GNSS multipath detection using three-frequency signal-to-noise measurements

Abstract

A new technique for detecting GNSS multipath interference by comparing signal-to-noise (SNR) measurements on three frequencies is presented. Depending on the phase lag of the reflected signal with respect to the direct signal, multipath interference can be either constructive or destructive, with a commensurate effect on the measured SNR. However, as the phase lag is frequency-dependent, the SNR is perturbed differently on each frequency. Thus, by differencing SNR measurements on different frequencies and comparing the result with that obtained in a low-multipath environment, multipath can be detected. Using three frequencies makes the process more robust. A three-frequency SNR-based multipath detector has been developed and calibrated using measurements from GPS Block IIF satellites in a low-multipath environment. The new detector has been tested in a range of urban environments and its multipath-detection capability verified by showing that the MP observables oscillate when the new detection statistic is above a threshold value determined using data collected in a low-multipath environment. The new detector is also sensitive to diffraction.

Multipath detection with the combination of SNR measurements – Example from urban environment

“…This work follows on the previous research of Strode and Groves, mainly demonstrated in (Strode and Groves, 2016). Presented paper introduce simplifi ed version of detection statistic (3) using only two frequencies, which allows also exploitation of other GNSS.…”

“…Finding that the presence of phase multipath has a different impact on SNR measurements at each of tracked carrier frequency, exploded Strode and Groves in (Strode and Groves, 2016). In general terms they proposed a detection algorithm which computes a test statistic from a set of current SNR measurements and then compares it with threshold that marked the limit of the system's normal performance.…”

“…Similar to function, also is elevation dependent, probably due to non-linear antenna gain pattern. In (Strode and Groves, 2016) is threshold T computed as a function by fi tting elevation dependent 3 rd order polynomial to values and then added t = 1, 2 and 3-fold multiplication of fi t RMS . These three levels of threshold serve as multipath severity assessment.…”

Precise Positioning of Uavs – Dealing With Challenging RTK-GPS Measurement Conditions During Automated Uav Flights

“…The error resulting from multipath effects is limited to one quarter of the carrier phase wavelength, which is about 5 cm for GPS L1 signals (Hofmann-Wellenhof et al, 2008). In contrast, NLOS reception has the potential to cause limitless errors (Strode and Groves, 2015). In practical applications the effects of multipath, diffraction and NLOS reception are typically combined.…”

“…The aim is to predict the satellite availability or detect possible signal deteriorations in order to improve the positioning solution on the meter level (Groves et al, 2012;Wang et al, 2013). Primarily the signal quality check serves for the mitigation of NLOS reception, since these effects have the potential to cause limitless errors in the range measurements (Strode and Groves, 2015). Alternatively, the satellite visibility can be determined from camera systems that are aligned to the zenith direction or are equipped with fish-eye lenses (Lohmar, 1999;Meguro et al, 2009;Moreau et al, 2017).…”