RNSS (full name: Radio Navigation Satellite System) is a satellite radio navigation service in which users receive satellite radio navigation signals. RNSS completes the distance measurement independently to 4 satellites at least, and calculates the user’s position, speed and navigation parameters. Systems such as GPS are typical RNSS systems.
RDSS (full name: Radio Determination Satellite Service) is another satellite radio determination service. The distance measurement and position calculation from the user to the satellite cannot be completed by the user itself, but must be completed by an external system through the user’s response. Its characteristic is that through the user’s response, while completing the positioning, it completes the user’s position report to the external system, and also realizes the integration of positioning and communication, and realizes the integration of NAVCOMM in the same system.
The so-called RNSS and RDSS integration concept is to integrate RNSS and RDSS two services in the navigation satellite and operation control application system of the satellite navigation system at the same time. The system can not only provide users with continuous positioning and speed measurement capabilities (so-called passive navigation and positioning), but also perform high-security position reporting without information transmission. The integration of its navigation and communication can be embedded in each other and enhance each other.
For example, China’s Beidou-1 test satellite navigation system is a regional system that provides satellite navigation information round the clock all-weather. The frequency band registered by the ITU for this system is the Radio Positioning Satellite Service (RDSS) frequency band, the upper line is the L band (frequency 1610~1626.5MHz), and the lower line is the S band (frequency 2483.5~2500MHz). The registered satellite positions are 80°, 140° and 110.5° east longitude above the equator (the last one is the backup star position).
China’s Beidou satellite navigation system currently provides three frequency signals: B1, B2, and B3, of which B3 is used for military use.
In order to provide better interoperability with other systems, the center frequency of the civilian signal B1C of the BDS global system is set at 1575.42MHz, which overlaps with the frequency points of GPS L1 and Galileo E1.
In order to support the interoperability between GPS L5 and Galileo E5, the BDS global system will broadcast broadband signals on two central frequency points of the B2 frequency band – B2a (1176.45MHz) and B2b (1207.14MHz). The signal should have high ranging performance and the ability to resist in-band interference.
The B3 frequency is located at 1268.52MHz, which will be mainly used to deploy military signals in the global stage of Beidou. While maintaining the long-term broadcast of the existing B3 signals, a modern military signal B3A will be added.
The public navigation frequency bands allocated by the ITU for downlink navigation signals of the radio navigation satellite service (RNSS) in 2011 include L-band, S-band and C-band. For example, the S-band 2483.5MHz ~ 2500MHz frequency band has been opened by ITU for Radio Determination Satellite Service (RDSS). The RDSS of the Beidou satellite navigation system and the satellite navigation signals of the Indian IRNSS all use this frequency band. The combination of S-band signal and L-band signal can improve the overall performance of RNSS services.
However, since the S-band only has a bandwidth of 16.5MHz, it is difficult for a single S-band signal to surpass the performance of the L-band signal; the intersystem interference of Globalstar and WIMAX is also a problem that needs to be considered in the S-band navigation application.