GPS System Segments - Understanding GPS: Principles and Applications - page 103

4

Rms URE
Max URE
Max RSS

3.5

3

2.5

2

1.5

1

.05

0

45

15 20 25 30 35 40

NAVSTAR number

Figure 3.22 Modernized signal message fit errors.

3.4 User Segment

The user receiving equipment, typically referred to as a GPS receiver, processes the
L-band signals transmitted from the satellites to determine PVT. Technology trends
in component miniaturization and large-scale manufacturing have led to a prolifer-
ation of low-cost GPS receiver components. GPS receivers are embedded in many of
the items we use in our daily lives. These items include cellular telephones, PDAs,
and automobiles. This is in contrast to the initial receiving sets manufactured in the
mid-1970s as part of the system concept validation phase. These first receivers were
primarily analog devices for military applications and were large, bulky, and heavy.
Today, receivers take on many form factors, including chipsets, handheld units, and
Industry Standard Architecture (ISA) compatible cards. In fact, there are many sin-
gle-chip GPS receivers that have leveraged low-voltage bipolar complementary
metal oxide semiconductor (BiCMOS) processes and power-management tech-
niques to meet the need for small size and low battery drain of handheld devices.
Selection of a GPS receiver depends on the user's application (e.g., civilian versus
military, platform dynamics, and shock and vibration environment). Following a
description of a typical receiver's components, selection criteria are addressed.
Detailed information regarding GPS receiver architectures and integrations for
cellular telephone and automotive applications is contained in Chapter 9.

3.4.1 GPS Set Characteristics
A block diagram of a GPS receiving set is shown in Figure 3.23. The GPS set consists
of five principal components: antenna, receiver, processor, input/output (I/O)
device such as a control display unit (CDU), and a power supply.