Bluetooth Auracast™

Rail Engineer issue 204 (Sep/Oct 2023) covered Wi-Fi 7 and explained how it will be the future standard for the final wireless connection between the internet and devices. However, Bluetooth is another wireless technology which is used for the exchange of data between devices over short distances.

The latest development in Bluetooth technology is the introduction of Bluetooth Low Energy (LE) and Auracast™. This will allow the broadcast of an audio signal to an unlimited number of in-range Bluetooth devices, such as Bluetooth earbuds or headphones and opens up the possibility of train announcements being readily available to rail customers with hearing difficulties.

A brief history

The development of the technology was initiated in 2109 by Nils Rydbec, of Ericsson Mobile in Sweden, as a ‘short link’ radio technology, though it would not be called Bluetooth until some years later. Bluetooth was designed to replace RS-232 cables, using short-range UHF radio waves between 2.4 and 2.485GHz. Although using very similar frequencies to Wi-Fi, Bluetooth has always been designed as a shorter range and lower power alternative.

Originally, Bluetooth was standardised by IEEE 802.15.1, but the IEEE no longer maintains the standard and today Bluetooth is managed by the Bluetooth Special Interest Group (SIG). Bluetooth SIG has more than 35,000 members consisting of telecoms, computing, and consumer electronic companies.

Bluetooth Classic radio, also referred to as Bluetooth Basic Rate, streams data over 79 channels with 1MHz spacing in the unlicensed Industrial, Scientific, and Medical (ISM) 2.4GHz frequency band. It is used for point-to-point device communications and mainly as an alternative to wired connections for such devices as wireless headphones, earbuds, or computer mice.

There have been many versions of the Bluetooth standard over the years, with ever increasing capabilities. The latest, Bluetooth 5.0, is twice as fast, can transfer eight times as much data, and has four times the range compared to Bluetooth 4.2. So that is around 240 metres – up from 60 metres in Bluetooth 4.2. This range allows coverage for Internet of Things devices such as security cameras, smart fridges, smart thermostats, and more, such as Auracast, which we will come to shortly. Bluetooth is so popular that it is now becoming difficult to obtain wired devices.

Interference is one of the biggest challenges for any wireless technology and because Bluetooth and Wi-Fi share the 2.4GHz frequency band it’s possible for a data packet to be corrupted or lost if it collides with another packet being transmitted at the same time and on the same channel. Bluetooth overcomes interference and avoids packet collision by using adaptive frequency hopping. It rapidly hops between the channels when transmitting packets and, to further reduce interference, adapts its hopping sequence so that channels which are noisy and busy are avoided.

Bluetooth Low Energy (LE)

Bluetooth Low Energy (LE) is designed for very low power operation. For example, the University of Michigan has developed a millimetre-scale device consuming just 0.6 milliwatts of power during transmission. This device would be able to broadcast for 11 years using a typical 5.8-millimetre ‘coin’ battery. Bluetooth LE transmits data over 40 channels with 2MHz spacing in the 2.4GHz ISM frequency band and along with point-to-point communications Bluetooth now supports broadcast and mesh technologies. Bluetooth LE can also provide high accuracy indoor location services and it includes features to enable a device to determine the distance and direction of another device.

Bluetooth LE applications will include the following:

• Health care devices: For example, blood pressure measurement, temperature measurement, and blood glucose monitoring.
• Mesh profiles: Used to communicate with other devices so that every device can pass information to other devices, creating a mesh network.Sports and fitness devices: For example, exercise bike sensors to measure speed and revolutions per minute.
• Smartwatches or smart bracelets and scales to monitor body weight.
• Environmental sensing profiles: Used to measure environmental factors such as illuminance, and ambient humidity, temperature, and pressure.
• Auracast is a Bluetooth application which uses the broadcast and mesh communications abilities.

Auracast broadcast

Auracast broadcast audio is designed to provide all types of public locations with an audio experience that enhances visitor satisfaction and increases accessibility. This could be large venues such as railway stations, airports, and conference centres, to smaller venues such as gyms, cinemas, and places of worship. An unlimited number of in-range Auracast receivers will be able to join a broadcast from an Auracast transmitter.

The transmitter begins an audio broadcast with information about the broadcast (e.g. name, content, codec configuration, left and right stereo audio streams). The receivers scan for the information and access a User Interface (UI) which enables them to select a broadcast to join, similar to the UI used to connect to Wi-Fi networks in public areas. Once a broadcast is selected, the receiver (such as a headphone, earbud, hearing aid, or speaker) is able to join the broadcast. 

Applications

Use cases could possibly include ‘silent screens’. Public locations that provide silent TV screens such as airports, gyms, and waiting rooms, could offer a ‘watching’ experience by allowing visitors to use their own Bluetooth earbuds with Auracast broadcast audio enabled or hearing devices to listen to audio broadcast from the TV.

Public locations that provide tours, such as museums, convention centres, and tourist attractions, could offer a tour experience by enabling visitors to use their own Bluetooth earbuds with broadcast audio or hearing devices.

Locations which support simultaneous multi-language translation services such as conference and meeting centres, could provide an enhanced audio experience and let participants use their own Bluetooth earbuds with Auracast broadcast audio or hearing devices to listen to audio in their desired language. Could this also feature at rail stations in the future?

Public Address (PA) systems such as railway stations, airports, cinemas, lecture halls, conference centres, places of worship, could provide a higher-quality audio experience by enabling customers and visitors to receive the PA audio directly into their own Bluetooth devices.

There may also be other applications which could all benefit from a high quality, low-cost, next-generation assistive listening system, to improve the audio experience for visitors with and without hearing issues.

Summary

Bluetooth is an established short-range point to point communication technology for devices. Bluetooth LE Auracast will provide a broadcast enhancement, which could provide PA broadcasts to customers at stations and on trains. It is early days for the Auracast standard, but in a few years’ time it may well be an established feature at many railway stations and on trains, much like Bluetooth is now established as the means to connect all kinds of devices?

Image credit: iStockphoto.com/DUXX