OFDM BER/MER Summary (DOCSIS 4.0 Downstream)

The OFDM BER/MER Summary trace shows the Bit Error Ratio (BER), Modulation Error Ratio (MER), and Codeword Error Ratio (CWER) for each profile used.

A displayed value of "***", "-780dB" or "-999" means no data is available.

Mod Format

Mod Fmt: The modulation format is a detected QAM value. NCP can only be QPSK, 16 QAM, or 64 QAM.

MER

MER: The average value of the Modulation Error Ratio (MER).
MER Pk: is the peak level of the Modulation Error Ratio (MER).

BER/CWER

BER/CWER measurements only show when BER Analysis is selected under the Format tab.

Bits Before LDPC: You can accumulate bit counts by enabling measurement averaging (MeasSetup > Average > RMS or RMS Exponential). The Pause Measurement after Bit Count feature uses the Bits before LDPC count.
Bit Errors Before LDPC: Bit error count before LPDC. After LPDC, codeword errors are measured instead of bit errors.
BER Before LDPC: Ratio of bit errors to total bits before LPDC. After LPDC, codeword errors are measured instead of bit errors.
Num Codewords(CW): Total number of codewords processed for CWER.
CW Errors Post LDPC: Codeword Error count after multiple iterations of the LDPC decoder and before the BCH decoder.
CWER post LDPC: Codeword error ratio after multiple iterations of the LDPC decoder and before the BCH decoder.
CW Errors post BCH: Codeword error count after the BCH decoder.
CWER post BCH: Codeword error ratio after the BCH decoder.
Average LDPC iterations: Average number of LDPC iterations used over all codewords in a profile.
Max LDPC iterations: Maximum number of LDPC iterations used over all codewords in a profile. The maximum number of iterations used in decoding is 20.

About Profiles

There are up to 16 profiles (A-P) plus NCP. The corresponding profile IDs are 0-15 for A-P and 255 for NCP.

When Initial Settings = Auto, only NCP and Profile A can be demodulated. Other profiles will be detected and shown in the BER/MER summary, but detected profiles B-P will display "Unknown" in the Mod Fmt row and undesirable MER values. This is an indication that the signal has B-P profiles that need to be manually defined to get correct overall MER and BER measurements for the signal. Unless the profiles corresponding to these code words are defined, VSA can not determine the modulation type associated with the code word, and so it is not possible to accurately calculate the MER.

To manually define Profiles B-P, set Initial Settings to Manual and then edit the User Profiles vectors.