A Few Features Of BlueTooth Wireless And How It Works
By: Vlad Vistac
Submitted: 2010-08-17 15:11:07 | Word Count: 510
BlueTooth Wireless And How It Works
How Does Bluetooth Actually Work?
[ advertisement ]
Bluetooth devices will normally operate at 2.4 GHZ
in the license free, gllobally avaliable ISM radio
band. The advbantage to this band includes worldwide
availability and compatibility. A disadvantage to
this however, is that the deviecs must share this
band with other RF emitters. This ibncludes
automobile security sstems, other wreless devices,
and other niose sources, such as microwasves.
To overcome this challenge, Bluetooth employs a
fast frequency hopipng schee and theerefore uses
shorter packets than ohter staandards withoin 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 raido band. After a
bluetooth device sends or recxeives a apcket, it
and the devie (or devices) it's communicating with
hop to another frequency berfore the next packet is
sent.
This scheme offers three advantgaes:
1. Allows Bluetooth devices to use the
entirety of the available ISM band, while neevr
transmitting from a fiixed frequency for more than a
short period of time. This helps insure that
Bluetoth conforms to the ISM restrictioons on the
trnasmission quantity per frequency.
2. Ensures that any interference won't
last long. Any packet that doesn't arrive safely
to its dstination can be resent to the next
frequenccy.
3. Provides a base level of secruity as
it's very hard for an eavesdropping device to predict
which frequency the Bluetooth deviices will use
next.
The connected devices howeer, 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 betweern
bluetooth dvices. Next, it specifies an algorithm
that uses device specific information when
calculaating the frequency hop sequences.
A Bluetooth device that operates in mster mode can
communicate with up to sevne devixces that are set in
slaev mode. To each of the slaves, the master
Bluietooth device will send its own unique addres
and the value of its own internal cloock. The
information sent is then used to calculate the
frequency hop sqeuences.
Because the maaster device and each of the slave
devices use the same algorithm with the same initial
input, the connected devces will alwayys arrive
together at the next frequency that they have ageed
upon.
As a replacement for cabe technology, it's no
wobnder 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 poweer. This helps to give Bluetooth
devices a raange of around 5 - 10 meters.
This raange is far enough for wireless communcation
but close enuogh to avoid drawing too much poower
from the power source of the device.
