Managing Bluetooth LE Advertising Congestion

Bluetooth LE advertising congestion happens when there are too many Bluetooth devices in an area. As we will show, this rarely happens but with new Bluetooth technologies this situation is becoming more likely. We provide some ways to mitigate congestion.

Bluetooth LE advertising transmits periodically the period of which is configurable from typically 100ms to about 10 seconds.

Bluetooth LE advertising (from Bluetooth SIG)

If two Bluetooth devices happen to transmit at the same time, it’s like two people shouting at the same time. The signal is corrupted, the receiver can’t make sense of the signal and it is lost. This usually doesn’t matter because it’s likely the signal is seen the next time it is sent. The random advDelay in the above diagram ensures that the two sends don’t clash again. It’s very unlikely advertisers clash in the first instance because the transmit duration is very small compared to the advertising period. The above diagram isn’t to scale. Here’s an oscilloscope trace showing some real timing:

The advertising duration is very small, of the order of 1 to 2 ms (milliseconds). Advertising is also sent three times, on three different radio frequencies, so that if one is blocked, the radio signal might be heard on one of the others. All this means that advertising collisions rarely occur.

However, there are some newer Bluetooth protocols that as they are starting to roll out, are making collisisons more likely:

  • Bluetooth 5 advertising extensions – This allows advertising of more data, that takes longer than the typical 1 to 2 ms and hence increases congestion.
  • Bluetooth longer range – This transmits further thus effectively increasing the number of beacons advertising in a given area.
  • Bluetooth Mesh – This works by having relay beacons listen and re-transmit advertising, usually several times, to improve reliability.
  • Bluetooth direction finding – This also has longer advertising to send a constant tone extension (CTE) that is received by AoA hardware. However, of more affect is advertising more frequently. While beacons on assets used to advertise typically every second or longer, direction finding tends to use faster advertising to improve latency.

You can check how many devices are advertising by using a scanning app on Android. We recommend Nordic Semiconductor’s nRF Connect because it can decode the latest Bluetooth protocols. Use Android for full visibility because Apple made the poor design decision to obfuscate iBeacon advertising to coerce developers to only use the Apple iBeacon-specific APIs. Apple also hides devices’ MAC addresses making them more difficult to physically identify.

If you have a problem with congestion you might be tempted to increase the transmission power or advertise more often to increase the chances of being seen. However, this is counter-productive because you will be increasing congestion, especially if your devices are the main contributor to the congestion.

Instead:

  • Lower the transmit power so that beacons cover a smaller area. You can fine tune this using nRF Connect to measure the distance you need rather than needlessly advertising further. This will also conserve battery life.
  • Increase the advertising period to make collisions less likely.
  • Increase the receiver scanning period to make detections more likely.
  • Seek out and remove unwanted devices advertising too frequently, such as fitness devices, smartphones, displays and even cars.

Need more help? Consider our consultancy services.

Asset Tracking For Manufacturers

Today’s just-in-time and busy manufacturing processes means that manual tracking of pallets for inbound and outbound shipments often can’t keep pace with the speed of production. Production and assembly requires the quick locating of components. Delays and inaccuracies due to lost components lead to increased costs, employee frustration and ultimately customer disappointment.

Competitive pressures are also driving the need to reduce labour thus reducing the capacity to manually search for items. Customisation using configured options and demand-driven production is also increasing the degree of inbound component searching that exacerbates the problems.

Even those companies using legacy tracking solutions find that location is only as good as the last barcode or RFID scan. Humans get lazy, make mistakes and don’t scan, causing pallets, crates and boxes to get lost. Many RFID readers don’t work reliably near metal components. Relying on a system that can’t find just a few items can be worse that a manual system that works but is slower. Bluetooth asset tracking solves these problems because the location is automatically collected in real-time and is continually updated.

Asset tracking can be applied to items such as components, pallets, cases, tools, returnable assets such as racks and cages as well as items on loan to ensure they are returned on time. It can improve worker safety and provide alerts in cases of congestion, perimeter deviation and lone worker distress. It can ensure forklifts are being fully utilised, are taking an optimum route, haven’t crashed into racking and haven’t gone out of an area.

The real-time visibility allows connected systems to generate confirmation and exception alerts and automatically trigger shipping processes, replacing costly manual workflows. Tracking outputs also allows confirmation that the correct things are loaded on the correct transport.

A Bluetooth-based real time location system (RTLS) increases visibility and allows the manufacturing process to adapt in real-time to short term business needs. It provides cost savings, greater efficiency and business intelligence that can be used to derive larger scale changes based on data rather than gut instinct. Overall reporting of input and outputs provides input to management reporting to monitor the business.

