Research And Implementation Of MQAM Synchronization Technology In UAC

In the course of development for decades,underwater acoustic communication technology has made great progress from analog to digital and from non-coherent to coherent.For MQAM coherent communication,carrier synchronization is the premise of system implementation.Therefore,this paper studies the MQAM synchronization technology in digital underwater acoustic communication and its implementation on ARM hardware platform.Especially study deeply on the residual frequency offset in digital phase locked loop.The carrier synchronization algorithm by compensating phase difference symbol-by-symbol based on phase rotation and the method to suppress frequency offset with variable step sample are proposed.The follows are detailed content of the study.Firstly,refer to the idea of DD algorithm,a carrier synchronization algorithm based on phase rotation is proposed and verified by simulation.The carrier is captured and tracked when the pilot signal is received.When the informational symbol is received,the output of the phase detector is compensated according to the symbol decision result base on phase rotation,and the carrier signal is continuously tracked.Secondly,with the proposed carrier synchronization algorithm as the core,16 QAM modulation,differential coding,TCM and underwater acoustic channel model based on Bellhop assisted design are introduced to construct the underwater acoustic communication system simulation model.The system simulation is carried out in Matlab.Then,the ARM as transceiver and receiver and the ultrasonic module are used to build the acoustic carrier communication hardware experimental platform.The simulation of acoustic underwater communication system was transplanted to the hardware experimental platform.To realize the acoustic carrier communication,the program was modified and adjusted according to the hardware condition.Finally,a method with variable step sample to suppress frequency offset is proposed in parallel with the phase rotation algorithm.Random noise is added to the sample step,and the perturbation of the sample interval is used to suppress the small steady-state frequency offset.Simulations were performed in Matlab and experiments were performed on ARM hardware platform.Through Matlab simulation and ARM experiments,the results show that the carrier synchronization algorithm based on phase rotation can overcome the interference of residual frequency offset,reduce the steady-state deviation of carrier synchronization,realize carrier synchronization of narrowband signals with residual frequency offset.In addition,the simulation and experimental results show that the variable step sample method can also effectively reduce the residual frequency offset.