About Bluetooth

Bluetooth is an industry standard that is specified in IEEE 802.15.1. It is used to exchange information between devices such as cell phones, computers, personal digital assistants, printers, digital cameras, and so on. Bluetooth uses a globally unlicensed short-range radio frequency and is designed for low-power consumption and low-implementation costs.

Bluetooth has three classes of devices, as shown in Table 9-1, that are defined by the maximum permitted power and range. With radio communication, all the participating devices do not need to have line of sight. As long as the received transmission is powerful enough, the devices may even be in different rooms.

Class

Maximum Permitted Power

Approximate Range

1

100 mW

Around 100 meters

2

2.5 mW

Around 10 meters

3

1 mW

Around 1 meter

Table 9-1

Bluetooth Device Classes

Adding an external directional antenna to a Bluetooth adapter can extend these ranges because it allows the signal emissions to concentrate in one specific direction instead of being dispersed in all directions. No vendor we know of supplies such external antennas, but, of course, you can modify hardware in a do-it-yourself way (see, for example, http://trifinite.org/trifinite_stuff_bluetooone.html).

Bluetooth can be used for a variety of applications and, therefore, the whole stack consists of different layers and protocols. The next few sections will highlight information about the details associated with the standard developed by the Bluetooth Special Interest Group (SIG). See http://www.bluetooth.org/ for more information.

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