Ofdm System Of Nonlinear Compensation Algorithm Research

Orthogonal Frequency Division Multiplexing (OFDM) is the multi-carriers modulation technique; it has been under extensive study and research in recent years, due to its high spectrum efficiency and strong immunity to severe multi-path fading. It has been widely used for the high speed digital communications such as digital video broadcasting (DVB), digital audio broadcasting (DAB), and asymmetric digital subscriber loop (ADSL) etc. However, the inherent weakness of the OFDM technique is its high peak-to-average power ratio (PAPR). This leads, in the presence of a nonlinear HPA, to worse performance of the OFDM scheme. More research will be studied to further the compensation method. This dissertation is supported by the key scientific and technological project of Henan province (No.0623051400): "Low PAPR algorithm of MIMO-OFDM systems in wireless communication". Based on the analysis of linearity technologies, this dissertation focuses on the nonlinear compensation method at the receiver, and the main innovations and contributions are:1. Solid state power amplifier (SSPA) and traveling wave tube amplifier (TWTA) have been analyzed and the influence has been verified by simulations in OFDM system. The simulations show that OFDM system is sensitive to nonlinear distortion caused by HPA. This conclusion also gives the reference for choosing the nonlinear compensation scheme.2. We propose a modified algorithm, considering the influence of the channel response and the attenuation coefficient of the useful signal, which can get the better BER performance. The simulations have also shown the effectiveness of the scheme.3. A novel compensation method has been proposed, which is to use the training sequence to estimate the coefficient of the transmitting HPA model at the receiver, then yield replica of the nonlinear distortion components, at last use the replica to cancel the nonlinear distortion components in received symbols. The simulation results have shown that the new algorithm can also have improved the BER performance.4. Based on the compensation algorithm combined the clipping and memory-less HPA, we propose a modified algorithm considering the attenuation coefficient of the useful signal, which has been verified by simulations. What's more, a new combined algorithm also has been proposed, if considering the influence of the clipping and memory HPA, the simulations has proved that this algorithm is effective too.