Design And Implementation Of DQPSK Modulation And Demodulation System In High Dynamic Scene

With the rapid development of high speed rail,5G,satellite communication and other technologies,wireless communication technology has started to be challenged by high dynamic scenarios.In the high dynamic environment,there is a large relative motion speed between the transmitter and the receiver,resulting in the received signal being affected by the Doppler effect,and the probability of the occurrence of error codes increases during the demodulation process,which seriously affects the performance of the communication system.Therefore,communication technologies for highly dynamic environments are of great research significance.At present,the solutions for the Doppler effect can be mainly classified into two types of techniques: estimation compensation and differential modulation demodulation.The frequency bias estimation and compensation methods need to add additional training sequences or guide frequencies to the signal,which has a large overhead.Therefore,this paper investigates differential modulation and demodulation techniques to overcome the Doppler shift in high dynamic scenes.DQPSK combines differential coding and QPSK techniques with excellent noise immunity,overcomes phase blurring,and resists single-path Rayleigh fading.In this paper,we investigate DQPSK and its anti-Doppler performance.First,the second chapter of this paper introduces the characteristics of wireless channels,analyzes the causes of fading,noise,and Doppler effect and the mechanism of their effects on signals;analyzes the characteristics of fast and slow fading;and models the Rayleigh channel and fast time-varying channel.Then the principles of DQPSK modulation and demodulation techniques,I/Q modulation,QPSK modulation,differential coding and decoding,and modulation of zero IF DQPSK signals are described.Then,Chapter 3 analyzes the effect of high dynamic environment on DQPSK modulation method and the information transmission efficiency of DQPSK modulation method.The differential coding schemes and improvement schemes in single-carrier and multi-carrier systems are discussed,respectively.Among them,the improved scheme,the bite head differential coding scheme in single-carrier system and the time domain differential coding scheme in multi-carrier system are the schemes that have some improvements for the high dynamic environment and information transmission efficiency.Then,the module design is completed for single-carrier and multi-carrier OFDM baseband systems,and the transmit signal at the transmitter is coded according to different differential coding schemes,and the demodulation at the receiver is completed by maximum likelihood detection at the receiver,and the anti-fading,multipath,and Doppler performance of each differential coding scheme is studied under different channel environments.The simulation results show that each differential coding scheme has certain anti-multipath fading capability,and in the simulation experiments of time-selective fading,i.e.,high dynamic environment,the bite first differential coding scheme and time domain differential coding scheme have the best simulation results in single-carrier system and multi-carrier OFDM system,respectively.Finally,in Chapter 4,based on the simulation results in Chapter 3,the design and implementation of the baseband signal transceiver is completed on the FPGA platform using the time-domain and bit-head differential coding schemes,and the related modules:differential codec,raised cosine filter,IFFT/FFT,bit synchronization,sampling judgment,frame synchronization,etc.are completed.And analyze the simulation results.