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The MAI performance of orthogonal codes for channel cover in Asynchronous CDMA system

Summary: The MAI performance of orthogonal codes for channel cover
in Asynchronous CDMA system
Miftadi Sudjai and Mosa N.A. Abu Rgheff
CDMA Research Group,
Department of Electronics and Communication Engineering, University of Plymouth, UK
Abstract: It is widely believed that the walsh code is the best to provide covering for a
CDMA channel due to its orthogonality. However, It exhibits a severe aperiodic ACF and
variation of its aperiodic ACF pattern for each code. Hence, the comparison of MAI
performances of walsh sequence with other three Orthogonal sequences as a channel
cover code in DS-CDMA was established. The aperiodic ACF and CCF that are directly
correspondent with average system performance are examined. It is shown that walsh code
has the worst among the others in term of aperiodic ACF and CCF. The average system
performance is assessed by AIP-based computation and simulation based on gaussian
approximation method. However, the result shows the other orthogonal codes provide
slightly lower BER performance in the simulation. The computation shows both Luke type I
and Cubic polyphase code produce a strongest resistance to MAI with significant margin
than walsh code, while OCPS code generates the weakest resistance to MAI. It is due to
that the aperiodic auto correlation of both polyphase code which directly influence the AIP
is better than walsh and OCPS code. On the contrary the simulation shows walsh code
outperform the polyphase codes and OCPS for Eb/No > 4 dB, due to the effect of filtering


Source: Abu-Rgheff, Mosa Ali - School of Computing, Communications and Electronics, University of Plymouth


Collections: Engineering