Comparison of 6 Indoor RTLS (Real-time Location Systems) Technologies

RTLS is abbreviation for Real Time Location Systems.

RTLS is a signal-based radiolocation method that can be active or passive. Among them, the active is divided into AOA (arrival Angle positioning) and TDOA (arrival time difference positioning), TOA(arrival time), TW-TOF(two-way flight time), NFER(near-field electromagnetic ranging) and so on.

Talking about positioning, everyone will first think of GPS, based on GNSS(Global Navigation Satellite System) satellite positioning has been everywhere, but satellite positioning has its limitations: the signal can not penetrate the building to achieve indoor positioning.

So, how to solve the indoor positioning problem?

With the continuous development of indoor positioning market demand driven and wireless communication technology, sensor identification technology and big data interconnection technology, the Internet of Things and other technologies, this problem has gradually been solved, and the industrial chain has been continuously enriched and mature.

Bluetooth indoor positioning technology

Bluetooth indoor technology is to use several Bluetooth LAN access points installed in the room, maintain the network as a multi-user based basic network connection mode, and ensure that the Bluetooth LAN access point is always the main device of the micro-network, and then triangulate the newly added blind node by measuring the signal strength.

At present, there are two main ways to locate Bluetooth iBeacon: based on RSSI(received signal strength indication) and based on positioning fingerprint, or a combination of both.

The biggest problem based on distance is that the indoor environment is complex, and Bluetooth, as a 2.4GHZ high-frequency signal, will be greatly interfered with. In addition to various indoor reflections and refractions, RSSI values obtained by mobile phones are not much reference value; At the same time, in order to improve the positioning accuracy, the RSSI value has to be obtained several times to smooth the results, which means that the delay increases. The biggest problem based on positioning fingerprints is that the labor cost and time cost of obtaining fingerprint data in the early stage is very high, and the database maintenance is difficult. And if the store adds a new base station or makes other modifications, the original fingerprint data may no longer be applicable. Therefore, how to weigh and choose between positioning accuracy, delay and cost has become the main issue of Bluetooth positioning.

Disadvantages: Bluetooth transmission is not affected by line-of-sight, but for complex space environments, the stability of the Bluetooth system is slightly poor, interfered by noise signals, and the price of Bluetooth devices and equipment is relatively expensive;

Application: Bluetooth indoor positioning is mainly used to locate people in a small area, such as a single-storey hall or store.

Wi-Fi location technology

There are two kinds of WiFi positioning technology, one is through the wireless signal strength of mobile devices and three wireless network access points, through the differential algorithm, to more accurately triangulate the location of people and vehicles. The other is to record the signal strength of a large number of location-determined points in advance, by comparing the signal strength of the newly added equipment with a large database of data to determine the location.

Advantages: high accuracy, low hardware cost, high transmission rate; It can be applied to achieve complex large-scale positioning, monitoring and tracking tasks.

Disadvantages: Short transmission distance, high power consumption, generally star topology.

Application :WiFi positioning is suitable for positioning and navigation of people or cars, and can be used in medical institutions, theme parks, factories, shopping malls and other occasions that need positioning and navigation.

RFID indoor positioning technology

Radio frequency identification (RFID) indoor positioning technology uses radio frequency mode, the fixed antenna to adjust the radio signal into the electromagnetic field, the label attached to the item into the magnetic field after induction current generated to transmit the data out, in order to exchange data in multiple two-way communication to achieve the purpose of identification and triangulation.

Radio Frequency Identification (RFID) is a wireless communication technology that can identify a specific target by radio signals and read and write related data without the need to establish mechanical or optical contact between the identification system and the specific target.

Radio signals transmit data from a tag attached to an item via an electromagnetic field tuned to a radio frequency to automatically identify and track the item. When some labels are recognized, energy can be obtained from the electromagnetic field emitted by the identifier, and batteries are not required; There are also tags that have their own power source and can actively emit radio waves (electromagnetic fields tuned to radio frequencies). The tags contain electronically stored information that can be identified within a few meters. Unlike bar codes, RF tags do not need to be in the line of sight of the identifier and can also be embedded in the object being tracked.

