Key Technology Research On Carrier Acquisition And Tracking Loop For GNSS Receiver

With the gradually development of Beidou Satellite Navigation System,which is researched and produced by China,the application of the system will be extended from Asia-Pacific zone to the whole world.As the mobile terminal of satellite navigation receiver,there must be good prospects for development in military and civilian.Nevertheless,the receiver itself has some difficult problems such as badly robustness of carrier acquisition,low capture accuracy,poor performance in the condition of high dynamic carrier tracking and high complexity of base-band signal processing.What's more,the blockade is under way by developed countries.As a result,it is essential to self-develop low complex and high dynamic satellite navigation receiver,so that to enhance the performance of acquisition and tracking.The key research contents of this thesis are as follows,First,to solve the problem of low carrier frequency acquisition accuracy in satellite navigation receiver,the iterative fast orthogonal search algorithm(IFOS)is proposed as a method of carrier frequency acquisition.Applying this algorithm module to the signal samples after the regular coarse acquisition was completed to further refine the coarse estimations.Alongside this,we adopted a method of high-efficiency cyclic iteration orthogonal function that reduces the memory space required for signal processing.Then,this paper explains in detail the implementation structure of the proposed fine carrier acquisition method.Finally,to simulate the senario of the true satellite navigation signal,it is produced by satellite navigation signal simulator of Spirent company.Finally,the experiment results are analyzed and summarized.Second,to address the problem of high complexity and hardware resouces in Frequncy Lock Loop(FLL)and Phase Lock Loop(PLL),four-quadrant arctangent function discriminator based on improved coordinate rotation digital computer(CORDIC)algorithm is proposed.This algorithm uses the four-quadrant arctangent function module to implement the function of discrimination.Aiming at the characteristics of high data throughput and large resource usage for the CORDIC algorithm based on pipeline structure,this paper proposes an improved CORDIC algorithm pipeline structure,which divides the phaserotation into original phase rotation and approximate phase rotation.And the hardware structure diagram for the improved CORDIC algorithm of four-quadrant arctangent function discriminator is proposed.Finally,the experiment results are analyzed and summarized.Third,in the terms of Number Controlled Oscillator(NCO)of carrier tracking loop,the unidirectional coordinate rotation digital computer(CORDIC)algorithm based on phase rotation estimation method is proposed to reduce the usage of hardware resource and optimal structure.According to establish mathematical model,the pre-rotation phase is divided into fixed phase and variable phase.First of all,through phase mapping relationship,quadrate position is determined.Furthermore,unidirectional phase rotation is used to realize fixed rotation;under the condition of keeping the phase errors in a reasonable range,phase rotation estimation method could finish the final phase rotation.Based on the above,the hardware architecture is given.Firstly,using under-damping theory,a part of unidirectional phase rotations are carried out.Then performing original CORDIC algorithm and rotation phase estimation method completes the rest angle iterations.So far,high speed and accurate phase rotation is realized.We also always analyze the error brought by this algorithm.Finally,the experiment results are analyzed and summarized.Fourth,to maintain the tracking performance and reduce the complexity of carrier loop,two kinds of carrier loop structure are proposed.In the first place,this section puts forward a new carrier loop structure based on high-order Doppler parameter detection algorithm.Applied when the input of the tracking loop is the carrier signal,this solution begins by establishing a relationship between the first and second order changing rate of the Doppler frequency shift and the output of the discriminator,so that the Doppler frequency shift can be estimated.Following this,the combined frequency-lock loop and phase-lock loop methods is used to build a carrier loop structure for the high-order Doppler parameter detection algorithm.What's more,in order to verify the stability of the new architecture,this part respectively constructs the modules of discriminator,loop filter and NCO in Z domain.Alongside this,transfer function of closed loop system is deducted,so that drawing the stable condition of the new architecture,and the relationship between steady-state phase error and loop parameters.In the second place,a non-data-aided carrier tracking method based on variable dimension extended Kalman filter(EKF)is introduced,applying this module to instead of discriminator and loop filter.Thus it utilized the output of accumulatorafter symbol decision as the observation matrix of EKF.What's more,a variable dimension EKF structure is implemented to decrease the dimension of observation matrix.Through detecting the first and second order changing rate of Doppler frequency,the real time switching between monitor and non-monitor is realized to tracking the Doppler frequency effectively in high dynamic scenario.Finally,the experiment results are analyzed and summarized.