DOUBLE M-ARY SPREAD SPECTRUM COMMUNICATION-SYSTEMS/

In this paper, to obtain higher spectral efficiency than a conventiona l M-ary/Spread Spectrum (SS) communication system using an orthogonal code, we propose Double M-ary/SS communication systems in which transm itting sequences are produced by multiplying two sequences obtained fr om different M-ary/SS systems. First, we estimate the system performan ce of a Double Mary/SS in which transmitting sequences are composed of two kinds of sequences which have the same chip duration and the same sequence length in AWGN environment by theoretical analysis and compu ter simulations using random sequences. And we show that the bit error rate (BER) of the system can be improved, compared to that of the con ventional M-ary/SS. Next, we propose two concrete examples of the Doub le M-ary/SS systems. We investigate the performance of these systems i n AWGN environment by computer simulations, and show that the BER and spectral efficiency can be improved by the two systems compared to tho se of the conventional M-ary/SS. Further, we consider a modified metho d of the demodulation for one of the examples of Double M-ary/SS syste ms, and show that we can reduce quantity of calculations by the method .