1 Bluetooth Low Energy beacons

1.0 Purpose of this section

This section contains considerations and recommendations that are related to the whole lifecycle of using Bluetooth Low Energy (BLE) beacons as a technology solution for digital wayfinding.

Venue owners, their accessibility stakeholders and developers who are involved with beacon deployment can find information on:

• Installation of BLE beacons in a built environment
• Configuration of the BLE beacons in order to make the most out of the installation
• Maintenance and Operational considerations that should be taken into account in order to manage a fleet of installed BLE beacons.

1.1 What is a Bluetooth Low Energy beacon?

Bluetooth is a wireless technology standard for exchanging data over short distances – it was introduced in 1994 [3].

Bluetooth Low Energy (BLE) is a technology applied in Bluetooth 4.0 protocol and above. It was specifically designed with low power consumption in mind to support applications and services that require connected devices (smartphones, tablets, laptops for example) located nearby. Most recent mobile devices support BLE.

A BLE beacon is an electronic device that repeatedly transmits a radio signal at periodic intervals. The signal’s broadcast frequency and transmit power can be manually adjusted (see Section 5.1.4). This radio signal carries data, the so-called ‘advertising packets’, that allow each specific beacon to be identified by compatible devices once they are in range.

When a device receives the ‘advertising packets’ from the beacon, it can estimate how far away the beacon is located. Once the distance estimation is made, it prompts a number of things to happen depending on the code used in the app. The beacon may cause various triggers. For example, in audio-based wayfinding for vision impaired people the relevant audio instruction is triggered. All the logic about the triggering of the correct audio instructions is in the app. See for example the Wayfindr Demo iOS mobile app v0.4.

1.2 Sources of Bluetooth signal distortion

The BLE signal is transmitted in the 2.4 GHz radio frequency. This means that the BLE signal may be distorted by interference from specific elements in the environment [2], such as:

• Metallic surfaces bouncing the signal off the surface in unexpected ways as it is unable to penetrate the material
• Water absorbing BLE signal
• Human body mass absorbing and distorting BLE signal
• Concrete and bulletproof glass absorbing the signal
• Marble and bricks absorbing the signal
• Electronic devices operating in the 2.4 GHz frequency, thus emitting signal on the same radio frequency which might overlap with the beacon signal
• Fluorescent lighting emitting signal in the 2.4 GHz frequency, thus likely to distort beacon signal in unexpected ways
• Power sources such as electric railroad tracks or power lines also causing interference

When the Bluetooth signal is distorted, the mobile device will receive a signal that does not reflect the real situation, e.g. the distance to the beacon as read by the device might not be accurate. Installing beacons following the best practices proposed in the following section will mitigate this risk.

1.3 BLE beacon installation

5.1.3.0 Purpose of this section

Venue owners and other parties involved in BLE beacon deployment can find a description of the two main approaches for installing beacons (the proximity-based and the trilateration-based approach) along with best practices for BLE beacon positioning.

5.1.3.1 Proximity-based approach

Installing beacons following a proximity-based approach means that beacons are placed only at decision making points where people need to be instructed. These decision making points might be before and after doors, staircases and at pathway intersections.

Advantages of this approach

• The main advantage of the proximity-based approach is that a small number of beacons is needed to complete this type of installation.
• As a result the costs for beacon procurement, installation and configuration time, maintenance are reduced.

Disadvantages of this approach

• The decision making points in a venue where BLE beacons will be placed need to be decided carefully.
• There are likely to be areas that the beacon signal does not reach
• To detect the orientation of users, a combination of technologies might be needed.

NB. The Wayfindr Demo iOS app v0.4 is developed for beacon deployments with a proximity-based approach.

5.1.3.2 Trilateration-based approach

Installing beacons following a trilateration-based approach means that beacons are placed so that they provide coverage to the whole area. In this way, the location of the user’s smartphone device is estimated by measuring distance from the 3 closest beacons [7].

