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Go to Editorial ManagerThis paper presents an investigation to the performance of quantized direct-sequence spread spectrum system (DSSS) in mobile wireless communications systems. To obtain a real world value (RWV), the DSSS received signal is quantized to different levels of fixed-point values. These modes of quantization are evaluated by calculating BER under different channels environments (AWGN, Rayleigh, and Rician multipath fading). The effect of range of the represented values, the number precision and increasing in quantization noise on the performance of quantized DS in mobile wireless communications is also investigated. Based on simulation results, it is observed that quantized direct-sequence offers a trade-off between complexity and noise rejection compared to non-quantized DSSS and making a good representation of the digitized signals to implement the required DSSS in mobile wireless communications.
An orthogonal chaotic vectors based differential chaos shift keying (OCV-DCSK) digital communication system is presented. In this system the data transmission rates are increased by sending M bits in the same frame without needing for synchronization and channel state information since it use the benefit of non-coherent modulation of the DCSK and the orthogonality of chaotic vectors in the same scenario as QCSK system but instead of using Hilbert transform to create two orthogonal signals in QCSK, Gram Schmidt process is used to create M orthogonal chaotic signals from the M non-orthogonal chaotic signal. In the proposed system the analytical expression for OCV-DCSK are derived in AWGN and multipath fading channels. The simulation results show that the derived analytical expression have matched the Monte-Carlo simulation of the proposed system. Furthermore, comparison between orthogonal chaotic vectors and non-orthogonal, that are generated either as different initial conditions with the same chaotic generator or as different types of chaotic maps, reveals its superior BER performance in multipath fading channel.