What are Virtual Reference Stations? VRS vs Base Station
What are Virtual Reference Stations?
A virtual reference station is a fictitious, unoccupied reference station located just a few meters away from the RTK user.
For this position, observation data are generated using data from nearby reference stations as if they had been observed by a GPS receiver at that location.
To provide high precision, Virtual Reference Station (VRS) networks employ real-time kinematic (RTK) systems.
To achieve centimeter-level or even higher positioning accuracy, precise dual-frequency carrier-phase measurements are often required.
In addition, these measurements are typically analyzed using a differential GPS (DGPS) technique, such as real-time kinematic (RTK) or post-processing (PP).
Regardless of the differential algorithm used, the process implicitly assumes that the quality of the reference station data is commensurate with the desired level of positioning accuracy.
What is a Base Station?
According to the International Telecommunication Union’s (ITU) Radio Regulations (RR), a base station (or base radio station) is a “land station in the land mobile service.”
The phrase is commonly used in mobile telephone, wireless computer networking, and other wireless communications, as well as in land surveying.
In surveying, it is a GPS receiver at a known location, whereas in wireless communications, it is a transceiver that connects several other devices to one another and/or to a larger area.
It connects mobile phones to the rest of the telephone network in mobile telephony. In a computer network, it is a transceiver that acts as a switch for the network’s computers, potentially linking them to a/another local area network and/or the Internet.
It can refer to the dispatch hub of a dispatch fleet such as a taxi or delivery fleet, the base of a TETRA network used by government and emergency services, or a CB shack in traditional wireless communications.
Base Station Overview
A base station is a GPS receiver that is installed in a well-known fixed position. It’s used to generate correction data for adjacent portable GPS devices. The location precision and accuracy of GPS receivers would be less precise if these corrections were not used.
The correction data, in particular, permits any effect obtained by the mobile stations to be rectified out of the position data.
Understanding Virtual Reference Station
To achieve centimeter-level — or even better — positioning accuracy, precise dual-frequency carrier phase observations are typically required.
Furthermore, these observations are typically processed with a differential GNSS (DGNSS) algorithm, such as real-time kinematic (RTK) or post-processing (PP).
Regardless of the differential algorithm used, the process implicitly assumes that the quality of the reference station data is consistent with the desired level of positioning accuracy.
The virtual reference station (VRS) concept, which employs a network of reference stations, can assist in meeting this requirement.
To recap, a typical DGNSS configuration consists of a single reference station from which raw data (or corrections) are sent to the rover receiver (i.e., the user).
The user then forms the carrier phase differences (or corrects their raw data) and uses the differential corrections to process the data.
GNSS network architectures, on the other hand, frequently employ multiple reference stations.
This method enables more precise modeling of distance-dependent systematic errors caused primarily by ionospheric and tropospheric refractions, as well as satellite orbit errors.
A GNSS network, in particular, reduces the error budget’s reliance on the distance to the nearest antenna.
The receiver network is linked to a computation center, and each station contributes raw data to aid in the creation of network-wide models of distance-dependent errors.
The computation of errors based on the carrier phase measurements of the entire network requires, first and foremost, the resolution of carrier-phase ambiguities and knowledge of the reference station positions. (The latter is typically determined as part of the network configuration.)
Simultaneously, the rover computes its approximate position and transmits it to the computation server, for example, via GSM or GPRS in a standard National Marine Electronics Association (NMEA) format.
The computation center creates a virtual reference station at or near the initial rover position in real-time.
This is accomplished by geometrically translating the nearest reference station’s pseudo-range and carrier phase data to the virtual location and then adding the interpolated errors from the network error models.
This generated VRS data is then transmitted to the user over a wireless connection, which is frequently accomplished utilizing the Networked Transport of RTCM via Internet Protocol (NTRIP).
Finally, in near-real-time kinematic or post-processed modes, the rover receiver employs normal single-baseline methods to identify the coordinates of the user’s receiver, just as if the VRS data had originated from a physical reference station.
Advantages of VRS
They are as follows:
- Using the VRS approach, greatly enhanced RTK positioning can be achieved within the network area.
- Because the multiple reference station network better represents spatially correlated GNSS errors over longer baselines, the VRS concept allows for a less dense antenna network without sacrificing accuracy.
