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

Recent development in cognitive radio (CR) brings significant technical challenges in the design of robust and flexible transmission technique in hostile communication environment with varying channel condition. An adaptive orthogonal frequency division multiplexing (OFDM) system, with a precoded cyclic prefix (PCP), is proposed in this paper to address these challenges. Besides the basic function as a guard interval for the OFDM systems, the PCP provides an efficient way of sending the transmission system parameters of the cognitive radio simultaneously with the data carrying OFDM signal. These parameters may include the bandwidth, total number of OFDM subcarriers, modulation and coding schemes used. Overall spectrum efficiency can be improved due to the elimination of the preambles and handshaking signaling required when there is any change in the CR transmission parameters. The receiver design particularly a hybrid domain equalizer for the PCP-OFDM system is presented in this paper. Implementation related issues including exploitation of the PCP structure, interference cancellation and complexity reduction are investigated. The performance of the proposed OFDM systems and the channel estimators are analyzed and verified through numerical simulations.