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How Bluetooth Works

man with headphones
Although Bluetooth technology has become synonymous with headphones, it's used for all kinds of wireless devices. Bloom Productions/Getty Images

As our world has grown increasingly connected, we've adopted many technologies to help us stay in contact with our friends and family. One of the most popular is Bluetooth technology, which can be found in many of the devices we use every day. The wireless technology connects mice and keyboards to our computers. It connects our phones to our cars to catch up on the latest podcasts during our morning commutes and it connects our smartwatches and activity trackers to our smartphones.

When any two devices need to communicate with each other, they have to agree on a number of points before the conversation can begin. The first point of agreement is physical: Will they talk over wires, or wireless signals? If they use wires, how many are required — one, two, eight or 25? Once the physical attributes are decided, several more questions arise:

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  • How much data will be sent at a time? For instance, serial ports send data 1 bit at a time, while parallel ports send several bits at once.
  • How will they speak to each other? All of the parties in an electronic discussion need to know what the bits mean and whether the message they receive is the same message that was sent. This means developing a set of commands and responses known as a protocol.

With no physical connection required, the Bluetooth Special Interest Group (SIG) create wireless technology standards for hardware manufacturers to use when they create new devices. As technology evolves, wireless communications technology does, too. At the time of this writing, there are two Bluetooth technology standards that developers use to keep you connected. Although similar, there are subtle differences that make them useful for different applications. We'll learn about the two types of Bluetooth technology below.

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Wireless communication is now a common phenomenon. Many of us have WiFi internet connections in our offices and homes. But Bluetooth devices communicate directly with each other, rather than sending traffic through an in-between device such as a wireless router. This makes life very convenient and keeps power use extremely low, improving battery life.

Bluetooth devices communicate using low-power radio waves on a frequency band between 2.400 GHz and 2.483.5 GHz [source: Bluetooth Special Interest Group (SIG)]. This is one of a handful of bands that is set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

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Many devices that you may already use take advantage of this same radio-frequency band, including baby monitors, garage-door openers and the newest generation of cordless phones. Making sure that Bluetooth devices and other wireless communications technologies don't interfere with one another is essential.

There are two types of Bluetooth technology as of 2020: Bluetooth Low Energy (LE) and Bluetooth Classic (more formally known as Bluetooth Basic Rate/Enhanced Data Rate, or BR/EDR) [source: Bluetooth SIG]. Both operate using the same frequency band, but Bluetooth LE is the more popular option, by far. It needs much less energy to operate and can also be used for broadcast or mesh networks in addition to allowing communication over point-to-point connections between two devices.

The classic Bluetooth technology can deliver a slightly higher data rate than Bluetooth LE (3 Mbs compared to either 1Mbs or 2 Mbs) but can only be used for communication directly between two devices using point-to-point connections. Each of the two types of Bluetooth technology has its particular strengths and manufacturers adopt the version that best fits the needs of their product.

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Bluetooth BR/EDR devices must always be paired and this procedure results in each of the two devices trusting the other and being able to exchange data in a secure way, using encryption.

When Bluetooth BR/EDR devices come within range of one another, an electronic conversation takes place to determine whether they trust each other or not and have data to share. The user doesn't usually have to press a button or give a command — the electronic conversation happens automatically. Once the conversation has occurred, the devices — whether they're part of a computer system or a stereo — form a network.

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Bluetooth LE works differently. Devices may also be paired to form a trusted relationship between them but not all types of product require this. A Bluetooth LE device which wants to be discovered broadcasts special messages (known as packets) in a process called advertising. Advertising packets contain useful information about the advertising device. Another suitable device will find the advertising device by scanning (listening) for advertising packets and selecting those which are from appropriate devices. Usually scanning only happens when the user triggers it by say, pressing a button in a smartphone application. Typically the user is then presented with details of appropriate devices that were discovered and then selects one to connect to.

Bluetooth peripherals (e.g., an activity tracker and a smartwatch) that are connected to the same central device (e.g., a smartphone) form a personal-area network (PAN) or piconet that may fill an entire building or may encompass a distance no more than that between the smartphone in your pocket and the watch on your wrist. Once a piconet is established, its members hop radio frequencies in unison so they stay in touch with one another and avoid interfering with other Bluetooth piconets that may be operating in the same room or devices using other wireless technologies such as WiFi. Bluetooth technology even learns which radio channels are working well and which ones are experiencing interference so that it can dynamically avoid bad channels and just use the channels that are free from interference. This process, called adaptive frequency hopping allows Bluetooth devices to work really well, even in environments where there are very large numbers of wireless devices operating.

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smartphone and smart speaker on pink background
Bluetooth technology powers both smartphones and smart speakers. Yagi Studio/Getty Images

Although many think of Bluetooth primarily as a short-range technology, it can also be used to connect devices more than a kilometer (3,280 feet) apart [source: Bluetooth SIG]. In fact, many types of product such as wireless headphones, require the devices' communication range to be very short. But because Bluetooth technology is very flexible and can be configured to the needs of the application, manufacturers can adjust the Bluetooth settings on their devices to achieve the range they need whilst at the same time maximizing battery life and achieving the best quality of signal.

