Application Study Of DDS To OFDM System

At the present, OFDM is widely applied on communication systems. It has been a hot research topic to optimize the OFDM systems. Thus, in this paper, it is studied how to use the direct frequency synthesizer DDS to replace the local oscillator, frequency offset correction and FFT/IFFT on OFDM Systems.The firstly, in order to eliminate the OFDM sub-carrier frequency deviation, DDS is applied as the local oscillator and deviation correction part in OFDM RF part by simulation. The secondly, for reducing the complexity of OFDM systems, it is studied to apply DDS to replace IFFT modulation and FFT demodulation modules, which realized OFDM baseband signal modulation and demodulation in OFDM system. Through the simulation and analysis of the OFDM system, the constellation diagram and bit error rate curve illustrate the feasibility of that DDS replaces IFFT modulation and FFT demodulation modules in OFDM system. Compared with two BER curves of OFDM system based on IFFT/FFT and OFDM system based on DDS, the results show that the DDS can completely replace the IFFT and FFT module in the OFDM system. Finally, it is studied that DDS replace the IFFT/FFT and digital up and down conversion of OFDM radio systems two modules on the OFDM system simulation by simulation. In different conditions, the simulation results of the constellation diagram and the bit error rate show that DDS could completed the functions of the baseband signal spectrum shifting and modulation and demodulation on OFDM system.According to above, DDS can be applied to remove the OFDM RF system carrier frequency offset and replace the IFFT/FFT module on the OFDM system baseband modem. All of this can greatly improve the speed of OFDM Systems, reduce system resources, system cost and design complexity.