A low-complexity MSK-based M-ary cyclic-shift keying transceiver for direct sequence spread spectrum system over multipath fading channels

In this paper, a low-complexity spread spectrum system with M-ary cyclic-shift keying (MCSK) symbol spreading is proposed. In addition, by using the minimum-shift-keying (MSK) as the chip-level modulation, we obtain a high-rate QPSK-MCSK transceiver scheme which not only provides a constant-envelop and continuous-phase transmitted signal, but can also achieve a better performance than the conventional direct sequence spread spectrum (DSSS) system. At the transmitter, the data stream is first mapped into QPSK-MCSK symbols in terms of orthogonal Gold code sequences, then followed by the cyclic prefix (CP) insertion for combating the interblock interference, and finally applying the MSK scheme to maintain the constant-envelope property. The receiver first performs MSK demodulation, then CP removal, and finally the channel-included MCSK despreading and symbol demapping. Furthermore, the single input single output (SISO) QPSK-MCSK transceiver can be easily extended to the multiple input single output (MISO) case by incorporating the spacetime block coding for high-link quality. Simulation results show that the proposed SISO and MISO QPSK-MCSK systems significantly outperform the conventional DSSS counterparts under the AWGN channel, and attain a more robust performance under the multipath fading channel. Copyright (C) 2011 John Wiley & Sons, Ltd.