Advantages

• The main advantage of this approach is that the majority of a venue area is covered in beacons and as a result there are unlikely to be areas where the user position cannot be estimated.
• With the trilateration method, the orientation of the user’s smartphone device can be determined dynamically and as a result, the instructions given to the user can reflect that orientation.

Disadvantages

• Location accuracy cannot be guaranteed as there are a few variables that are likely to affect the stability of the Bluetooth signal such as the ones mentioned in Section 5.1.2 “Sources of Bluetooth signal distortion”.
• Changes to a built environment such as new construction, signage, temporary fixtures, and sources of 2.4 GHz being introduced or removed can change the profile of the space and affect a trilateration algorithm.  If physical changes are common, system calibration will be an on-going task and expense.
• Digital navigation services that do not use a trilateration algorithm to calculate routes might have difficulties providing a good user experience in built-environments where beacons have been installed with trilateration in mind. Thus, ensure that beacons are positioned on decision making points, landmarks or point of interests as described in the following section.
• A larger amount of BLE beacons is required to achieve trilateration compared to the proximity-based approach. This means increased costs for the beacon installation, configuration and maintenance

5.1.3.3 Best practices for BLE beacon positioning

BLE beacons can be installed in both indoor and outdoor environments. There is no single way to install beacons, as layout and material vary across different environments. The following best practice guidelines can be applied for efficient positioning across environments:

• Place the beacons above head height (above 2.5 metres) in order to avoid interference from human body mass, likely to absorb beacon’s signal in busy environments.
• If the ceiling is up to 4 metres high, then place the beacon on the ceiling.
• If there is an arch, then place the beacon at the top and centre of the arch.
• If the ceiling or the top of arch is higher than 4 metres then use walls, placing the beacon at a height of around 2.5 metres (up to +1.5 metre) from the floor level. Alternatively, if possible, suspend the beacon from the ceiling on a cable.
• When the optimal position of a beacon interferes with other venue elements such as metallic signage, major power conduit or fluorescent lighting, place the beacon 1 metre away from these elements.
• If the beacon is to be placed in a corridor below 4 metre width, then place the beacon in the middle of the corridor to cover the full width equally.
• If the corridor is wider than 4 metres, consider using more beacons to cover the area evenly. In this case, place a beacon at 4 metre intervals. For example, in an entrance of a venue with multiple doors, the area is likely to be wider than 4 metres. In this instance, to cover all doors with beacon signal, place a beacon every 4 metres.
• Place a beacon 4 +/-1 metres before any landmarks or point of interests that people are likely to go through or interact with. This should be the case both for the proximity and the trilateration-based approach to installation. These landmarks and objects might be for example:
  • Entrance doors
  • Pathways
  • Escalators
  • Stairs
  • Lifts
  • Ticket control gates

Read more about the information that needs to be provided when interacting with these landmarks in the Section 4.1 “Guidelines for various environmental elements”.

• Most BLE beacons are suitable for outdoors installations, check with your beacon supplier if their BLE beacons are waterproof and what temperatures they work well in.
• Consider the orientation of the BLE beacon directional antenna. Based on the beacon manufacturer, some BLE beacons might not emit an all-round symmetrical signal, but instead they emit a signal of elliptical form depending on which way the beacon antenna is facing. Ask your beacon manufacturer for details and orientate the beacon in a way that supports your needs.

1.4 The parameters of a BLE beacon

Configuration settings of BLE beacons vary based on the protocol on which they are configured. There are two main beacon protocols open to any beacon manufacturer in the market at the moment:

• iBeacon: The iBeacon protocol [1] is a communication format developed and introduced by Apple in 2013 and is based on Bluetooth Low Energy technology. The protocol is compatible with any iOS or Android device that supports Bluetooth 4.0 and above. The minimum requirements for the operating system is iOS 7 or Android 4.3 (Jelly Bean) and above.
• Eddystone: The Eddystone is an open beacon format developed and introduced by Google in 2015 [4]It is compatible both for iOS and Android devices that support Bluetooth 4.0 and above.

