Technologies Used For Indoor Positioning Systems
Indoor localization employs technologies different from satellite-based systems, such as GPS and Galileo. Building materials stand in the way of radio waves, so satellite signals cannot reach the receivers in surface and underground facilities. Indoor positioning technologies use various types of signals that can fall into the following categories:
- IPS using radio signals
Such systems detect object locations with the help of radio signals propagating from transmitters to receivers. They include NFC, RFID, Wi-Fi , Bluetooth, Thread, ZigBee, ultra-wideband , Radio Detection and Ranging .
- IPS using sound signals
These systems rely on echolocation and the measurement of the time period during which an emitted ultrasonic signal returns to a receiver. For example, Sound Navigation and Ranging is used to position underwater objects.
- IPS using light signals
This IPS type comprises light-emitting and light-reflecting objects and includes Light Detection and Ranging , infrared systems, and computer vision systems.
- IPS using inertial navigation
These systems include inertial measurement units that use a set of sensors such as an accelerometer, a gyroscope and, sometimes, a magnetometer to track the motion of an object in three-dimensional space.
- Angle of arrival /Angle of departure
- Received signal strength indication
- Dead reckoning
- Simultaneous Localization and Mapping
Bluetooth 51 Packet Architecture
Bluetooth 5.1 packets include a CTE comprising digital 1s to ensure that for this part of the signal the antenna receives a constant frequency . In addition, this data string is not whitened . A suitably configured Bluetooth Low Energy radio receiving a packet incorporating a CTE signal proceeds by taking IQ samples during the CTE period. A single IQ sample consists of the signals amplitude and phase angle represented as Cartesian coordinates .
Figure 1: Direction finding applications commence with the receiving Bluetooth LE device taking phase angle and amplitude IQ samples during the CTE portion of a Bluetooth packet for each antenna in an array. These samples are represented as Cartesian coordinates.
The Bluetooth Core Specification v5.1 details changes to the Bluetooth LE controller that enable AoA and AoD techniques to use either connected or connectionless communication. However, AoA will typically be used for connected applications such as asset tracking, while AoD will be used with connectionless applications such as IPS.
Connected direction finding uses standard Bluetooth 5.1 packets with the CTE appended to the end. In contrast, connectionless direction finding uses a CTE added to Bluetooth periodic advertising packets .
Figure 2: Bluetooth 5.1 packet structure showing location and duration of CTE. Connected applications append the CTE to standard packets while connectionless applications use an advertising packet.
Direction Finding With Multiple Anchors
Multiple static anchors featuring multi-antenna arrays can be used to meet the needs of use cases with more demanding requirements in terms of accuracy. In this case, the position of an asset can be calculated accurately through triangulation, using the angle of the incoming or outgoing signals from several anchors and determining where they intersect.
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Updates To Bluetooth 51
Bluetooth 5.1 demands changes to the RF software protocol , and depending on the chipmaker, some hardware enhancements. First, the revised protocol adds a continuous tone extension to any Bluetooth packet used for direction finding.
CTE is a pure tone sent at the Bluetooth carrier frequency plus 250 kilohertz for between 16 to 160 microseconds . The tone consists of an unwhitened sequence of 1s transmitted long enough for the receiver to extract the IQ data without the disruptive effects of modulation. Because the CTE signal is transmitted last, the packets cyclic redundancy check is unaffected.
The second significant addition to the specification makes it much simpler for the developer to configure the protocol to perform the IQ sampling. This configuration includes setting both the sample timing and antenna switching, which are critical to the precision of the positional estimation.
While various IQ sampling timing configurations can be employed, typically one IQ sample is recorded every 1 or 2 µs within the reference period for each antenna, and the results are recorded in the BLE SoCs random access memory . How the phase of the received signal varies as it is sampled by different antennas in the array is shown .
Figure 5: A signal from a single transmitter exhibits a different phase upon arrival at antennas that are different distances from the source.
Multipath Effects Also Called Reflections Of The Signals
UWB has major advantages in any environment where so called multipath effects can occur. This effect occurs everywhere. Have you ever yelled “echo” in a large empty room? The echoes you heard are reflections. Imagine now many echoes can overlap each other and how difficult this would be to understand again. These difficulties extend to direction finding technology. A receiver has huge challenges when multiple copies of a signal arrive at it and overlay.
In Bluetooth 5.1, phase measurements of several receiver antennas can overlay due to reflections, which will result in inaccurate or even impossible measurements. In “clean” rooms and well-defined propagation channels direction of arrival based on a multi-channel receiver will work, but real life use cases, industrial areas, buildings, etc. are different.
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What Are Ble Beacons
BLE beacons are small, versatile, and low-power Bluetooth transmitters that can be detected by wireless devices like BLE-enabled smartphones. Beacons can be deployed in fixed positions, such as mounted on walls or structures, or placed on mobile assets, to provide location references for indoor positioning applications. This supports bring-your-own-device concepts, allowing anyone to interact with a BLE-enabled application using their smartphone or other embedded devices. BLE beacons can be used to find a devices location and deliver relevant content, such as documents, videos, apps, and more, or offer guidance concerning the time or location of the user, keeping users informed and engaged.
