This is the third part of the series ” Communication Protocols in IoT”. The first part can be found here
Bluetooth is a technology that is probably not unfamiliar to anyone today since literally every smartphone comes with the technology as standard. But how is this technology that historically is most known for audio streaming/handsfree use cases relevant for IOT?
The roots of Bluetooth can be traced back to 1994 when an engineer working for Ericsson, Jaap Haartsen was tasked to develop a wireless alternative to RS-232 (serial cables). Similar ideas also emerged in other companies around the same time and it quickly became clear that for products from different vendors to be compatible and interoperable. Some sort of standardization was required. In 1996 five companies (Ericsson, Nokia, Intel, Toshiba, and IBM) met in Lund Sweden and agreed that a Special Interest Group (SIG) was to be formed to drive and standardize the technology. Two years later in 1998, the Bluetooth Special Interest Group (Bluetooth SIG) was officially established.
Technicalities and Standards
The Bluetooth technology standard(s) and specification(s) are governed by the Bluetooth SIG. Membership is free for any company (Adopter level) but a higher-level membership (Associate) is available for a yearly fee. Associate membership brings several possibilities for companies who wants to actively participate in working groups, have early access to new specifications and contribute to the development of the Bluetooth standard. There is also a higher (Promoter) level membership which you cannot pay for, this small group of companies consists of the most active contributors to the standard and each company has one seat on the highest governing body of the SIG, The Board of Directors.
Since the release of Bluetooth 1.0 in 1998, a large amount of work has been done to the specifications and profiles covered within Bluetooth technology and the most recent core specification (2018) is at 5.0.
To sell a product with Bluetooth branding/technology, certification is mandatory. This is mainly enforced to secure interoperability between different devices and brands. Although the certification historically has not guaranteed a 100% interoperability between every device supporting the same profile(s) on the market. It does provide a quite rigorous suite of tests and requirements to push for well-implemented products.
When talking about Bluetooth technology it is nowadays a bit problematic to talk about ”one technology” due to a significant change that was introduced in the core 4.0 standard in 2010. The introduction of Bluetooth Low Energy (BLE) meant that Bluetooth now consisted of 2 different stacks from the physical layer up to the application. Some parts were of course reused and there are absolutely no problems finding chipsets that support both the traditional (Basic Rate (BR)/Enhanced Data Rate (EDR)) standard as well as the new (BLE) standard.
The traditional Bluetooth stack which is still very relevant today (although maybe not so much in an IoT context) contains profiles for media streaming and control (A2DP/AVRCP), Handsfree (HFP), serial port emulation (SPP), Text message synchronization (MAP) and internet tethering (PAN) to mention some of the most commonly known profiles and use cases. All profiles are described in detail in specifications that are released by the Bluetooth SIG and all vendors are required to implement mandatory parts to enable interoperability. The maximal theoretical (not practical!) transfer speed using EDR is 3 Mbit/s (a ”High Speed” (HS) standard also exist where actual data transfer is handed over to WiFi, but this is very seldom used).
Bluetooth low energy (BLE) on the other hand, was specifically developed and tailored to be used for IoT use cases. The standard offers very low power consumption with several powerful features suitable for IoT use cases.
Devices can broadcast limited amounts of data even to devices that are not trusted/paired.
- Dedicated advertising channels:
Compared to BR/EDR, BLE uses 3 dedicated advertising channels allowing for a much quicker device discovery (scan 3 physical channels instead of 79 as is the case with BR/EDR). Limiting advertising to only 3 channels also has a positive impact on energy consumption.
- Flexible protocol definition:
While some common profiles defined by the Bluetooth SIG exists (Blood Pressure Profile, Heart Rate Profile and Insulin Delivery profile to name a few). BLE makes it very easy to define and create your own profile for your specific needs. By using the protocols and capabilities available in the BLE stack you can easily implement your use case(s).
To improve things further, the latest core specification (Bluetooth 5.0) and the additional MESH specification adds a few more powerful features:
- 2 Mbit/s PHY:
Compared to Bluetooth 4.0/4.1/4.2, it’s now possible to have 2x the maximum throughput if your IoT use case require some heavier data transfer (theoretically up to 2 Mbit/s compared to 1 Mbit/s for earlier BLE standards. It is however important to mention that these numbers are solely theoretical and deals mainly with modulation, practical data throughput is far less.).
- 4x Range:
The Bluetooth 5.0 standard also introduces another new PHY (Physical layer) that allows Bluetooth to achieve up to 4x the range compared to Bluetooth 4.0/4.1/4.2. Note that despite some less than clear claims during the release of the standard stating ”2x the speed and 4x the range”, you can only get one of these properties at a time. You don’t get both since the PHY is significantly different.
BLE now supports Mesh technology making it a suitable technology candidate for large-scale deployments and use cases where each edge device doesn’t need to have a direct connection to a more central node.
Bluetooth is a huge technology (the core 5.0 specification alone is over 2800 pages!) so it’s safe to claim that the technology can support a vast number of different use cases. This is also obvious when looking at the market. Bluetooth has an extremely impressive market penetration since its available in more or less every smartphone. A list of all even common use cases would be extremely long, but you can easily find it in everything from common products such as smart watches, fitness trackers and smart lighting to more exotic implementations in toasters, toilets, and toothbrushes.
//Erik Dahlgren, Software Developer