1.4.1 iBeacon

The iBeacon protocol [1] is a communication format developed and introduced by Apple in 2013 and is based on Bluetooth Low Energy technology. The protocol is compatible with any iOS or Android device that supports Bluetooth 4.0 and above. The minimum requirements for the operating system is iOS 7 or Android 4.3 (Jelly Bean) and above.

iBeacon Identifiers

A beacon configured with the iBeacon format transmits its Unique ID, an advertising packet that contains three customisable identifiers: the UUID, the Major and the Minor. These three identifiers make an iBeacon identifiable and distinguishable from other iBeacons.

• Universally Unique Identifier (UUID): It is a 16 byte (128 bit) number that can be used to identify a large group of beacons. It is formatted in 32 hexadecimal digits, split into 5 groups, separated with hyphen characters [8].
  An example of a UUID is f3af8c82-a58a-45a1-b9b6-21e3cf47ded9.
  It is common practice that the same UUID is being used to identify all the beacons that belong to the same company or organisation. For example, a transport operator can have the same UUID for all the stations they manage. This is only a common practice and not a constraint, as the same company or organisation can generate more than one UUID. Although it is called “unique identifier”, there is a possibility that different companies or organisations might be using the same UUID.
• Major: It is a 2-byte (16-bit) value that can be used to identify a subgroup of beacons that are under the same UUID. The Major can be an integer value between 1 and 65535. It is common practice that the same Major is being used for all the beacons that belong to the same region or venue of the organisation. In the transport operator example, the beacons that belong to the same station, would be under the same Major. In this case, the Major becomes the venue identifier.
• Minor: It is a 2-byte (16-bit) value that can be used to identify an individual beacon within a group of beacons with the same Major. Similar to the Major, the Minor is an integer value between 1 and 65535.

Things to keep in mind:

• The iBeacon format requires all three identifiers to be assigned.
• These three identifiers are advertised publicly. This means that anyone with an app or a device that can detect beacons will be able to capture these identifiers. However, this does not necessarily mean that they can connect with them. Many beacon manufacturers have solutions to prevent “piggybacking” onto a fleet of beacons.
• Since Major and Minor are integers, they cannot include characters other than numbers. Therefore, every venue needs to be related to a number, which very often will be represented by the value of the Major.

1.4.2 Eddystone

Where the iBeacon transmits one advertising packet that includes the UUID, the Major and Minor, the Eddystone beacons broadcast more than one type of advertising packet [4]. These advertising packets are called “frames”.

• The Eddystone-UID frame broadcasts a unique 16-byte Beacon ID. It consists of two parts: the 10-byte Namespace ID and the 6-byte Instance ID. The Namespace ID can be used to specify a particular group of beacons, similar to the UUID in iBeacon.  The Instance ID can be used to identify individual beacons in a large fleet of beacons.
• The Eddystone-EID frame broadcasts an ephemeral identifier recognised by only a controlled set of devices, whereas the Eddystone-UID and Eddystone-URL frames can be publicly recognised. The identifier can only be translated to useful information if these devices have access to a resolution service. The resolution service shares a key (the Ephemeral Identify Key) with the individual beacon and maps the beacon’s current identifier to stable data. In this way, Eddystone-EID is intended to give control to developers over the security and the privacy of the beacon signal.
• The Eddystone-URL frame broadcasts a URL in a compressed encoding format. Once received by a device, the URL is decoded and the user can select if they want to visit the broadcasted URL. Although this advertising packet might not be very helpful for wayfinding applications, it is useful for applications intended for web content discovery.
• The Eddystone-TLM frame broadcasts data about the beacon’s own operation, the so-called telemetry information. This data is useful for monitoring the fleet of beacons. When the Eddystone-TLM frame is transmitted, the following data can be captured:
  • Beacon battery level, in an encrypted format with the shared key, similar to the Eddystone-EID
  • Time that the beacon has been active since last time it was switched on
  • The number of frames, i.e. advertising packets, the beacon has transmitted since last time it was switched on
  • Beacon temperature

