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Last updated: 2014-11-28
Loopback Bit Error Ratio (BER) Measurement Description
Loopback Bit Error Ratio (BER) Measurement Parameters
Loopback Bit Error Ratio (BER) Measurement Results
3GPP TS 34.122 F.6.1.1 defines bit error ratio (BER) as follows: "The Bit Error Ratio is defined as the ratio of the bits wrongly received to all data bits sent. The bits are the information bits above the convolutional/turbo decoder."
When the test set measures loopback bit error ratio, it sends a known data pattern on the downlink DTCH to a UE that is configured in loopback type 1 (see UE Loopback Scenario). The UE decodes the data and re-transmits it on the uplink DTCH. The test set analyzes the uplink data to see how closely it matches the data bits originally sent on the downlink and reports the BER results.
To decrease test time, you may set Confidence State to On and specify the BER Requirement , which allows the test set to stop testing when an early pass or early fail event occurs, and to report a Confidence Test Result (see 3GPP TS 34.122 F.6 and 3GPP TS 34.901).
To perform the loopback BER measurement while in Active Cell operating mode , you must be on an RB test mode call and:
if the Channel Type is 12.2k RMC SC or 12.2k RMC MC, the UE Loopback Scenario should be Type1, RLC TM.
if the Channel Type is 12.2k RMC + HSDPA, the UE Loopback Scenario setting is not applicable but Type1, RLC TM will be used by default by the test set.
The loopback BER measurement is not applicable for the CW and Cell Off operating mode.
When set to Off, this parameter determines the number of data bits to test during the measurement. However, the actual number of bits tested is always the largest multiple of the number of bits needed to fill a DTCH transport block for the transmitted format.
When set to On, this parameter determines the maximum number of bits to test during the measurement. However, the actual number of bits tested will be less than this number if an early pass or early fail event occurs (see Confidence Test Result). If a Confidence Test Result of Max Bits Tested is returned, then the actual number of bits tested is the largest multiple of the number of bits needed to fill a DTCH transport block for the transmitted format, as explained above.
Trigger Arm: see Trigger Arm.
Measurement Timeout: see Measurement Timeout.
To decrease test time, you may set the Confidence State to On and specify the BER Requirement, which allows the test set to stop testing when an early pass or early fail event occurs, and to report a Confidence Test Result (the Confidence Level is fixed for the measurement).
3GPP TS 34.122 F.6 defines TR = Test Requirement. As testing progresses, the bit error ratio trajectory converges to a value (see 3GPP TS 34.122 Figure F.6.1.9). The BER value that the UE is converging to shall not exceed the Test Requirement. The BER Requirement parameter is equivalent to Test Requirement expressed as a percentage.
Bad CRC Block determines whether the bad CRC block will be counted for BER calculation. If it is set to Exclude, the number of error bits, the number of tested bits, and the BER will not be updated by this bad CRC block; else this block will be used for BER calculation.
The following are fixed settings in the test set:
3GPP TS 34.122 F.6 defines:
F = probability of a wrong decision
(1 - F) = probability of a correct decision
The probability (risk) to fail a good DUT shall be </= F according to the following definition: A DUT is failed, accepting a probability of </= F that the DUT is still better than the specified error ratio (Test requirement).
The probability to pass a bad DUT shall be </= F according to the following definition: A DUT is passed, accepting a probability of </= F that the DUT is still worse than M times the specified error ratio. (M>1 is the Bad DUT Factor ).
The Confidence Level parameter is equivalent to (1 - F). 3GPP TS 34.122 table F.6.1.8 specifies an F of 0.2% ( Confidence Level of 99.8% ) for all Receiver and Performance Characteristics tests in 3GPP TS 34.122 sections 6 and 7 (except for the fail limit for 6.5 Blocking Characteristics).
Confidence Level is thus fixed to 99.8%.
Similarly,
Bad DUT Factor (M) is fixed to 1.5.
Test Limit (Test requirement *Test Limit Factor) is fixed to 1.234
Target Number of Error Bits is fixed to 345
Bit Error Ratio: the ratio of incorrectly received bits to the bits tested, expressed as a percentage (%).
Number of bits tested to determine the Bit Error Count and Bit Error Ratio results.
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. If the TFCI indicates that there is no data block sent for that TTI, the test set reports a missing block. When a missing block occurs, Bit Error Count and Bits Tested are not incremented;
In TD-SCDMA Test Operating Mode, if the UL DPCH TFCI State is set to Manual, the test set does not monitor the uplink TFCI, thus the reported number of missing blocks will always be zero.
To determine if an uplink CRC error has occurred, the test set calculates the CRC for the data sent in the uplink DTCH transport block, and compares the result to the CRC sent by the UE for that transport block. When a CRC error occurs, the data within the block is not analyzed, and the number of Bits Tested is not incremented.
Loopback Delay: the delay between received downlink radio frames and their corresponding uplink radio frames (produced from the received data). It can not be obtained when DL DTCH Data is set to All Zeros, All Ones or Alternating.
The Confidence Test Result is only available when Confidence State is On.
Pass: Few enough bit errors were detected for a large enough number of Bits Tested that the test set is able to predict that the bit error ratio trajectory is converging to a value below the BER Requirement. An early pass event is determined.
Fail: Enough bit errors were detected for the number of Bits Tested that the test set is able to predict that the bit error ratio trajectory is converging to a value above the BER Requirement. An early fail event is determined.
Max Bits Tested: After testing the number of bits specified by Number of Bits to Test, the test set is unable to predict whether the bit error ratio trajectory is converging to a value above or below the BER Requirement.
The test set can synchronize to the UE's signal only if the bit error ratio is less than 10% on a block-by-block basis for three consecutive blocks.
GPIB Commands: SETup:TBERror, FETCh:TBERror