To compute the resulting SNR margin, we first need to compute the resulting output signal-to-noise ratio ( SNR out ) and then take the difference from the reference SNR value (SNR ref ) that corresponds to a bit error rate (BER) of 10 -7 . Table 9.2 lists the SNR ref values [8] for the uncoded signal constellations considered in this study. To include the gain effects of the trellis code, the coding gain is subtracted from the uncoded signal's SNR ref . The output signal-to-noise ratio (SNR out ) of the decision feedback equalizer in the CAP/QAM receiver is computed by [8]
The output signal-to-noise ratio of the DFE in the PAM receiver is computed by [8]
Table 9.2. List of Reference Signal-to-Noise Ratios of Various Line Codes
The SNR margin ( M ) is computed as follows :
where G TC is the coding gain of the trellis code and SNR ref,uncoded is the reference SNR of the uncoded line code (second column in Table 9.2). Alternatively, this equation may be expressed as
where SNR ref , coded = SNR ref , uncoded - G TC . |
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