Reserch On Modulation Classification And Spread Spectrum Estimation Based On Signal Characteristics

In recent years,with the rapid development of wireless communications,the number of mobile users has increased explosively.It leads to the continuous innovation of modulation mode in the communication system,which makes the signal monitoring more difficult.Since the signal monitoring is done at the angle of third party without any known parameters,it is necessary to estimate the signal parameters before the next analysis and processing.For spread spectrum system,signal processing includes two steps:descramble and reconciliation.Therefore,modulation and spreading codes need to be estimated when monitoring spread spectrum signals.From the actual needs,this paper mainly focuses on the two problems,signal modulation classification and spread spectrum code estimation.In the existing literature,the algorithm of signal modulation classification is mainly divided into two categories:likelihood function and signal feature based.The likelihood function method is theoretically optimal,but requires a priori knowledge,and the complexity is relatively high.The recognition method based on signal features is favored by researchers because of its low complexity and ability to recognize in blind signal conditions.In this paper,a modulation classification method based on higher order cumulants and softmax classifiers is proposed.The proposed algorithm is divided into two stages:signal feature extraction and classification recognition.In the signal feature extraction stage,a number of higher order cumulants are calculated and combined together,it is as the feature vector in classification recognition stage.At the stage of classification and recognition,the softmax classifier is adopted.The classification process is regarded as a matching process between signal features and modulation types.The weight matrix between signal features and modulation types is introduced,and the optimal classification model is realized by continuously optimizing the weight matrix.In the aspect of spectrum code estimation,this thesis analyzes the characteristics of spread spectrum code in spread spectrum system,and proposes an algorithm based on density clustering to estimate spread spectrum code.Finally,the simulation and practice work of the proposed algorithm is carried out in this paper.The results show that the proposed algorithm in this paper is superior to the traditional algorithm in terms of performance,and it is also practical.