Tech Chat | How does CORS work?

2022-08-09

CORS system (Continuous Operational Reference System) is one of the development hotspots of modern GPS, which introduces the concept of network into the application of geodesy. The establishment of this system not only brings huge changes to the surveying and mapping industry, but also brings new ideas and modes to the spatial information service in the modern network society.

A CORS system can be defined as one or more fixed, continuous operation of GPS reference stations. With modern computers, data communication and Internet (LAN/WAN) technology of the network, it can provide users with different types of real-time data, such as viewing different types of GPS observations (carrier phase, pseudo-range), various correction data, status information, and other systems related to GPS services.

What is CORS?

It consists of five parts: reference station network, data transmission system, data processing center, positioning & navigation data broadcasting system and user application system. Each reference station is connected with the monitoring and analysis center through a data transmission system to form a private network.

1) The reference station network consists of reference stations uniformly distributed within the range. Responsible for collecting GPS satellite observation data and sending it to the data processing center to provide system integrity monitoring services.

2) The data of each reference station is transmitted to the monitoring and analysis center through a dedicated optical fiber line.

3) The data processing center is used to receive the data of each base station, process the data, form differential positioning user data of multiple base stations, and form a data file in a certain format, and distribute it to users. The data processing center is the core unit of CORS and the key to realizing high-precision real-time dynamic positioning.

4) The broadcasting system broadcasts positioning and navigation data to users through mobile networks, UHF radio stations, the Internet, etc.

5) User application system, which can be GNSS receiver, RTK rover, driving assistance system, personnel positioning equipment, etc.

At present, the CORS system can adopt FKP technology, CBI technology, ARS technology, MAC technology and VRS technology. It is generally believed that VRS technology is relatively mature in system security, stability and software application, so VRS technology is commonly used in CORS systems.

What is VRS technology?

VRS is known as the Virtual Reference Station technology. The Virtual Reference Station first sets up a certain number of reference stations (at least three) in a certain area. The base station receives the satellite signal and then transmits the information to the information processing center.

According to the location of the rover, the data processing center selects the information of several nearby reference stations, virtualizes a reference station, and then broadcasts the correction data of the virtual reference station to the rover. The location of the virtual reference station is usually within 1 km of the rover.

Since the differential correction is derived from the observation data of multiple reference stations, errors in the ionosphere, troposphere and satellite orbits can be effectively eliminated. Even if the rover is dozens of kilometers away from the reference station, it can achieve centimeter-level fast real-time positioning.