Research On Tracking Algorithm Of BeiDou Navigation Receiver Under The Weak Signal

In order to break the monopoly position of GPS,our country has been accelerating the development of Beidou navigation system.It has been successfully applied to transportation,disaster reduction and public safety.So it has greatly contributed a critical effect to the national defense construction and national economic development of our country.The successful launch of the BDS-3 satellite indicates that the Beidou system has officially entered the third stage of construction.As the Beidou industry has entered a high-speed development stage,the requirements of the reveiver performance are also increasing.With the rapid development of economy,there is more and more demand for navigation and location in the city,mountains and canyons.However,the satellite signal received in these environment is weak,and only the high-sensitivity receiver can meet the work requirements.Therefore,it is of great significance and wide prospect to research the high sensitivity tracking technology of Beidou navigation receiver for weak signal.In this paper,the signal structure of BDS-2 satellite is analyzed,and the characteristics of BDS-3 satellite are introduced too.First,the paper studies the traditional tracking loop.Then it designs the structure of carrier and code tracking loop for weak signal,and the corresponding loop error is analyzed too.The influence of loop bandwidth and other loop parameters on receiver performance and weak signal tracking capability is explored,and an appropriate verification scheme is selected to verify the loop tracking performance.Long time coherent integration is an effective means of high sensitivity receiver,but extending the coherent integration time has many limitations.A bit synchronization method based on maximum likelihood estimation is improved for weak signal.It can accomplish the bit synchronization,strip NH code,and reduce the error rate of the bit synchronization at the same time.On this basis,the high gain coherent integration algorithm can be realized to track the weak signal.The effectiveness of the algorithm is verified on software receiver,and then the influence of the algorithm on tracking loop performance is analyzed too.The use of long time coherent integration can enhance tracking weak signal performance,but with the increase of coherent integration time,the performance of tracking loop will decrease,and the tracking accuracy will also become worse.In order to ensure the high gain coherent integration effect,the frequency stability transfer has been used.It can compensate frequency deviation in weak signal channel by using auxiliary signal,in order to eliminate the energy loss of coherent integration caused by frequency deviation.Lastly,the effectiveness of frequency stability transfer is verified through software receiver.Besides using software receiver to modify and verify some of the tracking algorithm,a receiver verification platform based on FPGA and DSP is also built.First,the paper designes the overall scheme of the verification platform,and then focus on the design of function module of the baseband signal processing platform based on FPGA and DSP.It is used to complete the validation of tracking algorithm for weak signal in this paper.