Phase Noise On Ofdm Systems And Inhibition

OFDM is the key technology of the future 4G communications. It has been widely adopted and implemented in wireless communications due to superior performance. However, it is extremely sensitive to phase noise. OFDM suffers from severe performance degradation in the presence of phase noise, which leads to common phase error (CPE) as well as inter-carrier interference (ICI) and further destroys the orthogonalties among OFDM sub-carriers. The dissertation focuses on the phase noise on the performance of OFDM systems and the corresponding phase noise cancellation algorithms in-depth study.In the dissertation, the nature of CPE and ICI introduced by phase noise are firstly analyzed and researched. The elimination of CPE is easy because of the same CPE to each sub-carrier in an OFDM symbol. But the ICI is random, the estimation and the elimination are more difficult than CPE. Based on the Wiener noise, the influence of main parameters of OFDM systems on the ICI and systems is discussed. The traditional elimination method is to use pilot signals to complete the phase noise estimation and elimination, including CPE compensation method and the MMSE algorithm. But they can eliminate CPE only, with less effectively to the ICI elimination. To mitigate this problem, this dissertation proposed a simplified iterative phase noise suppression (IPNS) algorithm based on the IEEE 802.11a WLAN standard. It directly uses the frequency-domain output signals after FFT operation to estimate the CPE of phase noise, and then executes phase noise iteration estimation by the corrected signals without CPE, finally implemented multiplication operation to compensate for the ICI of phase noise. Numerical results are presented to illustrate the effectiveness of the proposed algorithm in AWGN channel and multi-path Rayleigh fading channel. Only a few iterations can efficiently eliminate the effects of phase noise and improve the performance of OFDM systems. Compared to the traditional algorithms, it has better performance as well as low complexity.The dissertation summarized and analyzed the existing four kinds of ICI self-cancellation algorithm. Four kinds of algorithms are compared and analyzed in two aspects of bit error rate and carrier-to-interference ratio, and simulated in two different channel conditions. The conjugate methods have good performances in AWGN channel, but are not so effective in the multi-path Rayleigh channel. An improved ICI algorithm is proposed and the simulation results show that the algorithm performance is superior to the original four kinds of algorithms. It can efficiently eliminate the effect of phase noise in multi-path channel, as well as AWGN channel.