Drive Testing General

Drivetesting involves driving in a vehicle and collecting network data by making a lot of calls. The data collected includes data for serving cell as well as the neighbors.

This data collected helps us to find and analyze the problems in the network.

These data can also be loaded on the planning and optimization tools like Pegasos, Planet nemo etc. and usefull plots can be generated such as serving cells coverage plots, Quality plots etc. Equipment necessary for Drivetesting.

– Vehicle

– Drive test mobile phone (e.g.Ericcson TEMS/ ZTE NEMO) – External vehicle mounted GPS

Laptop with drivetest software and GPS connection capability

Drivetest Outputs

Using the drivetest equipment we can monitor the following – Status Information – Error reports – Mode reports – Layer 2 messages – Layer 3 messages Status Information

In status information we get the following information

– General Information: This includes the Latitude ,longitude data, server call name, Marker ,data, time , log file name etc.

– Serving cell: This includes Cell Identity, BSIC, ARFCN ,MCC, MNC, LAC.

– Serving + Neighbor cell data: This includes CI, BSIC, ARFCN, Rxlev, C1 and C2 for the serving and the best 6 neighbors.

– Dedicated channel: This includes data such as Channel number, Timeslot number, Channel type and TDMA offset,hopping information and channel mode.

– Radio Environment: This includes serving cell,lat , long, rxlev, rxqual, TA, DTX and RL Timeout counter information.

Error reports

If any errors are reported during the call they can be analyzed from this report.

Mode reports

These are the channel mode reports.

Layer 2 messages

All the layer 2 messages can be analyzed.

Layer 3 messages

All the layer 3 messages can be analyzed.

Drivetest types:

Drivetest can be categorized in three types – Routine drive test

– Problem specific drive test Cell coverage analysis drive test

Routine drive test

As we have discussed earlier optimization is a ongoing process and the network needs to be monitored on a daily basis.

Routine drive test forms a integral part of this process.

Drive test routes are decided by the Network operator and these routes are regularly drive tested and any problems found are reported.

These problems are then further analyzed and solved.

Hence it is important that these drive test routes are selected carefully.

Drive test routes should include all the major road, important location, airports etc. Also they should be able to cover most of the cells.

Each drive test route should be typically 2 - 3 hours long.

Typical Optimization Process using routine drive testing

The drive test routes must be decided by the operator and a priority set on the routes for testing.

The drive test routes are usually 2 - 3 hours in duration in order to ensure that the data generated is of a manageable size.

The drive test teams use the Test Mobile equipment (e.g.TEMS) to make test calls to the MSC test number on the network of 2 minute duration with a 15 second break.

All data is logged on the computer, location information is also taken using a GPS receiver.

During or after completion of the drive test route, analysis of the data collected is performed to identify areas of dropped or noisy calls.

This will be done using FICS or other similar software.

Should the analysis of the route indicate problems of either dropped or noisy calls then with the aid of the RF design and Database parameters, an assessment is made to identify the possible source of interference causing the noisy or dropped call.

If a call is dropped and no interference is present a retest is made in the same area, if the scenario of the dropped call can be repeated, the identity of the problem cell will be obtained and corrective action taken. To assist in confirming possible sources of interference there may be a requirement to remove the suspected interfering channel.

This would be done by the optimization engineers.

The suspected interfering carrier would be removed temporarily from service and test calls made again in the problem area, this would show if the interference had been removed.

The process for temporarily removing carriers would have to be agreed with the operator, this usually varies as to the importance of the cell as to what time of day it can be taken out of service.

After conformation as to what is causing the problem with the drive test route, the drive test engineer will attempt to find a solution to the problem.

This can be one of a number of possibilities i.e. Power Change to BTS, Frequency Plan change, Neighbor addition required, etc.

Once a possible solution to the problem has been found it may be possible in some circumstances to immediately attempt the solution via the OMC, this usually relates to minor database changes and adding neighbors.

The solution is implemented and proven immediately.

If the problem is rectified the change remains in place and a change request is raised for the solution for the purpose of keeping records of all changes in the network.

If the solution requires a major database change or antenna work a change request must be raised via the Optimization Control Engineers.

After the solution is implemented a retest of the problem area is carried out to confirm the problem has been solved

Problem drive testing

Any problem reported by statistical analysis, routine drivetesting, customer care centre , alarms need to be analyzed in detail to find a solution.

Problem specific drive testing is a important tool which helps us do it.

Here we make a list of problematic cell and drive test them thoroughly to analyze the problem. There may be many different methods which a optimization engineer may employ for the analysis.

As an example, if a particular cell is being interfered the frequency of the cell may be changed temporarily to identify the interferer.

Also the levels and TA at which the cell is being interfered may be analyzed. Here the data collection and analysis are done simultaneously.

Cell Coverage Analysis Drive Test

It has been found that normally that the coverage and server area of the cells differ from the planned area. Hence it is often found that new cells that come on air serve far more or much less area than initially planned and same could be the case with the coverage.

This could lead to two problems. If the server area is less than planned it could lead to coverage holes or poor cover areas. If the coverage area is more than planned it may cause interference in the network. Hence it is important that once new cells come on air they must be thoroughly drive tested to determine their server and coverage areas.

If any major deviation from the initially planned design is found the cell sites should be optimized.

Scanning

This is a important feature of the drive test software.

It enables us to lock onto a particular frequency during the drive test which is helpful in determining the server area of a cell.

Also we scan a set of frequencies and have a graphical display of the same or can also be stored for further analysis.

This is helpful in finding interfering frequencies and also in finding clear frequency.

Optional Features

Some drive test equipment provide supplementary features which help during drive test.

Map displaying the drive tested area showing the major roads, location, cell sites is provided ,this helps us to be always aware as to where we are in the network.

Also some vendors provide spectrum analyzer which helps in finding the interfering frequencies and to find clear frequencies.

Typical Information Available From A Drive Test Tool

Graphical Representation

General Information Obtained During Drive Test

Layer3 Information Obtained During Drive Test

Serving Cell and Neighboring Cell Information adio Environment Information

Radio Environment Information

9.4.3 OMC Tools