Multi-channel Reception And Algorithm Verification Of GNSS-over-fiber Signals

The application of multi antenna GNSS(Global Navigation Satellite System)-overfiber to attitude measurement and positioning of high-speed railway can greatly improve the accuracy.Under the condition of multi antenna coverage and interference of the whole vehicle,the existing GNSS-over-fiber faces technical challenges such as multi antenna signal coherent acquisition,real-time reception and stable operation of the system.Therefore,in this paper,I conducted research about the verification of multi-channel acquisition algorithm,the real-time reception of the signal of GNSS-over-fiber and the interference suppression of GNSS-over-fiber.Firstly,in order to verify the multi antenna array signal processing algorithm in GNSS-over-fiber,multi-channel satellite signals need to be collected coherently and continuously.Therefore,in this paper,I used the RF acquisition board fmcomms5 embedded with dual AD9361 chips as the RF front-end of the signal acquisition platform.Based on the Lib IIO software provided by ADI(analog devices,Inc),the continuous acquisition of multi-channel signals is realized.Then,multi-channel phase alignment is realized by MCS(Multi Chip Sync)technology,and the transmission and cache of highspeed data are completed on the evaluation board ZC706 which based on ZYNQ.In order to demodulate the received multi-channel baseband data,in this paper,the open source software receiver is expanded to a multi-channel array software receiver,and I verified that the multi-channel software receiver verification platform has the ability to collect multichannel data and evaluate the algorithm through the positioning algorithm.Secondly,in order to realize the real-time demodulation and reception of the signal of GNSS-over-fiber,a baseband module based on FPGA(Field Programmable Gate Array)is designed in this paper.Based on the typical GNSS signal systems and receiver principles such as Beidou and GPS,the module adopts the classic baseband processing architecture of GNSS receiver,and makes adaptive design for multi-system,multi-channel parallel acquisition,tracking and demodulation.I completed the RTL(Register Transfer Level)design and function verification of 11 sub modules such as carr＿nco,ca＿generator and time＿and＿clock,and completed the packaging and integration in the satellite channel module.Through the baseband processing module,the real-time signal acquisition and tracking can be realized,and the waveform simulation of navigation signal can also be realized.Finally,based on the requirements of the stable operation of GNSS-over-fiber,the types and suppression methods of interference which may be faced in GNSS-over-fiber are studied.Taking the Power Inversion algorithm in GNSS application as an example,the anti-interference hardware in the loop simulation experiment is carried out on the software receiver verification platform.The results showed that the system can suppress the interference with INR(Interfere to Noise Ratio)of 60 d B under various array geometric arrangements.For the optical array processing of multi antenna system,we designed an optical Blass matrix synthesis method with low dissipation power,which can be used to realize the array beamforming algorithms such as GNSS-over-fiber.This structure can not only ensure the system to resist interference and stable reception by using spatial diversity,but also greatly reduce the power dissipation of the system.