ON THE APPLICATION OF SEQUENCE ESTIMATION ALGORITHMS IN THE DIGITAL COMPACT CASSETTE (DCC)

In the current Digital Compact Cassette (DCC) recorder, a straightforw ard threshold detection scheme is applied which does not exploit the d istance properties of the 8-to-10 modulation (ETM) code. More advanced detection schemes are investigated to see if they Improve system perf ormance. Two soft decision sequence estimation algorithms are consider ed: a fully-fledged Viterbi algorithm realizing Maximum Likelihood Seq uence Estimation (MLSE) and a suboptimal trellis detection algorithm. With either of the algorithms, an asymptotic gain of 3 dB versus thres hold detection level in the presence of additive white Gaussian noise (AWGN) is expected. The suboptimal detection algorithm is based on the sunning Digital Sum (RDS) trellis underlying the ETM code. Performing the suboptimal algorithm requires a minimum of 48 additions, 19 compa risons, 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-hedged algorithm. Compared to the fully-hedged scheme, the suboptimal algorithm leads to a large reduct ion in computational complexity. The performance of either of the algo rithms in the presence of AWGN is determined by means of a computer si mulation, 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(-4)...10(-5) In this range of the symbol error rate, the suboptimal algorithm shows a loss of less than a quarter of a dB compa red to the fully-fledged scheme. The suboptimal trellis detection algo rithm thus results in only a slight degradation in error late performa nce compared to the fully-Hedged scheme. The examination of experiment al data showed the feasibility of both sequence estimation algorithms on the auxiliary data track of the DCC system.