Read about BeaconRTLS™
Read about PrecisionRTLS™

Using Beacons on Buses

Some of the first uses of beacons was on buses. For example, in 2015 in London, 500 buses sent targeted in-app messages to passengers. It didn’t work, Proxama ceased to be in business and thankfully the use of beacons for spamming went away. Today, the use of beacons has matured as has their use on buses.

There’s a useful presentation by Texas A&M Transportation Institute and Houston METRO on Bus Stop Beacons: Transit Wayfinding for People with Visual Impairments (pdf). They classify accessibility challenges as locating stops, knowing which routes serve stops, obtaining real-time information and boarding the vehicle. They conclude that multiple location sources, using Bluetooth with GPS, work better than a single source alone. Also, sound shouldn’t be the only way riders receive information from an app because noisy environments make listening difficult. Vibrations can be used to provide additional notifications.

There are insights from Connecthings/CTS in Strasbourg on helping the blind catch the right bus. There’s also guidance in In–Vehicle Positioning for Public Transit Using BLE Beacons that shows locating a passenger to at least 1 meter across the length of the bus vehicle is possible using Bluetooth beacons. This can be used to assess crowding.

The current state of the art is using beacons with ticketless payment and automatic boarding and un-boarding detection. The pioneer in this area is one of our consultancy clients, UrbanThings, who has an article on Increase ridership through mobile ticketing and case studies.

Another one of our customers, Lothian buses, uses beacons to aid accessibility:

Next Stop Announcements: when on a bus, the customer can select which bus route they are on and the app will announce the name of the next stop as the bus approaches (with buses fitted with Bluetooth beacons, the customer doesn’t even need to select which bus route they are on – the app knows automatically)

Read about Beacons in Transportation

CoreHW AoA Hardware

CoreHW in Finland is a new entrant in the Bluetooth direction finding ecosystem. Their main product is the CHW10x0 chip that supports switching of complex antenna arrays needed for Bluetooth direction finding. It allows designs with only one component where three to five are usually required. The switch has a fast settling time for RF signals and a good phase balance between antenna ports providing better position accuracy.

CoreHW also has reference antenna arrays and 2D software for angle and position estimation to shorten time-to-market for AoA locator and AoD beacon manufacturers. They have a demo kit including 4 locators, 2 tags, a CorePatch antenna array board with CHW1010 chip, a Bluetooth T5.1 chip for IQ sampling and a USB interface (Ethernet) to connect locators with a Windows PC.

The CoreHW reference boards have some intriguing Medusa-type printed circuit board (PCB) tracks, presumably to keep the track length the same to each antenna to normalise RF signal delays.

We look forward to seeing CoreHW components in their customers’ production devices.

TRBOnet Beacon Setting Tips

TRBOnet is Motorola MOTOTRBO 2-way radio control room software. The system uses GPS outside and beacons indoors. The handsets detect iBeacon advertising that shows on TRBOnet plans or maps in the control room.

Here are some tips for setting up beacons for TRBOnet:

  • Each beacon has a unique UUID, major and minor values. Change the UUID from the default to prevent overlap with someone else’s iBeacon network. The actual values you should use are ‘invented’ by you. We have an article on Choosing UUID, Major, Minor and Eddystone-UID For Beacons.
  • Set the beacons to ONLY send out iBeacon advertising. This shows in the manufacturer configuration app as using just one channel for iBeacon. If extra channels such as Eddystone or ‘info’ are enabled, the beacon will still be detected but the beacon battery will be depleted much sooner.
  • Motorola has a useful table that specifies the recommended beacon advertising interval based on the handset scan interval. See our post on Why Bluetooth LE Scanning Doesn’t Always See Devices to better understand this mechanism.
  • When the beacon device is configured for a lower advertising interval it consumes more power. There is a roughly 1:1 correlation between beacon advertising interval and battery life. Longer scan interval ON times increase the probability of beacons being detected but increase the time (latency) to detect beacons and report new positions in the control room.
  • Some radio vendor guides mention a specific to-the-millisecond advertising period so as to prevent beacon advertising and handset scanning from being permanently out of sync. This is a misleading information. All Bluetooth advertising includes a small randomisation in time between successive advertising to prevent this situation.
  • Use standard 0dbm transmit power unless you have special need to boost or reduce the beacon range. We have an article on Choosing the Transmitted Power. See our post on Testing if a Beacon is Working that shows how to measure the received signal strength (RSSI). This allows you to determine the area covered by a beacon and detect areas that are not covered.

2D vs 3D Bluetooth AoA Direction Finding

Current AoA locators only have antennas in one plane which means they can only provide angles in two (elevation and azimuth) dimensions. A locator therefore sees assets as being somewhere along an imaginary line or ray emanating from the locator.

