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How Bluetooth Works

The technology of Bluetooth wireless is a short range communications method intended to replace the cables that connect portable or fixed devices while maintaining the highest levels of security. The key features offered by Bluetooth include low power and low cost. The specification in Bluetooth defines a uniform structure for a wide range of devices to communicate and connect with one another. The technology behind Bluetooth has achieved global satisfaction such as enabled devices, almost everywhere in the world. Bluetooth devices will connect and communicate without wires through short range and networks known as piconets.

Each device will simultaneously communicate with up to seven other devices within a single piconet, meaning that each device can also belong to several piconets simultaneously. The piconets are dynamically established as Bluetooth enabled devices enter and leave the proximity of radio. A fundamental to Bluetooth strength is the ability to handle both data and voice transmissions simultaneously. This will enable users to enjoy varieties of innovative solutions such as hands free talking, printing and fax capabilities, and other applications.

Specifications

Unlike other standards of wireless, the Bluetooth specification gives product developers both a link layer and application layer definitions, which will help support data and voice applications.

Spectrum

The Bluetooth technology operates in the industrial and scientific band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping signal.

Interference

he adaptive frequency hopping of Bluetooth technology was designed to reduce interference between wireless technologies that share the 2.4 GHz spectrum. Adaptive frequency hopping (AFH) works well within the spectrum to take full advantage of the frequency available. AFH hopping allows for more efficient

Transmission

within the spectrum, which provides users with greater performance even if they are using other technologies along with Bluetooth.

How Bluetooth Works

Bluetooth devices will normally operate at 2.4 GHZ in the license free, globally available ISM radio band. The advantage to this band includes worldwide availability and compatibility. A disadvantage to this however, is that the devices must share this band with other RF emitters. This includes automobile security systems, other wireless devices, and other noise sources, such as microwaves.

To overcome this challenge, Bluetooth employs a fast frequency hopping scheme and therefore uses shorter packets than other standards within the ISM band. This scheme helps to make Bluetooth communication more robust and more secure.

Frequency hopping

Frequency hopping is basically jumping from frequency to frequency within the ISM radio band. After a bluetooth device sends or receives a packet, it
and the device (or devices) it's communicating with hop to another frequency before the next packet is sent. This scheme offers three advantages:

Allows Bluetooth devices to use the entirety of the available ISM band, while never transmitting from a fixed frequency for more than a short period of time. This helps insure that Bluetooth conforms to the ISM restrictions on the transmission quantity per frequency.
Ensures that any interference won't last long. Any packet that doesn't arrive safely to its destination can be resent to the next frequency.
Provides a base level of security as it's very hard for an eavesdropping device to predict which frequency the Bluetooth devices will use next.

The connected devices however, must agree upon the frequency they will use next. The specification in Bluetooth ensures this in two ways. First, it defines a master and slave type relationship between bluetooth devices. Next, it specifies an algorithm that uses device specific information when calculating the frequency hop sequences.

A Bluetooth device that operates in master mode can communicate with up to seven devices that are set in slave mode. To each of the slaves, the master. Bluetooth device will send its own unique address and the value of its own internal clock. The information sent is then used to calculate the frequency hop sequences. Because the master device and each of the slave devices use the same algorithm with the same initial input, the connected devices will always arrive
together at the next frequency that they have agreed upon.

As a replacement for cable technology, it's no wonder that Bluetooth devices are usually battery powered, such as wireless mice and battery powered cell phones. To conserve the power, most devices operate in low power. This helps to give Bluetooth devices a range of around 5 - 10 meters.This range is far enough for wireless communication but close enough to avoid drawing too much power from the power source of the device.