Local positioning technology. Part I
The use of RTLS (Real Time Location System, real-time positioning systems) depends on the objectives and goals. In order to choose the right system you need, you need to understand on the basis of which of the many technologies it works.
The company RTL-Service is developing such solutions, so we regularly participate in various exhibitions, we analyze the market for various systems of local positioning and conduct the necessary research. In the course of our work, we faced the problem of the lack of a more or less complete classification of local positioning technologies, in connection with which we attempted to create it.
It is convenient to identify the main groups of local positioning technologies with their further disclosure, more detailed characteristics, identified advantages and disadvantages, the main methods used in these technologies:
I. So, the most extensive group comprising several subgroups is the radar technology. We propose to consider it in this article.
Radio frequency is the technology in which radio signals are used to determine the location of objects. This technology includes:
1) UWB is all radio frequency technology, in which the radio frequency channel exceeds either 500 MHz or it contains 20% of the magnitude of the central modulation frequency. Based on this technology, RTLS systems are characterized by high positioning accuracy. The main advantage of the described technology is the ability to maintain efficiency in rooms with a complex geometry and a large amount of interference.
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Benefits:
Disadvantages:
Used methods: TDoA / ToA / AoA / ToF.
2) Wi-Fi is a medium-range data transmission technology, usually covering tens of meters, that uses unlicensed frequency bands to provide network access. Since Wi-Fi was not originally intended for use as a local positioning technology, the standard network only provides information to the access point, so RSSi is used to improve the accuracy of positioning or, for some modifications, other specialized methods (for example, TDoA).
Benefits:
Disadvantages:
Methods used: based on RSSi / TDoA.
3) WiMax - wireless networks of a city scale (implementation of the “last mile” technology). This is a technology operating in 2 frequency bands (2-11 GHz - for connecting a base station with a subscriber station, 10-66 GHz - between base stations for transmitting data over long distances within line of sight).
This technology is not originally adapted for location (like Wi-Fi).
Benefits:
Disadvantages:
Methods used: based on RSSi / OTDoA.
4) MiWi is a wireless protocol developed by Microchip, designed to build low-cost radio networks with data transmission over short distances. In fact, is a simplified analogue of ZigBee.
Benefits:
Disadvantages:
Methods used: RSSi based.
5) ZigBee is a standard for a set of high-level communication protocols using small, low-power digital transceivers based on the IEEE 802.15.4 standard for wireless personal networks. ZigBee is designed for radio frequency devices that require guaranteed secure data transmission at relatively low speeds and the possibility of long-term operation of network devices from autonomous power sources (batteries).
Benefits:
Disadvantages:
Methods used: based on RSSi / TDoA / ToF.
6) NFER (Near-field electromagnetic ranging) is a relatively new positioning technology that uses tag transmitters and one or more receiving devices. The technology is based on the fact that the phase shift between the electric and magnetic components of the electromagnetic field changes with distance from the radiating antenna.
Near the small (relative to the wavelength) antenna, the electric and magnetic components of the radio wave field are shifted in phase by 90 degrees. As the distance from the antenna increases, this difference decreases. With a sufficient distance from the antenna, the phase shift goes to zero.
The optimal distance for measuring the distance between the receiver and transmitter lies within half the wavelength. Accordingly, in order to provide a sufficiently large distance, the tag transmitters must use relatively low frequencies. Usually from 1 MHz (wavelength 300 m, optimal distance up to 150 m) to 10 MHz (wavelength 30 m, optimal distance up to 15 m). Depending on the choice of frequency, NFER has the potential to achieve accuracy up to 30 cm at a distance of up to 300 meters.
Benefits:
Disadvantages:
7) NanoLOC is Nanotron technology, in many respects similar to the older NanoNET version. In addition to the information transfer rate of 1 Mbit per second at a distance of several hundred meters, this technology allows determining the distance between transceivers. The error in determining the distance is 2 meters, which allows to determine where the transceiver is located relative to other such transceivers. If a definition in a three-dimensional coordinate system is necessary, four (or more) NanoLOC transmitters will be needed, the coordinates of which are already known.
Benefits:
Disadvantages:
Methods used: based on RSSi / TDoA / ToF.
8) DECT is a wireless communication technology at frequencies of 1880-1900 MHz with GMSK modulation (BT = 0.5), used in modern radio telephones. This technology allows you to determine the location of the object with an accuracy of a certain base station without using specialized software, as well as with an accuracy of 5-10 meters in open space or within the premises located in the service area of ​​the system with specialized software. As with most technologies, accuracy is significantly reduced when working in structures whose structural materials have a heterogeneous structure.
Benefits:
Disadvantages:
Methods used: RSSi based.