1.4.3 Estimating the distance from a BLE beacon

As seen above in Section 5.1.2 the Bluetooth signal is open to distortion from different sources. As a result it is difficult to accurately estimate the distance from a BLE beacon to a device. Depending on the BLE beacon format that is used, i.e. iBeacon or Eddystone, there are various parameters that could give an indication of the beacon’s distance from the device:

• Received Signal Strength Indicator (RSSI): This is an indication of the BLE beacon signal strength as measured by a device. The RSSI is measured in dBm (Decibel-milliwatts). The bigger the RSSI value, the stronger the BLE beacon signal. Based on the changes of the RSSI value, we can tell if a user is heading towards or away from a BLE beacon. The RSSI values are specific to each beacon manufacturer and based on how they have calibrated their BLE beacons (see “Measured Power or Ranging Data” in Section 5.1.4.4). The RSSI values as read by smartphones vary between devices as it also depends on the Bluetooth chip that the device has on board.

• Proximity zones: For the iBeacon format only, the area around a beacon is divided in four proximity zones based on the RSSI.
  • Immediate, when the device is very close to the beacon in distances less than 50cm
  • Near, when the device is estimated to be in distances between 50 centimetres and 3 metres from the beacon
  • Far, when the device is further away or the signal is fluctuating due to distortions
  • Unknown, when the distance cannot be estimated mainly because the distance from the beacon is too far and also due to distortions of the signal

The proximity zones can be used as filters in order to trigger content in context. For example, when a device enters a beacon in the “Near” zone, then a particular set of content can be triggered, whereas when the device is in the “Immediate” zone a different set of content can be triggered.

• Accuracy: This is a parameter in the iBeacon format only that indicates the proximity value measured in metres. More specifically, it indicates the one sigma horizontal accuracy, a parameter used in statistics [6]. The iBeacon documentation suggests that the Accuracy parameter can be used to differentiate between beacons with the same proximity value. However, the iBeacon documentation suggests that the Accuracy should not be used to identify the exact distance of a user’s device from a beacon. The reason is that the Accuracy levels are affected by various sources of signal distortion and might not reflect the actual distance in metres.

1.4.4 BLE beacon configuration settings

Regardless of their protocol format, i.e. iBeacon or Eddystone, a BLE beacon can be configured by adjusting the following parameters in order to achieve best results:

• Advertising interval: It specifies how often a beacon transmits its signal. The values for the advertising interval range from 100 milliseconds to 2000 milliseconds. The shorter the interval, the more often the beacon transmits its signal. Also, the shorter the interval, the more stable the beacon signal is. Reducing the interval, i.e. making the beacon emitting its signal faster, has a big impact on the beacon’s battery life. In most cases an advertising interval adjusted between 300-350 milliseconds will maintain a good balance between signal stability and battery life.
• Broadcasting or Transmission (TX) Power: It determines how far a beacon emits its signal. The broadcasting power is measured in dBM (Decibel-milliwatts) and ranges between -100 dBM and +20 dBM. The more power, the further the signal is emitted. The maximum distance that a Bluetooth Low Energy signal can travel is several hundred metres, assuming that there are no walls or other sources of signal distortion.

Finding the right broadcasting power for a BLE beacon depends on the context. For example, a beacon installed in a large concourse might need to be set to a higher broadcasting power. In cases where a beacon must be triggered only when in the boundaries of a point of interest or landmark, the broadcasting power will need to be lower so that the beacon is not detected from further away.

The broadcasting power also has an impact on the beacon’s battery life, but not as greatly as Advertising Interval.  As a rule of thumb, battery usage is 30% higher at Maximum power than at a Minimum power.

