The Purpose of Drive Testing

Drive testing is principally applied in both the planning and optimization stage of network Development. However, there are other purposes for which drive testing can be used:

•To provide path loss data for initial site survey work

•To verify the propagation prediction during the initial planning of the network.

•To verify the network system parameters, as defined in the EG8: GSM/DCS

System-Specific Parameters.

•To provide the initial test parameters used in Benchmarking (as defined in the

“Analysis” section of the Network Performance and Monitoring Guideline).

•To verify the performance of the network after changes have been made e.g.

When a new TRX is added; the removal or addition of a new site; any power

Adjustments or changes to the antenna; any changes in clutter or traffic habits

Such as the addition of new roads etc.

•To measure any interference problems such as coverage from neighboring

Countries.

•To locate any RF issues relating to traffic problems such as dropped or blocked

Calls.

•To locate any poor coverage areas.

•To monitor the network against a slow degradation over time, as well as

Monitoring the network after sudden environmental conditions, such as gales

Or electrical storms.

•To monitor the performance of a competitor’s network.

When to Drive Test

Drive testing can take place during the day or at night and is dependant upon the

Operator’s requirements and subscriber habits.

Drive testing during the day will mimic the conditions as seen by subscribers, but may

Clog up the network if call analysis is being performed.

Drive testing during the night will allow a greater area to be surveyed due to the reduction in vehicular congestion. It will also allow for certain test signals to be transmitted and tested, particularly when setting up a new site, without interrupting normal operation.

However, night-time testing does not mimic the conditions experienced by subscribers.

For planning purposes, drive testing is typically performed at night and for maintenance

purposes, drive testing is performed during the day.

Where to Drive Test

Some areas of a network will have greater performance problems than others. Drive

testing should not be uniform throughout the whole network, but should be weighted

towards areas where there are significant RF problems.

There may be other areas of the network that require temporary coverage during a certain time of the year e.g. an exhibition centre or a sports stadium. These areas should be examined and planned in greater detail.

It is important that a drive test is documented. This is specified by the Operator and can either take the form of creating a new item of documentation or filling in an existing document. All documentation will be passed to Analysts and Engineers, who will need accurate records of any test work carried out.

Route Plans

The area to be drive tested is ascertained before leaving the office. There are three levels

of drive testing depending on the purpose of the test:

Primary Route: This includes all major roads, highways and throughfares and should be given priority to all other roads when conducting a coverage test, unless a new site is put into service for a specific objective.

Secondary Route: This includes all streets, by-streets and compounds, where accessible, such as a University Campus.

Secondary routes are used in areas where problems have been located during a primary route test and further investigation is needed.

Miscellaneous Routes: This includes in-building and non-access routes to vehicles such

as shopping malls, golf courses, airports, hotels, conference centers etc.

A route is prepared by photocopying a map and highlighting the route to be driven. For

Primary routes, a map of scale no less than 1:20,000 should be used, and a map of scale 1:10,000 is recommended for secondary routes. It is recommended that the route is marked in a contiguous circuit, taking account of one-way streets at this stage.

A drive test should be planned in both directions, where possible, and at the same speed.

This minimises any errors and checks the point of handovers and cell dimensioning. For new sites that are being tested, it is recommended that the transceiver is forced to camp onto the cell (forbidding any handovers) in order to ascertain the full coverage of the cell.

The test should be re-driven with any forced handovers removed.

Layer 1 Messages

Other Layer 1 criteria that is useful for field measurements include:

C1 criteria •

ARFCN of Serving Cell - (TCH in dedicated mode, BCCH in idle mode)) •

Time Slot (TS) •

Layer 3 Messages

All Layer 3 messages should be collected where possible. Layer 3 Messages are used by

Analysts to determine more accurately the cause of a problem within the network.

Some field test equipment can perform basic analysis of particular Layer 3 messages

during data collection. This enables certain conditions such as call classification or

handovers to be flagged to the survey technician.

Call Classification

In principle there are five call classifications, some of which can be sub-divided further.

Good Calls: These are calls that are successfully placed on the network and maintained for the required duration.

Dropped Calls: These are calls that are successfully placed on to the network but are terminated without authorization. Using Layer 3 Messages, these calls can be sub-divided into:

End User Hang-up •

System Hang-up •

Other •

Blocked Calls: These are calls that cannot be placed on to the network. Again, using

Layer 3 messages; these can be sub-divided as follows:

System Busy •

End User Engaged •

No Service •

Other •

Roamed Calls: These are calls that are successfully placed on another network. Roamed

Calls may also be good calls or dropped calls.

Noisy Calls: These are calls which have been successfully completed for the duration of

The call but which experienced a number of noise bursts that a subscriber may find

Intolerable. The threshold for determining the level of poor audio is programmed during the set-up of the test.

In GSM, this particular classification is very difficult to determine with great accuracy. It should be noted that it is not enough to monitor just the RxLEV and the RxQUAL.

Troubleshooting

No Data Collected

Occasionally, the equipment fails to trigger the collection device to save the data to file.

Check all cables •

Ensure the Processing Unit is powered •

Re-start the laptop computer •

Re-start the equipment •

Re-drive the test. •

No Positional Information Collected

If data is collected using GPS only, it may be possible that satellite reception was lost

during a drive through a tunnel etc. It is important that back-up equipment is used, such as a Dead-Reckoning device, since a GPS receiver will re-transmit the last known position until it receives an update. If the vehicle moves without GPS cover, the data will be inaccurate and cannot be analyzed.

Check the GPS antenna cable to the receiver •

Drive to an open area and ensure that the GPS system is working correctly •

If required, install a back-up positional device to safeguard against lost GPS •

Coverage Holes

If there are patches of poor coverage in unexpected areas, it may indicate the fringes of a coverage hole. It is important to re-drive this particular area.

Complete a route plan using secondary roads as far as possible •

Make notes of any buildings / obstructions that may cause shadowing •

Take note of pedestrian / vehicular habits in the area •

Dropped Calls

Dropped calls can be caused by either RF environments or incorrect system parameters.

The following data should be checked to ensure that it has been collected properly.

Layer 3 Messages •

Neighbor Cell List (BA Table) •

RxLEV (Server • & Neighbor)

RxQUAL (Server • & Neighbour)

Finally, ensure that the automatic setting for the call length is not shorter than that for the Timer monitoring for unauthorised call drop-outs. The setting should be a minimum of 30 Seconds.

Handover Problems

Handover problems are generally caused by inaccurate settings of the handover boundary.

This can cause ping-ponging, where the server will keep changing, and congestion at the

switch. Check the following.

The transceiver antenna is fitted correctly •

Collection of Layer 3 Messages •

Collection of Neighbour Cell List (BA Table) •

Collection of Scanning Information •

Collection of Cell Identities •

Collection of T.Adv for the Serving Cell •

Also, ensure that the collection of data from the new serving cell immediately after the

handover has occurred (particularly RxLEV and RxQUAL) is not timed to occur prior to

the-synchronisation of the transceiver itself.

If a particular serving cell can be isolated as a potential cause of handover problems,

Slowly drive around the cell in a radius of around 500m - 1km, checking when handovers occur.

Blocked Calls / System Busy

If calls are repeatedly classified as blocked, it is recommended that the drive test is

Temporarily halted in order to try and locate the cause.

Check that the number called is fully functional •

Check that there is adequate coverage from the expected serving BTS •

Check the equipment transceiver is functioning correctly by using an ordinary •

Mobile to call the office

If all appears functional, try to place calls through an alternative BTS. If this •

Succeeds, inform the office immediately and re-suspend the drive test.