Research On Key Technologies Of Spectrum Controlled Direct Sequence Spread Spectrum Communication System In Cognitive Radio

The wireless spectrum resource is increasingly shortage due to the high speed development of wireless communication services.Therefore,the new wireless communication thchnologies with high efficient spectrum resource utilization have been the hot reseach topic.As the typical representative of wireless communication technologies with high efficient time utilization,cognitive radio improves the spectrum utilization effectively through dynamic spectrum access mechanism.Spectrum controlled direct sequence spread spectrum communication technology not only has the advantage of spread spectrum communication,but also it is able to generate spectrum with nulls,and the characteristics of these nulls can be controlled.It can be used as the realization technology of cognitive radio,which can effectively reduce the interference to primary users when secondary users access the spectrum,and ensure the communication performance of secondary users at the same time.A type of new cognitive radio communication system can be constructed by combing spectrum controlled direct sequence spread spectrum communication technology with cognitive radio,which is named spectrum controlled direct sequence spread spectrum communication system in cognitive radio.This dissertation mainly researches on the key technologies of spectrum controlled direct sequence spread spectrum communication system in cognitive radio,combing the application of compressed sensing in cognitive radio and spread spectrum communication,the following research works have been done.(1)Focusing on the wideband spectrum sensing in cognitive radio,compressive wideband spectrum sensing based on compressed sensing theory is an effective method to solve the high sampling rate requirement in the front end of system.In compressive wideband spectrum sensing,the dependence of signal spasity limits the wide application of it in practice.To solve this problem,a sparsity adaptive compressive sampling matching pursuit algorithm is proposed,and theoretical analysis of this algorithm can be used to reconstruct sparse signal is given.The proposed algorithm does not depend on the sparsity of signal,and has a well reconstructed performance.On the condition of unknown sparsity,this algorithm can be applied to compressive wideband spectrum sensing to realize spectrum detection effectively.(2)In order to achieve spectrum controlled spread spectrum sequence,by referring to the idea of mW composite sequence,spectrum controlled composite sequence based on spectral null code and block code have been proposed.The power spectral density of composite sequence is derived.The spectrum controllability and corresponding relationship between spectrum characteristics and sequence parameters,sequence composite method is analyzed.The design method of desired spectral shape is given,and the characteristics of each composite sequence are compared.Finally,the direct sequence spread spectrum communication system in cognitive radio has been constructed,and the spectrum access of secondary users is realized by using all the proposed composite sequence.In this system,the bit error rate performance of primary users and secondary users has been analyzed.(3)Focusing on the parameter estimation of mW composite sequence,the methods of parameter estimation by using spectrum and cyclic spectrum of composite sequence are proposed.In order ot reduce the high sampling rate requirement,modulated wideband converter in compressed sensing is introduced to reconstruct the spectrum of mW composite sequence,and then the Walsh sequence number and signal carrier frequency can be estimated through detecting the peak positon of spectrum.In order to improve the performance of estimation,the cyclic spectrum expression of mW composite sequence is derived,and the corresponding relationship between parameters of composite sequence and peak positon of spectrum is described.Focusing on the high sampling rate requirement of obtaining mW composite cyclic spectrum,the theory of compressive cyclic spectrum is introduced to solve this problem.Finally,the Walsh sequence number,chip rate of m sequence and signal carrier frequency can be estimated through detecting the cyclic spectrum section of mW composite sequence.(4)The features of composite sequence can be used to enhance performance of spread spectrum receiver,so we introduce a novel receiver which called compressive spread spectrum receiver.From the perspective of spread spectrum signal sparsity,compressive spread spectrum receiver receives signal with the theory of compressed sensing.The structure of compressive spread spectrum receiver is extremely simple.However,bit error rate performance of this receiver is worse than conventional correlation receiver.On the basis of researching on composite sequence parameter estimation method,a compressive spread spectrum receiver based on the estimation of support set is proposed.The proposed receiver obtains support set of the received signal by parameter estimation,and then the bit error rate performance of receiver can be improved with the known support set of signal.