The formal introduction of Bluetooth 5 in mid-2016 was a key milestone in the development not only of the standard in general, but also for the emergence of services based on Bluetooth beacons. For the consumer, smartphones and tablets that support the standard are coming to the market – Samsung and Apple led the way with, respectively, the Galaxy 8 generation and onwards, and the iPhone 8 and X. For the developer, chips such as Nordic’s nRF52810 and nRF52840 SoCs are in place to build beacons providing extended range, exploiting increased data capacity and, crucially, delivering long battery life to underpin the proliferation of beacon technology.
Bluetooth Beacons are now an established market, with a range of manufacturers, specialist suppliers and distribution channels in place. In a 2017 market analysis, the Bluetooth Special Interest Group (SIG) — custodians of all things Bluetooth — cited a study that forecast a compound annual growth rate of over 130 percent, out to 2021. The report anticipated, for example, the 2017-to-2018 figures for units shipped would rise from 26 million to 83 million. 2018 also finds the market for Bluetooth beacons in a state of transition: No sooner had the original concept of a beacon taken hold, then the uprated specifications have become available, opening a far wider range of potential applications.
Better with 5
The basic beacon technology supported by Bluetooth Low Energy (Bluetooth LE) versions 4.0, 4.1, and 4.2 defined a simple device that uses, in effect, one side of a full Bluetooth exchange. Any Bluetooth device that wishes to be discovered sends a periodic “advertisement” message that invites initiation of pairing and subsequent data exchange. A beacon’s advertisement contains a reserved address that identifies it as not soliciting pairing, and that precedes a fixed-length, short, data “payload” that’s to be acted on directly. Consumers automatically received the short beacon communication when in close proximity, but such was the limitation on payload that an associated app had to be triggered or browser opened to provide useful information. This restriction limited beacon applications.
In Bluetooth 5, the available payload of the advertisement channel is increased in size eight-fold, from 37 to 255 bytes, and a concatenated mode can string packets together for even longer messages. That means consumers can receive useful information from the beacon transmission alone, without having to open an app. (Bluetooth 5 also handily offers improved channel coexistence making it somewhat easier for a beacon to negotiate a crowded radio environment which ultimately saves power and extends battery life.)
iBeacon and Eddystone, from Apple and Google respectively, are in effect “special cases” of the Bluetooth LE beacon specification targeted at developers, and both are evolving. Eddystone is an open format that supports a variety of data frames for specific tasks. For example, it can alert a feature called Nearby Notifications in Android, without the need for a specific app to be running the handset. (Although the handset does still need its Bluetooth transceiver switched on.) On the Apple side of the fence, one of the changes in iOS 11 is that turning off Bluetooth now disconnects running apps from the radio but does not shut down the transceiver (that takes some deeper delving into the handset’s UI.)
Finding the way
The advertising extension capability of Bluetooth 5 has seen a recent upswing in developments that center on the location-determining aspect of beacon technology, especially in the Industrial Internet of Things (IIoT) space. Determining the location, at any given time, of a mobile entity — either a person or an object — enables people- and asset-tracking. Location fixes are enabled by estimating the distance from beacon to receiver, using received signal strength indication (RSSI). Knowing the transmitted signal strength, and the rate at which the signal strength diminishes with distance, enables a simple calculation that gives the distance of the receiver from the beacon.
Ideally, this strategy might provide “indoor GPS” functionality, where GPS signals are unavailable; the reality is somewhat more complex, as signal propagation is strongly affected by building structure, internal walls, furnishings and even people. Within a specified area, beacon signal strength can be mapped, and that map — sometimes termed a signature — can be made available to an app. Using measured rather than calculated signal profiles offers improved accuracy – the app can access the profile of the signal strength map to refine its determination of where its host is located. A reasonable expectation of accuracy in such solutions is in the one-to-several meter range. However, the Belgian semiconductor and systems research centre, IMEC, has recently published claims of accuracy to as good as 30 cm, using Bluetooth LE beacon technology. The improved performance rivals that currently achieved by (considerably more expensive) ultra-wideband (UWB) and, say the developers, can be applied to high precision track-and-trace and industrial applications.
Beacons for asset tracking
For asset tracking, the beacon deployment strategy is reversed. The beacon is fixed to the item to be tracked and its signal is received by a network of Bluetooth LE nodes distributed around the infrastructure. When a beacon’s signal is received by three (or more) terminals, triangulation allows a location fix to be obtained. The asset in question can be almost anything – or anyone, as beacons are already deployed in, for example, healthcare to track patients, or on sensitive sites to verify the movements of staff and visitors.
When the beacon becomes the mobile element in the system, it is termed a tag, which brings the possibility of overlap with Near Field Communication (NFC) tags. In practice there is likely to be little conflict, with Bluetooth 5 applications using the version’s extended range feature expanding to exploit increases in range of tens to hundreds of meters, while NFC is associated with close-proximity, present-to- reader use cases. The concept of an unpowered or “passive” Bluetooth tag has been floated, and at least one start-up company asserts that it is feasible, in environments where there is sufficient ambient RF energy to be harvested. Using a “conventional” System-on-Chip (SoC) such as Nordic’s nRF52810, the designer of a beacon/tag always has the option of employing an energy harvesting source such as a photovoltaic cell, to dramatically extend battery life. Nordic has a reference design for such a solution available from www.nordicsemi.com.
The additional data payload of the beacon message in Bluetooth 5 means that a useful amount of data (for example, some measured parameter, or status) can be transmitted, still without recourse to an app or browser. Temperature measurement is one example allowing, for instance, a check of whether a pharmaceutical package has been stored outside its temperature limits. One difference of this application compared with the fixed, preset message of the basic beacon, is that the host microcontroller must re-assemble the message frame for every transmission. As part of that, it must compute and include a checksum to verify the message’s integrity – but this is typically not a significant burden for an MCU of ARM Cortex class such as that employed in the Nordic nRF52 Series.
As more services come to depend on location information determined by Bluetooth, attention is also turning to the question of security. A beacon signal is not immune to assorted malicious attacks (any more than are other technologies, including GPS). A degree of hardware security (tamper detection) can be built into devices using Nordic’s silicon, and software security suites are promised.
In 2019, Bluetooth beacons are finding their place in a spectrum of location-determining technologies that includes GPS, Wi-Fi, and NFC (RFID). While all have a role to play, none of the alternatives can offer the range that comes with Bluetooth 5, together with months-to-years of battery life from a small battery cell. For its part, Nordic was quick to support Bluetooth 5 for beacon applications with its ARM Cortex M4 CPU-powered nRF52810 SoC positioned to meet both the performance demands yet price-sensitivity of the sector.