If the height, perhaps of a worn lanyard, is known and tends to not change much then it’s possible to estimate the 3D location. Obviously, if the person climbs some steps for kneels down then the location becomes less accurate in all dimensions.

The other solution is to use multiple locators to triangulate two or more locator lines. This is more accurate because it doesn’t rely on a known average height and provides the opportunity to use more than two locators to increase accuracy still further.

3D provides the best accuracy. 2D location allows use of fewer locators with the trade off of less accuracy. For example, the four locators in the Minew AoA kit can be placed in different rooms or areas rather than covering an overlapping area. 2D location also has the implicit advantage of supporting more beacons because the locators and subsequent systems are doing less work.

Read about PrecisionRTLS™

Aging in Place Assisted by Bluetooth Beacons

There’s recent research on Active Aging in Place Supported by a Caregiver-Centered Modular Low-Cost Platform (pdf) by João Paulo Rangel Marques Capinha of Nova School Of Science And Technology, Portugal. Aging in place is where the elderly reside in their own homes rather than being taken into care.

A platform is proposed that supports aging in place with a focus on Ambient Assisted Living (AAL), the use of Information and Communication Technologies (ICT) to stimulate the elderly to remain active for longer, remain in society and live independently.

The paper describes beacon advertising protocols, received signal strength (RSSI), real time location systems (RTLS), trilateration and fingerprinting. It lists similar projects such as CarePredict, SANITAG, DOMO, 2PCS, CARU, LIFEPOD.

Knowing the routine of daily activities allows detection of activities, critical situations and vocal calls for assistance.

The system uses Bluetooth beacons, Bluetooth temperature/humidity sensors, ESP32-based gateways and Bluetooth wearables. It uses machine learning techniques to identify situations of potential risk, triggering triage processes and consequently any necessary actions so that a caregiver can intervene in a timely manner.

A receiver within Bluetooth bracelets detects beacons in rooms. When in a room, sensors in the room are triggered by the platform through the gateway located in the room.

Bluetooth Direction Finding Antenna Arrays

Bluetooth direction finding Angle of Arrival (AoA) uses multiple antenna in one device that uses the phase difference of signals received at different antenna to determine the angle and hence location of a beacon.

We are seeing a variety of designs but most use printed circuit board patches for antennas for reasons of cost and compactness.

Silicon Labs
IOSEA
Crepak
CoreHW
Telink Dipole
Telink PCB
Minew AR1
ublox
Texas Instruments

All these designs use a radio frequency switch that switches each antenna, in turn, to just one Bluetooth chip to save cost and complexity. You can see this in some of the designs as tracks leading from each antenna to one chip and then one track from that chip to the Bluetooth system on a chip (SoC). The switch is very fast, of the order of 1 microsecond, to capture the same origin signal across all antennas.

Take care to purchase production-ready hardware. While there are currently many antenna array designs, some are just prototype or reference boards not intended for production. The software accompanying prototype or reference boards also tends to be non-existent and in cases where it does exist, it won’t scale to more than a few beacons.

In practice, a location engine employing AoA radiogoniometry is required to process the radio signals from the Bluetooth SoC. The radio signals are also wirelessly noisy and have to be processed to mitigate reflections, interference and signal spread delays. Additional processing is needed to triangulate the angles from multiple locators. All this isn’t trivial given that the algorithms are computationally expensive and have to be executed extremely quickly to support a large number of beacons.

Minew AoA Kit

Read about BluetoothLocationEngine™
Read about PrecisionRTLS™

Bluetooth LE in Smart Cities

Researchers from Spain have a recent paper on Experimental Application of Bluetooth Low Energy Connectionless in Smart Cities that considers the increased range and improved robustness provided by Bluetooth 5.x.

The paper describes the various types of communication:

The paper includes a description of Bluetooth LE including advertising and the different physical layer modes.

There’s an experimental evaluation of the new, more-robust, long-range radio mode when used in smart cities scenarios. The I2V scenario is evaluated, where reception is measured against variation in distance and vehicle speed. The I2P scenario is evaluated against interference from WiFi and classic (non LE) Bluetooth.

The researchers found an overall packet loss of 20–30%, regardless of mobility speed, compared to the static scenarios. The classic Bluetooth 4 mode was found to be more immune to coexistence with the WiFi protocol than any BLE 5.x mode. The researchers say this is because Bluetooth 5 extended advertisements 1) make use of more than one channel and 2) have longer data are both can cause more susceptibility to interference. Nevertheless, the updates introduced with Bluetooth 5 allow broadcasting over much longer distances.

The paper concludes the maturity and low cost of the technology could enable fast, easy deployment in smart cities compared to other solutions.