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Last updated: February 28, 2014
3GPP TS 34.121, F.6.1.1 defines block error ratio (BLER) as follows: "A Block Error Ratio is defined as the ratio of the number of erroneous blocks received to the total number of blocks sent. An erroneous block is defined as a Transport Block, the cyclic redundancy check (CRC) of which is wrong."
To perform a block error ratio measurement, you must be on a Radio Bearer Test Mode call. The block error ratio measurement can be performed for both Symmetrical RMCs and Asymmetrical RMCs . For RMCs with a downlink rate of 12.2, 64 or 144 kbps, the test set sends a block every 20 ms. For RMCs with a downlink rate of 384 kbps, the test set sends a block every 10 ms.
The data sent on the downlink is determined by the DL DTCH Data setting.
For Symmetrical RMCs (which use Transparent Mode (TM) RLC entities on the DTCH), the test set measures block error ratio by sending data and CRC bits in the downlink transport blocks to a UE that is configured in loopback mode 2 (UE Loopback Type must be set to Type 2 ). The UE then loops the data bits and CRC bits from the downlink transport blocks into the uplink transport blocks and transmits them in the uplink. The test set then generates a CRC from the data bits received in the uplink transport block and compares this calculated CRC against the CRC received in the uplink transport block (this CRC is the downlink CRC for the downlink transport block, looped back up by the UE). If the CRCs do not match, the transport block is defined to be a "block error."
To perform the block error ratio measurement for symmetrical RMCs, Uplink DTCH RMC CRC Presence must be set to Used for Data . This disables the uplink CRC, to allow room for the UE to loop back the downlink CRC for each block (there are an equal number of available bits in the uplink and downlink, if the UE were to transmit an uplink CRC, it would not be able to loop back the downlink CRC).
For Asymmetrical RMCs (which use Acknowledged Mode (AM) RLC entities on the DTCH), the test set increments the Block Error Count when it receives a retransmission request from the UE. (The UE generates a CRC from the data bits received in the downlink transport block, and compares this calculated CRC against the CRC received in the downlink transport block. If the CRCs do not match, the UE sends a retransmission request to the test set.)
The FDD Test Operating Mode does not provide radio bearer setup control of the UE for test mode operation. You must configure the UE in loopback mode 2 and synchronize it to the test set's downlink signal in order to make this measurement in FDD test operating mode.
The uplink transport format must include both the DTCH and the DCCH; however, only the DTCH information is used for the block error ratio measurement.
Note that Asymmetrical RMCs are not available in FDD test operating mode.
Sets the number of blocks to test during the measurement.
Note, the time for the measurement to complete increases linearly with the Number of Blocks to Test . For example, to test 500 blocks while on a 12.2k RMC takes approximately 10 seconds (500 blocks x 20 ms/block = 10 seconds).
See Measurement Timeouts . Ensure that the Measurement Timeout is greater than the time the measurement needs to measure the desired Number of Blocks to Test .
The trigger source for this measurement is always protocol-based (see Trigger Source Description ).
The ratio of incorrectly received blocks to the total blocks sent to the UE, expressed as a percentage (%).
The number of incorrectly received blocks, or "block errors".
Number of blocks tested to determine the Block Error Ratio and Block Error Count results.
Note, you set the number of blocks to test during the measurement using the Number of Blocks to Test setting. However, for Asymmetrical RMCs , the actual number of Blocks Tested may be greater than the Number of Blocks to Test . For asymmetrical RMCs, every 200 ms the UE indicates to the test set whether the blocks received in the last 200 ms period were received correctly or if any retransmissions are required. Depending upon the alignment of this 200 ms measurement period with the TTI boundary, and depending upon how many blocks are sent every 200 ms (based on data rate), it is quite likely that the UE will provide acknowledgment/retransmission information for more blocks than requested by the Number of Blocks to Test setting. These extra blocks are included in the Blocks Tested , Block Error Ratio and Block Error Count results.
The UE sends a TFCI for each uplink DTCH transport block. When operating in Active Cell Operating Mode , the test set monitors the uplink TFCI, and can report uplink missing blocks. For Symmetrical RMCs , if the TFCI indicates that there is no data block sent for that TTI, the test set reports a missing block. When an uplink missing block occurs, no block comparison is done on the block, and the number of Blocks Tested is not incremented. The test set returns a Questionable MS-to-Cell Data Integrity Indicator .
The Uplink Missing Blocks result does not apply to Asymmetrical RMCs , because data is not returned on the uplink, only periodic status reports.
When in FDD Test Operating Mode , the test set does not monitor the uplink TFCI; rather, it assumes that a data block is sent in every TTI. Thus, errors resulting from uplink missing blocks are included in the Block Error Count result when in FDD test operating mode.
The expected power into the test set must be set in order to maintain the link with the UE. This is done using the UE Target Power setting or by using manual receiver power control and specifying the expected power level. See Receiver Control .
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Manual Operation: How Do I Make a Block Error Ratio (BLER) Measurement?
Programming a Block Error Ratio Measurement
Block Error Ratio Troubleshooting
HSDPA Block Error Ratio Measurement Description
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