Other Regional Systems

Other Regional
Title	Other Regional Systems
Edited by	GMV A.D.
Level	Basic
Year of Publication	2011

There are nowadays three regional navigation satellites systems under development: the Japanase QZSS, the Indian IRNSS and the Chinese BeiDou. The first two are explained in dedicated articles and BeiDou system is going to be explained next.

BeiDou-1

COMPASS/BeiDou Logo

BeiDou-1 is the Chinese experimental regional navigation system. In 1994, the Chinese government authorized to start the development and deployment of an experimental satellite navigation system based on the twin-satellite navigation system. The two GEO satellites, Beidou 1A and Beidou 1B, were launched in 2000. The system began to provide positioning service in late 2001. In May 2003, the successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 system. The BeiDou-1 service is available to civilian users since 2004, and the system services and performance characteristics at this time (2004) were:

• Positioning: 100m (1σ); 20m (1σ, with reference stations).
• Regional Service short message service (SMS): up to 120 Chinese characters.
• Timing: 20 ns.

Method of Operation

The following procedure is used (extracted from article Compass Satellite Navigation System (Beidou), on Sinodefence.com):

Firstly, the central control station sends inquiry signals to the users via the two satellites. When the user terminal received the signal from one satellite, it sends responding signal back to both satellites. The central station receives the responding signals sent by the user from two satellites, and calculates the user’s 2D position based on the time difference between the two signals. This position is then compared with the digital territorial map stored in the database to get the 3D position data, which is then sent back to the user via satellites using encrypted communications. The user can also transmit encrypted text messages (up to 120 Chinese characters) to the central station via the satellites.

The system provides positioning data with accuracy of 100m. By using ground- and/or space-based (the 3rd and 4th satellites) differential methods, the accuracy can be increased to under 10m and the timing accuracy 100 nanoseconds. The system capacity is 540,000 users per hour, and serve up to 150 users simultaneously. As well as positioning service, the system can also transmit encrypted text messages between the central control station and the end users.

Because the Beidou 1 system requires dual-way transmissions between the user and central control station via satellites at high-altitude geostationary orbit, its user segment needs extra space for transmitter and a more-powerful battery. Therefore Beidou 1’s user segments are much bigger (20cm antenna), heavier and more expensive compared with GPS user receivers. Additionally, the number of users can be served by the system is limited by the communication capacity of the network.

Applications

BerDou-1 positioning service has been used in different applications, including:

• Disaster Control.
• Marine application.
• Transportation application/fleet management.

In 2008 Sichuan earthquake, around 1000 BeiDou-1 terminals provided positioning, monitoring, and emergency information services. Also in 2008, BeiDou-1 gave services for the search and rescue fleet management for Shenzhou-7 Manned Space Program. Since October 2009, the Yunnan border guards are equipped with BeiDou-1 terminals.

BeiDou-2 Phase 1

The initial phase of the COMPASS/BeiDou-2 global navigation system is the implementation a Chinese regional system, with much higher accuracy to replace BeiDou-1. By December 2011, the COMPASS system went into operation on a trial basis providing initial passive positioning navigation and timing services for the whole Asia-Pacific region with a constellation of 10 satellites (5 GEO satellites and 5 IGSO satellites). The BeiDou Navigation Satellite System Signal In Space Interface Control Document (Test Version) was released in December 2011. During 2012, the system is going to launch another 6 satellites.

The list of BeiDou-2 satellites can be found in article COMPASS Space Segment. The system is providing for the whole Asia-Pacific region:

• initial passive positioning navigation;
• timing service;
• and short message communication (120 Chinese characters per message) service.

The aim of the regional BeiDou system (completion expected by end of 2012) is to provide two types of services:

• Open service: a free service for civilian use targeting a positioning accuracy of within 10 meters, velocity accuracy of within 0.2 m/s and timing accuracy of within 20 nanoseconds;

• Authorized service: a licensed service with higher accuracy even in complex situations for authorized and military users only.

These services are available for the BeiDou coverage area, i.e. China and its neighboring countries.

For further description of BeiDou-2 including its global service, developed in Phase 2, please check the COMPASS articles.