13-WCDMA Network Optimization Cases Study

WCDMA Network Optimization Cases study

ZTE University

TD&W&PCS BSS Course Team

Content

WCDMA DT Cases

WCDMA Network optimization Cases

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

PSC’s coverage exceeds defined threshold, and may cause negative influence on remote region.

Over Shoot Analysis

WCDMA DT Cases

Call drop

Monitor set 267&283 arestrong

Adjacent cell problem

Handover problem analyze

WCDMA DT Cases

Content

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 hand

over region or sudden change of signal strength?

Before the call is dropped, the Ec/Io reported by the UE is very po

or.

Once in the idle mode, the UE sets up connection with the new cel

l.

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 al

so 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

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.

Problem analysis:


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 route 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 Erria

dh TT site become weak suddenly because the cell is sheltered.

Spot B is about 2km from CTT Skanes site. The seaside road that B loc

ated 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 penetrati

ng several 2~3-layer buildings. At around spot B, the pilot signal strengt

h is reduced to be below -100dBm.

The NodeB in Sahaling is quite restricted by the environment. The site h

eight is only 25m; there is little space for increasing the height.

Problem analysis:


Case3

Adjust the transmit power of

common channels;

Increase the pilot transmit

power

Solution:


The coverage effect and the

call-drop rate is optimized.

There is almost no dropped

call along the express way.

Channel Before adjustment Afteradjustment

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 line testing, it is found that the 425 (scramble) cell of the site provides cross-cell coverage. Cell sig

nals are still strong in the First Zhongshan Road, which is far from the Flower hall site. As the 425 cell is not c

onfigured as the Neighbor-Cell of cell 436 in the first sector of the Shuqianlu site located on the First Zhongsh

an Road, calls are easily dropped in this area.

The above figure shows the pilot Ec/Io route 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 ce

ll; Cell3 is not in the Neighbor-Cell list o

f 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 42

5 cell;

Add Huachang site 425 cell into the Neighbour-Cell list of Shuqia

nlu site;

Reduce the maximum transmit power, public channel power and

pilot channel power of Flower hall site 425 cell by 3dB.


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 cross-cell 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 e

nvironment 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 cours

e, the specific height of the antenna should be determined according to the local radio transmission e

nvironment.

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 radi

o 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 ante

nna 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 r

equirement 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 betwee

n 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 ca

n 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 route testing data.


Case 5

According to repeated route tests, it is found that calls are usually dropped during the handover in the dir

ection from the Flower hall site to the Yunshan Hotel site; in the opposite direction from the Yunshan Hot

el site to the Flower hall site, no call-drop occurs.


Case 5

Problem analysis: According to testing data analysis, the section 20m from the call-drop venue is mainly covered by sign

als from the third sector (scramble 426) of the Flower hall site instead of signals from the first sector (s

cramble 424) of the Flower hall site. The reason might be the third sector (scramble 426) of the Flowe

r hall site is sheltered by a tall building in front of it; signals of this sector are reflected to the road seg

ment 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 sit

e 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.


After the Neighbour-Cell is configured, route 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 automaticall

y generated via the network planning tool.

Optimization of the Neighbour-Cell list can be executed via route tests and

statistics analysis of the route testing data.

The Neighbour-Cell list optimized via route 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 route test data, Neighbour-Cells not configured in the Nei

ghbour-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 g

enerated 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 t

o 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 di

sappear; but downlink Eb/No failures occur in the same area.


Zoom in

Pilot pollution

Case 6


Case 6

In the precondition of satisfying coverage, adjust the tilt angle, azimuth and po

wer parameters of Neighbour-Cells so that signals of one cell become a domi

nant server.

Add a site in the problematic area; adopt one cell of the new site into the domi

nant server.

Solution:


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

JinanShenzhen

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


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13-WCDMA Network Optimization Cases Study