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Block Error Ratio (BLER) Measurement Description
Last updated: January 16, 2009
How is a Block Error Ratio Measurement Made?
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.
Symmetrical RMCs
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).
Asymmetrical RMCs
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.)
UE Control During FDD Test Mode Operation
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.
Block Error Ratio Measurement Parameters
The trigger source for this measurement is always protocol-based (see
Trigger Source Description
).
Block Error Ratio Measurement Results
-
Integrity Indicator
-
Block Error Ratio
The ratio of incorrectly received blocks to the total blocks sent to the UE, expressed as a percentage (%).
-
Block Error Count
The number of incorrectly received blocks, or "block errors".
-
Blocks Tested
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.
-
Uplink Missing Blocks
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.
Block Error Ratio Input Signal Requirements
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