GNSS-SDRLIB: An open-source and real-time GNSS software defined radio library

Global navigation satellite system (GNSS) is rapidly gaining in popularity because of their wide range of current and potential applications. As a result, GNSS software receivers, which are based on software-defined radio (SDR), have attracted significant attention in recent years. Software GNSS receivers are widely recognized and used because of their configuration flexibility and ease of use in GNSS research. Many GNSS (or GPS) software receiver projects have been undertaken by researchers and companies. In particular, some are being developed as open-source projects. However, the current open-source GNSS receivers support a few specified front-ends for real-time processing and partly support multi-GNSS or do not support multi-frequency signals. We have developed a novel open-source and real-time processing capable GNSS software receiver, called GNSS-SDRLIB. GNSS-SDRLIB is a very simple and easy-to-use GNSS signal processing tool written in C, and it consists of several application programs written in C++/CLI. GNSS-SDRLIB provides GNSS signal acquisition, tracking, pseudorange generation, navigation message decoding, and spectrum analysis functions for GNSS signal processing, which is required for position computation. For real-time positioning, GNSS-SDRLIB supports many commercially available front-ends. In addition, it supports any recorded intermediate-frequency (IF) data obtained by any front-end for post-processing. It can output the observation data such as the pseudorange, carrier phase, Doppler, and carrier-to-noise density (CN0) in the RINEX or RTCM format. GNSS-SDRLIB can be used with a conventional hardware receiver if a front-end device and laptop computer are prepared. We carried out tests to evaluate the performance of GNSS-SDRLIB and developed actual applications. Based on a static positioning test with multi-GNSS constellation, we determined the receiver positions within 2 m using multi-GNSS LI pseudoranges generated by GNSS- SDRLIB. We expect it to be widely used for research and educational purposes to learn GNSS signal processing.