization stage, the Optimization/Planning/Drive-Test responsibles, optimize
the radio frequency (RF) access part of the 3G network.
This aims to control pilot pollution and SHO Factor based on DT in optimizing signal coverage, so
that the distribution of radio signals is normal in next service parameters optimization stage (or
Network QoS optimization phase).

1.1 Contents of RF Optimization

RF optimization includes the following aspects:

A. Pilot signal coverage optimization
This includes the following two parts:


 Weak coverage optimization for ensuring seamless coverage by pilot signals in the
network

 Primary pilot cell optimization for ensuring proper coverage areas by each primary pilot
cell, clear edge of primary pilot cells, and that alternation of primary pilot cells is reduced
as much as possible.


B. Pilot pollution optimization
Pilot pollution refers to that excessive pilots of approximately equivalent strength covering an area
without a primary pilot. Pilot pollution might cause increasing of downlink interference, call drop
due to frequent handover, low network capacity. The problems must be solved by adjusting
engineering parameters.

C. Handover optimization
It consists of two parts:


 Checking missing neighbor cells, verifying and improving the list of neighbor cells, solving
handover, call drop, and downlink interference problems.

 Ensuring proper SHO Factor based on DT by adjusting engineering parameters properly.



2. Basic Processes for RF Optimization

Once all the sites are installed and verification is complete, the RF optimization starts. In some
situations for a tight schedule, RF optimization might start after the construction of partial sites is
complete. RF optimization is usually performed after 80% of total sites in a cluster are
constructed.
RF optimization stage is one major stage of RNO. It aims at the following aspects:


 Optimizing signal coverage
 Control pilot pollution
 Control SHO Factor based on DT

Page 2

RF optimization also involves optimizing list of neighbor cells.
When the indexes like DT and traffic measurement, after RF adjustment, meets KPI
requirements, RF optimization stage ends. Otherwise you must reanalyze data and adjust
parameters repeatedly until all KPI requirements are met. After RF optimization, RNO comes to
parameter optimization stage.

2.1 Flow Chat of RF Optimization

RF optimization includes the following four parts:


 Test preparations
 Data collection
 Problem analysis
 Parameter adjustment


RF optimization flow chat.

Page 21

5.3.4 Coverage restriction due to antenna blocked by roof



At the optimization stage after network construction, in front of the traffic lights below antennas,
video quality declines due to VP mosaic and PS384K service is reactivated.
Analysis
In terms of planning, 3G and 2G antennas are mounted in a co-location site. According to
coverage test data of 2G antenna, 2G signals does not fluctuate sharply under the site and under
the traffic lights. Namely, if the 3G and 2G antennas are in the same location, 3G signals will
cover the areas around traffic lights. The problem lies in that the 3G antenna is mounted too close
to the wall on the roof and the wall blocks signals so the special installation conditions of
antennas are not met. In addition, the 2G antenna and its installation parts affect the pattern of
3G antenna. This changes the radiation pattern of 3G antenna. According to the installation
scene, adjusting location of 3G antenna is difficult.
Solutions
According to discussion between 2G and 3G engineers, the minimum adjustment solution without
affecting 2G coverage is as below:
Connect the 3G and 2G TX/RX feeder to two feeders of outside wideband polarization antenna
Connect the 3G and 2G RX feeder to two feeders of inner wideband antenna.
0 shows the connection.





Optimizing antennas by adjusting feeders



6 Pilot Pollution Problem Analysis

6.1 Pilot Pollution Definition and Judgment Standards

6.1.1 Definition
The pilot pollution is that excessive strong pilots exist in a point but no primary pilot is strong
enough.

6.1.2 Judgment Standards
Pilot pollution exists if all the following conditions are met:


 The number of pilots that meet the following condition is more than

Th

N
CPICH_RSCP > Th

RSCP_Absolute



(CPICH_RSCP

1st
- CPICH_RSCP

(ThN +1)th
)< Th

RSCP_Relative

Page 22

Assume that Th
RSCP_Absolute

= –100 dBm, Th
N

= 3, and Th
RSCP_Relative

= 5 dB, and then pilot pollution

exists if all the following conditions are met:


o More than three pilots meet the following condition CPICH_RSCP > –100 dBm.


o (CPICH_RSCP
1st

- CPICH_RSCP
4th

) < 5 dB



6.2 Causes and Influence Analysis

6.2.1 Causes Analysis
Ideally the signals in a cell is restricted within its planned range. However the signals cannot
reach the ideal state due to the following factors of radio environment:


 Landform
 Building distribution
 Street distribution
 Waters


Pilot pollution is the result of interaction among multiple NodeBs, so it occurs in urban areas
where NodeBs are densely constructed. Normally typical areas where pilot pollution occurs easily
include:

 High buildings
 Wide streets
 Overhead structure
 Crossroad
 Areas round waters


Improper Cell Distribution
Due to restriction to site location and complex geographic environment, cell distribution might be
improper. Improper cell distribution causes weak coverage of some areas and coverage by
multiple strong pilots in same areas.

