MQAM modulation and RS codes for SS-CDMA communication over Rician fading channels

The use of bandwidth efficient high level modulation systems such as quadra ture-amplitude modulation (MQAM) and multiphase (MPSK), together with Reed- Solomon (RS) codes, provides substantial coding gain on fading channels. Th e author derives the optimum modulation and coding parameters of RS coded M PSK and MQAM schemes. The transmission channel is subject to flat Rician fa ding and spread-spectrum code-division multiple-access (CDMA-SS) interferen ce. For RS codes defined over GF(M-m), the encoded symbols are mapped to th e signal points of an expanded set with cardinality of M such that each RS code symbol consists of concatenation of In M-ary symbols. It is shown that there is an optimum selection of m which minimises the bit-error rate. The Gaussian approximation is used to derive a simple expression of the probab ility of error (P-c) using RS codes. Finally, the optimum modulation and co ding parameters which optimise the bit-error performance are obtained by se tting partial derivatives of P-c to zero and solving the resulting equation s. It is shown that the optimum choice of modulation and coding parameters depends on the channel interference and fading conditions. Although exact a nalysis can be used, the present approach yields a general solution, and op timum design parameters can be related to channel conditions.