OFDM Demodulation Design And FPGA Implementation For Secondary User Receiver Based On Cognitive Radio

Cognitive Radio has the ability of sensing the surrounding radio environment and improving the spectrum utilization and communication capacity. Orthogonal frequency division multiplexing is a highly recognized communications technology to improve the utilization of spectrum effectively. It is inevitable for the cognitive radio technology to use OFDM modulation and demodulation technology in secondary user communications, design and put it into practice with FPGA. This paper gives the design and implementation of OFDM demodulation with FPGA hardware platform.First, this paper gives the background of the subject, research trends and application status of cognitive radio and OFDM technology. It elaborates the basic principle of OFDM modulation and demodulation, as well as the key technical principles, including symbol synchronization, carrier synchronization and channel equalization and so on, that used in demodulation system of receiver. The main parameters and frame structure of the physical layer, as well as the entire OFDM receiver demodulator program has been designed according to the actual requirements of the project.Second, this paper emphasizes the algorithm, block diagram and processes of modules implemented on FPGA, including ADC sampling, quadrature demodulator, low pass filtering, frame synchronization, carrier synchronization, conversion rate, the FFT demodulation, channel equalization, the remaining phase tracking and descrambling, and QAM inverse mapping. The OFDM demodulation system was built in Altera FPGA board with VHDL language. The application project worked on the cognitive radio verification platform shows that the OFDM demodulation designed in this paper could accomplish the data demodulation in the receiver, while the functions and indicators are able to meet the project requirements.Finally, this paper gives a introduction to several common FPGA design ideas that used in the subject, descrips the practical problems encountered in the development of this subject, and gives some commonly used methods to solve them.