Research On Carrier Tracking Loop Technology For Deep Space TT&C Communication

According to the deep space exploration mission plan issued by China National Space Administration,China will carry out planetary exploration missions such as asteroid sampling,Mars sampling,Jupiter,Uranus,and so on in the next 10-15 years.Deep space TT&C transponders play an important role in conducting deep space exploration missions,including not only ranging,velocimetry,telecontrol,telemetry,and scientific exploration data transmission functions,but also solving multiple problems such as low carrier to noise ratio and high dynamic in deep space scenarios.Therefore,deep space TT&C transponders will inevitably adopt unique advanced technologies to provide the possibility for implementing deep space exploration missions.In the baseband system of deep space TT&C transponder,carrier synchronization is an indispensable part,which is mainly divided into two stages: acquisition and tracking.This paper mainly studies carrier tracking technology.Currently,traditional receivers still commonly use PLL based carrier tracking loops,which set the phase of the output signal by the phase difference of the input signal.The disadvantage of this loop is that the setting of its loop filter bandwidth needs to consider the trade-off between noise and dynamics.For the current deep space exploration scenario,this paper analyzes the loop filter bandwidth characteristics of the carrier tracking loop,which determine the noise limit and dynamic limit of the normal working range of the loop filter bandwidth,respectively,based on the dynamic and noise in the current environment.Using this characteristic,a new PLL carrier tracking loop based on the optimal bandwidth LUT of the loop filter is proposed,which has higher robustness compared to the original loop,It has high practical value in engineering implementation.However,PLL based carrier tracking technology cannot adapt well in future deep space exploration scenarios,as these ultra long distance,low carrier to noise ratio,and high dynamic operating conditions exceed their original design application scope.Therefore,a more robust carrier tracking technology is needed to replace the traditional PLL carrier tracking loop.From the perspective of optimal filtering,KF is clearly a more powerful option.Its advantages mainly include adaptive bandwidth and providing a general framework for optimal estimation of signal parameters.Under the assumption of additive Gaussian white noise,it can automatically adjust the filter gain coefficient to minimize the mean square error between the input signal and the regenerative signal.However,the Kalman gain eventually tends to stabilize,resulting in its bandwidth eventually becoming a stable value.If this steady-state bandwidth still cannot effectively filter the noise of the current communication environment,the entire loop will still not work properly.Therefore,this paper proposes a three-stage bandwidth KF carrier tracking loop,which can quickly lock high dynamic signals with a wider bandwidth in the early stage and effectively reduce the impact of phase noise with a narrower bandwidth in the later stage.This has great application value in deep space TT&C communication with high robustness requirements.