8 wcdma rf optimization&case study-60

WCDMA RF Optimization
&Case Study
ZTE University
TD&W&PCS BSS Course Team

Content
WCDMA RF Optimization Process
WCDMA RF Optimization Policy
WCDMA DT Cases
WCDMA Network optimization Cases

Single station
check
Base station group
optimization
Whole network
optimization
Satisfythe
indexesornot?
Find out base station
group that do not
satisfy requirements
No
Common RF Optimization Process

RF Optimization Step 1: Single Station Check
 Confirm site information
 Longitude and latitude, configuration, height above sea level, peripheral
environments and so on;
 Confirm antenna feeder information
 Antenna type, azimuth, down-tile angle and height;
 Check antenna feeder link
 Standing wave ratio, primary set and diversity RSSI check, primary set and
diversity lock balance;
 Confirm system parameters
 List of adjacent areas, overhead channel transmitting power, SC
configuration, switching parameters;
 Check and test basic functions
 Basic call process, soft switching, softer switching;
 Check station coverage

RF Optimization Step 2: Base Station Group
Optimization
 Spectrum scanning
 Load-free test
 Load test

RF Optimization Step 3: Whole Network Optimization
 Test on various radio indices of the system
 Analysis on test results
 Confirm whole network adjustment scheme

Performance Test Indexes
 Voice quality--BLER
 Call connection rate (call completion rate and paging response
rate)
 Resource utilization—CPU utilization-
 Handover success rate
 Call drop rate
 Network coverage rate
 Forward coverage
 Pilot coverage
 Service coverage
 Backward coverage

Common RF Problems
 Call Drop
 Discontinuity
 Access Failure

Call Drop Analysis
 UL/DL coverage is not satisfactory (Ec/Io and Ec)
 Improve the coverage of the points.
 List of adjacent cells are not complete
 Configuration of list of adjacent areas is not complete.
 Interference
 There is internal interference source.
 Pilot pollution is serious
 Faults with base stations
 Incorrect connection of antenna feeders, GPS fault causes
asynchrony between the time and the system, interruption of
transmission.
 Hard handover failure

Discontinuity Analysis
 UL/DL coverage is not satisfactory (Ec/Io and Ec)
 Improve the coverage of the points.
 List of adjacent cells are not complete
 Configuration of list of adjacent areas is not complete.
 Interference
 There is in-band interference source.
 Pilot pollution is serious

Access Failure
 Interference
 Coverage over weak areas, blind zones or pilot pollution
areas makes it impossible for signaling interaction
between the base station and the mobile phone to be
completed during the access.
 Mobile phone performance

RF Optimization Policy
 Adjust the antenna down-tilt angle
 Adjust the antenna directional angle
 Adjust the antenna height
 Change the antenna type
 Appropriately adjust the base station transmitting power
 Adjust the base station location
 Increase the base stations

 Antenna directional angle
 During optimization, attention
should be paid to antenna
directional angle, as shown in
the figure on the right:
 If the antenna coverage area is
a vast space of residence, and
the buildings are of the similar
structure, the antenna direction
shall be alongside the direction
of the buildings (as the red
arrow on the left); if the antenna
direction is the same as the
arrow on the right, the quality of
signals in the coverage area
may not be good.

 RF Optimization Policy for Pilot Pollution
 Pilot pollution is caused by too strong signals in some cells out
of the coverage area in most cases. Measures for RF
optimizations are as follows:
 Adjust the antenna down-tilt angle, so as to reduce the coverage
area, and further reduce the number of pilots in the pilot pollution
area;
 Appropriately reduce the transmitting power of the cell, so as to
reduce the signal strength to narrow the coverage area, and also
further reduce the number of pilots in the pilot pollution area;
 If the two measures are of no use, we can increase base stations
in the pollution areas, so that there will be a master pilot signal, to
solve the pollution. But be careful in taking this measure, as it may
impose great influence on the entire network .

导频强度分析
Weak coverage area
DT （ Best Ec ）
WCDMA DT Cases

Ant reverse
No domi server
Over cover
DT （ Best SC ）
WCDMA DT Cases

TX is high
Uplink/downlink unbalance
WCDMA DT Cases

Over Shoot Analysis
 PSC’s coverage exceeds defined threshold, and may
cause negative influence on remote region.
WCDMA DT Cases

Call drop
Monitor set 267&283 arestrong
Adjacent
cell
problem
Handover problem analyze
WCDMA DT Cases

Case1(Handover problem)
 In especially urban environment, the handover region between two cells
might be too small.
 If the UE passes such an area in a very quick speed, the call might be
dropped.
There might be sudden changes of
signal strength at crossroads of the
city.

