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GNSS Solutions : How Does Non-Line-of-Sight Reception Differ From Multipath Interference ?
| Content Provider | Semantic Scholar |
|---|---|
| Author | Petovello, Mark G. |
| Abstract | I t is well known that GNSS signals may be reflected by buildings, walls, vehicles, and the ground. Glass, metal, and wet surfaces are particularly strong reflectors. These reflected signals can interfere with reception of the signals received directly from the satellites, a phenomenon known as multipath interference, or just multipath, because the signal is received via multiple paths. However, cases also occur where the direct signal is blocked and only a reflected signal is received. This non-line-of-sight (NLOS) reception is particularly common in dense urban areas where tall buildings block a lot of the signals. Figure 1 illustrates both phenomena. Within the GNSS community, it is commonplace to classify NLOS reception as multipath. However, the two effects are not the same, although they sometimes occur together. If the signal is only received via reflection, no multiple paths exist, only a single reflected path. The ranging measurement errors that result from NLOS reception are quite different from those produced by multipath interference and are not corrected by most multipath mitiga-tion techniques. Therefore, to improve positioning in urban areas by addressing NLOS reception, we must first acknowledge its existence as a separate phenomenon. This article describes the differences between multipath and NLOS reception, and explains why different techniques are generally required to mitigate their effects. These techniques may be antenna-based, receiver-based, or post-receiver, and many may be used in combination. Where multipath interferes with directly received signals, the reflected signals distort the code correlation peak within the receiver, as shown in Figure 2. As a result, the code phase (used to generate the pseudorange) of the direct line-of-sight (LOS) signal cannot be accurately determined by equalizing the power in the early and late correlation channels. A positive ranging error occurs when the direct and reflected signals are in-phase, a phenomenon known as constructive interference, while a negative ranging error occurs when the signals are out-of-phase, which is known as destructive interference. The magnitude of the resulting code-tracking error depends on the path delay of the reflected signal with respect to the direct, the relative strengths of the two signals, their Multipath vs. NLOS signals " GNSS Solutions " is a regular column featuring questions and answers about technical aspects of GNSS. Readers are invited to send their questions to the columnist, Dr. will find experts to answer them. His e-mail address can be found with his biography below. FIGURE 1 Multipath … |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.insidegnss.com/auto/novdec13-Solutions.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
