GNSS multipath interference and non-line-of-sight (NLOS) reception are different measurement problems. With a direct signal and a reflection present, their combination can distort the receiver's estimate of signal arrival time. With the direct path blocked and only a reflection tracked, the receiver is measuring a longer route. Suppressing distortion around a direct signal and identifying an indirect-only measurement are therefore different tasks.
This distinction matters to integrators comparing antenna and receiver claims. A receiver can keep tracking a satellite without obtaining an unbiased range to it. A statement about “multipath mitigation” needs to identify which reception condition it addresses, rather than being treated as a promise to correct every reflected signal.
First separate three reception conditions
Here, multipath interference means reflections combining with a usable direct signal. NLOS reception means the direct component is unavailable and reception depends on an indirect route. Some publications use “multipath” as an umbrella for both; the definitions below keep the mechanisms separate.
| Reception condition | What reaches the receiver | What the measurement problem is |
|---|---|---|
| Direct path with no significant reflection | A usable line-of-sight signal | Other measurement errors still exist, but this comparison has no significant reflected-path contribution. |
| Direct path plus reflection | A mixture of differently delayed versions of the same satellite signal | Their combination changes the measured signal, potentially biasing code or carrier tracking. |
| Direct path blocked; reflection received | An indirect version, possibly accompanied by other reflections | The tracked route is longer than the direct geometric distance; additional reflections can also interfere with it. |
NovAtel's multipath explanation distinguishes direct-plus-reflected reception from blocked-direct-path reception. These are propagation conditions, not three receiver product categories. A moving platform can encounter more than one during the same run.
A delayed copy can move the tracking point
The receiver estimates code delay by comparing the received signal with a locally generated ranging code. A reflection carries that code too, but arrives later. When the contributions overlap, the combined correlation shape can differ from the direct signal's shape. The tracking estimate need not remain at the direct-path delay.
Relative delay, amplitude and phase all matter, as does the receiver's processing. Do not equate the extra path length with the resulting tracking bias when both components are present. That bias can have either sign. The existing GNSS correlation guide explains how a receiver finds and follows a code; the additional issue here is that several copies can contribute to that result.
Multipath also affects carrier-phase observations, not just code pseudoranges. ESA-hosted Navipedia's multipath reference describes frequency-dependent effects and the relationship to reflector geometry. Consequently, one signal's behavior does not establish the error on every band, and continued tracking does not establish an undistorted measurement.
NLOS adds a path-length error, not just a distorted peak
If only an indirect signal is available, a clean-looking tracking result can follow the wrong path. Reducing distortion around that received component does not make its propagation distance equal to the missing direct route. The Inside GNSS technical explanation separates this excess-path error from direct-plus-reflected tracking error.
Consider an illustrative calculation, not a test result. Assume a single reflected route is 30 metres longer than the blocked direct route. Using the speed of light, the extra propagation time is:
30 m ÷ 299,792,458 m/s ≈ 100.1 ns.
That is a positive 30 m contribution to this idealized range observation before considering other errors. It is not a prediction of a 30 m horizontal position error. A position solution combines multiple observations and estimates other quantities, including receiver clock offset. The result depends on the other measurements, geometry and processing. Navipedia's basic-observables model shows why a pseudorange contains more than geometric distance.
Nor should this 30 m be inserted into the preceding direct-plus-reflected case as its tracking bias. That would replace a combined-signal problem with a different, indirect-only model.
What a choke-ring or reception-pattern claim can establish
Antenna design acts on the signals admitted to the receiver. Navipedia's antenna reference describes choke-ring structures and their rejection of low-elevation and ground-reflected contributions. It also distinguishes reflections arriving from below, at low elevation and from higher objects. The arrival direction therefore matters; “reflection” does not imply one universal rejection angle.
Attenuating an unwanted component can help when a usable direct component remains. But attenuating the only received reflection does not shorten its route. If that component remains tracked, its indirect-path problem remains; if reception is lost, the measurement becomes unavailable rather than corrected. This is the practical difference between reducing a contaminating contribution and recovering a valid direct observation.
For a choke-ring comparison, look for the documented reception pattern and the tested reflection geometry. Do not infer complete NLOS correction from a multipath-rejection label. The separate multipath versus RF-interference buying guide retains the equipment-category decision; this article explains the measurement boundary behind it.
Receiver mitigation also has a defined target
Septentrio's APME+ explanation gives a specific manufacturer example: extra correlators estimate multipath error, and the estimated contribution is removed from measurements. The documentation emphasizes short-delay reflections, whose proximity to the direct component makes separation difficult. Those implementation details belong to Septentrio, not ResiNav.
A useful comparison therefore asks whether the evidence concerns a direct signal contaminated by reflections, indirect-only reception, or both. A short-delay multipath result answers an important question, but not automatically the separate NLOS question. Likewise, identifying a suspect observation is different from correcting it: a navigation solution may instead exclude or reduce the weight of that measurement.
UCL's published research on a portfolio of mitigation methods treats NLOS and multipath techniques as complementary rather than interchangeable. Its abstract describes correlation-based limitations and combinations of evidence. It does not establish that any one antenna or algorithm eliminates both effects in every environment.
Read the outcome, not only the number of tracked satellites
More retained measurements and smaller measurement errors are different outcomes. Navipedia's receiver-characteristics discussion explicitly identifies a trade-off between retaining reflected signals for availability and their effect on accuracy. An evaluation should make that trade-off visible.
For example, compare two hypothetical processing outputs from the same recorded conditions. One retains every tracked observation; the other rejects observations classified as indirect. The second output may use fewer satellites. That count alone cannot identify the better result. Compare both against the same independent position or range reference, and report intervals with no acceptable solution rather than dropping them from the comparison. This is an evaluation principle, not a claim that either hypothetical classifier is correct.
The useful conclusion is conditional: direct-plus-reflected evidence supports a claim about that condition; an NLOS claim needs evidence for blocked-direct-path reception. If both matter, retain both in the comparison instead of substituting one favorable demonstration for the other.
Where interference-protection products fit
Reflections do not, by themselves, demonstrate an interfering transmitter or a spoofing attack. ResiNav's product catalogue is the appropriate next step when the requirement includes documented GNSS reception protection. Compare the selected model's published signals and interfaces, then use its existing enquiry route for that scope. This article does not assign choke-ring supply, NLOS correction or a multipath-mitigation result to a ResiNav model.
For a reflected-signal problem, first identify whether the direct component is usable and which measurement or solution behavior needs improvement. That makes an antenna-pattern result, a receiver mitigation result and a navigation-level rejection result comparable on their actual merits.
NEXT STEP
Turn available platform information into an engineering review.
Use the Technology centre to frame the discussion, review relevant application scenarios, then send the available platform and receiver details for confirmation.