Specifications

IntroductionGPS and Assisted GPS
11Operating Manual 1171.5248.12 ─ 15
2.3 Use of navigation data
The C/A code used is fundamental to the simulation of GPS signals. The C/A code speci-
fies the satellites to be simulated.
Real navigation data (the almanac) contains the information about the currently valid
space vechicle IDs. When using real navigation data, only valid SV IDs can be selected
in the operating menu.
When using arbitrary data, the complete range of IDs, 1 to 37, is available.
In addition to this, navigation data play an extremely important role, since they are essen-
tial for calculating the positions of the four satellites, which are the minimum prerequisite
for localization purposes. However, even if only one satellite is available, real navigation
data can be used to check the decoding of navigation information (such as GPS time,
almanac and ephemeris) in addition to the recognition of the C/A code.
Current almanac data can be downloaded via the Internet and stored on the harddisk of
the R&S Signal Generator. The almanac data is also used for extracting the satellite-
specific navigation information (ephemeris).
Almanacs are currently available at the following internet sites:
●
U.S.Coast Guard Navigation Center GPS Homepage http://www.navcen.uscg.gov/
GPS/almanacs.htm
The almanac files are named xxx.alm (for YUMA files) or xxx.al3 (for SEM files)
whereas xxx denotes the day of a year.
●
http://www.celestrak.com/GPS/almanac/
The naming convention of the almanac file is: almanac.sem/
yuma.weekXXXX.YYYYYY.txt
whereas xxxx denotes the GPS week and yyyyyy the time of almanac (TOA).
For more detailed information on the content and frame structure of navigation data, as
well as C/A code generation, refer to the specifications.
2.4 Functional Overview Option GPS (R&S-K44)
This chapter gives an overview of the option GPS (R&S-K44).
The GPS implementation in the R&S WinIQSIM2 is a simplified offline version of the real-
time one and provides only the capability to generate an one-satellite static generic signal
with constant Doppler shift.
The generic workflow is described in chapter 2.8.8, "Generating an one-satellite static
generic GPS signal with R&S WinIQSIM2", on page 24, and chapter 2.8.9, "Loading
and Processing an GPS Waveform in the ARB of R&S Signal Genera-
tor", on page 25.
Use of navigation data