Several factors affect the range of Bluetooth devices:

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  • Radio spectrum: Bluetooth technology's frequency band makes it a good choice for wireless communication.
  • Physical layer (PHY): This defines some key aspects of how the radio is used to transmit and receive data such as the data rate, how error detection and correction is performed, interference protection, and other techniques that influence signal clarity over different ranges.
  • Receiver sensitivity: The measure of the minimum signal strength at which a receiver can still receive and correctly decode data.
  • Transmission power: As you may expect, the higher the transmitted signal strength, the longer the range that can be achieved. But increasing the transmission power will also deplete your battery faster.
  • Antenna gain: Essentially, this is changing electrical signals from the transmitter into radio waves and back again on the receiving end.
  • Path loss: Several factors may weaken the signal, including distance, humidity, and the medium through which it travels (such as wood, concrete or metal).

One of the most recent Bluetooth technology updates introduced a technique called forward error correction (FEC) to improve receiver sensitivity. FEC corrects data errors that are detected at the receiving end and improves a device's effective range by four or more times without having to use more transmission power. This means a device can successfully receive data when it is at a much longer range from the transmitter, where the signal will be much weaker [source: Bluetooth SIG].

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Bluetooth technology includes a number of security measures that can satisfy even the most stringent security requirements such as those included in the Federal Information Processing Standards (FIPS).

When setting up a new device, users typically go through a process called pairing. Pairing equips each device with special security keys and causes them to trust each other. A device that requires pairing will not connect to another device which it has not been paired with.

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Those security keys allow Bluetooth technology to protect data and users in a number of ways. For example, data exchanged between devices can be encrypted so that it cannot be read by other devices. It can also allow the address which acts as the identity of a device and which is included in wireless data exchanges to be disguised and changed every few minutes. This protects users from the risk of being tracked using data transmitted by their personal electronic devices.

If you own Bluetooth-enabled devices, you have experienced this for yourself. For example, if you buy a cordless mouse, the first time you turn it on, you pair it to the device you plan to use it with. You might turn the mouse on, then go to the Bluetooth settings on your computer to pair the device once you see its name in a list of nearby Bluetooth accessories. A computer can handle many Bluetooth connections at once by design. You may want to use a cordless mouse, keyboard and headphones.

The makers of those accessories, however, are going to limit connections to one at a time. You want your keyboard to type only on your computer, or your headphones to listen specifically to your phone. Some allow the user to pair the device with multiple computers, tablets or phones, but they may only be allowed to connect with one at a time. It all depends on what the manufacturer decided was sensible for their product.

Some devices require a code for security while being paired with another device. This is an example of authentication and it ensures that the device you are setting up that trusted relationship with is the one you think it is, rather than another device somewhere else in the environment. For example, many cars let you take calls without taking your hands off the steering wheel. The first time you want to use this facility, you will have to pair your phone and the car's audio system using the car's entertainment display and your smartphone together. The car gives you a number to type in. Your phone lets you know a device wants to pair using a numeric code. You enter the code off the entertainment display to confirm that this is an authorized pairing. After that, you can use the hands-free phone system without ever needing to pair again.

The user also has control over a device's visibility to other Bluetooth devices. On a computer or smartphone, for example, you can also simply switch the device's Bluetooth mode to "nondiscoverable" or simply disable Bluetooth until you need it again.

Originally Published: Nov 11, 2019

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More Great Links

Sources

  • Afaneh, Mohammad. "5 Things You Don't Know About Bluetooth Range." Bluetooth.com. (Aug. 26, 2020) https://www.Bluetooth.com/bluetooth-resources/5-things-you-dont-know-about-bluetooth-range/
  • Bluetooth Special Interest Group (SIG) (Oct. 21, 2019) http://www.Bluetooth.com
  • Bluetooth SIG. "Bluetooth Core Specification v5.1." Jan. 21, 2019. (Oct. 28, 2019). https://www.Bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=457080
  • Bluetooth SIG. "Learn about Bluetooth: Radio Versions." (Aug. 25, 2020) https://www.Bluetooth.com/learn-about-Bluetooth/bluetooth-technology/radio-versions/
  • Bluetooth SIG. "Understanding Bluetooth Range." (Oct. 27, 2019) https://www.Bluetooth.com/bluetooth-technology/range/
  • Goodman, Ralph. "How Smart Locks and Bluetooth Work to Keep Your Home Safe." June 14, 2016. (Aug. 25, 2020) https://www.bluetooth.com/blog/part-2-how-do-smart-locks-and-bluetooth-work-to-keep-your-home-safe/
  • Woolley, Martin, senior developer relations manager, EMEA, Bluetooth Special Interest Group, Inc., personal interview. (Aug. 31, 2020)

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