The Research And FPGA Implement Of All Digital OQPSK Demodulation Algorithms

With the increment of the amount for all kinds of communication systems, for the sake of using the frequency spectrum resource sufficiently, more and more modulation technology with high spectrum utilization ratio are being used. OQPSK (Offset Quadrature Phase Shift Keying) modulation technology is a constant envelope modulation technology, which possesses the features of high spectrum and power utilization ratio. The modern method has been widely employed in satellite communication system and mobile communication system. So there is some theoretical value for doing the research in OQPSK all digital demodulation.This paper successfully designs and realizes OQPSK digital demodulation based on FPGA, which is guided by the correlated theory of Software-defined Radio and demodulation with digital method. The paper first introduces the principle of OQPSK digital demodulation and the structure of digital receiver based on the idea of Software-defined Radio, and then elaborates some common used algorithm for carrier frequency synchronization, carrier phase frequency synchronization, timing synchronization and frame synchronization for OQPSK digital demodulation. After the choice in these algorithms, three system design schemes are established and simulated in MATLAB to choose a FPGA scheme. Based on this, on the Altera FPGA development platform QuartusⅡ,by using Verilog HDL every module in the demodulation system is designed and implemented. By the timing simulation in ModelSim, some error in the FPGA design has been corrected. At last, FPGA debugging tool embedded logic analyzer SignalTapⅡare adopted to do the hardware factual test, the paper has made the last improvement and adjustment to the design.The factual hardware test shows that, the design of OQPSK demodulation system can meet the scheduled object and requirement. After the timing and resource optimization for the FPGA system design, this design can be transformed to ASIC and SOC design to reduce the size and cost, also enhance the reliability of the circuit for the system, so the design of this paper also has good practical value.