A new OFDM-CDMA uplink concept with M-ary orthogonal modulation

This paper proposes the application of M-ary orthogonal Walsh modulation for an OFDM-CDMA uplink transmission. Beside the examination of general system properties, it is shown that decision-directed phase estimation represents a channel estimation concept suitable for the new system. The Walsh modulation can also be interpreted as a linear block code with low decoding complexity, and the paper concerns the serial concatenation of convolutional codes (CC) with Walsh modulation. New aspects arise since the CC mainly operates in time domain, and the Walsh modulation is merely arranged in frequency domain. In this context, we derive the bit specific reliability information for maximum likelihood (ML) soft decoding of the CC and discuss the trade-off between coding and spreading in case of sufficient and non-sufficient frequency interleaving. Throughout the discussions, the results are always compared with BPSK modulation performance, and it can clearly be demonstrated that M-ary Walsh modulation significantly outperforms BPSK modulation in all aspects considered in this work. Although the specific simulations are related to the European Hiperlan/2 standardization, the results are valid in general.