In the current digital compact cassette (DCC) recorder, a
straightforward threshold detection scheme is applied which does not
exploit the distance properties of the 8-to-10 modulation (ETM) code.
More advanced detection schemes are investigated to see if they improve
system performance. Two soft decision sequence estimation algorithms are
considered: a fully-fledged Viterbi algorithm realizing maximum
likelihood sequence estimation (MISE) and a suboptimal trellis detection
algorithm. With either of the algorithms, an asymptotic gain of 3 dB
versus threshold detection level in the presence of additive white
Gaussian noise (AWGN) is expected. The suboptimal detection algorithm is
based on the running digital sum (RDS) trellis underlying the ETM code.
Performing the suboptimal algorithm requires a minimum of 48 additions,
19 comparisons, and a single table look-up for both detection and
decoding of an ETM codeword, versus a minimum of 4234 additions, 421
comparisons, and 423 table look-ups for the fully-fledged algorithm.
Compared to the fully-fledged scheme, the suboptimal algorithm leads to
a large reduction in computational complexity. The performance of either
of the algorithms in the presence of AWGN is determined by means of a
computer simulation. The fully-fledged Viterbi algorithm achieves a gain
of about 2.3 dB versus threshold detection level for symbol error rates
in the order of 10<sup>-4</sup> to 10<sup>-5</sup>