Research On Interference Suppressing For GNSS Receiver With Multiple Antenna Array Structures

Global Navigation Satellite System (GNSS) provides all-day, high-accuracy, continuous and real-time services for positioning, navigation and timing (PNT), and has been universally constructed as military and civil infrastructures since applied extensively in areas of production and living. There have been existing common developments of four systems such as GPS, Galileo, BeiDou and GLONASS, and induce the modernization of GNSS.GNSS is an imperfect system which needs modernization to improve sercive performances, and novel navigation signals and modulations are presented and transmitted. While more and more signals are crowded in L band owing to the limited frequency resources, and form inter-system and intra-system interfere with each other, and spread the receiver bandwidth form several MHz or tens of MHz to hundreds of MHz. What’s the worse, limited to satellite power and height, the signal power received on ground is too weak to make receivers work when existing powerful radio interferences, which is not able to be recolved by GNSS modernization, and it is the greatest threat for the expensive GNSS with low cost.In this thesis, the research of suppressing interferences begins with the characters of GNSS signals and receiver principles, and the interference suppressing technologies are studied based on array signal processing and multiple antenna array structures are proposed for different applications, and the resolutions are presented for the following questions:1. Compatibility among signals and performance evaluation parameters for interference/interference suppressing. The compatibility is the precondition of GNSS interoperability, and the conventional and modern signals are described firstly for the modulations and generations, as well as the receiver principle, then the effects between signals of inter and intra system are analyzed according to signal characters, and the quantitative criteria are set up. After that, the signal models of typal interferences are introduced, and the analysis methodology of compatibility evaluation is extended to powerful radio interference environments and the evaluation criteria as well as quantitative parameters are proposed, and finally the effectiveness of the evaluation parameters are verified by acquisition performance of receiver, and those are the basis for the performance evaluation of the following interference suppressing algorithms.2. Practical applications for interference suppressing in single-frequency GNSS receivers. The antenna array can be seen as a coherent model for single-frequency signal, and algorithms for realization of adaptive digital beamforming (ADBF) in GNSS receivers are investigated based on GNSS signal characters. Firstly the blind ADBF without direction of arrival (DOA) are presented since it is hard to estimate DOA for satellite signals, which will reduce the complexity of receiver and avoid performance degradation induced by DOA error. Then the null broadening algrothim for circular array is proposed for receivers moving with high speed and rolling over, which makes the interference suppressing performance of receivers robust and interference is able to be suppressed effectively even when departing from null direction. After that, in order to be implemented in hardware, numerical solution without divider for inverse matrix is presented to reduce hardware cost. Finally the performances of algorithms are verified by the test combining software simulator, software receiver and hardware development platform.3. The limination of antennas number for the array of GNSS receiver. The performances of antenna array are determined mainly by the number of antennas, while the mobility of GNSS receiver limites the array size, and for L band the antennas number is limited. As a result, the main concern for GNSS receiver is not to reduce the computational complexity as in phased array radar system, but to obtain better performances with fewer antennas. Dense overlapped subarray architectures are presented for linear and planar array respectively, not only to reuse received signals on each antenna and obtain additional gains by two-level weighting, but also avoid grating lobes induced by subarray outputs. Weighting modes at element level and subarray level are different and discussed, three modes are proposed for different applications. The simulation results demonstrate the advantages of the proposed architectures in both output performance and computational amount, and a low complex GNSS receiver with interference suppressing ability can be developed.4. The incoherent receiveing problem for wideband GNSS signals and sparse arrays. Aiming at multi-frequency GNSS signals, wideband signal model in incoherent array is presented, and space-time adaptive processing (STAP) architecture is adopted and the signal model is presented, as well as the blind interference suppressing algorithm. Then ADBF methodology based on STAP architecture is presented for sparse array in which the distance between adjacent antenna elements is much larger than half wavelength, the time delay is adjusted by time taps weighting and the output signals are coherent, combining with phase weighting the interference signals are suppressed. Further, the fixed sparse array is extended to dynamic multi-user antennas, and cooperative beamforming for multiple nodes based on Ad-hoc networks is presented. The DOA ambiguity is resolved independ on array geometry, and the time delay is compensated by time weighting combining with phase weighting to provide interference suppressing ability for handheld users.