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 ).
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.
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 .
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.
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 .
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
Blocks_initialreturns the number of blocks tested to calculate the first BLER result.
Bler_initialreturns the BLER result, in percent (%) when the downlink PDTCH power levels of both bursts are at -90 dBm.
Blocks_secondreturns the number of blocks tested to calculate the second BLER result.
Bler_secondreturns 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.