Rate Adaptation with CDM versus Adaptive Coding for Next Generation OFDM Systems

This paper proposes data rate adaptation based on code division multiplexing (CDM). Under investigation are OFDM systems with cyclic delay diversity (CDD) and with spatial phase coding (SPC). These schemes are promising candidates for future broadband wireless systems. As lower bound, maximum ratio transmission (MRT) is chosen as reference. Imperfections due to channel estimation are taken into account in the investigations. The comparison of adaptive CDM versus adaptive coding shows that adaptive CDM outperforms adaptive coding, especially when spatial transmit diversity schemes are applied. This result is of interest for the design of future broadband adaptive transmission systems like IMT-Advanced.