Reliable and Secure Pre-Coding OFDM-DCSK Design for Practical Cognitive Radio Systems With the Carrier Frequency Offset

In this paper, we present a pre-coding (PC) orthogonal frequency division multiplexing-aided differential chaos shift keying (OFDM-DCSK) scheme over non-contiguous (NC) spectrum bands for cognitive radio (CR) systems. In practical CR systems, the offset of fundamental clocks of transceivers or non-ideal components induce the carrier frequency offset (CFO), which will reduce the spectrum sensing accuracy and degrade reliability performances. Additionally, CR systems probably suffer from eavesdropping or malicious attacks due to the broadcasting property of wireless channels. With the aim to simultaneously combat the CFO and to enhance the security performance, in our OFDM-DCSK design, the information bits are modulated by reference chaotic sequences, then the data-bearing chaotic symbols and reference symbols are delivered to the pre-coding module, wherein we interleave chaotic chips, add the chaotic mask and duplicate chips. After OFDM modulations, the chaotic signals are transmitted over channels. At the receiver, reverse operations are performed. Moreover, we derive the theoretical bit error rate (BER) and information leakage expressions. Simulations are provided to verify the effectiveness of our derivations, and to demonstrate that more reliable and secure performances can be achieved by the presented system compared with counterpart systems.