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Bit Error Measurement Description

Last updated: May 8, 2002

The Bit Error Measurement is applicable to both GSM and GPRS. This measurement description contains two sections:

• GSM Bit Error Measurement
• GPRS Bit Error Measurement

How is a Bit Error (BER) Measurement Made?

During BER measurements, the test set generates a downlink TCH with pseudo-random binary sequence, PRBS-15, data at a known level. The mobile station receives the data, loops it back to its transmitter, and returns the data to the test set. The test set compares data sent to data received, and BER is calculated.

SETup subsystem commands are sent to the test set to specify the time taken to close its loopback path, whether to open or close a loop during downlink signaling operations (for example, channel assignment), the number of bits to test, measurement type, speech frames delay, measurements units, trigger arm, and measurement timeout values.

When a call is established on the TCH, the loopback type corresponding to one of the BER measurement types must be sent to the mobile station. The test set closes the loopback automatically and re-opens it when the measurement is closed (that is, when INITiate:BERRor is OFF).

You must set the measurement type from one of the six measurement types available, (see SETup:BERRor[:TYPE] ). If you query a residual result when a non-residual measurement is initiated, the test set returns 9.91 E+37 (NAN). The Measurement type must be set before initiating a BER measurement. See BER Measurement Types

The loop must be closed before a BER test can start, using the close loop signalling delay time feature allows time for the loop to close. See SETup:BERRor:CLSDelay[:STIMe] for more details.

Each mobile station may have a different time delay between receiving a speech frame and re-sending it on the uplink. By default, the test set is configured to LDControl:AUTO:ON, and the amount of delay needed is determined automatically when the test set has, for two frames, correctly received 80% of the downlink bits back on the uplink. The test set can be queried for the speech frames delay value.

If necessary, you can manually set the delay (see SETup:BERRor:LDControl:AUTO ).

In case the test set is not able to correlate the data it transmits on the downlink with the data it receives on the uplink, a Measurement Timeout value should be set. If a timeout is not set and the test set is unable to correlate, the measurement will appear to "hang".

BER Measurement Types

Residual:

• Residual Type IA (50 bits per speech frame)
• Residual Type IB (132 bits per speech frame)
• Residual Type II (78 bits per speech frame)

Loopback Type A is sent to the mobile station when one of these residual measurement types is selected. A BER measurement with FE will return the frame erasure count or ratio results. The mobile station will indicate in the speech frame, if the downlink frame was received with CRC (cyclic redundancy check) errors the speech frames are erased. The mobile station sets all bits in the uplink speech frame to 0, indicating speech frames were erased.

Non-residual:

• Type IA (50 bits per speech frame)
• Type IB (132 bits per speech frame)
• Type II (78 bits per speech frame)

Loopback Type B is sent to the mobile station when one of these non-residual measurement types is selected. A BER measurement with CRC's (cyclic redundancy check) will return the CRC count or ratio results. The mobile station will not indicate if any speech frames in the downlink were erased.

BER Measurement Results

The results of a BER measurement can be displayed in two ways, (number of errors counted) or (the ratio bad bits (errors) to total bits counted). If you are using the test set manually, select either Count or % from the Measurement Units field. If you are using the test set remotely, these results are available using the FETCh command, see FETCh:BERRor:COUNt[:BITS]? or FETCh:BERRor:RATio[:BITS]? . Alternatively the FETCh:BERRor[:ALL]? or FETCh:BERRor:FULL? can also be used to return the results.

Related Topics for GSM

Programming a Bit Error Measurement

Test Adherence to Standards

Fast Bit Error Measurement Description

Programming a Fast Bit Error Measurement

CALL:TCHannel:LOOPback

Bit Error Troubleshooting

GPRS Bit Error Measurement

Note

Types of Signal BER can Measure

BER measurements can be made on these types of input signals:

• One or more GPRS uplink and downlink PDTCH pairs with the mobile station in active cell mode and the data connection type set to ETSI Type B. If you want to optimize measurement speed, it is important that the mobile station is set up for the same number of uplink and downlink PDTCHs.
• One or more GPRS uplink and downlink PDTCH pairs with the mobile station in GPRS BCH+PDTCH test mode (see CALL:OPERating:MODE for details on setting the cell operating mode). Note that you have to manually set your mobile station to synchronize its internal frequency and timing reference with the test set. You also have to command the mobile station to loop back the PDTCH data.

BER Measurement Results

The results of a BER measurement can be displayed in two ways; the number of errors counted or the ratio of bad bits (errors) to total bits counted. If you are using the test set manually, both Count and Bit Error Ratio are displayed on the Bit Error measurement screen. If you are using the test set remotely, these results are available using the FETCh command, see FETCh:GBERror:COUNt? or FETCh:GBERror:RATio? . Alternatively the command FETCh:GBERror[:ALL]? can be used to return all of the following results:

• Integrity Indicator
• Bit Error Ratio
• Bits Tested
• Bit Error Count

In addition, the Intermediate Count of Bits Tested result can be queried using FETCh:GBERror:ICOunt? and the Block Delay can be queried using FETCh:GBERror:DELay? .

Related Topics for GPRS

Programming a Bit Error Measurement

Test Adherence to Standards

Bit Error Troubleshooting

Receiver Sensitivity Testing in GPRS