Interference, Multipath, and Scintillation - Understanding GPS: Principles and Applications - page 243

CHAPTER 6
Interference, Multipath, and Scintillation

Phillip W. Ward
NAVWARD GPS Consulting
John W. Betz and Christopher J. Hegarty
The MITRE Corporation

6.1 Overview

This chapter discusses three general classes of RF channel impairments that can
degrade GNSS performance. The first class of impairments discussed is interference ,
which is the focus of Section 6.2. RF signals from any undesired source that are
received by a GNSS receiver are considered interference. The interference is often
unintentional (e.g., out-of-band emissions from other licensed RF systems). The
interference may also be intentional, in which case it is commonly referred to as
jamming .
Section 6.3 discusses the second class of RF channel impairments, which is
multipath . Invariably there are reflective surfaces between each GNSS spacecraft
and the user receiver that result in RF echoes arriving at the receiver after the desired
(LOS) signal. These echoes are referred to as multipath, a term that originated from
the fact that each transmitted signal is transiting over multiple paths to the
receiver—the single direct path and a number of indirect (reflected) paths.
The third and final class of channel impairments considered in this chapter, in
Section 6.4, is ionospheric scintillation . Ionospheric scintillation is a signal-fading
phenomenon that is caused by irregularities in the ionospheric layer of the Earth's
atmosphere.

6.2 Radio Frequency Interference

Because GNSS receivers rely on external RF signals, they are vulnerable to RF inter-
ference (unintentional interference or jamming). RF interference can result in
degraded navigation accuracy or complete loss of receiver tracking. This section
first describes types and sources of interference in Section 6.2.1. Next, the effects of
interference on receiver performance are discussed in Section 6.2.2. Finally, Section
6.2.3 discusses mitigation techniques.

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