Spread-spectrum multiple-access performance of orthogonal codes for indoor radio communications

Direct sequence spread spectrum with its inherent resistance to multipath is a promising technique for indoor wireless communication. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. This correspondence analyzes the bandwidth efficiency of M-ary CDMA systems in fading multipath indoor radio channels. It is shown that M-ary signaling improves the bandwidth efficiency significantly as compared to binary signaling. N. M-ary equally likely data symbols are transmitted at a rate of one every T seconds. The signal transmitted by the kth user to send the pth symbol during the interval [0, 7) is