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.