Design Of High Dynamic Spread Spectrum Communication System

In the space measurement and control,missile navigation in spread spectrum communication system,due to the relative velocity and acceleration between the transmitter and the receiver,the receiver needs to bear the high frequency offset and frequency offset of the high dynamic environment.In this case,the synchronization of the receiver will become extremely difficult.In this paper,a feasible scheme of spread spectrum communication system is designed for the high dynamic environment,The main works of this paper were as follows:(1)The basic principle of spread spectrum communication is analyzed,and the design principle of direct sequence spread spectrum communication is emphatically analyzed.Then the generation principle and application of two kinds of codes(Walsh codes and PN codes)for spread spectrum communication systems are analyzed.Then,the acquisition and tracking technology of spread spectrum system is introduced in detail.The advantages and disadvantages of the traditional acquisition algorithm and the application scenarios are analyzed.In the end,the acquisition and tracking algorithm is proposed.(2)The design scheme of spread spectrum communication system is proposed,which uses direct sequence spread spectrum communication method.The whole design is divided into two parts,transmitter and receiver design.The transmitter design part mainly includes three modules:channel encoding,spread spectrum scrambling and filter modulation.Among them,the channel encoding uses the classic Turbo encoding to ensure the reliable transmission of communication systems;Spreading codes are orthogonal Walsh codes,can guarantee the various business channels are mutually orthogonal,scrambling code depending on the I and Q using two short PN code;In order to limit the bandwidth and guarantee the optimal sampling points of the inter code interference as small as possible,using the root raised cosine shaping filter,modulation is used QPSK modulation.(3)The design of receiver is especially important in the design of spread spectrum communication system,which affects the performance of the whole system.In this paper,the design of the receiver is divided into four parts,the sample value level processing unit,the synchronous processing unit,the code chip level processing unit and the bit level processing unit.The sample value level processing unit mainly completes the automatic gain control(AGC),the frequency offset compensation,the RRC(root raised cosine)filter,and the sample value sequence of the given level module is generated under the control of the synchronization unit;Synchronous processing unit mainly completes the acquisition of PN code and frequency offset,timing tracking and frequency tracking;The chip level processing unit mainly completes the solution to the received signal,the solution,the channel estimation,the channel compensation;the bit level processing unit mainly completes the Turbo decoding of the business channel.(4)According to the design of the receiver,the FPGA implementation of the receiver is accomplished.The overall block diagram of the receiver is given,and the function of each module is realized according to the block diagram.And the simulation is carried out on the Modelsim,finally,the board test is finished on the Cyclone V FPGA.