Case1
 For successful handover, the
increase and decrease speed of
the signals received by the UE
can enable the UE to complete
the necessary active set
updating process.

Case1
 The handover region should
be big enough to ensure the
UE to complete the active set
up-dating process before
being interfered or
compressed.

Case1
 Cover the crossroad with one
cell.

Case1
 The antenna of the cell should be
put higher than the buildings
along the street so that the cell
coverage area can be bigger.

Case1
 How to determine that the call-drop is caused by too small
handover region or sudden change of signal strength?
 Before the call is dropped, the Ec/Io reported by the UE is very
poor.
 Once in the idle mode, the UE sets up connection with the new
cell.
 The Ec/Io reported by the UE becomes very good.
 The big difference of Ec/Io indicates that the call-drop is caused by
these reasons.
 The pilot strength data of the two cells recorded by the Scanner
also proves the above conclusion.

Case2
 It is found that the call-drop rate is very high on the seaside express
way from TRI002 to TRI004. According to the testing data analysis, the
coverage distance of 404 is very short at the call-drop venue.

Case2
 To take a bird’s-eye view from the sky, it is found that
there are several tall buildings in front of the 404 cell.

Case2
 Problem analysis:
 As the handover region is short and the call-drop venue on
the seaside road is close to the TRI002 site (only 400m),
signals might be strong at first but disappear quickly. This
can cause slow speed of strong signals of the adjacent 404
cell in adding the active set. It can also cause a lot of ping-
pang handover and result in call-drop.

Case2
 Optimize the handover parameter: Adjust 1A and
1B event handover parameters so that adding
events can easily occur and deleting events occur
slowly and difficultly. The values of handover
parameters 1C and 1D events are adjusted.
Replacement threshold with strongest pilot is
reduced; replacement observation duration is
increased. The advantage of such adjustment is to
enable high percentage of the user’s using
strongest and stable scramble.
Solution:
Event Setting before
optimization
Setting after
optimization
1A event
 Reporting Range
Constant
3 5
Hysteresis 3.5dB 2dB
 Time to trigger 200ms 200ms
1B event
 Reporting Range
Constant
7 6
Hysteresis 3.5dB 4dB
1C event
Hysteresis 6dB 4dB
1D event
Hysteresis 6dB 4dB
Effect after optimization:
 According to the driving testing after
handover parameter adjustment, the handover
success rate on this section is greatly
improved; the call-drop rate is reduced.

Case3

Case3
 Spot A is about 2.7km from Sousse2 site. A is the entrance of a
uptown highway and has a turn of about 90 degrees. Signals of
cell 228 of Erriadh TT site become weak suddenly because the
cell is sheltered.
 Spot B is about 2km from CTT Skanes site. The seaside road that
B located is at a lower sea level than the CTT Skanes site.
Signals of cell 332 of CTT Skanes site can be received by the
mobile phone after penetrating several 2~3-layer buildings. At
around spot B, the pilot signal strength is reduced to be below
-100dBm.
 The NodeB in Sahaling is quite restricted by the environment. The
site height is only 25m; there is little space for increasing the
height.

Case3
 Adjust the transmit power of
common channels;
 Increase the pilot transmit
power
Solution:
Effect after optimization:
 The coverage effect and the
call-drop rate is optimized.
There is almost no dropped
call along the express way.
Channel Before adjustment After
adjustment
CPICH 10% 15%
BCH -3dB 0dB
FACH 0dB 3dB
PCH -3dB 0dB
PSCH -4dB -3dB
SSCH -4dB -3dB
PICH -7dB -4dB
AICH -7dB -4dB

Case 4 (High Sites problem)
 Flower hall site is located on the Gaoxun Tower beside the Quzhuang cloverleaf junction. Its is at a height of
70m. After driving testing, it is found that the 425 (scramble) cell of the site provides overshoot coverage. Cell
signals are still strong in the First Zhongshan Road, which is far from the Flower hall site. As the 425 cell is
not configured as the Neighbor-Cell of cell 436 in the first sector of the Shuqianlu site located on the First
Zhongshan Road, calls are easily dropped in this area.
The above figure shows the pilot Ec/Io driving testing result on the
First Zhongshan Road (affected by signals from the Flower hall site,
Ec/Io in area A is very poor; call-drop rate in the area is high;
however, the pilot strength of the area is good.)

