Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 619

• The POC;
•

Handheld, mobile, and integrated user transmission and reception sets;

Fixed ground sites used to calibrate the navigation signals, called benchmarks;

•

Fleet management centers connected by a wide-area communications net-
work or via BeiDou itself;

•

Ground support and tracking system for spacecraft support [43, 44].

•

11.2.7.1 BNTS Constellation
As stated earlier, the BNTS is composed of two BeiDou satellites placed at 80ºE and
140ºE longitude. A spare third satellite is currently at 110ºE longitude. While in this
position, the spare satellite enhances the basic RDSS coverage in areas where one or
the other primary satellite is blocked by terrain or buildings (urban canyons). The
third satellite can allow testing of an experimental three-dimensional RDSS capabil-
ity and act as an on-orbit spare to replace either of the primary RDSS satellites if
either fail [43, 44].

11.2.7.2 POC
The tasks performed by the BNTS POC have been described in the introduction to
Section 11.2.7. Its location has not been identified by the Chinese.

11.2.7.3 BNTS User Equipment
The Chinese are developing and marketing handheld, mobile, and integrated user
sets for both Chinese military and civil applications. Originally, the Chinese issued a
set of industry standards for 11 types of user sets grouped into five classes. The five
classes are listed here and detailed in Table 11.4 [43, 44]:

• General mobile class for positioning, communications, and fleet management;
• Communication class for text messaging;
• Time synchronization class for one- and two-way time transfer;
• Fleet management class for low-volume fleet management that do not require
wide area network (WAN) connections;
• Multimode class , which is a combined use of BeiDou with GPS and
GLONASS [43, 44].

Currently, a number of companies are marketing various types of user
equipment.

11.2.7.4 BNTS Benchmarks
Benchmarks are a network of fixed ground sites used to calibrate the errors in the
RDSS signals. In a similar manner as DGPS, the POC uses data from the benchmark
sites to improve the user accuracy. The POC applies corrections to the calculated
position fixes and then transmits these to the mobile users near the benchmark.