|Operating Mode||ETSI B Unack||ETSI B Ack||BLER||Auto1||SRB Loopback|
|Active Cell||GPRS||Loopback||Loopback or Polling||Polling||Polling||This connection type is not applicable to the BLER Measurement|
The test set generates one or more downlink PDTCHs at a known level with data using the payload pattern you specify. (See Payload Patterns .) The default payload pattern is a pseudo-random binary sequence, PRBS-15, which is the most appropriate for this measurement. The mobile station receives the data, loops it back to its transmitter, and returns the data to the test set in the available uplink PDTCHs. You can specify the first downlink burst to be looped back in the first uplink burst using the command CALL:(PDTCH|PDTChannel):MSLot[:FIRSt]:DOWNlink:LOOPback[:BURSt] . The test set compares data sent to data received. A block that is received which has one or more bit errors within it is marked as having a block error.
Each mobile station may have a different time delay between receiving a block of data and re-sending it on the uplink. By default, the loopback delay control mode is set to automatic, and the amount of delay needed is determined when the test set has, for four consecutive blocks, correctly received 80% of the downlink bits back on the uplink. The test set can be queried for the block delay value using FETCh:BLERror:DELay? .
If necessary, you can manually set the delay. First, change loopback delay control to Manual using the command SETup:BLERror:LDControl:AUTO , and then set the delay using SETup:BLERror:LDControl:AUTO .
The BLER measurement result is calculated irrespective of the Layer 1 reported demodulation status. The BLER measurement result a will vary depending on the setting for the BLER Bad Block Handling setting (see SETup:BLERror:BBLocks for more information on the BLER Bad Block Handling parameter).
Exclude. Radio blocks that fail the CRC (cyclic redundancy check or frame check sequence) are considered invalid an are excluded. See FETCh:BLERror:CRC? for more information on the CRC Error Count parameter.
The test set periodically polls the mobile station, deriving the BLER measurement result from the Radio Link Control (RLC) layer's Packet ACK/NACK (Acknowledged/Not Acknowledged) message. Polling the mobile station for this message provides an indication of which blocks have been successfully received, and which blocks have been received with an error.
Number of blocks
parameter is used to define the number of blocks to be measured in the BLER measurement. However, the actual number of blocks measured are always larger than the
Number of blocks to test
parameter is set to
. Set the
will make the actual number of blocks measured equal to the
Number of blocks to test
. The Blocks Tested parameter can be set using
The number of blocks indicated to be in error and the total number of blocks received are counted. The polling interval can be set using CALL:FUNCtion:DATA:BLER:POLLing:INTerval .
For the ETSI B Ack connection type, the BLER measurement can be performed in using either the Loopback or Polling measurement method. You can select the method to be used by the measurement with the following command: SETup:BLERror:ETSIB:MODE .
BLER measurements cannot be made when the data connection type is set to ETSI Type A in Active Cell operating mode, nor in BCH test mode. The test set's operating mode can be set using CALL:OPERating:MODE . The data connection type can be set using CALL:FUNCtion:CONNection:TYPE .
You may want to collect BLER results for different GPRS coding schemes. Use the command CALL:(PDTCH|PDTChannel):CSCHeme:UPLink to change the GPRS coding scheme.
You may want to collect BLER results with different modulation and coding schemes for EGPRS. Use the command CALL:(PDTCH|PDTChannel):MCSCheme to set the EGPRS modulation coding scheme.
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".
The results of a BLER measurement can be displayed in two ways; the number of block errors counted or the ratio of bad blocks (errors) to total blocks counted. If you are using the test set manually, both Count and Block Error Ratio are displayed on the Block Error measurement screen. If you are using the test set remotely, these results are available using the FETCh command, see FETCh:BLERror:COUNt? or FETCh:BLERror:RATio? . Alternatively the command FETCh:BLERror[:ALL]? can be used to return all of the following results:
In addition, the Intermediate Count of Blocks Tested result can be queried using FETCh:BLERror:ICOunt? , Block Delay can be queried using FETCh:BLERror:DELay? , and the CRC count can be queried using FETCh:BLERror:CRC? .
When using the Polling measurement method, you can also retrieve the following measurement results for individual timeslots using FETCh:BLERror:BURSt<|2|3|4|5>[:ALL]? .