AbstractThe Open Source GNSS Reference Server (OSGRS) exploits the GNSS Reference Interface Protocol (GRIP) to provide assistance data to GPS receivers. Assistance can be in terms of signal acquisition and in the processing of the measurement data. The data transfer protocol is based on Extensible Mark-up Language (XML) schema. The first version of the OSGRS required a direct hardware connection to a GPS device to acquire the data necessary to generate the appropriate assistance. Scenarios of interest for the OSGRS users are weak signal strength indoors, obstructed outdoors or heavy multipath environments.This paper describes an improved version of OSGRS that provides alternative assistance support from a number of Global Navigation Satellite Systems (GNSS). The underlying protocol to transfer GNSS assistance data from global casters is the Networked Transport of RTCM (Radio Technical Commission for Maritime Services) over Internet Protocol (NTRIP), and/or the RINEX (Receiver Independent Exchange) format. This expands the assistance and support model of the OSGRS to globally available GNSS data servers connected via internet casters. A variety of formats and versions of RINEX and RTCM streams become available, which strengthens the assistance provisioning capability of the OSGRS platform.The prime motivation for this work was to enhance the system architecture of the OSGRS to take advantage of globally available GNSS data sources. Open source software architectures and assistance models provide acquisition and data processing assistance for GNSS receivers operating in weak signal environments. This paper describes test scenarios to benchmark the OSGRSv2 performance against other Assisted-GNSS solutions. Benchmarking devices include the SPOT satellite messenger, MS-Based & MS-Assisted GNSS, HSGNSS (SiRFstar-III) and Wireless Sensor Networks Assisted-GNSS. Benchmarked parameters include the number of tracked satellites, the Time to Fix First (TTFF), navigation availability and accuracy.Three different configurations of Multi-GNSS assistance servers were used, namely Cloud-Client-Server, the Demilitarized Zone (DMZ) Client-Server and PC-Client-Server; with respect to the connectivity location of client and server. The impact on the performance based on server and/or client initiation, hardware capability, network latency, processing delay and computation times with their storage, scalability, processing and load sharing capabilities, were analysed.The performance of the OSGRS is compared against commercial GNSS, Assisted-GNSS and WSN-enabled GNSS devices. The OSGRS system demonstrated lower TTFF and higher availability.
Weak signal acquisition enhancement in software GPS receivers – Pre-filtering combined post-correlation detection approach