• Bluetooth Explained

    Bluetooth is an open specification created by the five founding companies of the Bluetooth Special Interest Group (SIG). Those five founders are Ericsson, IBM, Intel, Nokia, and Toshiba. Since then, three companies have joined-Agere, Microsoft, and Motorola-to form the PromoterGroup for the Bluetooth SIG. More than 2,000 companies have become members of the Bluetooth SIG.

    Bluetooth specifies a standard by which electronic equipment can make its own wireless connections to other electronic equipment. Computers and cell phones are obvious candidates for Bluetooth technology, with computer peripherals such as keyboards, mice, monitors, printers, scanners, and fax machines being other almost equally worthwhile choices. Beyond that, any electronic equipment could conceivably be made more effective by a wireless connection with other equipment. Music file players and headphones, televisions, even your coffee maker might benefit.

    Among the many advantages to the Bluetooth solution, perhaps the following stand out:

    1. Bluetooth is wireless. Other standards can claim this as well, of course. Wi-Fi, infrared, and cable synchronizing systems are all wireless. And with good reason. Wires are a pain to deal with. Bluetooth is one solution to that problem.

    2. Bluetooth is portable. Your Wi-Fi network stays in one place. Bluetooth, you can take on the road. Your Bluetooth devices fit in your briefcase and talk to each other. Take them back home and they talk to the Bluetooth devices you left behind.

    3. Bluetooth is inexpensive. Adding Bluetooth technology to a device won't cost the manufacturer an arm and a leg. You won't have to pay a lot to get a lot.

    4. Bluetooth is automatic. Once you've taught two Bluetooth devices to "see" each other-a simple process called "pairing"-they'll find each other automatically anytime they come within range.

    How It Works

    Bluetooth uses radio waves around the 2.45 GHz band to communicate. This is the same band used by devices such as some cordless phones, garage door openers, and baby monitors.

    A Bluetooth device sends out a comparatively weak signal-only 1 milliwatt. Cell phones can send out a signal 3,000 times as powerful. They need to reach the nearest cell tower. Your Bluetooth device only needs to reach about 10 meters (33 feet). Its purpose is to get nearby devices to talk to each other. This weak signal helps minimize interference with a computer, cell phone, or television. But the signal is still a radio wave. It goes through walls and into the next room without difficulty.

    Another way Bluetooth avoids interference is by frequency hopping. We said earlier that Bluetooth uses the band "around" 2.45 GHz to communicate. To be specific, it takes the range from 2402 to 2480 MHz and divides it up into 79 channels of 1 MHz each. Bluetooth then "hops" from channel to channel at a rate of 1600 times per second. Even with many Bluetooth devices in the same room, it's unlikely they'll interfere with each other. And if they do, it will only be for 1/1600th of a second. The error correction can easily take care of whatever information was missed.

    Bluetooth devices are introduced to each other via a simple process called "pairing." Once they've been paired, they're friends for life (or until you decide to unpair them). Once they are paired, they form what is called a "piconet." A piconet can consist of up to 8 Bluetooth devices with one playing the role of "master" (receiving information) and the other 7 of "slave" (giving information).

    That means when the devices come in range of each other, they automatically strike up an electronic conversation. This conversation consists of each device asking the other one or both of two questions (depending on how you have it set up): 1) Do you have any information to share with me? 2) Do you need me to share any information with you? If the answer to either question is "yes," the devices will automatically configure themselves as a "master" that receives information and a "slave" that gives information. If information needs to travel both ways, they can then switch roles.

    That example uses a "half-duplex" link in which information can travel both ways, but only one way at a time. For other uses, such as a cordless phone, Bluetooth can establish a "full-duplex" link, allowing information to travel both ways simultaneously. Bluetooth can send data at greater than 64,000 bits per second in a full-duplex link. That's enough to support several human voice conversations simultaneously.

    So even at full-duplex, Bluetooth is plenty fast. At half-duplex, though, Bluetooth connection can be more than 10 times as fast. This is useful for a device such as a printer. Mostly, you want to send information to the printer; you don't need a lot of information back. Bluetooth can accommodate this by transmitting data to the printer at 721,000 bits per second in a half-duplex link. For the printer's response, only 57,000 bits per second or so needs to be allocated. That's plenty for the printer to send back messages about paper jams and being offline.

    It's possible for one Bluetooth device to be part of more than one piconet at a time. This is called a "scatternet." Here's a simple example. You may get a Bluetooth headset for your cell phone. You pair the headset with the cell phone and you can talk on the headset via the cell phone without any wires connecting the two devices. That's one piconet-the headset and the cell phone.

    Now your cell phone also has an address book that you would like to synchronize with your Outlook Contacts folder on your desktop PC. So you pair the cell phone with the PC. Now changes to one address book will get recorded in the other. The PC and the cell phone form a second piconet. The PC and the headset don't need to be aware of each other at all.