Beacons broadcast signals on regular intervals that can be detected by other BLE-enabled devices. Location data from the beacons is collected by a BLE device and forwarded to the IPS to determine the devices location. This can support various location-aware applications and even trigger specific actions.
Virtual beacons allow organizations to add BLE beacon technology without the need for much extra hardware. With virtual Bluetooth beacons, antennas can be added to compatible Wi-Fi Access Points, and leveraged with additional software tools for various indoor positioning applications.
Enhanced Asset Tracking Accuracy
Bluetooth® RTLS solutions are used for tracking important assets in a facility, from locating the position of pallets, forklifts, and workers in a warehouse to ultrasound machines and patients in a hospital, helping to ensure safety and optimize response time in an emergency.
In a RTLS solution, low-power, battery-operated Bluetooth transmitters, commonly called tags, are attached to critical assets. These tags transmit their current location and received signal strength to Bluetooth receivers, often referred to as locators, in fixed locations throughout a facility. This provides facility managers with a general positioning of a tracked asset.
With the addition of a new direction finding capability, the location engine in an RTLS solution can now receive both the signal strength and the direction of tags and use that data to improve location accuracy down to centimeter-level. This will allow a factory to track the location and flow of materials with greater precision, as well as track and alert workers before they go into unsafe work areas.
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How Bluetooth Location Services Work
The indoor positioning relies on Bluetooth Low Energy beacons mounted on objects, walls, ceilings, and other places from where they emit radio signals at predetermined intervals. Devices within the emission area can then detect the signals and this helps to establish if the two are within the range of each other.
Although one beacon is sufficient in establishing the presence of an object, it cannot pinpoint the specific location. Usually, the location accuracy increases with the number of beacons. After establishing that two objects are near each other, the Bluetooth location services can use the Received Signal Strength Indicator to estimate the distance between them.
Usually, the BLE beacons do not have inbuilt location intelligence but have standard protocols that determine what the beacon transmits. For example, common protocols such as iBeacon and Eddystone transmit the beacons unique IDs transmit power and other identifiable information.
A typical deployment involves assigning physical coordinates to the beacons in an external database or inside a mobile app. This ensures that the values the beacons transmit are converted to real-world coordinates. Comparing the signal values, coordinates from the beacons and Received Signal Strength Indicator makes it possible to estimate the rough position of a device.
Using Angle Of Arrival For Direction Finding With Bluetooth 51
Source – Lightboard.io
Although Bluetooth location services have been successful, there is currently a demand for solutions that can provide more high productivity. For example, some real-time location services deployments require centimeter precision. Fortunately, a useful new feature has recently been added to the new Bluetooth standard to meet these requirements.
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What Are The Improvements Coming With Bluetooth 51
Bluetooth 5.1 is bringing a ton of new improvements which will make the upcoming compatible devices like homing missiles. Basically, it will allow you to find your Bluetooth 5.1 devices and to locate them to a couple of inches their exact location. This is made possible by a number of improvements coming with the Bluetooth 5.1. Here are the major improvements that you need to know about:
What Is An Indoor Positioning System And What Is It Used For
An indoor positioning system or IPS is a network of transmitting and receiving devices that can communicate together indoors.
As the name suggests, the major purpose of an IPS is to detect the position of an object that can be both animate and inanimate. Once it is detected, the system can keep track of the objects location and identify it from the set of like objects.
Having this information at hand can improve work processes and help with solving problems in many fields. Here are some IPS applications and purposes the system may serve:
- Production industries
- Shopping malls
- Airports, railway and bus stations
- Parking lots and garages .
To sum up, you can use indoor positioning in any business area and for a variety of purposes as far as your fantasy and budget permit. For example, wayfinding is an important feature suitable for lots of places, such as museums, exhibitions and trade shows, sports facilities, parks, and tourist attractions. An IPS is an essential part of most smart networks, including the Internet of Things applications.
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See Bluetooth Indoor Location Tracking In Action
With accuracies that compare to those achieved by advanced GPS receivers in open sky environments, Bluetooth indoor positioning systems can cover a critical blindspot shared by many real-time asset tracking solutions: the great indoors.
We conducted a proof of concept trial to test the technology in a real-world industrial warehouse.
Indoor Positioning Systems Wayfinding
Bluetooth indoor positioning system is a wayfinding technology that helps visitors to navigate through large and complex buildings such as malls, museums, hospitals, airports, and other facilities. In particular, it can assist or guide the visitors to find the right directions to their areas of interest.
Usually, IPS works differently from the RTLS system. The Bluetooth locator beacons or transmitters are mounted on fixed places throughout the facility, unlike the RTLS where they are on moving targets. The users then have the smartphone apps that listen to the radio signals from the fixed locator beacons as they move inside the building.
Using trilateration, RSSI, and the location information they hear from the beacons, the apps calculate the users current position, compare with saved values and then direct users to where they want to go.
