Abstract
Two major categories of CDMA signature codes, namely unitary codes and complementary codes, are of interest. All currently available 2–3G CDMA systems make use of the unitary codes, such as Gold codes, m-sequences, Walsh–Hadamard sequences and OVSF codes, all of which work on a one-code-per-channel basis. On the other hand, a CDMA system based on complementary codes works on a flock-of-codes basis. Each user in such a CDMA system is assigned a flock of codes which should be sent to a receiver via different carriers to reconstruct perfect autocorrelation and crosscorrelation functions. A comprehensive analytical study of a STBC-CDMA system using different spreading codes is given and their bit error rate performance is evaluated and compared with both analysis and simulation under Rayleigh fading and multiple-access interference. The results reveal that a STBC-CDMA system based on complementary codes offers a capacity similar to that achievable in a noise-limited system, while a STBC-CDMA system based on traditional unitary codes suffers serious interference-limited problems even with full STBC diversity gain.
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