13 Sep 2023

What is GNSS multipath mitigation?

GNSS multipath mitigation, also often called GPS multipath mitigation, is the process of minimizing or correcting multipath errors.

GNSS multipath visualization how it works in urban canyons

Link to download the multipath mitigation poster.

What is multipath error?

Multipath error is also often referred to as GPS multipath, GPS error, GNSS multipath, multipath effect, and multipath interference. These errors occur when satellite signals arrive at the receiver from different directions following different paths. They take place because the signals are diffracted or reflected by objects like buildings around the receiver rather than being received directly from the satellites (line of sight), resulting in an error in pseudorange measurements that affects positioning accuracy. All satellite constellations are affected by it.

A clear example of this is when one satellite signal travels for longer (due to reflections from objects) than another satellite signal (following a direct path with no reflections). This results in a correlation discrepancy in position.

Multipath errors in urban areas and rural environments 

Multipath errors occur much less often in open-sky rural environments, where there is almost no reflection of signals, compared to urban environments, where signals are often reflected.

Multipath has the most significant impact in dense urban environments, referred to as “urban canyons.” When buildings surround the receiver, satellite signals can reflect and diffract, sometimes multiple times, before finally reaching the receiver. While a product's positioning accuracy may be 2 m in a rural environment, it could drop to as low as 30 m in an urban area due to potential errors caused by multipath signals.

The table below shows the results of a typical car drive test comparing the positioning accuracy of L1 vs. L1/L5 band GNSS receivers:

Position accuracy CEP68Expected multipath mitigation effectL1 single-band GNSS receiverL1/L5 dual-band GNSS receiver
Rural areaMinor< 2 m< 2 m
Deep urban areaHigh< 30 m< 4 m

How can multipath be mitigated?

Tracking multiple satellite constellations increases the number of satellites within line of sight. While this approach can reduce multipath effects, it does not effectively mitigate the ones caused by signals bouncing off surrounding structures and objects.

The GNSS receiver does try to detect multipath signals and avoids using them for navigation. To effectively mitigate multipath within urban canyons, dual-band technology is required.

Significantly reducing multipath error with dual-band technology

Dual-band GPS/GNSS technology mitigates multipath effects from urban canyon interference by tracking signals in frequency bands that each take different paths to reach the receiver. Knowing that L5 signals are much more resilient to multipath effects, the GNSS firmware algorithm uses more L5 signals for navigation than L1 when it detects being in a multipath environment.

GNSS multipath visualization of car test drive in urban canyon

Dual-band GPS/GNSS applications:

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