Correlative M-ary Spreading-Code-Phase-Shift-Keying Modulation for Multiple Access Environments

Code phase shift keying (CPSK), an M-ary direct sequence spread spectrum (DSSS) modulation scheme, was proposed to increase the transmission efficiency of DSSS systems. Moreover, the M-SCPSK modulation scheme was proposed to provide multi-access capability and to increase the system flexibility. In this work, the correlative M-SCPSK modulation scheme, a type of memory modulation, is proposed to improve the system performance, and the performance in an AWGN channel exposed to multi-user interference is investigated. Based upon this correlative attribute, the Viterbi decision algorithm is applied to the demodulation, thereby greatly improving the system performance. According to the simulation results, the improvement is at least 2.7 dB in E_b/N₀ with one symbol memory.