On the Design and Performance of LDPC Coded MC-CDMA Systems

This paper presents and compares two different strategies for LDPC coded MC-CDMA system design. In general, Turbo multiuser detection is exploited by combining per-user MMSE-PIC detection and LDPC decoder together at the receiver end. First alternative, proposed earlier by the authors, is to apply the code across the substreams and transmit the coded data using MC-CDMA. The other approach, in turn, is based on applying the code(s) within each substream and form a MC-CDMA transmission symbol of these separately coded streams. The analysis shows some fundamental differences in the two alternatives, with the conclusion that the second system scenario has relatively better performance. This is confirmed using computer simulations in downlink channels. Furthermore, it is also shown that the second system scenario is easily applicable in the uplink case as well, and that in general relatively small spreading factors per MCCDMA multiplex can be utilized to maintain reasonable detection and receiver complexity as a whole. Index Terms – channel coding, code division multiple access, iterative decoding, multicarrier modulation, multiuser detection