Research On Baseband Processing Algorithms Of Space-Time Coded SOQPSK-TG Telemetry Signals

Recently,the Standard 106 of international telemetry organization IRIG(inter range instrumentation group)proposed a new generation of telemetry modulation signal mechanisms to cope with the large space propagation fading,insufficient spectrum resources,high bit rate and limited power in space telemetry environment.The shaping offset quadrature phase-shift keying(SOQPSK)modulation based on space-time coding is continuous phase modulation,it has high spectrum utilization and power utilization,and can overcome the dual antenna problem caused by omnidirectional radiation provided by the aircraft in telemetry.It is very important in the new generation of space telemetry systems.In the IRIG 106 standard,the SOQPSK signal with a special frequency shaping function is called the SOQPSK-TG signal.This dissertation studies the low-complexity baseband processing algorithms of modulators and demodulators.The main research aspects are as follows.(1)This dissertation proposed a baseband scheme of SOQPSK-TG signal modulator,which has been implemented on the hardware platform of FPGA and AD9361.The time-domain waveform and RF signal spectrum of the baseband signal output by the modulator meet the requirements of standard signals,which shows the correctness of the modulator design scheme.(2)To cope with the high computation complexity of the maximum likelihood sequence detection demodulation,this dissertation studied three low complexity demodulation algorithms,including truncated PAM-based decomposition suboptimal demodulation algorithm,the pulse truncation-based four-state demodulation algorithm,and the decision feedback-based two-state demodulation algorithm.Among them,the truncated PAM decomposition suboptimal demodulation algorithm is based on the PAM decomposition suboptimal truncated pulse function to reduce the calculation of the matched filter;the pulse truncation-based four-state demodulation algorithm,which reduces the number of matched filters by truncating the phase pulse shaping function;the decision feedback-based two-state demodulation algorithm,which is established based on the pulse truncation-based four-state demodulation algorithm and utilize the feedback decision to reduce the number of matched filters used in each detection time;Simulation analysis and hardware complexity analysis results show that the three methods can effectively reduce the demodulation complexity.Among them,the two-state demodulation algorithm based on decision feedback has the lowest complexity;and the four-state algorithm based on pulse truncation has the best performance.(3)This dissertation proposed the four state-based integration algorithm and the truncated PAM decomposition suboptimal-based hierarchical demodulation algorithm for the low-complexity demodulation requirements of the space-time encoded SOQPSK-TG signals.The former is based on the four-state demodulation algorithm of pulse truncation,integrates the branch metric and then makes a retrospective decision,and uses space-time coding to effectively improve the demodulation performance;the latter is based on the truncated PAM-based decomposition suboptimal demodulation algorithm,the branch metrics are layered and accumulated,and then the backtracking decision is made.The simulation results show that the former not only has lower complexity and but also has a performance gain of about 0.5dB.Besides,the simulations based on the AWGN channel and Rayleigh fading channel show that within a power ratio of 25 dB,a greater power allocation ratio of the two antennas can obtain a better demodulation performance respectively.