Block Error Rate (BLER) Reports Description

Block Error Rate ( BLER) Reports Description

Last updated: December 3, 2008

These reports are not applicable to GSM.

Block Error Rate (BLER) reports can be used in the production process to test the performance of a GPRS mobile station's receiver. The BLER result is derived from the Radio Link Control (RLC) layer's Packet ACK/NACK (Acknowledged/Not Acknowledged) message. BLER is simply the ratio of the number of negatively acknowledged blocks to the total number of blocks acknowledged by the mobile station.

The test set uses an Agilent proprietary data connection to enable BLER reports to be retrieved from the mobile station (For details on how to set the data connection type to BLER, see CALL:FUNCtion:CONNection:TYPE ).

The BLER reports which the test set provides are based on GPRS receiver tests defined in 3GPP 51.010 (formerly ETSI GSM 11.10), section 14.16 (GPRS) and section 14.18.1 (EGPRS).

As well as BLER reports, the test set also provides a Block Error measurement (see Block Error Measurement ). Starting or aborting a Block Error measurement does not affect the BLER reports. In addition, resetting the BLER reports does not affect the BLER measurement.

When are BLER Reports Made?

You obtain BLER results using the GPIB query CALL:STATus:(PDTCH|PDTChannel):BLERror? . This query returns the percentage of blocks tested that were in error and the total number of blocks used to generate the BLER result. To reset the BLER result you must use SYSTem:MEASurement:RESet . The BLER result does not reset automatically when you connect a different mobile station.

The BLER results are only available when the data connection status is transferring (TRAN). If you require details on data connection states, see Data Connection Processing State Synchronization .

Using Different Power Levels on Downlink Timeslots

The BLER results are calculated across all active downlink timeslots, not on any individual downlink timeslot.

When using the multislot configurations which provide two downlinks (D2U1 and D2U2), the test set requests Packet ACK/NACK (Acknowledged/Not Acknowledged) messages from the mobile station on timeslot 4. ETSI specifies that the mobile station must respond to these requests on the same timeslot. If the downlink on timeslot 4 degrades severely (and thus has a large number of block errors), the mobile station may be unaware of a request for Packet ACK/NACK messages. If this happens, the BLER reports may hang for long periods or stop completely. This may cause the data connection to stop after a few seconds.

Programming BLER Reports

This section provides an example of how to use BLER reports to test a GPRS mobile station's receiver via GPIB.

The following procedure assumes that a data connection has been established between the test set and the mobile station (connection status is Transferring). See Step 4: Make a Connection .

  1. Configure the BCH and PDTCH parameters using the CALL subsystem.
  2. Reset the BLER results using the SYSTem:MEASurement:RESet command.
  3. Use the CALL:STATus:PDTCH:BLERror? query to obtain the first BLER results.
  4. Re-configure the downlink PDTCH power level of one of the bursts using the CALL subsystem.
  5. Reset the BLER results again using the SYSTem:MEASurement:RESet command.
  6. Use the CALL:STATus:PDTCH:BLERror? query to obtain the second BLER results.

Programming Example

 
10    ! This code assumes that the current data connection state is Transferring.
20    !
30    ! Configure BCH and PDTCH parameters
40    OUTPUT 714;"CALL:PDTCH:BAND PGSM" ! Set the PDTCH band.
50    OUTPUT 714;"CALL:POW -60" ! Set the BCH level to -60 dBm
60    OUTPUT 714;"CALL:PDTCH:MSL:CONF D2U1" ! Set the multislot configuration to
70                                         ! two downlinks, one uplink.
80    OUTPUT 714;"CALL:PDTCH:PZER:LEV 30" ! Set the P0 reference level to 30 dB.
90    OUTPUT 714;"CALL:PDTCH:CSCH CS4" ! Set the channel coding scheme to CS4.
100   !
110   ! Perform a measurement reset to ensure a stable data connection.
120   OUTPUT 714;"SYST:MEAS:RES"
130   ! Read initial BLER ensuring that result is over 2000 blocks at least
140   REPEAT
150     OUTPUT 714;"CALL:STAT:PDTCH:BLER?"
160     ENTER 714;Bler_initial,Blocks_initial
170   UNTIL (Blocks_initial>=2000 AND Blocks_initial<=2300) ! <= required for
180                                                         ! NAN (9.91E+37) case.
190   !
200   ! Print results at initial downlink PDTCH power level
210   ! of -90 dBm(-60 dBm BCH level - 30 dB P0 level)
220   PRINT "Blocks tested at -90 dBm = ";Blocks_initial
230   PRINT "BLER Result at downlink PDTCH power of -90 dBm = ";Bler_initial
240   !
250   ! Set up and select the downlink PDTCH power reduction levels.
260   OUTPUT 714;"CALL:PDTCH:PRED:LEV1 11db"
270   OUTPUT 714;"CALL:PDTCH:PRED:LEV2 0dB"
280   OUTPUT 714;"CALL:PDTCH:PRED:BURS1 PRL1"
290   OUTPUT 714;"CALL:PDTCH:PRED:BURS2 PRL2"
300   OUTPUT 714;"SYST:MEAS:RES" ! Reset the BLER results
310   !
320   ! Now obtain the second set of BLER results when burst 1 has a lower
330   ! power level which introduces more block errors.
340   REPEAT
350     OUTPUT 714;"CALL:STAT:PDTCH:BLER?"
360     ENTER 714;Bler_second,Blocks_second
370   UNTIL (Blocks_second>=2000 AND Blocks_second<=2300)
380   !
390   ! Print results when downlink burst 1 is at lower downlink PDTCH
400   ! power level of -101 dBm(-60 dBm BCH level - 30 dB P0 level - 11 dB power
410   ! reduction level). 
420   PRINT
430   PRINT "Blocks tested at -101 dBm = ";Blocks_second
440   PRINT "BLER Result at downlink PDTCH power of -101 dBm = ";Bler_second
450   END

Returned Values

The BLER reports returned by this program are:

  • Blocks_initial returns the number of blocks tested to calculate the first BLER result.
  • Bler_initial returns the BLER result, in percent (%) when the downlink PDTCH power levels of both bursts are at -90 dBm.
  • Blocks_second returns the number of blocks tested to calculate the second BLER result.
  • Bler_second returns the second BLER result, in percent (%). This result has been obtained when the downlink PDTCH power level of the first burst has been reduced by 11 dB to -101 dBm.

Related Topics


Testing a GPRS Mobile Station

Receiver Sensitivity Testing in GPRS and EGPRS

CALL:STATus:(PDTCH|PDTChannel):BLERror?

Programming: Getting Started Guide for E1968A GSM/GPRS Mobile Test Application Revision A.02 and E6701C GSM/GPRS Lab Application Revision C.02

GPRS Data Connection Troubleshooting