BeiDou Receivers

BEIDOU
Title	BeiDou Receivers
Edited by	GMV
Level	Basic
Year of Publication	2011

The BeiDou Navigation Satellite System (BDS), also known as BeiDou-2, is China’s second-generation satellite navigation system that will be capable of providing positioning, navigation, and timing services to users on a continuous worldwide basis. The first and second generation of BeiDou receivers are already available, including the combination of GPS and BeiDou systems - currently limited to the available regional services - with already over a thousand users.

BeiDou Receiver

The BeiDou User Segment consists of Beidou user terminals. The first user terminals appeared in 2009 based in ASIC and comprising already GPS integration.

Particularities

Each GNSS system uses a specific Reference Frame; although a multi-constellation receiver is able to convert all information to the same common frame, a BeiDou-only receiver uses the China Geodetic Coordinate System 2000 (CGCS2000), consistent with the International Terrestrial Reference System (ITRS).

In an analogous way, each system has its own time reference defined by the respective control segments; the time reference for BeiDou is called “BeiDou Time” (BDT) and it is aligned with UTC.

Each GNSS System transmits its own navigation message, defined in the respective Signal In Space Interface Control Document, SIS ICD, and whose content is used by receivers to compute their positions. The first version of the SIS ICD for BeiDou B1I open service signal on 1561.098 MHz was released December 27 at a news conference held in Beijing by the Chinese State Council Information Office.

GNSS signals modulation, structure, navigation message contents and formats are often different among signals from the same system and from different systems. Most of these characteristics are easily implemented at the receiver (e.g. requiring only “software modifications”, such as the use of different PRN codes or the ability to cope with different message structures). The main difference among GNSS receivers falls into the specific characteristics that have impact at RF level, such as the Multiple Access Techniques employed. BeiDou (as GPS and Galileo) uses CDMA techniques allowing a simpler RF module (than for example GLONASS), since all signals in the same frequency band have a common carrier. Nevertheless, BeiDou supports a regional short message service, which allows the user to send information to the stations. This additional communication link adds complexity to the receiver, and therefore potentially higher costs.

It should be noted that the current trend consists on facilitating the access of each system to the receivers, i.e. fomenting multi-constellation receivers. Hence, most discussions and agreements among the systems’ responsibles are conducted in the sense of taking this effort out of the user segment, focusing on compatibility and interoperability aspects in the system design.