Orthogonal Code-Multiplexed Frequency-Domain Single-Carrier Spread Spectrum

Abstract The authors have proposed a frequency-domain single-carrier spread spectrum (SC-FDSS) transmission technique, which achieves better bit-error rate (BER) and better power amplifier-dependent energy efficiency comparing with time-domain spread spectrum (TDSS). However, its wider transmission bandwidth leads to low spectrum efficiency, implying that a multiplexing technique is necessary. In this paper, we introduce an orthogonal code multiplexing technique for the FDSS called multi-code single-carrier FDSS (MC-SC-FDSS) for code division multi-access. The signal block to be transmitted is firstly transformed into frequency-domain signal by discrete Fourier transform (DFT), and then code multiplexing is done to achieve narrower transmit bandwidth. Joint frequency-domain equalization based on minimum mean-square error criterion (MMSE-FDE) and de-spreading is carried out for acquiring frequency diversity gain. Theoretical analysis and simulation results in terms of BER and PAPR of both single-code and multi-code SC-FDSS are shown and compared with conventional TDSS and multi-carrier SS (MCSS