| Multicarrier system,particularly orthogonal frequency division multiplexing(OFDM),is an important transmission technique in the physical layer of wireless communications,for its high spectral efficiency and the robustness to narrow band interference and frequency selective fading.However,the conventional rectangularly-pulsed OFDM signal has high sidelobe.The superposition of sidelobes causes severe spectral leakage,which interferes the adjacent channels and reduces the spectrum efficiency.Therefore,to reduce the spectral leakage and enhance the spectrum efficiency,sidelobe suppression of the multicarrier signal becomes a key factor in future mobile communications.To effectively suppress the sidelobe,this dissertation researches several novel sidelobe suppression techniques in multicarrier transmission.According to the sidelobe suppression techniques for subcarrier block and single subcarrier,respectively,several new signal processing methods are proposed,in order to achieve promising tradeoff among multiple factors,such as error performance,spectral leakage and computational complexity.The research content of the dissertation is shown as follows.Firstly,the sidelobe suppression technique of the subcarrier block is studied.In Section 3,a novel time-domain N-continuous OFDM(TD-NC-OFDM)method based on the time-domain basis set is presented,where a sidelobe suppression signal is designed by the basis vectors.Then,by investigating the relationship between the time-domain smoothness and spectral sidelobe,the spectral expression of the TD-NC-OFDM signal is obtained.The closed-form expression of the signal-to-interference-plus-noise ratio(SINR)is theoretically analyzed.Furthermore,to improve the transmission performance of the TD-NC-OFDM method and to simplify the receptor,a low-interference TD-NC-OFDM algorithm is developed.The low-interference algorithm reduces the interference by optimizing the sidelobe suppression signal according to its time-domain distribution.Simulation results show that the proposed method can effectively enhance the system transmission performance.Secondly,the sidelobe suppression technique of the single subcarrier is studied.Based on the relationship between generalized frequency division multiplexing(GFDM)and discrete Gabor transform(DGT),a high-efficiency frequency-domain DGT(FD-DGT)algorithm for the GFDM signal detection is proposed.Meanwhile,the effects of the channel characteristics and the GFDM filter on the signal reception are analyzed.Furthermore,to reduce the implementation complexity,according to the local properties of the synthesis window and the analysis window in the frequency domain,a simplified frequency-domain DGT algorithm is presented.Theoretical analysis proves that by the optimal analysis window,the simplified algorithm can achieve a promising error performance in wireless fading channels.Thirdly,the joint sidelobe suppression of the subcarrier block and the single subcarrier is investigated.Based on TD-NC-OFDM and GFDM,a time-domain N-continuous GFDM(TD-NC-GFDM)method is proposed.In the proposed method,the basis set and the sidelobe suppression signal suited for GFDM are first designed.Then,the low-interference characteristic of the improved GFDM signal is analyzed.Lastly,an iterative interference cancellation algorithm is presented.Lastly,the joint suppression of sidelobe and peak-to-average power ratio(PAPR)is researched.By combing the TD-NC-OFDM method with the serial peak cancellation(SPC)method,a high-efficiency joint suppression algorithm is proposed.According to projection onto convex sets(POCS),the mutual effect between the frequency-domain sidelobe and the time-domain PAPR is analyzed.Additionally,a corresponding signal recovery algorithm in the receiver is presented to improve the error performance. |
