Bluetooth | The wireless standard

Transferring data between devices is usually no problem as long as you have the right connector cable. If you do not have one at hand, you will need to go the long way around via WLAN or the cloud to be able to share your photos from last night with a friend. However, there is another way to easily transfer photos, videos and audio files. It is called Bluetooth and it has a near infinite range of applications.

The term Bluetooth refers to a network technology which was based on the American Institute of Electrical and Electronics Engineers (IEEE) standard 802.15.1 for wireless connections. Bluetooth enables the connectionless or connection-orientated point-to-point transfer of voice and data between various digital devices. The main goal of this technology is to replace wired connections or make them completely obsolete, which is particularly good for mobile devices such as smartphones and tablets.

In comparison to data transfer technologies such as USB, LAN and WLAN, Bluetooth specialises in sending data over short distances with a simple, energy-efficient setup. However, since its transfer speed is generally slower than the other previously mentioned technologies, it may take longer to send large data packets. Bluetooth is however the ideal solution when it comes to individual files and simple services and applications.

Bluetooth was invented as a response to the well-known issue of “cable clutter”. Various attempts have been made since the 1980s to replace standard wired connection technologies with wireless alternatives. One promising contender was infrared technology, which could be used, for example, to communicate between computers and printers. However, its relatively high-power consumption as well as its need to establish and maintain direct “visual contact” between the devices to be connected prevented the technology from catching on.

In the 1990s, a consortium of electronics companies made up of Ericsson, IBM, Intel, Nokia and Toshiba founded the Bluetooth Special Interest Group (also referred to as Bluetooth SIG) to develop their own technological solution. At the time, “Bluetooth” was just the project’s code name, but it was soon adopted as the official brand name due to a lack of other suggestions.

The fact that Ericsson and Nokia both originate from Scandinavia may have played a large role in choosing the name. The word “Bluetooth” is supposed to refer to the Danish Viking king Harald Bluetooth. In the 10th century, he managed to unify the warring parts of Norway and Denmark into one kingdom. The iconic Bluetooth symbol is a combination of the Old Norse runes ᚼ and ᛒ which are Harald Bluetooth’s initials (HB).

Bluetooth emerged through the cooperation of multiple parties. For example, basic wireless technology can essentially be traced back to the work done by the Dutch professor Jaap Haartsen and the Swedish professor Sven Mattisson who both worked for Ericsson, a mobile communications and internet company. Other Bluetooth features can be largely attributed to the technology companies Intel and Nokia. In the following sections, we will take a look at the technical details.

For a digital device to be considered “Bluetooth capable”, it requires specific software for managing the data transfer as well as a special Bluetooth chip which has a transmitter and a receiver unit and is permanently installed in the hardware. Atheros, Nordic Semiconductor and Toshiba are some well-known manufacturers of these chips. It is also possible to connect a Bluetooth adapter to a USB port on a device to add this functionality to it.

The designated Bluetooth frequency operates in the license-free ISM band between 2.402 GHz and 2.480 GHz. Compatible devices that comply with the Bluetooth SIG standards are allowed to transmit in this frequency range as Short Range Devices (SRD) anywhere in the world without a license. All devices have their own individual 48-bit long MAC address which allows them to be uniquely identified.

A connection can originate from any device which then becomes the “master” over the “slaves” (i.e. the other devices involved) and set up a piconet (a Bluetooth network). The connection is maintained until the master disables Bluetooth in their system. Devices that want to connect to a piconet “listen” in scan mode every 2.56 seconds for a signal from the master. The connection is then established within 1.28 seconds on average. Connecting two or more devices via Bluetooth is called “pairing”.

In practice, members of a piconet need to be close to one another and have activated Bluetooth on their respective devices. Depending on the device, it may be activated through a special software, control panel or button that displays the Bluetooth symbol. The connection then needs to be authorised via a (usually four-digit) PIN which is displayed on the slave device’s screen or is recorded in the device’s manual. This procedure is referred to as “key allocation”. It provides security against third parties and usually can only be done once. The "paired" device is then stored in a list and will always automatically connect as soon as it is within range of the piconet as long as Bluetooth is activated.

A piconet may contain a maximum of eight actively connected Bluetooth devices. Furthermore, up to approximately 200 additional devices can theoretically remain in the network in power saving standby mode or in park mode and be activated on demand. A Bluetooth device can be registered as a slave in several piconets at once, but it can only be a master in one at a time. A scatternet is made up of up to ten piconets. Every device in the network can communicate with the others. However, the data transfer rate is negatively affected by this.

