Since Global Positioning System (GPS) keeps running forover 30 years, higher performance Global NavigationSatellite Systems (GNSS) has become one of the mostimportant demands for navigation and location services.New GNSS systems like Galileo and COMPASS aremaking their efforts to satisfy the demands of providinghigher measurement accuracy, better tracking robustnessand lower tracking sensitivity. These improvements canbe achieved through new signal structure, more frequencybands, system interoperation and so on. Thereby, Multi-System GNSS receiver developing would become a hardwork, including new architectures designed for newsystem navigation signal acquisition, tracking and datademodulation processes, especially for the globalnavigation satellite systems which are under construction,such as COMPASS and Galileo.Traditional GNSS signal simulator provides acomprehensive simulation platform for verifying andassessing the Multi-System GNSS receiver before thecorresponding new satellites are deployed. But when weneed to analyze how the key technical indicators, such ascold/worm/hot start Time to First Fix (TTFF), acquisitionsensitivity and tracking sensitivity, are implemented in thesignal processing level and information processing level,or testing and validating the solution for Multi-Systemcompatible design, we can get little help from it.Thereby, a Multi-Level GNSS signal simulator providingtesting methods for different design levels of the receivercan bring many benefits to the design and development ofMulti-System GNSS receiver. Overall, the Multi-LevelGNSS signal simulator can test three design levels ofreceiver, which can be defined as signal processing level,information processing level and system level,respectively. For receiver designers, testing the receiverfrom different levels can be used to figure out theinfluence of each processing level caused to the finalperformance of the receiver, verify the correctness of theprocessing algorithms in different levels and analyzewhether the design goals in different levels are reasonableas well.This paper presents a Multi-Level GNSS signal simulatorbased on Software Defined Radio (SDR) architecture andPXI bus, which can generate GPS, Galileo andGLONASS navigation signals, even the candidate signalsof COMPASS, on the common hardware platform. Thedesigned simulator provides different testing modes fortesting different levels of the receiver, and plays animportant role in the design and testing of a selfdevelopedMulti-System GNSS receiver.
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