9) Positioning in cellular networks - determining the location of an object based on the Cell Of Origin method - according to the coordinates of the cell to which the subscriber is connected. Positioning accuracy is determined by the radius of the cell. For the so-called "picosot" it is 100-150 meters, in most cases it is a kilometer or more. To increase the accuracy to tens of meters, it is necessary to use the EoTD / OTDoA methods.
Benefits:
Disadvantages:
Used methods: EoTD / OTDoA.
10) Bluetooth - the specification of a wireless personal area network (Wireless personal area network, WPAN), short-range, operating in the frequency range 2.4-2.4835 GHz. In Bluetooth, the carrier frequency of the signal changes 1600 times per second in a pseudo-random manner, this allows you to avoid problems with the operation of a group of devices in the immediate vicinity, as well as to increase the security of data transmission.
Benefits:
Disadvantages:
Methods used: RSSi based.
Below is a summary table of radio frequency technologies.
Author: Alevtina Oskolkova
In the next article we will look at other local positioning technologies.
The company RTL-Service is developing such solutions, so we regularly participate in various exhibitions, we analyze the market for various systems of local positioning and conduct the necessary research. In the course of our work, we faced the problem of the lack of a more or less complete classification of local positioning technologies, in connection with which we attempted to create it.
It is convenient to identify the main groups of local positioning technologies with their further disclosure, more detailed characteristics, identified advantages and disadvantages, the main methods used in these technologies:
- Radar technology.
- Inertial positioning technology.
- Technologies based on changing the magnetic field.
- Optical technology.
- Ultrasound technology.
I. So, the most extensive group comprising several subgroups is the radar technology. We propose to consider it in this article.
Radio frequency is the technology in which radio signals are used to determine the location of objects. This technology includes:
1) UWB is all radio frequency technology, in which the radio frequency channel exceeds either 500 MHz or it contains 20% of the magnitude of the central modulation frequency. Based on this technology, RTLS systems are characterized by high positioning accuracy. The main advantage of the described technology is the ability to maintain efficiency in rooms with a complex geometry and a large amount of interference.
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Benefits:
- High level of noise immunity;
- Difficult to detect transmission (high security);
- Practically no interference with other communications;
- The higher the frequency, the greater the accuracy, but the smaller the range.
Disadvantages:
- Small radius of action (up to 10 m);
- Complicated infrastructure.
- Interference for GPS;
Used methods: TDoA / ToA / AoA / ToF.
2) Wi-Fi is a medium-range data transmission technology, usually covering tens of meters, that uses unlicensed frequency bands to provide network access. Since Wi-Fi was not originally intended for use as a local positioning technology, the standard network only provides information to the access point, so RSSi is used to improve the accuracy of positioning or, for some modifications, other specialized methods (for example, TDoA).
Benefits:
- Wide use;
- Low cost of equipment.
Disadvantages:
- To increase accuracy, an increase in the density of base stations is required;
- Wi-Fi traffic load;
- Insufficient positioning accuracy for a number of tasks, even with the use of special Wi-Fi extensions (in ideal conditions 3-5 meters, in reality 10-15 meters).
Methods used: based on RSSi / TDoA.
3) WiMax - wireless networks of a city scale (implementation of the “last mile” technology). This is a technology operating in 2 frequency bands (2-11 GHz - for connecting a base station with a subscriber station, 10-66 GHz - between base stations for transmitting data over long distances within line of sight).
This technology is not originally adapted for location (like Wi-Fi).
Benefits:
- Coverage area (several kilometers);
- Reliability;
- High throughput.
Disadvantages:
- Expensive equipment and maintenance;
- Low positioning accuracy.
Methods used: based on RSSi / OTDoA.
4) MiWi is a wireless protocol developed by Microchip, designed to build low-cost radio networks with data transmission over short distances. In fact, is a simplified analogue of ZigBee.
Benefits:
- It is a cheap alternative to the ZigBee protocol stack;
- It is an ideal solution for cheap network devices with limited memory;
- Provided by a company without a license (subject to the use of the MRF24J40 transceiver and Microchip microcontrollers);
- Supports message encryption;
- Supports mesh, node-to-node (peer-to-peer) connections and other topologies.
Disadvantages:
- The need to install additional software;
- Proprietary technology;
- Costly maintenance;
- Low data transfer rate leads to restrictions on the size of the network segment.
Methods used: RSSi based.
5) ZigBee is a standard for a set of high-level communication protocols using small, low-power digital transceivers based on the IEEE 802.15.4 standard for wireless personal networks. ZigBee is designed for radio frequency devices that require guaranteed secure data transmission at relatively low speeds and the possibility of long-term operation of network devices from autonomous power sources (batteries).
