Diversity-Coding-Orthogonality Trade-off for Coded MC-CDMA with High Level Modulation

Deepshikha GARG
Fumiyuki ADACHI

Publication
IEICE TRANSACTIONS on Communications   Vol.E88-B    No.1    pp.76-83
Publication Date: 2005/01/01
Online ISSN: 
DOI: 10.1093/ietcom/e88-b.1.76
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Multi-carrier Signal Processing Techniques for Next Generation Mobile Communications--Part 1)
Category: Diversity
Keyword: 
MC-CDMA,  high-level modulation,  spreading factor,  frequency diversity,  channel coding,  orthogonality,  

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Summary: 
In MC-CDMA, the data rate can be increased by reducing the spreading factor SF or by allowing multicode transmission. In this paper, we examine by computer simulations which gives a better bit error rate (BER) performance--lower SF or multicode operation--when high level modulation is used in addition to error control coding. For a coded system in a frequency selective channel, there is a trade-off among frequency diversity gain due to spreading, improved coding gain due to better frequency interleaving effect and orthogonality distortion. It is found that for QPSK, the performance of OFDM (MC-CDMA with SF = 1) is almost the same as that of a fully spread MC-CDMA system. However, for 16QAM and 64QAM, the BER performance is better for lower SF unlike the uncoded system, wherein higher SF gives a better BER.