Options 6113-450 and 6113-451 extend the capability of the 6113 EDGE base station test set to allow AMR-capable base stations to be tested. These options are available on both new units and as an upgrade to existing test sets.

As with any other type of base station, the transmitter and receiver paths of AMR-capable base stations need to be appropriately tested as part of ongoing preventive maintenance. In addition, new test requirements to ensure that rate-adaptation is working correctly are introduced.

For the transmitter and receiver paths, tests such as maximum output power are unaffected by AMR and can be tested using standard GSM full rate traffic channels. Other tests need to be modified so that the AMR specific elements of the base station are adequately tested; in particular those that include AMR codecs in the signal path such as bit error rate (BER) and frame erasure rate (FER).

The key features of the AMR option are:

• Addition of key transmitter and receiver AMR measurements
• Full rate and half rate AMR channels
• ‘BOSS’ live testing for non-intrusive AMR measurements
• Rate-adaptation test
• Combined traffic/signaling BER test

Two key additional AMR capabilities that are offered are a rate-adaptation test and a combined traffic/signaling channel BER test. With the rate-adaptation test,the BER/FER for different codec rates is measured and logged. This test can be used not only for checking that the base station is correctly measuring carrier to interference ratio (C/I) but also as a tool for optimizing the thresholds and hysterisis settings used to trigger rate-adaptation.

The combined traffic/signaling BER test is included to help operators diagnose problems where calls are dropped despite AMR successfully maintaining speech quality in poor signal conditions. One potential cause of this is that although AMR successfully protects the traffic channel, the signaling channel does not use AMR and there are occasions when interference on the signaling channel causes the call to be dropped. The combined test allows the BER on the AMR traffic channel and on the signaling channel to be looked at simultaneously.

RATE-ADAPTATION TEST
During live test, a call is set up from the 6113 to the base station. The signal level is then steadily reduced and FER and BER measurements are performed and logged. At the end of the test, a summary is produced of rate change power measurements versus expected rate power thresholds as well as key BER/FER measurements before and after each instruction to change the AMR rate. The process is illustrated below:

Correct measurement of C/I by the base station can be checked by comparing the FER and BER values for given signal levels with the pre-defined limits set for the network. If both are incorrect, this will indicate a problem with the base station receiver. If only the FER is incorrect, then it is most likely the C/I measurement that has a problem.

This same data can also be used for optimizing the AMR thresholds. The results will show the FER immediately prior to the instruction to change the AMR rate. This can be used as a basis for analysis as to whether the thresholds are appropriately set.

Base Station Manufacturers Supported
The following BTS manufacturers' specific A-bis software is supported on the 6113 for AMR. If support for other manufacturers is required, please contact us.

* Ericsson
* Nokia
* Nortel
* Siemens

Software Support
The GSM standards and base station software continue to evolve as new features are introduced. In order to maintain compatibility between the 6113 and the base station under test, annual software support contracts are offered. The software support contract also provides minor enhancements to the 6113 functionality as and when released and access to the Aeroflex Helpdesk for technical support and assistance in using the 6113.