Specifications

IntroductionGPS and Assisted GPS
9Operating Manual 1171.5248.12 ─ 15
2 Introduction
The R&S Signal Generator provides you with the ability to generate signals of up to four
Global Positioning System (GPS) satellites per baseband path.
An instrument equipped with two-path is able to generate the GPS signal of eight satel-
lites.
Signal generation is done in real-time and thus it is not limited to a certain time period.
The GPS implementation in the R&S WinIQSIM2 is a simplified offline version of the real-
time one and provides the capability to generate an one-satellite generic signal.
The Global Positioning System (GPS) consists of several satellites circling the earth in
low orbits. The satellites permanently transmit information about their current position
(ephemeris) and about the orbits of all satellites (almanac). Additionally transmitted time
information enables the GPS receiver to determine the runtimes of the transmitted sig-
nals. The 3D position of a receiver on the earth can be determined by carrying out delay
measurements of at least four signals emitted by different satellites.
Being transmitted on a single carrier frequency, the signals of the individual satellites can
be distinguished by means of correlation (Gold) codes.
With GPS, the folloing two ranging codes are defined:
●
the Coarse/Acquisition code (C/A code) The C/A code (f_ca= 1.023 MHz) is freely
avalilable and used for civilian purposes.
●
the Precise code (P-Code).The P-Code (f_p=10.23 MHz) is restricted and used for
military applications.
Both ranging codes are used as spreading code for the navigation message which is
transmitted at a rate of 50 baud.
There are two carriers available:
●
L1 (f_L1= 1.57542 GHz), which is modulated by both C/A code and P-code (QPSK)
●
L2 (f_L2=1.2276 GHz), modulated only with P-Code (BPSK).
2.1 GPS system parameters
The table 2-1 gives an overview of the GPS system parameters.
Table 2-1: GPS system parameters
Carrier frequency L1=1.57542
GHz L2=1.2276 GHz
Signal level, after antenna Approx. –115 dBm, depending on receive conditions
Doppler shift -100 kHz to +100 kHz selectable (individually for each
satellite)
Symbol rate 1.023 Mcps (C/A code)
10.23 Mcps (P-code)
GPS system parameters