CXD1968AR
Performance Monitoring
Pre-Viterbi BER
Pre-Viterbi BER readings are available from the VIT_BER register. The sampling period is adjustable
in the VIT_CTRL register.
Reed-Solomon BER
Pre- or Post-Reed-Solomon BER can be either measured or estimated using the BER_ESTIMATE
register. In measurement mode, NULL packets must be used. In estimate mode, any data can be used.
Estimation mode assumes that all post Viterbi errors are corrected by the Reed-Solomon decoder.
Measurement mode is selected by setting the Measurement_Sel bit in the FEC_PARAMS register.
Readings should be taken whenever the NEW_BER bit is set. If too many errors have been recorded
during the specified measurement period, then the BERCNT_Overflow bit will be set. Should this occur,
the reading should be discarded and a lower measurement period selected. The measurement period
is set using the BER_PERIOD register.
Uncorrected Errors
Errored Second
This indicates that the Reed-Solomon FEC block could not correct all the errors found in one or more
204-byte packets received during the last second. This is because >8 errors were found in the packet.
Errored second can be determined from reading the FEC_STATUS register, or from the
INTERRUPT_SOURCE register.
Severely Errored Second
This indicates that the Reed-Solomon FEC block has been unable to correct the errors found in N or
more 204-byte packets received during the last second. This is because >8 errors were found in each
of the packets.
N is set using the LT_QLTY_THRESHOLD register. Typically, this can be used to set a threshold value
with regard to picture degradation, depending on the quality of service required. Severely errored
second can be determined from reading the FEC_STATUS register, or from the INTERRUPT_SOURCE
register.
Codeword Reject Count
This indicates the number of rejected codewords (MPEG-2 packets) in one second. This is recognized
to be a particularly useful measurement as it is more closely aligned to receiver picture failure than
BER.
Signal-to-Noise Estimate
The CHC_SNR register can be used to obtain an estimate of the signal-to-noise ratio of the received
signal either for each carrier individually or as a mean across the channel.
If the mean bit in the SNR_CARRIER_2 register is set, then a mean value across the channel can be
read from the CHC_SNR register.
If the mean bit in the SNR_CARRIER_2 register is reset then the carrier number can be selected by
programming the SNR carrier number bits in the SNR_CARRIER_1, 2 registers and after at most one
symbol the SNR for that carrier can be read from the CHC_SNR register (the host controller must wait
for one symbol to be sure that the data is ready).
A higher value indicates a lower operating SNR. The estimated value is independent of the channel
response, and accurate to about ±1dB. The value in this register (N) can be converted to an
approximate dB value using the following empirical formula:
CHC_SNR
SNR[dB] = ------------------------------
8
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SONY [ SONY CORPORATION ]
