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

The use of bandwidth efficient high level modulation systems such as quadrature-amplitude modulation (MQAM) and multiphase (MPSK), together with Reed-Solomon (RS) codes, provides substantial coding gain on fading channels. The author derives the optimum modulation and coding parameters of RS coded MPSK and MQAM schemes. The transmission channel is subject to flat Rician fading and spread-spectrum code-division multiple-access (SS-CDMA) interference. For RS codes defined over GF(M ^m), the encoded symbols are mapped to the signal points of an expanded set with cardinality of M such that each RS code symbol consists of concatenation of m 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 probability of error (P_c) using RS codes. Finally, the optimum modulation and coding parameters which optimise the bit-error performance are obtained by setting partial derivatives of P_c to zero and solving the resulting equations. It is shown that the optimum choice of modulation and coding parameters depends on the channel interference and fading conditions. Although exact analysis can be used, the present approach yields a general solution, and optimum design parameters can be related to channel conditions