Case 4
 Analysis of the call-drop reason:
 As there is shadow fading, the
occurrence of the following events
can be detected from the active set
upgrading report.
 Cell2 is the best service area;
 Cell1 is deleted from the activation
cell;
 Cell3 is not in the Neighbor-Cell list
of Cell2; strong signals from Cell3
result in poor Ec/Io;
 Poor Ec/Io results in call-drops.
 Solution:
 Add Cell3 into Cell2’s Neighbor-Cell list;
 As Cell3 is in a far distance, it is not expected to be a member of the active set in
the problematic area;
 Reduce the transmit power of Cell3 and increase its tilt angle in order to control
its signal coverage range. At the same time, take into consideration the coverage
range to be provided by Cell3.

Case 4
 Execute solution:
 Add the mechanical tilt angle of the antenna of Huachang site 425
cell;
 Add Huachang site 425 cell into the Neighbour-Cell list of
Shuqianlu site;
 Reduce the maximum transmit power, common channel power
and pilot channel power of Flower hall site 425 cell by 3dB.
 Effect after optimization:
 After optimization, the pilot Ec/Io of area A is obviously improved.
 After optimization, there is no call-drop.

Case 4
 There is no strict definition for the high site. It is a relative
concept.
 It is not necessarily wrong to put the UMTS base station on the
top of the hill.
 The high site can easily receive uplink interference generated
by other users.
 The bigger the loads in the high site coverage area, the more
possible the problem might occur.
 If the network is vacant or lightly loaded, the effect of the high
site is not obvious. But it still cause overshoot coverage, pilot
pollution and call-drop.

Case 4
 Suggestion
 In urban areas, buildings are densely located and the penetration loss is big; the
radio transmission environment is complicated and the NodeB coverage distance is
small. Hence the antenna should not be put too high. According to the present
building density and average height, the antenna height can be about 35m; it should
be 10~15m higher than the average height of surrounding buildings. Of course, the
specific height of the antenna should be determined according to the local radio
transmission environment.
 In rural areas, population is relatively small and buildings are not densely located;
distances between base stations are big. Hence the antenna should be high; in
general, the antenna height in rural areas is around 50m and should be 15m higher
than the average height of its surrounding.
 In the sea, the radio transmission model is similar as the transmission model for free
spaces. The radio transmission environment is good; radio electric waves can be
transmitted to a far distance. The site can be located on a high hill (higher than
100m) in order to expand its coverage.
 In deserts and Gobi areas, signals are transmitted to a farer distance than in ordinary
plains. The antenna height is usually 60m or higher in order to expand the signal
coverage area.

Case 5
 the Neighbour-Cell list problems
 The Neighbour-Cell list is a cell list that might be added into
the active set;
 Cells in the Neighbour-Cell list will be measured as whether
they meet the requirement for soft handover or softer
handover with the main service cell;
 The number of cells in the Neighbour-Cell list is up to 32;
 Avoid missing Neighbour-Cells with best signals in the
Neighbour-Cell list.

Case 5
 The network planning tool can use proper algorithm to automatically
plan the Neighbour-Cell list; such planning is always based on the
interference among cells;
 If the pilot signals of one cell is very strong but the cell is not added in
the active set, signals of the cell will become strong interference;
 Either single-directional configuration or bi-directional configuration
might be adopted between Neighbour-Cells;
 In setting the Neighbour-Cell list, take into first considerations about
the cell interference and the cell’s possibility of becoming a main
service cell of the MS;
 The method of automatically creating the Neighbour-Cell list via the
network planning tool can be regarded as an initial reference of the
Neighbour-Cell list. Manual adjustment is needed. The Neighbour-Cell
list should finally be optimized by using the driving testing data.

Case 5
 According to repeated driving tests, it is found that calls are usually dropped
during the handover in the direction from the Flower hall site to the Yunshan
Hotel site; in the opposite direction from the Yunshan Hotel site to the Flower
hall site, no call-drop occurs.

Case 5
According to testing data analysis, the section 20m from the call-drop venue is mainly covered by
signals from the third sector (scramble 426) of the Flower hall site instead of signals from the first
sector (scramble 424) of the Flower hall site. The reason might be the third sector (scramble 426) of
the Flower hall site is sheltered by a tall building in front of it; signals of this sector are reflected to the
road segment of 20m between the Flower hall site and the Yunshan Hotel site. Check the Neighbour-
Cell list; it is found that the third sector (scramble 414) of the Yunshan Hotel site has configured the
third sector of the Flower hall site as an Neighbour-Cell, while the third sector (scramble 426) of the
Flower hall site does not configure the third sector (scramble 414) of the Yunshan Hotel site as an
Neighbour-Cell. This has caused a failure in single-directional handover and resulted in call-drop.
 Solution:
Configure the third sector (scramble 414) of the Yunshan Hotel site as an Neighbour-Cell of the
third sector (scramble 426) of the Flower hall site.
 Effect after optimization:
After the Neighbour-Cell is configured, driving tests are made on the road segment between the
Flower hall site and the Yunshan Hotel site. No call-drop occurs.

