Research And FPGA Implementation Of SOQPSK Telemetry Signal Modulation And Demodulation Technology

In the field of wireless communication,the requirements for real-time data transmission rate and system reliability are increasing.In order to achieve efficient and reliable communication,more efficient modulation techniques are needed to meet the requirements.Compared with the traditional digital modulation technology,the Shaped Offset Quadrature Phase Shift Keying(SOQPSK)signal is widely used due to its excellent spectrum and power characteristics.In addition,due to the high speed relative movement of both parties,the received signal produces a large Doppler shift.Therefore,the SOQPSK signal is demodulated with low complexity,and accurate carrier synchronization is achieved under the condition of low signal-to-noise ratio and Doppler shift,which has important research significance.In order to solve the above problems,this paper first studies the modulation algorithm of SOQPSK signal.By optimizing the frequency pulse function of the original SOQPSK-MIL signal,an improved modulated signal is obtained,and its spectrum is more concentrated.The nonlinear modulation of SOQPSK leads to very complex demodulation.Next,the partial response signal is regarded as a full response signal by pulse truncation(PT)technique,and the solution is solved by the maximum likelihood sequence detection method based on soft output Viterbi algorithm(SOVA).The simulation results show that the demodulation performance of the improved SOVA algorithm is improved.Then,for the large frequency offset problem of SOQPSK signal,a carrier synchronization technique based on FFT and RPA(Rotational Periodogram Averaging)is proposed to assist the COSTAS ring.The FFT or RPA algorithm is used to roughly estimate the Doppler frequency offset.The frequency is pulled to a smaller frequency range,and the improved COSTAS loop is used to track the carrier's small frequency offset and phase.The simulation results show that the proposed algorithm can not only track the majority of the frequency offset,but also the performance of the small Doppler shift is better than the traditional method 1~2dB.If the signal-to-noise ratio is low,the FFT algorithm is used to estimate the frequency offset roughly.When the signal-to-noise ratio is high,the RPA algorithm is used for rough estimation.Finally,this paper uses Verilog HDL hardware description language,combined with Quartus II13.0 and Modelsim,based on FPGA simulation to realize the modulation and demodulation and carrier synchronization algorithm in SOQPSK system,and analyzes the comprehensive compilation report and timing analysis report,and simultaneously modulates Part of the code was downloaded to the Xilinx FPGA zynq7010 development board.The combination of the Chipscope and 610 Zi oscilloscopes to observe the signal waveform and spectrogram confirmed that the design was correct.