Advantages: RFID indoor positioning technology is very close, but it can get centimeter-level positioning accuracy information in a few milliseconds; The size of the label is relatively small, and the cost is low.

Disadvantages: no communication ability, poor anti-interference ability, not easy to integrate into other systems, and the user's security and privacy protection and international standardization are not perfect.

Application: RFID indoor positioning has been widely used in warehouses, factories, shopping malls in the flow of goods, commodity positioning.

Zigbee indoor positioning technology

ZigBee (low-power LAN protocol based on IEEE802.15.4 standard) indoor positioning technology forms a network between a number of nodes to be tested and reference nodes and the gateway. The nodes to be tested in the network send out broadcast information, collect data from each adjacent reference node, and select the X and Y coordinates of the reference node with the strongest signal. Then, the coordinates of the other nodes associated with the reference node are calculated. Finally, the data in the positioning engine is processed, and the offset value from the nearest reference node is considered to obtain the actual position of the node under test in the large network.

ZigBee protocol layer from bottom to top are physical layer (PHY), media access layer (MAC), network layer (NWK), application layer (APL) and so on. Network devices have three roles: ZigBee Coordinator, ZigBee Router, and ZigBee End Device. Network topologies can be star, tree, and network.

Advantages: low power consumption, low cost, short delay, high capacity and high security, long transmission distance; It can support the network topology, tree topology and star topology structure, the network is flexible, and can realize multi-hop transmission.

Disadvantages: The transmission rate is low, and the positioning accuracy requires higher algorithms.

Application: zigbee system positioning has been widely used in indoor positioning, industrial control, environmental monitoring, smart home control and other fields.

UWB positioning technology

Ultra wideband (UWB) positioning technology is a new technology, which is very different from the traditional communication positioning technology. It uses pre-arranged anchor nodes and bridge nodes with known positions to communicate with newly added blind nodes, and uses triangulation or "fingerprint" positioning to determine the position.

Ultra-wideband wireless (UWB) technology is a high-precision indoor wireless positioning technology proposed in recent years, with a high danosecond level of time resolution, combined with the arrival time-based ranging algorithm, theoretically can reach centimeter-level positioning accuracy, which can meet the positioning needs of industrial applications.

The whole system is divided into three layers: management layer, service layer and field layer. The system hierarchy is clearly divided and the structure is clear.

The field layer is composed of positioning Anchor point and positioning Tag:

· Locate Anchor

The location anchor calculates the distance between the Tag and itself, and sends packets back to the location calculation engine in wired or WLAN mode.

· Location Tag

The tag is associated with the person and object being located, communicates with Anchor and broadcasts its own location.

Advantages: GHz bandwidth, high positioning accuracy; Strong penetration, good anti-multipath effect, high safety.

Disadvantages: Because the newly added blind node also needs active communication, the power consumption is high, and the system cost is high.

Application: Ultra-wideband technology can be used for radar detection, as well as indoor accurate positioning and navigation in various fields.

Ultrasonic positioning system

The ultrasonic positioning technology is based on the ultrasonic ranging system and developed by a number of transponders and main rangefinder: the main rangefinder is placed on the object to be measured, the transponder transmits the same radio signal to the fixed position of the transponder, the transponder transmits the ultrasonic signal to the main rangefinder after receiving the signal, and uses the reflection ranging method and triangulation algorithm to determine the location of the object.

Advantages: The overall positioning accuracy is very high, reaching the centimeter level; The structure is relatively simple, has a certain penetration and the ultrasonic itself has a strong anti-interference ability.

Disadvantages: large attenuation in the air, not suitable for large occasions; Reflection ranging is greatly affected by multipath effect and non-line-of-sight propagation, which causes the investment of underlying hardware facilities requiring accurate analysis and calculation, and the cost is too high.

Application: Ultrasonic positioning technology has been widely used in digital pens, and such technology is also used in offshore prospecting, and indoor positioning technology is mainly used for object positioning in unmanned workshops.

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