Every Bluetooth chip comes with a protocol stack. This is a software packet which includes the services for using various Bluetooth profiles. Much like computer drivers, these profiles define the type of data two devices can exchange and which services are available to them. You can usually find the profiles a device is compatible with in its technical data. For certain functions to be useable, all devices involved must be compatible with the same profiles. Missing profiles can often be obtained and added. This can be done for example via the chip manufacturer or the stack provider’s website.

The following table contains some commonly used standard profiles. However, this table is not intended to be completely comprehensive, since new profiles are constantly being added in order to be able to flexibly adapt to new device requirements.

Bluetooth has a wide range of uses and applications. The following are just a few examples.

• Computers and notebook computers: Many current Windows and Linux operating systems support Bluetooth by default. A chip built into the hardware makes it possible to connect to various peripheral devices such as mice, keyboards, headphones and printers. Additionally, wireless technology is used for security tokens as part of two-factor authentication.
• Mobile devices: Bluetooth chips can be found in virtually all modern cell phones and tablets. You can use them to synchronise files, photos and videos with your home computer, for example.
• Audio output devices: Many wireless speakers and headsets come equipped with Bluetooth which enables you to play MP3 files directly from your smartphone.
• Hands-free systems: If your smartphone is paired via Bluetooth with the hands-free system in your car radio or motorcycle helmet, you can answer incoming calls directly. In properly equipped vehicles, the on-board computer will also be compatible with wireless technology. This enables you to use the cockpit display to navigate through the contacts and menus on your cell phone.
• Fitness devices and smart home technology: Some fitness trackers and smartwatches send health data via Bluetooth directly to a health app on your smartphone. Bluetooth-enabled kitchen appliances, alarm systems, electronic keys and digital picture frames have also contributed to the worldwide success of smart home systems.
• Toys and video game consoles: The toy industry is constantly introducing new dolls and action figures to the market which can communicate and interact with each other via Bluetooth. Controllers for popular video game consoles such as the Nintendo Switch, PlayStation 4 and Xbox One also use this wireless standard.
• Medical technology: High-priced hearing aids can be equipped with hands-free features using Bluetooth. It is also possible to configure technologically advanced arm and leg prostheses, insulin pumps and blood sugar monitors wirelessly.
• Industrial applications: Last but not least, wireless communication technology is driving industry itself forward by connecting machines and manufacturing facilities to one another in networks and thus enabling production processes to be largely automated.

Bluetooth 1.0a, the first version of the wireless standard, was released in 1999 and had a data transfer rate of 732.2 kbit/s. Unfortunately, like its successor 1.0b, it struggled with some initial flaws and security problems. Bluetooth 1.1 (early 2001) was the first to establish a solid foundation for marketable products. Since then, the system has been continuously refined and improved upon with a focus on security, interference resistance and connection speed.

This has resulted in a wide variety of Bluetooth versions which build on each other and differ mainly in their maximum data transfer rate but also in their range of uses and applications.

There are now more than ten different Bluetooth versions, all of which are compatible with each other with the exception of the low energy (LE) 4.0 version. However, versions older than Bluetooth 3.0 are rarely used.

While many users and experts compared Bluetooth to a falling star, version LE 4.0 managed to revitalise the technology. With the help of the low energy protocol stack, it became possible to save an unprecedented amount of energy. This also enabled Bluetooth to be able to be used in small devices such as smartwatches, electronic door locks and smart light bulbs. Since then, this almost 20-year-old wireless standard has been regarded as one of the most important driving forces behind the Internet of Things (IoT).

Version 4.1 now allows small devices to communicate with other devices without an "intermediary". For example, a fitness wristband can directly access a heart rate monitor without having to go through a smartphone. Another innovation is the support of IPv6 which gives every Bluetooth-capable IoT device its own IP address enabling its user to access it from the Internet. However, version 4.2 is considered to be the most technologically advanced version to date. It is known for its smaller data packets as well as its faster data transfer speed, longer battery life and better security.

But it does not end there. In December 2016, SIG released the long-awaited Bluetooth 5.0 which still specialises in IoT devices and has improved upon its predecessor in very big way. It is supposed to have increased its data transfer capacity by 800% and extended its range to up to 200 metres (outside) or 40 metres (inside) while maintaining its low energy consumption. It is also expected to help further advance the development of beacons. Beacons are small Bluetooth transmitters, which can be used in museums, for example, to send additional information to visitors’ smartphones.

