Research On GNSS Receiver Baseband Signal Processing Technology Assisted By IMU

The navigation satellite system has been widely used in many fields,but in the case of satellite signal obscured or high dynamic motion and so on,satellite navigation receiver can't meet more navigation requirements.Inertial navigation system can navigate and position independently without external information interference,but the positioning error of the system will accumulate gradually with time.The GNSS receiver aided by IMU is complementary to each other,which overcomes the limitation of satellite navigation and improves the dynamic performance of the receiver.It can also correct the accumulated errors of inertial navigation system in time and give full play to the advantages of both.The paper mainly focuses on the acquisition and tracking technology of baseband signal processing of GNSS receiver aided by IMU.And the tightly couple integration is also studied,so is the anti-spoofing positioning technology using weighted tightly couple integration.Firstly,taking GPS as an example,the composition of satellite navigation system,the structure and generation of satellite signal,the pseudorange location algorithm and the pseudorange rate velocity algorithm are introduced.The working principle and navigation algorithm of strapdown inertial navigation system are introduced briefly.Then module and function of receiver are introduced.The acquisition technology is analyzed in detail,including search principle,capture search algorithm and so on.The tracking technology is analyzed in detail,including carrier loop structure,code loop structure and principle of discriminator,and effective factors on the tracking error of the phase-locked loop are discussed.Aiming at baseband processing technology of GNSS receiver aided by IMU,the Doppler frequency is solved by using the speed provided by IMU.And the Doppler frequency is added to the receiver carrier numerical control oscillator to realize the assisted acquisition algorithm.The simulation results show that the static acquisition performance of IMU is improved by 22.6%.Then principle of PLL loop aided by IMU is analyzed.After being aided by IMU in the simulation experiment,the tracking loop composed of third order PLL(bandwidth 25 Hz)and second order DLL(bandwidth 2 Hz)can continue tracking in the loop of the third order PLL(bandwidth 2Hz)and the second order DLL(bandwidth 1Hz).It means that the noise can be removed by reducing the loop bandwidth,with the dynamic performance being improved.Then the solution of tightly integrated navigation system of IMU/GNSS receiver is described,the state equation and measurement equation of the system are established.The navigation filtering is carried out by using EKF.In the simulation experiment,it is proved that the tightly integration can be still used for filtering estimation when the number of satellites is less than four.The anti-spoofing positioning of satellite signal is carried out by using IMU/GNSS weighted tightly couple integration.In the simulation experiment,pseudorange information of a single satellite is changed,and it's proved that receiver can reduce the influence of spoofing satellite by using the weighted tightly couple integration.Finally,based on DSP/FPGA integrated experimental development platform for satellite navigation and evaluation kit EV30 for Inertial Measurement Unit,the software realization about IMU processing module,tracking channel and inertial assistance in FPGA,and navigation solution in DSP is designed.