Nonlinear Distortion Cancellation Based On The Received Compensation Algorithm In OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a popular multi-carriers modulation technique for achieving wireless environment, with its advantages of better anti-multipath ability and high spectral utilization. Specially, OFDM and multiple access, such as Code-division multiple access(CDMA) and Space-division multiple access(SDMA) can be combined to design a strong communication system, fully make use of the spectral resource. So OFDM technique is the most promising candidates for the next generation of wireless system. However, the most weakness of OFDM signal is the high peak-to-average power ratio (PAPR), which show great need of the linearity of HPA. When the OFDM signals go through the nonlinear amplifier, will produce nonlinear distortion and harmonic interference. The main innovations of this paper are:1. Introduce the basic principle and key technology of OFDM techniques; derive the mathematical model of the amplifier. Then analyze the mostly used amplifier: Solid state power amplifier (SSPA) and traveling wave tube amplifier (TWTA). The simulations show the nonlinear impact on the OFDM signals.2. We propose a nonlinear compensation algorithm combined with channel estimation. The new algorithm considers the nonlinear impact on pilot data during channel estimation, so as to improve the accuracy of channel estimation and the performance of nonlinear cancellation. The simulation result shows the great improvement on the system BER.3. We propose a iterative algorithm for nonlinear distortion cancellation in SDMA-OFDM system. The new algorithm make the traditional algorithm extend to the multiple users and multiple antenna’s SDMA-OFDM system, by iterative make improvement on the original method. Simulation results show the algorithm show great performance.4. Nonlinear channel equalization is an emerging technology in nonlinear cancellation, due to time limitation, we only study and introduce the existing nonlinear channel equalization algorithm, By simulations, analyze the weakness of the existing algorithm,put forward the further research direction and prospect.