Multilevel block codes with interdependency among component codes for Rayleigh fading channels

In this paper, in order to improve error correction capacity, the following method is proposed for constructing multilevel codes with interdependencies among the levels. First, one of the component codes of a basic multilevel code is divided into 2(i) (i = 1, 2,...) subcodes. Then, the number of codewords of the other component code is expanded by a factor of 2(i) and partitioned into 2(i) subcode groups. One-to-one assignments among the levels are made between these subcode groups, a code array is constructed by using only the codewords contained in these subcodes, and an interdependency among the levels is introduced. In QPSK and 8PSK modulation, multilevel codes that have superior performance in fading channels are determined through a computer search. Furthermore, the bit error rate performance in the Rayleigh fading channel is determined by computer simulation. Then, although the decoder complexity of the multistage decoding method is increased after the introduction of the interdependencies, the bit error rate becomes equivalent to that of maximum likelihood decoding. Compared with previously published results, it is demonstrated that codes can be constructed with higher coding gain. (C) 1998 Scripta Technica.