Over High NodeB or Highly-mounted Antenna
If a NodeB is constructed in a position higher than around buildings, most areas will be with in the
line-of sight range. Therefore signals are widely transmitted. Over high site cause difficult control
of cross-cell coverage, which causes pilot pollution.

Improper Antenna Azimuth
In a network with multiple NodeBs, the antenna azimuth must be adjusted according to the
following factors:

 NodeB distribution of the entire network
 Coverage requirements
 Traffic volume distribution


The sector azimuth of each antenna is set to cooperate with each other.
If the azimuth is improperly set:

 Some factors might cover the same area. This causes excessive pilot pollution.
 Weak coverage exist in some areas without primary pilot.


The previous two situations might lead to pilot pollution. Therefore you must adjust the antenna
according to actual propagation.

Improper Antenna Down Tilt
Setting antenna down tilt depends on the following factors:

Page 42

RSCP for candidate of 4th Best ServiceCell



8 Adjustment Methods

The adjustment during RF optimization stage include adjusting neighbor cell list and adjusting
engineering parameters.
Most coverage and interference problems can be solved after adjusting the following site
engineering parameters (from superior to inferior):
Adjust antenna down tilt
Adjust antenna azimuth
Adjust antenna height
Adjust antenna location
Change antenna type
Add TMAs
Change site type (such as changing a site supporting 20 W power amplifier to a site supporting
40 W power amplifier)
Change site location
Construct new site or add RRU



9 Summary
This document describes the content of RF optimization in network optimization. RF optimization
concern the improvement of signal distribution, and it helps to provide a good radio signal
environment for the following parameter optimization.

Page 43

The test during RF optimization is usually DT, with other tests as supplementary. The problems to
be analyzed during RF optimization is primarily about coverage, pilot pollution, and handover,
with problem as supplementary. RF optimization help to solve handover, call drop, access, and
interference problems. The parameters to be adjusted during RF optimization are primarily
engineering parameters. Cell parameters are adjusted during parameter optimization stage
(excluding adjusting neighbor cell list).
This document is mainly for RF optimization of new network. How to optimize an existing network
for expansion needs further tracing. The methods for optimize SHO Factor based on DT and the
judgment conditions for removing neighbor cells are still under research, and they will be
supplemented in the future versions.




10 Appendix: Coverage Enhancement Technologies

10.1 Coverage-enhancing Technologies

10.1.1 TMAs
Using TMAs helps to reduce the total noise figure of NodeB receiver subsystem, so the uplink
coverage performance is improved. The coverage gain depends on the mechanism of receiver
subsystem and loss of related feeders. If the system downlink capacity is restricted, using TMAs
will shrink system capacity. The typical capacity shrinkage is 6%–10%.

10.1.2 Receive and Transmit Diversity
Increase the number and improve the quality of RAKE receivers of UE by using time switched
transmit diversity (TSTD) and space and time transmit diversity (STTD) in the downlink. Therefore
the coverage range is expanded, system capacity increases, and the number of NodeBs
decreases.
Using four-antenna receiver diversity reduces requirements on Eb/No needed in demodulation. In
line of sight, compared with the gains of 2 antennas with 2 receiver diversity, the gain of 2
antennas with 4 receiver diversity is 2.5–3.0 dB. You can adjust the uplink sensitivity by 2.5–3.0
dB and reduce the sites by 25%–30%.

10.1.3 RRU
Remote radio unit (RRU) physically detach NodeB RF module from baseband module, so you
can place RF module afar without using very long feeders. The uplink and downlink link budget is
improved. Remote RF indicates that the coverage performance is improved but the system
capacity remains the same. Compared with remote RF, using TMAs increases maximum path
loss and lowers NodeB EIRP due to bringing insertion loss.

10.1.4 Micro Cells
NodeBs are densely distributed in urban and dense urban areas, so selecting a site is difficult.
Using micro cells is a solution to high capacity and caters for urban and dense urban
environment. A feature of using micro cells is that buildings are
used to block signals so that the interference from neighbor cells is lowered and downlink
capacity is increased.

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