Influence Of Phase Noise On APSK System And Research On Optimization Algorithm

With the continuous development of communication technology,high-order modulation has become an important technology to overcome the contradiction between the shortage of spectrum resources and high-speed transmission demand.With joint amplitude and phase modulation,APSK systems have many advantages,such as higher modulation efficiency and spectrum utilization.With the increase of the constellation points,the concentric ring structure of the APSK constellation approximates the normal distribution,thereby obtaining a higher channel capacity.In the satellite channel,the signal transmission attenuation is large,and the transmitting end needs sufficient transmitting power.The noise generated at the transmitting end is likely to have a large impact on the APSK system,such as phase noise.Phase noise is a kind of multiplicative noise,and the fluctuation error of the carrier is the main cause of phase noise.Phase noise causes phase rotation of the signal and affects the performance of the communication system.In addition,phase noise can cause spectrum leakage,interfere with out-of-band channels,and affects the system capacity.It is of great significance to study the influence of phase noise and its optimization algorithm in APSK system.In order to improve the performance of the APSK system,constellation optimization can be performed on the transmitted signals.Constellation optimization is to design the radius and phase difference of the constellation diagram and the points of each circle constellation according to the system performance index as a consideration,and generally follow the principles of maximizing the minimum Euclidean distance and maximizing mutual information.To make the distribution of constellation points more sparse under the condition of limited power,you can increase the minimum distance between constellation points,or reduce the number of constellation points adjacent to each constellation point.In order to maximize the system capacity,the influence of the channel should be considered first.APSK signal points have characteristics similar to Gaussian distribution,and Gray mapping can be used to obtain greater mapping gain.In addition to constellation optimization,adding an equalizer at the receiving end of the system is also an effective way to improve system performance.The traditional adaptive equalization algorithm includes the LMS equalization algorithm.However,the training sequence-based equalizer occupies part of the bandwidth and increases system overhead.In other communication systems,such as non-cooperative communication where training sequences are not available,the equalizer will lose its effect.In order to further improve the reliability of the system,a blind equalization algorithm without training sequences is considered.This thesis studies the effect of phase noise on the APSK system firstly,analyzes a variety of phase noise models,establishes a simulation model for phase noise,and analyzes and discusses the simulation results.In the constellation optimization part,based on the existing research conclusions and the characteristics of the influence of phase noise on APSK,a constellation optimization construction method is proposed to make the optimized constellation map follow the criterion of minimizing the maximum Euclidean distance and effectively reduce the phase noise impact on the system.Finally,combined with the training sequence-based adaptive equalization and blind equalization,the dual-mode adaptive switching is used in the blind equalization process.The characteristics of the APSK and the phase noise channel are considered,and the CMA equalization algorithm is optimized to further improve the performance of the system.