Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 622

• Two-way text messaging. The BNTS RDSS also provides an on-demand
text-messaging capability for civil users in and around China. The BNTS
should be able to provide a text-messaging service similar to the
text-messaging service offered by Blackberry. The BNTS is designed to send or
receive short messages (up to 120 Chinese characters) in the text mode, or up
to 480 numeric characters in the data mode. The Chinese indicate that the
BNTS can encrypt the data for secure communications [43, 44].
• Dissemination of Chinese atomic time for synchronization. The BNTS RDSS
provides both passive-mode (users receive only) and active-mode (users trans-
mit and receive) time dissemination and synchronization for military and civil
users in China. The Chinese indicate that the BNTS provides 100-ns time
accuracy in the passive mode and 20-ns time accuracy in the active mode.
BNTS allows remote users to synchronize to Chinese atomic time for use by
communications networks, computer networks, and power grids. Typically,
the Chinese equipment also uses GPS and GLONASS as part of the time syn-
chronization ensemble [43, 44].
• Communication of GPS-derived mobile users' positions for civil fleet manage-
ment. The Chinese indicate that BNTS RDSS is used to relay GPS- or
GLONASS-derived positions from the users to the fleet management center.
Typically, GPS and GLONASS provide positions to within 5-10m. The cur-
rent marketing strategy in China is to use cellular phone networks for local
fleet management communications and BeiDou for long-distance fleet man-
agement services [43, 44].

The basic performance for services is shown in Table 11.5 [43, 44]:

11.2.9 RDSS Navigation Signals
The BNTS satellite broadcasts to the users at 2,492 MHz (S-band). The user equip-
ment transmits a short-burst, spread-spectrum response at 1,616 MHz (L-band).
The signals are modulated with 4.08-Mbps spread-spectrum signals (8-MHz band-
width). At the time of this writing, there was no publicly available ICD or similar
document defining the BeiDou signal structure [43, 44].

Table 11.5 BeiDou Service Performance

Function Advertised Performance

RDSS positioning accuracy 20-100m (two-dimensional)

within vicinity of benchmarks

GPS/GLONASS enhancement 2-5m (two-dimensional)

Text messaging 120 Chinese characters;

480 numeric characters

Chinese time dissemination 20 ns (two-way communications mode);

100 ns (one-way communications mode)

Communications for GPS-based
tracking and fleet management

5-10m (two-dimensional)