Design And Implementation Of Spread Spectrum Communication System Based On Residue Number System

At present,spread spectrum technology is still an important communication technology and has been widely used in mobile communication,sensor network,measurement and control systems,etc.The traditional spread spectrum technology based on fixed sequence has been very mature,and its communication security is difficult to guarantee.Although the emerging chaotic spread spectrum technology can improve the anti-decoding ability of the system by using high-complexity chaotic sequences,due to the limitations of chaotic systems in digital circuit applications,it faces problems such as high complexity in system design and difficulty in synchronization,etc.Aiming at the above problems,this thesis studies a pseudo-random sequence generation method based on residue number system(RNS)and permutation polynomial,and discusses the periodic degradation of this method in the process of digital circuit implementation with a detailed theoretical proof.Then a pseudo-random sequence generator based on memory-computation structure is designed.Based on this,this thesis proposes a synchronization method based on time-phase mapping.Then a long-period spread spectrum communication system is designed and implemented,which can effectively reduce the complexity of system while improving the security performance of physical layer communication.The main work of this thesis are listed as follows:First of all,this thesis studies a pseudo-random sequence generation method based on RNS and permutation polynomial,and puts forward some improvement schemes in view of its limitations in the application of digital circuit.Based on this,an efficient digital circuit structure is designed in this thesis.Only 10 BRAMs and a small amount of logic units are used to generate high-speed and extremely long-period pseudo-random sequences.The sequence has extensible period,and the period length can reach 2⁸³ easily.In addition,a fast switching sequence phase method is proposed,which requires only 26clock cycles from phase input to sequence output.The NIST test results show that the pass rate of each item is above 98.65%.And the sequence has good autocorrelation,cross-correlation and equilibrium according to other test results.Then this thesis studies a synchronization method based on time-phase mapping,which can effectively solve the synchronization problem of long-period spread spectrum system.The principle of the method is to establish a mapping between time and phase of the sequence.The system can quickly establish time synchronization by adjusting the mapping rule between time and phase.On this basis,this thesis designs a spread spectrum communication system based on the“slow sequence assisted synchronization”scheme,and tests the BER performance of the system under the AWGN channel and the Rayleigh channel respectively.Finally,this thesis designs a set of long-period spread spectrum communication system based on RNS through hardware description language,and simulates the function of each key module in the system through Modelsim.At the end,the system is tested on the communication hardware platform based on XC7Z045 and AD9361.The test results show that the system can be used for burst communication successfully.