As a result, the maximum distance between the rover and the nearest reference station can be increased without compromising the accuracy of the single reference station situation.
- Another advantage of a VRS is that the reference data are devoid of site-specific defects like multipath because the VRS computation assumes the virtual station is in an ideal position.
- Geodetic accuracy is improved by utilizing a VRS.
Disadvantages of VRS
- The expense of the additional equipment and network service for the creation and maintenance of a virtual reference station may be prohibitive for some applications.
- A single-baseline solution might not be available for operation in inaccessible terrain or in areas where significant reflections make carrier phase observations unreliable on multiple paths.
- The VRS concept can be more susceptible to ionospheric disturbances that have a significant effect on the virtual station’s locations and associated noise levels.
- The creation of a VRS depends on an accurate and reliable network of reference stations, which is not always possible when working with a limited number of antennas.
In the past, due to limitations in the accuracy available from single-antenna reference station data, it was necessary to deploy one reference station per location where positioning was required, often resulting in large numbers of antennas.
In contrast, the use of multiple reference stations in a GNSS network enables more precise modeling of the distance-dependent errors and thus necessitates fewer stations overall.
Using a VRS is a convenient way to increase the coverage area of a GNSS network when high-accuracy positioning is needed over long distances.
When the VRS approach is combined with near-real-time kinematic techniques, centimeter-level positioning can be achieved with only two antennas.
Advantages of a Base station
The main advantages of a base station are listed below, including the following:
- Stability in reference station position.
- Minimization of the error sources of the base station by minimizing the error sources at the same location as other components.
- The base station is widely placed and receives a large number of measurements, which achieve a high elevation resolution with an accuracy of 50 m or better.
- The base station always has high-quality signals to provide stable data and reduce errors caused by multipath (GPS satellite signals) significantly.
- The base station is the only known “ground” or reference station, so with a variety of other base stations in reserve, it can provide the largest data volume.
- The total cost of the base station is lower than that of a rover receiver and other satellite antennas due to its simpler structure.
Disadvantages of a Base station
Furthermore, there are some disadvantages as well:
- One disadvantage of using a base station is that it must be manually configured, which can take time.
- Another disadvantage of base stations is that they can only operate in radio broadcast orbits that are shorter in range than cellular-based VRS networks.
- The biggest disadvantage of a base station is that it only works for one user at a time.
- Low-grade GPS signals at the base stations may cause errors due to multipath. They will affect both accuracy and positioning error estimation.
VRS vs base station Difference
Generally, a base station has a much bigger data volume than a VRS.
Although there is a cost difference between the two systems, the cost of software and equipment necessary for maintaining a base station are usually much higher than the costs necessary for developing and using VRS.
The base station is installed on the ground in an ideal location suitable for best reception, so it does not suffer from shadowing and multipath propagation at any point in time.
It can be placed at a high elevation and receive more signals, which yields a better elevation resolution than the VRS, resulting in more accurate and stable data.
The base station’s data volume is much higher than that of the VRS, and it is considered to be the main system for use in most applications.
In addition, the base station can provide a high-quality signal to ensure reliable and accurate data.
So basically, when you use VRS, you don’t need to set up a base station on every task, providing for a fast-paced work environment in which you can bounce from job to job without bringing a base station with you.
Base stations are also quite expensive, limiting the number of assignments you can work on at the same time.
VRS Network FAQs
What is VRS network?
The VRS is a network of reference stations that can be used to calculate high-precision ephemeris and position, planned by the World Meteorological Organization (WMO), and currently managed by the International GNSS Service Agency (IGSA).
What is a Geodetic station?
A geodetic station is a GPS receiver that is installed in a known fixed location. It is used to generate correction data for adjacent portable GPS receivers. The location precision and accuracy of GPS receivers would be less precise if these corrections were not used.
What is a VRS and how does it work?
VRS, like other types of TRS, enables deaf or hard-of-hearing people to communicate with hearing people over the phone.
Through a video hookup, they communicate in sign language with one other. The VRS CA then dials the phone number of the party the VRS user desires to contact.
What is a survey base station?
In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to extract correction information for nearby portable GPS devices.
How many GPS stations does the VRS system use to create a correction stream?
The network is made up of seven stations, each of which is equipped with a dual-frequency GPS receiver and is permanently linked to the Trimble Terrasat office through leased data lines.
