Research On Spectrum Sensing Technology In Ofdm-based Spectrum Sharing Radio Systems

In the cognitive radio network, the frequency and bandwidth for the available spectrum is often unstable, and may even be discontinuous. The orthogonal frequency division multiplexing (OFDM) can flexibly select sub-carriers and adjust the transmission power. Therefore, OFDM is most suitable for physical layer modulation techniques in cognitive radio systems.Spectrum sensing technology is the basis and premise for the application of cognitive radio. In this thesis, we focus on spectrum sensing technology in OFDM-based spectrum sharing radio systemsIn the third chapter, we introduce the method to eliminate the inter-carrier interference when the cyclic prefix is not inserted in the guard interval. An improved OFDM-based frame structure for cognitive user is proposed. We derive a frame size and throughput formula by analyzing the cases that cognitive user accesses the licensed spectrum. Then we analyze the formula to select the optimal frame size. Simulation results show the feasibility of the improved frame structure.In the fourth chapter, we study the OFDM system in which the traditional cyclic prefix is replaced by the sequence, precoded by the cognitive radio transmitter identification and system parameters. The method to cancel the inter-symbol interference and inter-carrier interference is analyzed. Then we study the spectrum sensing and user identification algorithm using the cyclic correlation between the local reference sequence and received signals. Simulation results show that robust detection performance can be achieved for the system parameter transmission technique using precoded cyclic prefix, and sensing algorithm still has satisfactory performance even at low signal-to-noise ratio environment.