Studies Of Space-time Coding And Modulation Technology Of Telemetry System

Flights testing requires that the telemetry system and ground stations maintain reliable and efficient communication.For telemetry systems,the dual-antenna transmission structure is mostly used to achieve omnidirectional communication between ground receiving stations and aircraft.If the ground receiving station receives the same signal from both antennas at the same time,there maybe a dual antenna problem where the two transmitted signals are canceled due to the opposite phase.Traditional telemetry system cannot be applicable for the space telemetry needs of high code rates in the future.Shaped Offset Quadrature Phase Shift Keying(SOQPSK)technology has better frequency band utilization and power utilization.In addition,space-time coding based on Multi-antenna technology has good performance in a multipath environment.Combining SOQPSK technology with space-time coding can not only improve the frequency band utilization of telemetry system,but also improve system reliability.SOQPSK modulation is a special continuous phase modulation with long memory length,which makes it difficult to demodulate.Due to the "2-antenna problem",combining space-time coding with SOQPSK technology requires consideration of a system model that reduces detection complexity and mutual interference between two transmitted signals.The characteristic of SOQPSK modulation and the difference between different SOQPSK signals are studied in this paper.Then it analyzes the optimal algorithm of SOQPSK-TG signal based on MAX-LOG-MAP demodulation.The propagation characteristics of wireless fading channels and diversity techniques which can resist multipath fading are discussed,and it focuses on space-time coding techniques.By analyzing and comparing typical types of space-time coding,space-time block codes are applied to telemetry systems.In the low-complexity demodulation algorithm of the SOQPSK-TG signal,the detection algorithm based on the XTCQM approximate representtation method is more stable in the code modulation system.This paper describes a low-complexity demodulation algorithm based on XTCQM approximate representtation method and MAX-LOG-MAP algorithm for receiving signals with differential delay.It can reduce the number of the XTCQM waveforms of the STBC-SOQPSK-TG signal from 2048 to 8,which greatly reduce the detection complexity of the receiver,and simulations show that it can reduce the system bit error rate in the case of dual-antenna interference.Finally,based on the transmitter platform with V4LX100 chip as the core,this paper studies an FPGA design scheme of the STBC-SOQPSK-TG modulator.The simulation software Modelsim and vector signal analyzer are used to verify the correctness of the scheme and measure the frequency band utilization,and this scheme provides a reference for its engineering application.