What is RTK base station?
Real-time kinematic positioning (RTK) is a system that corrects frequent mistakes in GNSS operations in real time. To transmit the correction signals, a base station often includes an internal or external radio or modem.
What is a base station?
A base station is a GPS receiver that is installed in a known fixed position. It’s used to generate correction data for adjacent portable GPS devices.
The location precision and accuracy of GPS receivers would be less precise if these corrections were not used. The correction data, in particular, permits any effect obtained by the mobile stations to be rectified out of the position data.
What is the role of base station?
A base station is a central connection point via which a wireless device can communicate. It connects the gadget to other networks or devices, typically by dedicated high bandwidth wire or fiber optic connections.
What is the range of a base station?
A base station provides Internet connectivity to end users by leveraging TVWS frequency bands over ranges comparable to today’s cellular systems, such as 0 to 10 km. The base station provides content access to customer premises equipment (CPE).
What is Category A base station?
Category A applies to all countries and sets more flexible rules than Category B, which only applies to Europe. The difference is around 23 decibels. All limits are given as absolute values in decibels (dBm). As a result, high power base station needs become more difficult to meet.
Does RTK GPS require base station?
RTK requires two GNSS receivers: one static and referred to as a “base station,” and one mobile and referred to as a “rover.”
While both receivers watch the same satellites at the same time, the static base station is located at a known coordinate location (a benchmark or a point measured beforehand).
What is full RTK?
Real-time kinematic positioning (RTK) is the use of surveying to account for frequent inaccuracies in today’s satellite navigation systems (GNSS).
In the context of GPS, the system is generally referred to as carrier-phase enhancement, or CPGPS.
What is the difference between RTK and static GPS?
The difference between RTK and Static mode is that in Static mode, the observation period is approximately one hour, depending on the baseline distance.
That is, the separation between the rover and the base receivers. Because of the longer observation period, this mode of observation is more accurate than RTK.
Where are base stations located?
Base stations are placed in the center of each cell or on the corner of a cluster of cells. The number of base stations needed in a given location is determined by the geography and the number of people who use mobile phones.
What are the dimensions of the cells?
Base stations are frequently located near where they can provide monitoring such as police and fire stations, parks, public buildings and other public facilities.
What are cells?
A cell is a geographical area consisting of several base stations and a network of coverage links that link the base stations together. Base station is also called radio site or internet center. There is one base station in each cell.
Advantages of Virtual Reference System?
- Low cost of implementation at the user equipment end
- Increased flexibility of network design
- No need for a survey of reference stations is needed, unlike in RTK or other TRS.
Disadvantages of Virtual Reference System?
- Dependency on satellite geometry and relatively high number of satellites to observe.
- Increased sensitivity to mobile station’s velocity and attitude. (The direction the receiver is facing)
- Lower level of accuracy than RTK in most instances.
Base station Advantage?
Transmit power levels are greater than a rover at the same distance, so it requires less power to communicate with base stations, which results in longer battery life.
Disadvantages of Base station?
- The location is fixed and can only be moved with considerable effort.
- Usually more expensive than a portable GNSS receiver.
- Base station use is usually limited to surveyors and professionals who deal with precise position data.
What is the difference between base and rover?
Base stations receive GPS satellite signals and generate a correction factor that eliminates GPS errors before sending it to the rover. Rovers compute grade, locate precise positions and elevations, and measure ground, saw cut, surface tie-in points, and as-built points.
How does a deaf person know when the phone is ringing?
A single lamp connected to a receiver and strategically placed throughout the house can serve as the light signaler.
Some light signalers are hardwired to the sound source. These lights flash in reaction to sounds, alerting the user to an aural source such as a doorbell or ringing phone.
How do base stations communicate with each other?
To communicate with mobile phones, each base station has a number of radio channels, or frequencies. Because the number of frequencies available is limited, frequencies are frequently reused in adjacent cells.
As you walk out of the cell, the phone will automatically hunt for signal from an adjoining base station.
Why is Differential GPS more accurate?
The Differential Global Positioning System (DGPS) is a more precise technology than the predecessor Global Positioning System (GPS) (GPS). DGPS accuracy is enhanced by employing two receivers rather than one, which finds the accurate location using relative positions.