Multiuser chaos communication through polyphase spreading for overlay cognitive radio

Chaos communication systems have received strong interest due to its performance and security advantages such as robustness in multi-path fading environments, resistance to jamming, and low probability of interception. With recent advances in cognitive radio, it is highly desired to combine the security advantages of chaos communication with the flexibility of cognitive radio to create a chaos based cognitive radio communication system that improves the spectrum usage while maintaining high security features. In this paper, we propose a multi-user non-continuous orthogonal frequency division multiplexing (NC-OFDM) based chaotic communication system employing orthogonal polyphase spreading codes. Specifically, a polyphase spreading code called carrier interferometry code is layered onto the frequency domain chaotic waveform to create multi-user support. The proposed system not only maintains the capability of operating over multiple non-contiguous spectrum holes, but also offers security features by chaos sequence modulation. For comparison purposes, we develop two benchmark schemes using both NC-OFDM and chaos modulation. Simulation results show significant performance advantage of the proposed scheme than the benchmark schemes. Finally, we point out that the proposed scheme allows flexible access control for different users and groups, in broadcast, multicast and unicast services.