Multipath Mitigation for GNSS

Global Navigation Satellite System (GNSS) broadcasts messages that enable the user’s GNSS receiver to determine the antenna position at the time of the signal transmission. However, performance in urban or semi-urban environments is reduced due to errors caused by the reception of signals that are reflected from objects and buildings.

Multipath error is the most important unavoidable source of error in GNSS receivers. This phenomenon refers to the combination of direct signals and indirect signals reflected off nearby obstacles one or more times before reaching the GNSS antenna. The indirect multipath signals distort the received signal used for acquisition and tracking.

Multipath in GNSS occurs in all environments, any objects such as buildings, vehicles, people, etc. all causing indirect signal reflections. Although, it is particularly noticeable in dense urban environments, such as city centers, where multipath is prevalent.

Multipath in GNSS signals limits the speed and accuracy of determining the tracking device position. Time-To-First-Fix (TTFF) is considerably slower in a positioning system where the satellite signals are distorted by the indirect multipath signals. Multipath represents a huge challenge to high precision positioning systems where accuracy matters. In a good multipath environment, approximately 1 meter of 2D positional accuracy (DRMS*) can be achieved; under an adverse multipath environment, the positional accuracy can be degraded up to 10 meters or more. Any tracking system like vehicles, drones, sport trackers and wearable devices, all suffer from undesirable effects of multipath.

In our white paper referenced we show that to mitigate multipath interference, GNSS antennas can be designed and optimized to reject multipath waves, providing better quality signals to the receivers. In the current market, antennas with multipath rejection are generally heavy and large structures, whether these are choke-ringed or contoured. In general, these options are physically large units. Taoglas has designed a relatively simple, lightweight, cost-sensitive compact antennas that can obtain similar levels of multipath rejection compared to conventional large and expensive geodetic antennas.

*Distance Root Mean Squared (DRMS), a statistical term commonly use in GNSS applications, is a single number that illustrates two dimensional accuracy. It is the probability of being within a circle, with a radius equals to DRMS, 68% of the time.

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