A New Adaptive OFDM System with Precoded Cyclic Prefix for Dynamic Cognitive Radio Communications

Recent development in cognitive radio (CR) communications brings significant technical challenges in the design of adaptive and robust transmission techniques in hostile communication environments due to the dynamic channel transitions and strong co-channel interference. A novel adaptive Orthogonal Frequency Division Multiplexing (OFDM) system with a precoded cyclic prefix (PCP) is proposed in this paper to provide a dynamic CR communication platform with fast transmitter-receiver interaction capability. Besides the basic function as a guard interval for the OFDM system, the PCP, combined from two oversampled precoded Kasami sequences, provides an efficient way of sending the system parameters without the requirement of additional signaling or feedback channels. Overall system and network efficiency is substantially improved due to the simplification of the preambles and handshaking signaling required when there is any change in the CR transmission parameters. Meanwhile, the real part of the PCP is uniquely assigned to each CR transceiver as identification label for spectrum sensing. The receiver design particularly the hybrid domain equalization and PCP induced interference cancellation for the proposed OFDM system is presented in this paper. Implementation related issues including exploitation of the PCP structure and complexity reduction are investigated. The performance of the proposed PCP-OFDM system is analyzed and verified through numerical simulations.