Case 5
 Summary
 In the network planning phase, the Neighbour-Cell list can be
automatically generated via the network planning tool.
 Optimization of the Neighbour-Cell list can be executed via driving
tests and statistics analysis of the driving testing data.
 The Neighbour-Cell list optimized via driving test data statistics
analysis is a short Neighbour-Cell list. And if necessary, the
preference sequence in the Neighbour-Cell list can be very clear.
 By analyzing the driving test data, Neighbour-Cells not configured
in the Neighbour-Cell list via planning tool can be found.

Case 6
 If the path loss values from the MS to multiple cells are similar, problems will be
generated as there is no dominant server.
 Such problems include poor Ec/Io, low downlink capacity, and frequent updating
of the active set.

Case 6
 Add loads on a small network with 7 omni-directional sites; there are
200 voice terminals in average; the connection rate is 100%.

Case 6
 Remove the central site; pilot pollution will be generated in the central area, which leads
to the emulated Ec/Io failure (the coverage probability now is 78%).

Case 6
 Increase the pilot power from 33 dBm to 38 dBm; simulated Ec/Io failures
disappear; but downlink Eb/No failures occur in the same area.

Zoom in
Pilot pollution
Case 6

Case 6
 Solution:
 In the precondition of satisfying coverage, adjust the tilt
angle, azimuth and power parameters of Neighbour-Cells
so that signals of one cell become a dominant server.
 Add a site in the problematic area; adopt one cell of the
new site into the dominant server.

Signal distribution in Donghu Road after the optimization
Case7(Antenna problem)

Case7
 Through the review of the DT data with optimization analysis
software ZXPOS CNA1 and the survey on the site, it is found that
in front of Sector 2 (with the scramble 437) of the Shuqian Road
base station, there are dense buildings which form a serious
barrier and influences in the coverage of the sector. Besides, the
areas within scores of meters in front of Sector 1 (with the
scramble 439) of Donghu base station is also completely blocked
by a row of high residential buildings, which makes Sector 1
unable to cover that area.
 Solution
 Change the direction angle of Sector 2 in the Shuqian Road base
station from 240o to 230o to enhance the coverage of that area of
Donghu Road.

Case7
 Effect after optimization
 From the analysis of DT data, it can be seen that in this part
of the Donghu Road, the UE receiving power is >-85dBm
and the pilot Ec/Io>-13dB, which meets the coverage
requirement.

Signal distribution of Baishi Road before the optimization
Case7

Case7
 Through the analysis of the DT data of Baishi Road, it is
found that pilot strength received in the middle part of road
is less than -95dBm, as shown in Area A in the
 DT test picture. it is found that the coverage of this area is
provided by Sector 2 of Shenzhen University base station.
The direction angle of Sector 2 is 110° and the downward
tilt angle is 4°. Both shall be adjusted to enhance the
coverage of Baishi Road.
 Solution
 Adjust the antenna direction angle of Sector from 110° to
120° and the downward tilt angle from 4° to 12°.

Pilot coverage of Baishi Road after the optimization
Case7
 Effect after optimization
 Conduct DT on the Baishi Road after the optimization. From the DT result
below it can be seen that the pilot strength is improved to more than
90dBm.

 Excellent and comprehensive Test Result with
CMII, CMCC, CNC, CTC, CRC;
 Rich Planning & Optimization experience is
acquired and prepared for the coming large-scale
commercial application of 3G.
Perfect WCDMA Trial Network
Planning & Optimization in China
Perfect WCDMA Trial Network
Planning & Optimization in China Beijing
Shanghai
Guangzhou
Nanjing
Jinan
Shenzhen
ZTE´s Rich Experience

 Tunisia 3G commercial System
 Libya 3G commercial System
 Success of ZTE WCDMA in Brunei
Perfect WCDMA commercial system
Planning & Optimization in the world
Perfect WCDMA commercial system
Planning & Optimization in the world
ZTE´s Rich Experience

8 wcdma rf optimization&case study-60

8 wcdma rf optimization&case study-60

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