Research On SOQPSK-TG Low Complexity Demodulation Algorithm

With the continuous advances in aviation technology in recent years,the user terminal and data throughput in the field of wireless telemetry is increasing.How to make efficient use of spectrum resources has become a hot research topic.We can use spread spectrum technology or efficient modulation method to improve the frequency utilization rate.The shaped-offset quadrature phase-shift keying(SOQPSK)signal belongs to a class of continuous phase modulation signal,and its constant envelope has the advantages of high frequency spectrum utilization and high power utilization,which has been included in IRIG106 aviation telemetry standard.The U.S.military has adopted this standard for satellite communications and aerospace.SOQPSK signal is a kind of continuous phase signal,which can be divided into full response signal and partial response signal according to the memory length.The SOQPSK-TG signal is a kind of partial response SOQPSK signal.If the optimal demodulation method is adopted at the receiving end,the optimal detector requires a512 state grid,and the number of matching filters used will reach 3~8.It will make its demodulation structure complex,the engineering implementation will increase the consumption of hardware resources and development cost.Therefore,phase state grid needs to be simplified,and the common simplification methods are:pulse truncation method,Laurent decomposition method,basis function method and so on.So as to solve the above problems,the pulse truncation method is adopted in this paper to simplify the phase state.The phase state is simplified from 512 state to 4 state,and the number of matching filters is reduced from 3~8 to 3.The demodulation structure of the four-state SOQPSK-TG signal is realized.Then,aiming at the problem of high synchronization complexity,a synchronization structure based on linear phase approximation is proposed to simplify the synchronization.Next,we use MATLAB platform to verify the effectiveness of the algorithm.The modulation and demodulation system of SOQPSK-TG is implemented on Vivado using hardware description language,and we analyze the use of hardware resources and performance loss under different structures by compiling reports and simulation results.Finally,the program code was downloaded to Xilinx XC7K325T-2FFG900I development board,and the online debugging tool Chipscope was used to observe the signal waveform and demodulation results,which verified the feasibility of SOQPSK-TG signal modulation and demodulation algorithm implemented on FPGA.