About GNSS
Satellite Navigation
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User Manual 1178.6379.02 ─ 01
Figure 4-1: GNSS frequency bands
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COMPASS/BeiDou
The fully deployed BeiDou navigation satellite system (BDS) is a Chinese satellite
navigation system. This navigation system is also referred as BeiDou-2 and is
expected in 2020. The BDS is a global satellite navigation system a constellation of
35 satellites to cover the globe. This constellation includes 5 geostationary orbit
satellites (GEO) and 30 non-geostationary satellites; 27 in medium earth orbit
(MEO) and 3 in inclined geosynchronous orbit (IGSO).
The BDS uses frequency allocated in the E1, E2, E5B, and E6 bands.
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Quasi-Zenith satellite system (QZSS)
The
Quasi-Zenith
satellite system is a regional space-based positioning system.
The system is expected to be deployed in 2013 and the satellites would be a visi-
ble Japan.
In its final deployment stage, the QZSS uses a total number of three regional not
geostationary and highly inclined satellites. The QZSS does not aim to cover the
globe but to increase the availability of GPS in Japan, especially in the larger
towns.
The QZSS uses signals that are similar to the GPS public signals.
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Assisted GNSS (A-GNSS)
Assisted GNSS (A-GNSS) was introduced to different mobile communication
standards to reduce the time to first fix (TTFF) of a user equipment (UE) containing
a GNSS receiver. This is achieved by transmitting information (assistance data)
mainly about the satellites directly from a base station to the UE.
For example, a standalone GPS receiver needs about 30 to 60 seconds for a first
fix and up to 12.5 minutes to get all information (almanac).
In A-GNSS "UE-based mode", the base station assists the UE by providing the
complete navigation message along with a list of visible satellites and ephemeris
data. In addition to this information, the UE gets the location and the current time at
the base station. That speeds up both acquisition and navigation processes of the
GPS receiver and reduces TTFF to a few seconds.
In A-GNSS "UE assisted mode", the base station is even responsible for the calcu-
lation of the UE's exact location. The base station takes over the navigation based
on the raw measurements provided by the UE. Since the acquisition assistance
GNSS Systems Overview