• Measured Power or Ranging Data: This parameter is used in estimating distance from a beacon (see Section 5.1.4.4). iBeacon and Eddystone define this parameter differently. In the iBeacon protocol, it is called Measured Power and it is the expected value of Received Signal Strength Indicator (RSSI) at one meter distance from the beacon. In the Eddystone protocol, it is called Ranging Data and it is measured at zero meter distance from the beacon. However, the Eddystone specification [4] proposes to “measure the actual output of the beacon from 1 meter away and then add 41 dBm to that. 41 dBm is the signal loss that occurs over 1 meter.”

Many beacon manufacturers have a default factory calibration for the Measured Power that cannot be changed. However, it is advised that when beacons are installed indoors, Measure Power or Ranging Data samples be taken in-situ and the value be set accordingly. In this case the real environment with the potential sources of Bluetooth signal distortion are taken into account (see Section 5.1.2).

Note that the Eddystone protocol is using the Ranging Data parameter only for the UID, EID and URL frames.

1.5 Maintenance and Operational considerations

As well as considering installation and configuration of beacons, it is important to consider maintenance and operation over the longer term for the fleet of installed beacons to remain functional and up to date.

Things to consider:

• Which department in the organisation will own the BLE beacon infrastructure and will be responsible for their installation, configuration and maintenance.
• What happens when BLE beacon battery is due to run out. There are two options: Replace the whole BLE beacon or replace the battery in the BLE beacon. The latter ensures continuity as the beacon does not change.
• What are the organisational needs for the battery health data collection. There are various options available:
  • The battery health data can be collected manually by someone in the organisation who will need to do a walk through all BLE beacons with a mobile device that will collect battery levels
  • The battery level can be automatically collected and sent anytime a mobile device is connected to the BLE beacon. In this case, the collection of battery levels is crowd-sourced through people passing through the venue
  • Some BLE beacons have the ability to connect to the Internet themselves if they are in the range of a wi-fi network. In this case they can send their battery levels automatically at periodic intervals
• What are the organisational needs for a dashboard to monitor status of the installed BLE beacon fleet.
• How the system administrator will be notified when beacon battery is running low in order to arrange action for maintenance.
• How battery life can be preserved while the venue is closed.
• What security actions can take place in order to mitigate the risk of someone else piggy backing on the fleet of beacons without the organisation’s permission. Although the BLE beacon identifiers are publicly transmitted data, there are ways available to increase the security of the beacon fleet.
• Where do the data from the user’s smartphone that is using the beacon network for travel ultimately end up.
• How is the users’ travel data stored/deleted or shared /protected.
• Disabling the whole system in case it is needed, for example when system maintenance is in progress.
• What are the available options for the BLE beacon firmware upgrades provided by the beacon manufacturer. Updating the firmware keeps the BLE beacon up-to-date with the latest software and security updates made by the beacon manufacturer.
• What is the performance of the beacon manufacturer’s SDK and API and how often they are updated.
• To what extent the beacon manufacturer’s SDK and API are documented. A well documented SDK and API will help developers integrate them better into their mobile app.
• How engaged is the online community around the beacon manufacturer in order to provide support and recommendations if any issues faced.
• How responsive is the beacon manufacturer’s support team, and what capability do they have to escalate questions to a developer when required.
• What capability does the beacon manufacturer provide in order to facilitate sharing of the beacon network with other third party developers who might be interested in utilising it.

1.6 References

1. Apple, iBeacon for Developers. (last accessed: 30 March 2016)
2. Apple, Potential sources of Wi-Fi and Bluetooth interference (last accessed: 30 March 2016)
3. Bluetooth, What is Bluetooth technology? (last accessed: 30 March 2016)
4. Google, Eddystone specification (last accessed: 27 April 2016)
5. Google Developers, Beacons (last accessed: 27 April 2016)
6. Wikipedia, Standard Deviation (last accessed: 30 March 2016)
7. Wikipedia, Trilateration (last accessed: 30 March 2016)
8. Wikipedia, Universally Unique Identifier (UUID) (last accessed: 30 March 2016)