Research Of Cognitive Radio Based On OFDM Technology

Currently, the internationally accepted policy is a fixed allocation of spectrum, which is based on whether the user is entitled to authorize the limited spectrum resource is divided into frequency bands used by authorized users and unauthorized users of the band. Most of these spectrum resources are need authorization, such as the television broadcast band. And those who do not need the authorization of the band is quite little, and many of the emerging wireless communications technology is mostly used non-licensed bands. The current spectrum allocation of spectrum based on fixed resource utilization is very low. This has resulted in the conflict between the limited spectrum resources and the inefficient utilization of spectrum resources, there is an urgent need for a wireless communication technology to alleviate this situation. Cognitive radio technology came into being.OFDM has the ability to flexibly control the spectrum, which provides a good spectrum management platform for cognitive radio system. The basic principle of OFDM technology is:the sending high-speed serial data stream into parallel low-speed data streams, these low-speed parallel data through the IFFT transform OFDM modulation; receiver will receive the demodulated signal, and converted by the string, FFT transform, and the converted string to achieve OFDM demodulation. OFDM technology have the flexibility to choose the frequency to facilitate the realization of the spectrum resource management, so it is bound to become the first choice of cognitive radio technology.This paper uses OFDM technology for a spectral algorithm to control the cognitive radio system, Matlab simulation results show that the algorithms the energy spectrum of OFDM data symbols can be further attenuated. Authorized users are using those frequency bands and frequencies, the use of OFDM technology features flexible control of the spectrum, by closing the relevant frequency band or sub-carrier OFDM data symbol to eliminate interference to authorized users. To further reduce the interference to authorized users, the algorithm is the Fourier transform of the OFDM data symbol after the mathematical relationship, for authorized users to use the band to strike a sub-carrier data symbols through the band of spectrum in the energy and its sub-carrier the functional relationship between the data symbols, through its derivative spectrum obtained extreme. Finally, the FPGA also QuartusⅡ8.0 software development built on the OFDM modulation and demodulation system, and detailed description of OFDM modulation and demodulation system composed of FPGA implementation of the function of each module and the port signal shows the FPGA implementation and test module the OFDM modulation and demodulation system FPGA implementation of the simulation results.