Spectrum Sharing Communication System To Receive And Perception Technology Research And Implementation

Fixed wireless spectrum assignment policy is the main reason of the lower and lower spectrum utilization efficiency. Spectrum sharing communication system is one of the solutions to solve the problem. Data transmission technology and spectrum sensing technology are two key technologies of the system. Because the spectral efficiency of Orthogonal Frequency Division Multiplexing technology is high, it is considered to be the best data transmission technology for the system. The dissertation focuses on the baseband receiver design and implementation based on OFDM technology. Because the sensing algorithm based on cyclostationary can be used for both signal detection and recognition, the dissertation also focuses on the signal detection and recognition technology based on cyclic spectral density function.Firstly, the physical layer data transmission scheme is analyzed in the dissertation. Then the baseband receiver FPGA link of the scheme is divided into several modules, including digital down converter, low pass filter, down-sampler and OFDM demodulator. Matlab simulation and FPGA implementation for each module are also described in the dissertation. Interface between FPGA and ADC, interface between FPGA and DSP are designed to meet the requirements of high-speed data processing of the system. All of the modules are tested and the result demonstrates that the baseband receiver FPGA link achieves expected function.Secondly, the basic theory of cyclostationary signals, especially cyclic spectral density function and its engineering estimation equation are researched in the dissertation. Cyclic spectral density of typical signals is simulated in Matlab by using the estimation equation. Single signal detection scheme which will use cyclic spectral density peaks on the cyclic frequency axis when general frequency f equals to zero is proposed. Matlab simulation, FPGA implementation and real performance testing are described in the dissertation. The result demonstrates that single signal can be detected in the low SNR(Signal to Noise Ratio) case.Finally, cyclic spectral density of the baseband OFDM signals is researched. Through the cyclic spectral density simulation for single and hybrid OFDM signals, hybrid OFDM signal recognition scheme is proposed. According to the special needs of the system, the detection performance of DTMB signal with cognitive user signal is simulated. The simulation result demonstrates that DTMB signal can be recognized in the low SNR and low SIR(Signal to Interference Ratio) case.