Chaos-based spread-spectrum using M-ary PSK and OFDM-MIMO

This paper proposes a chaos-based direct-sequence spread-spectrum (CDSSS) communication system using M-ary PSK modulation in combination with MIMO-OFDM technique. This combination aims at improving the performance as well as capacity of the conventional CDSSS systems over multipath fading channels. In the transmitter, the data is modulated by an M-PSK modulator whose output is fed to a MIMO encoder. Two resulting signals are spread by directly multiplying with chaos-NRZ sequences and then put into the corresponding OFDM modulators. The output signals are transmitted through a multipath fading channel using multiple transmitting and receiving antennas. In the receiver, beside the use of OFDM demodulation, chaotic despread-spectrum, and M-PSK demodulation, a V-BLAST algorithm with Minimum mean squared error (MMSE) equalization is applied to decode and recover the data. Schemes for the transmitter and receiver are described in detail and their BER performance over the multipath Rayleigh fading channel is evaluated by means of numerical simulations. The obtained results prove that the performance and capacity of the proposed system are significantly enhanced and can be adjusted by changing the values of M-ary level, spreading factor or the number of used antennas.