In the chart below, DominoEX 8 with FEC is compared with DominoEX 8 (without FEC) and DominoEX 4. The FEC result charted below uses the soft Viterbi decoder in cocoaModem. The decoder's trellis depth is set to 21. Please see the raw numbers in the parent page to compare the soft Viterbi decoder with cocoaModem's hard Viterbi decoder (not charted below). The soft decoder has about a quarter of a dB better sensitivity than the hard decoder.

fec8vs4



Observations

Notice that


  • DominoEX 4 has about the same character throughput as DominoEX 8 when FEC is used,

  • DominoEX 4 uses about half the bandwidth that is required by DominoEX 8 with FEC,

  • From the AWGN chart above, it can be seen that even though FEC improves the sensitivity of DominoEX 8 (0.4% CER compared to 3% CER at -15 dB SNR), DominoEX 8 with FEC is still not as sensitive as DominoEX 4 (0.12% CER for DominoEX 4 vs. 5% CER for DominoEX 8 with FEC at -16 dB SNR) when there is no multipath distortion.

    DominoEX 8 with FEC can, however, substantially improve copy under multipath conditions over DominoEX 4 (please see section on ITU Profiles, particularly the flutter and high latitude conditions).