| Abstract |
This work aims to propose a multiuser OFDM system with non-coherent differential quadrature chaos-shift-keying (OFDM-DQCSK) modulation. The proposed system is based on direct sequence spread spectrum where chaotic codes replace conventional spreading sequences. Orthogonal sets of chaotic spreading codes can be generated with excellent correlation properties. The proposed system uses duplicated reference subcarriers that are private and non-shared. These reference subcarriers carry the chaotic codes which are used to spread the modulated data symbols at the transmitter of a specific user. At the receiver, the reference subcarriers are used for the differential non-coherent de-spreading. The modulated data symbols are spread in time domain over shared subcarriers. Reference subcarriers are much less than data subcarriers to save bandwidth. At the receiver, neither complex channel estimators nor carrier synchronization is required for demodulation. The chaotic reference signals are averaged at the receiver so that the additive white gaussian noise (AWGN) on the reference signal is averaged to a negligible value. A simulation of the bit error rate performance is performed in the presence of AWGN, multipath Rayleigh flat-fading channels and multiple access interference. In conclusion, the proposed non-coherent system achieves a remarkable improvement due to the usage of the Reference Averaging Technique. |
