How does Bluetooth work?

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Bluetooth is a wireless technology that allows devices to communicate with each other without cables or wires. It relies on short-range radio frequency, and any device that incorporates the technology can communicate as long as it is within the required distance1. The working of Bluetooth consists of sending and receiving signals from one device to another. It sends and receives radio waves by using 79 different frequencies in a band of the spectrum which is centered at 2.45GHz, used for avoiding interference2. Creating a Bluetooth connection between two devices is a multi-step process involving three progressive states: Inquiry, Paging (Connecting), and Connection3.
  • Inquiry: If two Bluetooth devices know absolutely nothing about each other, one must run an inquiry to try to discover the other. One device sends out the inquiry request, and any device listening for such a request will respond with its address, and possibly its name and other information3.
  • Paging (Connecting): Paging is the process of forming a connection between two Bluetooth devices. Before this connection can be initiated, each device needs to know the address of the other (found in the inquiry process)3.
  • Connection: After a device has completed the paging process, it enters the connection state. While connected, a device can either be actively participating or it can be put into a low power sleep mode3.
Bluetooth networks, commonly referred to as piconets, use a master/slave model to control when and where devices can send data. In this model, a single master device can be connected to up to seven different slave devices. Any slave device in the piconet can only be connected to a single master. The master coordinates communication throughout the piconet. It can send data to any of its slaves and request data from them as well. Slaves are only allowed to transmit to and receive from their master3. Every single Bluetooth device has a unique 48-bit address, commonly abbreviated BD_ADDR. This will usually be presented in the form of a 12-digit hexadecimal value. The most-significant half (24 bits) of the address is an organization unique identifier (OUI), which identifies the manufacturer. The lower 24-bits are the more unique part of the address3. Bluetooth devices can also have user-friendly names given to them. These are usually presented to the user, in place of the address, to help identify which device it is. The rules for device names are less stringent. They can be up to 248 bytes long, and two devices can share the same name3. When two Bluetooth devices share a special affinity for each other, they can be bonded together. Bonded devices automatically establish a connection whenever they're close enough. Bonds are created through a one-time process called pairing. When devices pair up, they share their addresses, names, and profiles, and usually store them in memory. They also share a common secret key, which allows them to bond whenever they're together in the future3. Bluetooth is used in a wide variety of applications like headphones, phones, Bluetooth keyboard, Bluetooth headsets, Bluetooth-equipped printer, a GPS device that uses Bluetooth, Bluetooth-enabled webcam, stereo headset, television remote, and wireless speakers2.
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