Research On Multi-symbol Detection Technology Of PCM/FM Telemetry Receiving System

Pulse code modulation/frequency modulation（PCM/FM）is the most commonly used system in the telemetry field because of its good anti-interference ability and high transmitter efficiency.However,in the current telemetry system,the code rate is increasing and the practical application distance is also increasing.The traditional frequency discrimination demodulation can not resist its threshold effect,which will lead to poor demodulation performance.In addition,due to the large size of the traditional telemetry receiver,it has limitations in some special communication applications.In view of the above two problems,this thesis studies the demodulation technology to improve the demodulation performance of the receiving system and miniaturizes telemetry receiving system with strong versatility.The main work of this thesis is as follows:（1）A universal,miniaturized and highly sensitive hardware platform of telemetry receiving system based on AD9361+SOC is designed.The main RF processing module and baseband processing module schemes are demonstrated.（2）Multi Symbol Detection（MSD）technology is researched,which can improve demodulation performance.Introduced the decision criteria and algorithm principles of multi symbol detection algorithms;and conducted computational analysis and MATLAB simulation experiments to compare the impact of observation intervals of 3 symbols,5 symbols,and 7 symbols on the performance of multi symbol detection;Based on the simulation results,it is determined that a 5-symbol observation interval is the most suitable for hardware implementation.On this basis,bit synchronization technology based on multi symbol detection algorithms is studied.The bit synchronization scheme is discussed and conducted simulation experiments and performance analysis on it.（3）Hardware design and software implementation of the main modules of the telemetry receiving system.The hardware part mainly includes the circuit design of the RF module,baseband module,and power supply module;The software mainly includes PCM/FM demodulation simulation implementation and RF module program implementation.This receiving system can achieve data transmission and reception,and can fully utilize space,thereby reducing the appearance size and weight of the device.（4）Using vector signal generators,signal analyzers,oscilloscopes,and other instruments to build a test platform,the PCM/FM telemetry and reception system is tested and analyzed at room temperature in the laboratory,achieving multiple symbol detection and demodulation,bit synchronization,and other functions.The final test results show that when the observation interval is 5 symbols and the bit error rate is 10^-4,using multi-symbol detection and demodulation can achieve a gain of about 2.5 d B compared to traditional noncoherent frequency demodulation,which meets the expected goal.