The Principles and Performance of CORS, Network RTK and VRS

Issuing time:2020-07-20 08:47

CORS

CORS, also known as Continuously Operating Reference Stations, is one or several fixed and continuously operating GNSS reference stations, with the combination of computers, data communications and Internet (LAN/WAN) technologies to automatically provide multiple needs of users with different kinds of GNSS observations (carrier phase, pseudorange), various corrections, status and other GNSS service systems in real time.

Network RTK

GNSS network RTK, also known as multi-reference station RTK, is a positioning method that establish multiple (generally three or more) GNSS reference stations in an area to form a mesh coverage, and calculate and broadcast the GNSS correction information based on one or more of these reference stations and make real-time corrections to GNSS users in this area.

VRS

Virtual Reference Station. refers to certain number (at least three) of reference stations are set up in an area to receive satellite signals and transmit the information to the information processing center. The rover sends the location information of the receiver to the data processing center, and the data processing center will select the information of several nearby reference stations to "virtually" create a reference station based on the location of the mobile station, then broadcast the corrected data of the virtual reference station to the mobile station. The position of this virtual reference station is usually within 5 kilometers around the mobile station, but in fact, it is usually within a few meters. The error of the data obtained through this technology is greatly reduced.

Figure 1. Schematic diagram of VRS working principle

Comparison and Analysis of Several Network RTK Technologies　　

	VRS	FKP	MAC	CBI
Basic mathematical model	Interpolation model of double-difference observation model	Kalman Filtering of Non-Difference Observation Model of the Whole Network Global Solution	Double-difference observation model / compatible model	Interpolation model of double-difference observation model
Spatial error model	On the server side	On the mobile user side	On the mobile user side	On the server side
Reference station participating in the calculation	Need to select a master reference station, and all reference stations in the network participate in the positioning calculation	Do not select the main reference station, take the three closest reference stations to the rover	Need to select a master station, but it is not required to use the base station closest to the user as the master station	Flexible selection of the reference station according to the relative position of the rover and the reference station
Communication mode	Two-way communication	One-way communication	Two-way and one-way communication	One-way communication
	GPSNet of Trimble	SAPOS network of Germany	Spider of Leica	PowerNet of Wuhan University

VRS Fundamental

The Key technology of VRS software

The first is the fixation of the long baseline ambiguity of the base station. How to achieve fast and accurate fixation of the long baseline ambiguity is a key factor that affects the initialization time and availability of the system.

The second is the accurate modeling of regional spatial atmospheric errors. The modeling accuracy of atmospheric errors directly affects the positioning accuracy of users.