Cognitive Radio Scene In The Transform Domain Communication System

Cognitive radio has emerged as one promising technique of solving current spectrum resource scarcity. Although OFDM/OFDMA has been elected as the main trend technology of data transmission in cognitive radio, there is not a suitable solution for signalling transmission and mechanism in the cognitive radio context.This thesis investigates one spectrum agile transceiver technology - transform domain communication system. Current technical literature does not present the signal model of TDCS. In this thesis, the mathematical model of TDCS signal is presented, and OFDM-based TDCS and interleaved OFDM-based TDCS are proposed subsequently. Compared with conventional TDCS, OFDM-based TDCS has greater compatibility with current OFDM/OFDMA technology, adopts mature OFDM synchronization and channel estimation technologies, uses fast demodulation algorithms based on IFFT, and eliminates complex RAKE receiver. Interleaved OFDM-based TDCS can transform continuous spectrum availability into random spectrum availability by interleaving, thereby improving BER performance in the case of continuous spectrum availability. Single user and multi-user BER performances of interleaved OFDM-based TDCS are also investigated in the AWGN channel. The approximate BER formula and BER lower bound formula are derived. Simulation results validate the correctness of both formulas.In most of the practical scenarios, the transmit data are coded; therefore, soft-demodulation of coded TDCS signals are investigated in this thesis. Moreover, soft-demodulation algorithm of OFDM-based TDCS in the fading channel is proposed, and corresponding fast implementation based on IFFT is also derived. Compared with hard-demodulation, this algorithm trades little complexity increase for soft output, and makes it possible for soft and iterative decoding. Its superiority is validated in the IEEE 802.22 Profile C channel.In addition, an application scenario of OFDM-based TDCS, signalling exchange in the cognitive radio context, is proposed in this paper. Sensing statistic characteristics are analyzed. Consequently, a signalling mechanism based on exchanging is proposed, and validated from an information theoretic perspective. This mechanism includes implementable single link algorithm and multiple access mechanism. The signalling transmission candidate requirements are also discussed, and OFDM-based TDCS is proposed as a promising candidate for the signalling transmission.