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Direction Finding Angle Of Arrival
In the case of AoA, the mobile asset is equipped with a tag that transmits a Bluetooth direction finding signal, which includes a constant tone extension packet . In this scenario, measurements made by the antenna arrays are used to determine the angle of the incoming signals using a network-based engine. As illustrated below, the signals transmitted by the mobile client reach the individual antennas that comprise the anchors multi-antenna array with a slight phase shift relative to the rest. Assuming that the signal propagates a planar wave, the slight phase differences observed at each antenna can be used to calculate its angle of arrival.
Using phase differences to derive the angle of arrival. Adapted from Bluetooth SIG
AoA can be used to implement real-time location services or tracking use cases.
Bluetooth Direction Finding Introduced With Bluetooth 51 Lets Users Locate Assets People And Anything Else Indoors With Meter
Already prior to the release of Bluetooth 5.1, Bluetooth low energy technology had established itself as a leading solution for indoor positioning applications. The basic approach involved measuring the signal strength of the Bluetooth signal from fixed beacons using a Bluetooth receiver, for example, in a smartphone. Alternatively, fixed anchors could measure the RSSI of the Bluetooth signal transmitted by a moving device, also referred to as a tag. These RSSI-based methods typically achieve accuracy levels of a few meters and have been used to determine whether an asset or a person is in a room.
Recognizing the growing demand for more accurate indoor positioning solutions, the Bluetooth SIG released Bluetooth 5.1 in January 2019, with Bluetooth direction finding as its main feature. Using a constellation of multi-antenna anchors, Bluetooth direction finding can be used to triangulate the precise location of a mobile device or tag within the covered indoor environment.
Bluetooth 5.1-based indoor positioning can achieve meter-level accuracies. Compliance with standards defined by the Bluetooth SIG ensures that the message format used by devices is compatible across vendors. And the ubiquity of Bluetooth in connected devices targeting mass-market and niche applications promises to facilitate the adoption of the indoor positioning solution.
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Bluetooth 51 Angle Of Arrival Based Indoor Localization
- Citation Author:
The Bluetooth 5.1 Core Specification brought Angle of Arrival based Indoor Localization to the Bluetooth Standard. This dataset is the result of one of the first comprehensive studies of static Bluetooth AoA-based Indoor Localization in a real-world testbed using commercial off-the-shelf Bluetooth chipsets.
The positioning experiments were carried out on a 100m² test area using four stationary Bluetooth sensor devices each equipped with eight antennas. With this setup, a median localization accuracy of up to 18cm was achieved.
This dataset provides all necessary files that are needed to reproduce our results and may serve as a basis for own AoA-based Indoor Localization research.
The provided README file contains all necessary information that is needed for understanding and using the data.
Building A Direction Finding Solution
AoA is suited to applications like asset tracking where the transmitter is a mobile item such as a simple, low-cost tag, while the receivers are fixed reference points. The advantage of this implementation is that the tag only needs to transmit the Bluetooth 5.1 protocol packets using a single antenna and isnt required to run the computationally intensive algorithms that ultimately determine transmitter location .
While the design of a tag in an asset tracking system follows relatively straightforward radio frequency design principles, the tag does require a Bluetooth 5.1 transceiver so that packets can be configured to include CTEs. When selecting a transceiver, it is important to note that the CTE cant be sent over a Bluetooth LE Coded PHY rather the PHY must be of the uncoded type.
Depending on the performance and latency demanded in the application, a developer could consider a companion processorwith access to additional RAM and flashspecifically for the application software. Nordics nRF52811, for example, is designed to interface with a companion processor via Inter-Integrated Circuit and Serial Peripheral Interface interfaces.
The receiver requires an antenna array to detectvia the IQ datathe phase difference of the signal due to the difference in distance from each antenna in the array to the single transmitting antenna. It is the difference between the phase angle at each antenna that determines the AoA or AoD.
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Rf Direction Finding Techniques
Radio frequency direction finding based on RSSI provides distance approximation based on signal strength. Greater accuracy can be achieved by making multiple distance measurements from different points. A key advantage of RSSI is that it requires only one antenna per deviceeliminating the complexity, cost, and size of antenna arrays. The downside is a lack of precision, with the technique offering an accuracy of 3 to 5 meters .
A second common direction-finding technique is known as Time of Arrival , which is the travel time of a radio signal from a single transmitter to a remote single receiver. Again, this method requires only one antenna per device, but the downside is the requirement that each device carry a highly accurate synchronized clock. Positional accuracy for ToA systems can approach 1 m.
With the release of the Bluetooth 5.1 specification, the Bluetooth Special Interest Group elected to support a third direction finding technique based on AoA and AoD.
With AoA, a receiving device tracks arrival angles for individual objects, while with AoD the receiving device calculates its own position in space using angles from multiple beacons and their positions .
Figure 2: The angle of arrival of a radio signal can be calculated if the signal phase at each antenna, the wavelength , and the distance between adjacent antennas is known.
Combining the computed signal direction from two or more locators enables a transmitter to be pinpointed .