Multi-antenna Gnss-over-fiber Technology Based On Directly Modulated Microwave Photonic Link

With the rapid development of Chinese Beidou satellite navigation system,nearly 20 satellites of global positioning system(GPS)and Beidou system are visible,which has greatly improved the reliability and availability of the global navigation satellite system(GNSS)monitoring.However,traditional GNSS monitoring systems typically use cables to transmit GNSS signals,and receivers can only deal with and demodulate remote GNSS signal int point-to-point mode.Due to the large transmission loss of the cable,the susceptibility to electromagnetic interference,and the high cost of the receiver,the measurement area and application scenarios the conventional GNSS monitoring system are greatly limited.In view of the problems above,this thesis researched GNSS-over-fiber technology and scheme based on low loss,small volume and anti-electromagnetic interference of microwave photonic link.Around this theme,a series of researches are done in terms of the GNSS positioning principle,the design of GNSS-over-fiber differential scheme,and the implementation of multi-antenna GNSS-over-fiber scheme.Firstly,the signal structure of GPS and Beidou systems and their frequency band distribution are introduced,and the error sources that affect the accuracy of GNSS measurement are summarized in this thesis.Besides,the principle and algorithm of GNSS pseudorange single-point positioning,and the carrier phase differential positioning are analyzed,providing theoretical supports for the design of GNSS-over-fiber differential scheme and carrier phase double-difference differential positioning in subsequent chapters.Then,a remote single-antenna GNSS-over-fiber differential positioning scheme is designed based on the directly-modulated microwave photonic link,in which the GNSS signal transmission distance can reach 10 km.On this basis,using the open source package RTKLIB,to design the positioning program,the single point and differential positioning under GPS,Beidou,GPS/Beidou system are implemented,showing that the positioning under the GPS/Beidou system has higher reliability and measurement accuracy.At the same time,the real-time double-difference differential module in GNSS receiver is used for testing.Experimental results show that the real-time positioning results of GNSS signals are almost the same when the signals are transmitted by different lengths of fiber in static environment.The real-time measurement accuracy of three-dimensional coordinates is within several millimeters.The real-time measurement accuracy of the baseline length during a short period(about 10 minutes)in dynamic environment can reach 4 mm,and the response time is 5 s.Finally,a multi-antenna GNSS-over-fiber scheme is designed,in which a receiver can receive and demodulate multiple remote GNSS signals with the help of the time division mode using the optical switch.Thus,the high-precision positioning results of multiple remote GNSS monitoring points can be obtained.The experimental results show that the scheme here can significantly improve the cost performance on large-scale applications,without reducing the measurement accuracy compared with the traditional single-antenna scheme.At the same time,the error correlation among multiple baseline vectors of simultaneous observation is theoretical analyzed.The accuracy of the three-dimensional coordinate measurement of the remote static synchronization observation loop in two different time periods is improved to 0.3~1.2 mm,with the aid of the network adjustment processing method.