7) where 4-w-k-2 (4.128) In (4.128), W is the average waiting time and K is again the convolutional code constraint length. By choosing a Reed-Solomon (RS) outer code [15], we can take advan- tage of the bursty nature of the bit errors out of the inner code decoder. RS codes use higher order Q-ary symbols, where typically Q = 2m for some inte- ger m. In most applications m=8(Q = 256). By taking m = 8 bits or 1 byte to form a single Q-ary symbol, a burst of errors in the 8 bits results in only one Q-ary symbol error which tends to reduce the impact of bit error bursts. In Figure 4.22 the conversion from Q-ary symbols to bits and back again for the coding channel of the RS outer code is shown. In addition, to avoid bursts of Q-ary symbol errors interleavers and deinterleavers may be used to pro- vide a memoryless (non-bursty) Q-ary coding channel for the RS code. As mentioned above, the most commonly employed RS code has m = 8 (Q = 256) where each symbol is an 8-bit byte and a block length of N = Q - 1 = 255 Q-ary symbols. To be able to correct up to t = 16 Q-ary symbols the number of data Q-ary symbols must be K=0-1-2t = 223 result- ing in a (255,223) block code using 256-ary symbols that can correct up to t = 16 symbols. This is equivalent to a binary (2040, 1784) block code6 that can correct up to t = 128 bits in error as long as these bits are confined to at most 16 Q-ary symbols where Q = 256. Figures 4.25 and 4.26 show the performance of the concatenation system with no interleaving for two convolutional inner codes with Viterbi decod- ing. Ideal interleaving is assumed in Figure 4.27. These curves show the cur- rently most powerful (non-sequential) coding technique available. Sequential decoding of convolutional codes with large constraint lengths can also achieve similar performance but with the possibility of losing data caused by buffer overflows [1], [2]. For the above examples where a convolutional code with the Viterbi decoder forms the inner code, it is difficult to determine conditional Each 1784 dat