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Abstract. This paper proposes a plural ZCZ-CDMA system with binary frequency keying modulation. It is shown that this system achieves more advantageous bit error rate characteristics over Rayleigh fading channels than those of ASK or BPSK modulation scheme and have more advantageous for comprehensive spectral efficiency than BFSK modulation scheme. From the viewpoints of further improving their error rate performance over Rayleigh fading channel, this research on BFSK is conducted while introducing new techniques such as use of fading-independency between two keying frequencies to which a pair of balanced ZCZ sequences is allocated, and use of combining techniques with two demodulated outputs obtained by the two ZCZ sequences. Performance formulation and simulation on the proposed system are conducted under the comparison with the other ZCZ-CDMA systems or CDMA systems using the other codes. It will be proved that considerable improvement is achieved with the proposed system.