A Research And Implementation Of Spread Spectrum Communication Receiving Technology In Multipath Environment

The Spread spectrum communication technology is a spectrum extension technology.By this technique,the spectrum of the transmitted signal is broadened by a pseudo-random code having a rate much higher than the transmitted signal rate and then the received signal at the receiving end is dispreaded by using a pseudo-random sequence that is identical to the transmitting end to obtain the transmitted information.The pseudo-random code has good correlation characteristics and does not affect the transmission information,but only spreads spectrum.The receiving technology of spread spectrum communication system in multipath environment is studied in this thesis.Firstly,the basic theory of spread spectrum system is introduced,and the influence of multipath environment on communication performance is analyzed.Then,based on Simulin k,a simulation platform is built.The spread spectrum system using the Rake receiver and the spread spectrum system without the Rake receiver are simulated.The performance of the spread spectrum system in these two cases is compared.Then the hardware implementation of the Rake receiver is performed on the Field Programmable Gate Array(FPGA)hardware platform,and the correctness of the hardware implementation is verified.Finally,the hardware implementation is applied to a specific spectrum communication system,verified and tested based on the FPGA platform in the actual communication system.The main content of this thesis is divided into the following five aspects:At first,the basic principles of spread spectrum communication are discussed.The physical characteristics of multipath channels are introduced,and the impact of multipath environment on communication quality is discussed.Then,based on this,the Rake diversity receiving technology is studied.Several common modules of the Rake receiver are introduced,and the Rake receiver is divided into three categories according to the number of multipaths considered by the receiver.These three types of Rake receivers were studied and the performance and implementation complexity of these three types of receivers are discussed.Next,on the Simulink simulation platform,the spread spectrum system using Rake diversity reception and without Rake diversity reception is simulated.Comparing and analyzing the performance difference between these two systems under the multipath channel,it can be seen that the Rake receiver does have a certain improvement in system performance.The parameters affecting the performance of the spread spectrum system are analyzed through simulation.Then,the Rake receiver is implemented based on the Kintex series chip XC7K325t-2ffg990.The overall framework of the hardware implementation is given,as well as the hardware implementation of several important modules in the Rake receiver.The overall performance of the sub-module and Rake receiver is simulated by co-simulation.The correctness of the hardware implementation is verified by comparing with the Simulink simulation results.Finally,the hardware implementation of the Rake receiver was tested in the actual application system.The test is mainly divided into two test items: high speed mode and low speed mode.Through the comparative analysis of the test results in these two test modes,the correctness and practicability of the hardware implementation are further verified.