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:

1.  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.

2.  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.

3.  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.

In the United States, Bluetooth gets absolutely no respect.  It is however, becoming more and more common in notebooks, PDAs, and especially cell phones.  Bluetooth will provide wireless users a way to transmit small amounts of data over short distances.

Now, Bluetooth is facing stiff competition from new wireless technology.  Referred to as UWB or Ultra Wideband, it promises data transfer of up to 480 MB a second – while most current Bluetooth devices transfer data up to 721 KB a second.

For the time being, Bluetooth devices are surely cropping up.  Below, we will look at some of  the accessories offered with Bluetooth technology.

Talking to the dashboard

When pairing it with a cell phone, the CCM Blue Warrior car kit becomes a great speaker phone that plugs into the power adapter of your vehicle.  The noise cancelling microphone will reduce background noise efficiently, with the large buttons making adjusting the speaker volume a snap.  Although the Blue Warrior is far from sexy or sleek, it’s
very practical.

Tiny tuning box

Part MP3 player and part hands free phone, the compact and lightweight Sony HBM-30 is an attractive gadget that lets you accept calls with minimal interruption of your tunes.  When you get an incoming call it will automatically pause your music, then you speak into the built in microphone that you  can wear around your neck or clip to your clothes.

The pen

With Nokia’s SU-1B digital pen, you can doodle and make hand written notes in ink on a special pad then transmit them from the pad to your Bluetooth phone.  Being an alternative to typing on a cell phone keypad, the pen is very handy, although a pricey tool from MMS fans.

Snapshots

If you want to make slide shows with your camera photos, the Nokia SU-2 image viewer will let you disply your pictures on a TV or projector.  Simply hook this square gray device to your TV’s input with the built in cable, then beam the pictures to the SU-2 from your Bluetooth enabled phone and the photo fest will begin.

This device is a snap to set up and use, although it displays resolutions of up to 640 by 480.  If you have a newer phone that takes high resolution photos, you won’t be able to use the Nokia SU-2 image viewer.

Keep in mind, the 640 by 480 pixel photos will appear blocky on TV screens, no matter what you  do.  If your phone can send batches of photos, you can create a slide show – although Nokia claims you can use sequentially beamed shots as well.