SNRdetector

SNRdetector is a MATLAB based tool for detection of multipath in GNSS observation using Signal-to-Noise ratio measurements. Tool implements the method proposed in (Strode and Groves, 2016) which use measurements in low-multipath environment to "calibrate" user equipment (receiver, antenna) to use for multipath detection. Output of calibration are coeficients of polynomial regression of SNR differences for different frequencies. In settings of calibration one can choose if wants to use universal calibration (coefficient estimated for all satellites together) or individual calibration (each satellite has its own calibration coefficients). Original estimator uses three frequency to compute detection statistic, however this tool can be used also with just two frequencies and then it is possible to process not only data from GPS, but also from Glonass, Galileo and Beidou.

To start the program just run processDetection.m script from MATLAB command prompt. Example input files are included in obs/calibration (data from low-multipath environment) and obs/testing (data at site where reflections should occur). To compute position of satellites in these observation files the navigation messages are needed. These can be automatically downloaded for all navigation system, however gzip utility have to be installed on your computer and available on the path to uncompress the navigation messages automatically!

Every source file in eph or fun folder has documentation string and simple explanaition of its funcionality, so if you want to change something, you should be able to understand what's going on in particular function file.

Calibration phase

At this stage the user equipment should be placed in so called "low-multipath" environment, so no obstacles allowing signal to reflect from should be in the vicinity of antenna. The figure below represent the example (see attached file obs/calibration/example_calibration.18o) how calibration polynomial functions fitting SNR differences can looks like.

Note: There is a branch of utility oscillating pattern in measured SNR values caleed GNSS reflectometry (for more details see e.g. (Larsonn et. al., 200X)). For this reason I would recommend to set the antenna height as it will be used in the real measurement campaign.

Example of calibration for data acquired in low-multipath environment

Detection phase

Example of multipath detection using SNR detector

References

Strode, Philip R. R. and Paul D. Groves. GNSS Multipath Detection Using Three-Frequency Signal-to-Noise Measurements. GPS Solutions 20, no. 3 (July 2016): 399–412. https://doi.org/10.1007/s10291-015-0449-1.

http://xenon.colorado.edu/portal/index.php?action=publications