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Prepared By : Shashank Sharma

What is Drive Test?

Drive test involves setting up a call to best carrier

and driving along the roads.

While driving, the radio parameters and air interference

signal data are collected as a log file.

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Drive Test Setup

Drive Test system comprises of a test mobile phone,

software to control and log data from the phone anda Global Positioning System(GPS) receiver for position

information

External Antenna for Test mobile phone & GPS can also

be used for drive test.

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Objective of Drive test

a) To verify whether the network meets the given

requirements, on the basis of which network wasdesigned.

b) To verify whether the parameters and configurations

are defined correctly or not.

c) To investigate network problems related to poor

quality, signal level, interference etc

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Objective of Drive test

Following steps are taken to fulfill the objective of using

a drive test tool.

a) Collection of Data and extraction of relevant

information from it.

b) Analysis of the extracted data.

c) Suggesting changes in the network configurations

based on the analysis.

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a) Collection of Data

During drive test, the radio parameters and air

interference signal data are collected as a log file.

Following parameters are checked during the drive test

for different clutters categories like dense urban,

sub-urban, open, rural etc.

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a) Collection of Data

1) Rx Level

2) Rx Quality

3) Timing Advance

4) Handover messages

5) Details of six best neighbor cells

6) Layer 2 and layer 3 messages.

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a) Extraction of relevant information

From the data collected various information can be

extracted which depict the performance of BTS sites

and the network as a whole.

Following information can be extracted from this drive

test data-

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1) Coverage probability (edge & area prob. can be

extracted for cell/site if detail drive test is done

for cell/site

2) Speech quality

3) Frequency and BSIC reuse

4) Neighbor cells details

5) Handover details

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6) Additional features like Hopping, DTX, power

control etc.

7) Typical n/w settings such as LAC, CI, Tx power,

RLT

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Cell edge probability

With the help of drive test tool, coverage boundary

of the cell based on received signal level (RXLEV),

is obtained and is plotted over the geographical map

of the area.

The coverage boundary of a cell is considered to

be made up of equal received level points on the field.

With the help of this coverage plot, edge probability

or the probability of getting a signal level better than a

specific value over the boundary of all cells is obtained

which helps in determining the performance of the network

with respect to coverage boundary requirements.

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Cell area probability

The obtained signal levels from the cells at all the points of

the network, are then used to make, a best server plot.

This best server plot is drawn by categorising it on the basis

of in building coverage, in car coverage and on street

coverage.

With the help of this server plot, area probabilityor the probability of getting a signal level better than a

specific value over the areas of all cells is obtained

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RxQual measurement

RXQUAL, is the Bit error rate (BER) derived from the 26 bits

midamble on TDMA burst. Speech quality is inferred by the

RXQUAL measurements during the drive test. Its level

characterizes speech quality where 0 indicates the highest

quality and 7 the worst.

Thus during drive test, poor quality areas can be found and

marked by looking over the quality on the scale of 0 to 7.

RXQUAL can be poor due to poor RXLEV, Co-channel

interference, adjacent channel interference or Multipath.

RXQUAL is measured and tested for all the categories of

clutters.

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Frequency & BSIC reuse

The frequency plan& BSIC (Base Station

Identity Codes) planning for the cells can be obtained

from the collected data .

This gives an idea of the freq reuse pattern & reuse

distance.

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Neighbor Cell details

With the help of collected data, details of 6 best serving

neighbours can be determined.

The details like-

BSIC

BCCH ARFCN

Cell Id

Rx Lev

C1 & C2

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Layer 2 & 3 messages

Decoding of layer 2 and 3 messages helps in

analysing the cause of call set-up failures, delayed

call set-ups, blocking, drop calls, causes of

handovers, reasons for selecting particular target

call & handover failures or any other abnormality

in the performance of the network.

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Drive tests applications

Drive test activity can be utilized for the following

applications-

a) CW test

b) RF coverage verification

c) Optimization

d) Troubleshootinge) Competitive analysis

f) Interference Monitoring

g) Planning Tool Model Tuning

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Optimization

The optimisation of the network, is done to check the

performance of the network, just after it is made

operational and to get best possible quality of service.

Optimization includes-

Suggesting changes in the defined parameters &

configurations on the basis of drive test data analysis.

Changes can be of two types - Hard & Soft conf. changes

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Hard configuration

The hard configuration parameters include antenna

type, antenna gain, antenna orientation, effective height

of antenna and effective isotropic radiated power

(EIRP), TRX, cables/feeder cables

Changes are made to meet the requirements and to deal

with the analysed problems.

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Soft configuration

The soft configuration parameters include categories

such as common BTS parameters, cell access

parameters etc. GSM defines around 150 soft

parameters for each cell. e.g.BSIC, BCCH,

neighbors cells, Tx power, Handover margin, enable or

disable add-on features etc-

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Optimization

Optimisation of the network using drive test system is

an iterative process. Thus after deploying discussed

changes in the network,drive test is done again and

mentioned steps are repeated until required

performance objective is fulfilled.

Drive test is very effective part of the optimisation of

the network but drive test data is not very effective tofind out some of the very specific problems their cause

and solutions to rectify them. On the other hand drive

test is the only medium with the help of which users

perspective of quality of service can be visualised hence

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simultaneous monitoring of the BSS statistics and

drive test data gives most practical and optimum

cause and the solution of a problem.

Optimization

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