Research On Modulation And Demodulation Technology In Broadband Wireless Communication System

With the continuous progress of communication technology,wireless broadband has become the trend of development,and new requirements for delay and anti-jamming capability are proposed.In this paper,according to the wireless channel processing technology,the modulation and demodulation process of the broadband wireless communication system is designed,implemented and tested.It mainly completes the multi-rate transmission and communication tasks of multiple data lengths in the physical layer.In addition,in order to solve the problems encountered in the engineering implementation and testing process,on the one hand,this paper proposes a synchronous identification optimization scheme and realizes it.On the other hand,it realizes the artificial control of the fast AGC working mode and improves the gain adjustment performance.Firstly,the background and current situation of the broadband wireless communication system are described,and the related technologies in the system are explained in detail.The transmitter performs direct sequence spread spectrum processing of frame header data,broadening data spectrum and enhancing anti-jamming capability.To reduce the interference of multipath fading,single carrier frequency domain equalization technology is adopted.In order to correct the error codes in the transmission process,the Turbo coding and decoding technology is adopted.Scrambling and descrambling are used to enhance the random characteristics of data and improve the accuracy of data transmission.Secondly,the multi-frame and multi-rate modulation and demodulation process is designed.According to the requirements of the project,we design the transmission data frame structure.In this paper,we design five types of data frames,namely,ultrashort frame,short frame,common frame,long frame and super long frame.Each data frame type has different processing flow,summarizes system performance,explains the feasibility of the solution,and provides theoretical comparison and reference for hardware implementation.Finally,hardware design and implementation are carried out according to the theoretical scheme.Using ZYNQ-7030 and AD9361 to build a small hardware development platform,design Verilog program,actually carry out data transceiver test,realize broadband wireless communication function.Completing the configuration of AD9361 is the foundation of building the test platform,and configuring the clock and AGC of AD9361 according to the requirements.The sending end carries out the spread spectrum processing to the frame head data,the data module carries on the Turbo code and scrambling processing,after the data and the frame head combination,carries on the QPSK modulation,the four times interpolation and the shaping filter processing.The data of the receiving end are matched and filtered,and the data are located by synchronous.Then the phase correction of the frame head is corrected.,and the data frame type and transmission rate are identified.The data part includes frequency correction,phase correction,frequency domain equalization,descrambling and Turbo decoding.