Design And Implementation Of COFDM Wireless Communication System

DVB-T is a kind of digital television transmission standard that using terrestrial transmission media,and it has been one of the international mainstream digital television terrestrial broadcasting standards.It has been widely used in UAV image transmission and video monitoring systems as its outstanding performance in mobile reception.COFDM System in DVB-T achieves a good balance between transmission efficiency and reliability by combining OFDM technology with channel coding technology.Channel coding is very important in COFDM System,which has a great impact on the performance of the whole system.Generally,in COFDM System,concatenated code is used in channel coding,in which outer code is RS(204,188)and inner code is(2,1,7)convolutional code.Turbo code adopts the structure of parallel concatenated convolutional code,and has become one of the channel coding standards of CCSDS because of its excellent performance in anti-fading and anti-interference.Based on this,this paper attempts to combine turbo code with OFDM technology to realize a COFDM wireless communication system.To realize the COFDM wireless communication system based on Turbo code,the first step is to complete the channel coding.In this paper,firstly,the codec principle of Turbo code is introduced,,and the performance of different decoding algorithms is analyzed,including MAP,Log-MAP and Max-Log-MAP.In addition,the hardware design of coder and decoder is completed and the related improvements are made as follows: first,parallel decoding is adopted;second,interleaving and deinterleaving are realized by searching interleaving mapping table;third,pipeline structure is used to optimize the storage and reading of prior information.Baseband channel modulation is designed after the accomplishment of baseband channel coding.Based on the communication model of OFDM system,the baseband channel modulation system is studied from the aspects of symbol frame structure,modulation and demodulation,constellation mapping,synchronization technology and cyclic prefix,and the simulation results and design scheme of corresponding modules are given.The synchronization technology in the system is mainly introduced,including the principle and hardware design of symbol timing and carrier frequency synchronization algorithm.Finally,the overall design and implementation scheme are given,and the overall simulation and verification of the system are carried out by using VHDL in the FPGA software development platform environment.The experimental results show that the COFDM System can realize wireless video transmission continuously and stably,achieving the expected function,and it has a certain practical value and development space.