While the number of devices which support the new version is still rather modest, some experts are already treating Bluetooth 5.0 as a “technical milestone” which could even overtake WLAN (at least in terms of the IoT).

There are currently three classes for the maximum range of Bluetooth, each based on the device’s requirements.

It should be noted that a compromise always has to be made between the data transfer rate/range and energy consumption when using Bluetooth technology. For example, version 4.0 requires very little power in low energy mode, but it can only achieve a rate of 1 Mbit/s and a maximum range of 10 metres. When operating normally, it can achieve a maximum rate of 25 Mbit/s which increases both the range and the energy requirement proportionally. Manufacturers of Bluetooth-capable devices must therefore precisely calculate how to configure their products so that they are suitable for their intended use. Only the latest version Bluetooth 5.0 is capable of achieving a range of 200 metres outdoors and 40 metres indoors due to its advanced energy-saving techniques. However, it can also be used in LE or EDR mode.

Ultimately, a Bluetooth-capable device's maximum range always depends on whether it is being used outdoors or indoors (e.g. inside an apartment). This is because obstacles such as walls, large furniture or metallic structures can interfere with the connection. Additional factors which can have a large impact on the range of a Bluetooth connection include the structure of the transmitting and receiving antennas used for the wireless communication channel and the type of data packets being sent.

Various methods which can be grouped together under the term “frequency hopping” have been able to consistently reduce Bluetooth’s susceptibility to interference from one version to the next. In frequency hopping, the frequency band being used is divided into individual channels of equal size. These channels are rapidly switched between several thousand times per second or as required to ensure constant interference-free transmission. This ensures that Bluetooth communication and other wireless connections, such as WLAN, LTE and microwaves, do not interfere with each other.

Thanks to encryption and various other security mechanisms, Bluetooth is generally regarded as relatively secure. However, it has already been proven on several occasions that even the newer versions of this wireless standard are vulnerable i.e. due to incorrect implementations on the manufacturer’s side).

The most popular target is almost always the key allocation in the pairing process during which cybercriminals try to obtain the PIN used for authorisation. Since it usually only needs to be allocated once when establishing the connection, the window for this type of attack is typically very short.

However, there is a trick which does not require advanced computer skills or specific technology. An attacker can use a “BlueSmack attack” to interfere with an already existing Bluetooth connection. This forces unsuspecting users to change their PIN again which the attackers then intercept to gain access to the device. As a result, they can intercept and tamper with data streams ("bluesnarfing") and cause financial damage by calling fee-based hotlines and text messaging services ("bluebugging"). For this kind of attack to be successful, however, the attackers must stay close to the devices they are hacking.

As a Bluetooth user, you can take some precautions:

• Before purchasing a digital device, ask if it is possible to manually assign a PIN for Bluetooth connections (standard keys set by manufacturers such as "0000" or "1234" do not provide sufficient security).
• Deactivate the "Secure Simple Pairing" option (connects automatically to new devices without a PIN such as with Bluetooth 2.1 + EDR) and then set up each Bluetooth connection manually.
• Choose a long PIN with at least eight numbers if the software permits it.
• Use “invisible mode” to hide your Bluetooth username.
• Avoid using Bluetooth in crowded places, such as public spaces, where a specialised hacker is more likely to be in your immediate vicinity.
• Store trusted devices on your Bluetooth device list. This way you will not need to re-enter your PIN when connecting later which eliminates an important point of attack.
• If you need to enter your PIN again to re-authorise an existing connection, this should set off alarm bells. If this happens, stop trying to connect for the time being and move to a new location to get out of range of a possible attacker.
• Disable Bluetooth immediately after use. Only turn Bluetooth on if you really want to use it. This also helps by using less of your device’s battery.

Bluetooth has been declared dead many times. This wireless technology was judged to be too complicated and slow when compared to how wonderfully simple and fast it was to send data over wired connections. However, this view has long since become outdated. Bluetooth has since most recently made a name for itself with its energy-saving version 4.0. It is regarded as the driving force behind the revolutionary Internet of Things. And if experts agree on anything, it is that commonplace smart products such as fitness trackers, smart home devices and on-board computers in vehicles are the future. So, we can assume that Bluetooth is going to remain an industry standard for a long time to come.