Key Techniques For A GPS-over-Fiber Multi-antenna Receiver System

Attitude determination and deformation monitoring system based on GPS multi-antenna has been widely concerned because it has the advantages of fast speed, high precision and continuous working. The conventional systems usually use cable to connect antennas and receivers for carrier phase acquisition and baseline calculating. However, the conventional systems have small measuring areas and short baseline due to the large loss and susceptible to electromagnetic interference of cable.Considering this problems in the conventional systems, in this paper, we proposed a GPS-over-fiber multi-antenna receiver system. Thanks to the advantages of low loss and immunity to electromagnetic interference of the optical fiber, the proposed system can achieve longer baseline and larger measuring areas than conventional systems. In this paper, main research contents are: Calculating principle of the baseline, Designing principle of the multi-antenna receiver, Implementation of the GPS-over-fiber system and the relative hardware delay monitoring.Firstly, we analyzed the linearization of observation equation and the decoding algorithm of integer ambiguity. Then, we designed a multi-antenna receiver. It can avoid cycle slips while introducing parallel decoding module. This receiver provides direct carrier phase observations for baseline calculating.Secondly, we build a GPS-over-fiber multi-antenna receiver system based on MZM. We set the baseline length are 2.25 m, 40 m and 110 m respectively. Then, we measure the 3D coordinate and baseline length when the distance between antennas and receivers are 150 m and 2km. Experimental results show that the proposed GPS-over-fiber multi-antenna receiver system can measure the baseline accurately and the measurement error is only a few millimeters.Lastly, we also build a GPS-over-fiber system based on photonic microwave down conversion. We get the 9.42 MHz intermediate frequency successfully. The precision of 2.25 m length baseline measurement is millimeter level. Since the local oscillator signal transmits in this system bidirectionally, we can obtain the carrier phase change by measuring the local oscillator signal phase change. The proposed relative hardware delay monitoring module can use to improve vertical precision due to the measurement error of optical fiber change is just a few millimeters.