Benefits:
- Supports both simple network topologies (“point-to-point”, “tree” and “star”), as well as a mesh (mesh) topology with relay and message routing;
- Contains the ability to select a routing algorithm, depending on the requirements of the application and the state of the network;
- Ease of deployment, maintenance and upgrades;
- Ability to self-organization and self-healing;
- Low power consumption.
Disadvantages:
- Low data rate.
Methods used: based on RSSi / TDoA / ToF.
6) NFER (Near-field electromagnetic ranging) is a relatively new positioning technology that uses tag transmitters and one or more receiving devices. The technology is based on the fact that the phase shift between the electric and magnetic components of the electromagnetic field changes with distance from the radiating antenna.
Near the small (relative to the wavelength) antenna, the electric and magnetic components of the radio wave field are shifted in phase by 90 degrees. As the distance from the antenna increases, this difference decreases. With a sufficient distance from the antenna, the phase shift goes to zero.
The optimal distance for measuring the distance between the receiver and transmitter lies within half the wavelength. Accordingly, in order to provide a sufficiently large distance, the tag transmitters must use relatively low frequencies. Usually from 1 MHz (wavelength 300 m, optimal distance up to 150 m) to 10 MHz (wavelength 30 m, optimal distance up to 15 m). Depending on the choice of frequency, NFER has the potential to achieve accuracy up to 30 cm at a distance of up to 300 meters.
Benefits:
- Suitable for use in rooms with complex geometry;
- Positioning with an accuracy of 0.5-1 meters (in theory) at a distance of 20-30 meters.
Disadvantages:
- Relatively low antenna efficiency. The antenna is most effective, commensurate with the wavelength - usually a quarter-wave monopole. In the case of NFER, the size of such an antenna would have to be tens of meters, which is unacceptable;
- The inconsistency of the antenna requires an increase in transmitter power and leads to relatively large dimensions and weight tags.
7) NanoLOC is Nanotron technology, in many respects similar to the older NanoNET version. In addition to the information transfer rate of 1 Mbit per second at a distance of several hundred meters, this technology allows determining the distance between transceivers. The error in determining the distance is 2 meters, which allows to determine where the transceiver is located relative to other such transceivers. If a definition in a three-dimensional coordinate system is necessary, four (or more) NanoLOC transmitters will be needed, the coordinates of which are already known.
Benefits:
- Ability to work in unlicensed bands with power up to 100 mW;
- The positioning methods used make it possible to localize objects outside the perimeter of the service area with a decrease in accuracy;
- Large selection of ready-made software (with open source codes);
- Autocorrelation properties of the signal make the technology resistant to external interference.
Disadvantages:
- Restrictions on the number of devices in the segment;
- Proprietary technology.
Methods used: based on RSSi / TDoA / ToF.
8) DECT is a wireless communication technology at frequencies of 1880-1900 MHz with GMSK modulation (BT = 0.5), used in modern radio telephones. This technology allows you to determine the location of the object with an accuracy of a certain base station without using specialized software, as well as with an accuracy of 5-10 meters in open space or within the premises located in the service area of ​​the system with specialized software. As with most technologies, accuracy is significantly reduced when working in structures whose structural materials have a heterogeneous structure.
Benefits:
- Ease of deployment of DECT-networks;
- Does not require specialized maintenance;
- Does not require licensing;
- Good integration with fixed corporate telephony systems.
Disadvantages:
- Relatively short range of communication (due to the power limitation of the standard itself);
- Low data rate;
- Requires specialized equipment.
Methods used: RSSi based.
9) Positioning in cellular networks - determining the location of an object based on the Cell Of Origin method - according to the coordinates of the cell to which the subscriber is connected. Positioning accuracy is determined by the radius of the cell. For the so-called "picosot" it is 100-150 meters, in most cases it is a kilometer or more. To increase the accuracy to tens of meters, it is necessary to use the EoTD / OTDoA methods.
Benefits:
- The ability to use the existing infrastructure of mobile operators.
Disadvantages:
- Licensed frequency range;
- Low positioning accuracy.
Used methods: EoTD / OTDoA.
10) Bluetooth - the specification of a wireless personal area network (Wireless personal area network, WPAN), short-range, operating in the frequency range 2.4-2.4835 GHz. In Bluetooth, the carrier frequency of the signal changes 1600 times per second in a pseudo-random manner, this allows you to avoid problems with the operation of a group of devices in the immediate vicinity, as well as to increase the security of data transmission.
Benefits:
- Increased safety and immunity;
- Low power consumption (BLE);
- Inexpensive equipment;
- Compact modules.
Disadvantages:
- The inability to achieve high accuracy of location.
Methods used: RSSi based.
Below is a summary table of radio frequency technologies.
Author: Alevtina Oskolkova
In the next article we will look at other local positioning technologies.
Source: https://habr.com/ru/post/281837/
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