Design And Implementation Of Multirate Incoherent DSSS System

At present,in the field of Aerospace TT & C,Unified spread spectrum system is widely used,and coherent spread spectrum technology and incoherent spread spectrum technology are two typical branches.Incoherent direct sequence spread spectrum technology retains all the advantages of coherent direct sequence spread spectrum technology,and has stronger security performance and flexibility of variable data rate,so it has attracted a lot of attention,It is often used to transmit telemetry and remote control information in Spread Spectrum TT & C channel between satellite and ground.The data information generation clock and spread spectrum code generation clock in non coherent direct sequence spread spectrum system can be non homologous,and the data information rate is also variable,which destroys the corresponding relationship between data information and spread spectrum code phase in conventional coherent direct sequence spread spectrum system,so the implementation of receiver becomes more difficult.First,aiming at the difficulties of system implementation under incoherent conditions,this paper studies the basic principles of transmitter and receiver of multi rate incoherent DSSS system,designs its related algorithms,focuses on the solutions to overcome the impact of data information flip and jump under incoherent conditions,and designs spread spectrum code synchronization,carrier synchronization,bit synchronization and other algorithms,The spread spectrum code synchronization acquisition algorithm is the most important one.Three methods to overcome the data information flip and jump are analyzed,including delay multiplication,half bit method and full bit method.Finally,the matched filter synchronization acquisition method based on SRL16 with full bit method is selected as the spread spectrum code synchronization acquisition scheme,and the algorithm is simulated to verify its correctness.Secondly,This paper introduces the relevant knowledge of AD9361 chip,and describes its main function modules.In this system,AD9361 completes the function of RF frontend.The configuration and data transmission of AD9361 are studied.SPI configuration interface is designed and implemented.With AD9361 evaluation software,thousands of registers in AD9361 are configured.LVDS data transmission interface is designed and implemented to realize data transmission between AD9361 and FPGA.Finally,This paper introduces the FPGA hardware platform,briefly describes the chip related knowledge,and completes the hardware implementation of the whole multi rate incoherent DSSS system with ad9361 RF chip.The FPGA implementation of transmitter mainly includes data information generation,gold code generation and spread spectrum,while the FPGA implementation of receiver mainly includes spread spectrum code synchronization,carrier synchronization,bit synchronization and demodulation.The above algorithms are deeply studied and detailed description and implementation scheme are given.Finally,the design and implementation of the whole system are completed,and the actual test results meet the expected requirements of the system.