Personal Area Network: A Bluetooth Primer

by Albert Proust


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Anyone who's ever wrestled with an octopus of black and beige cords coming out of the back of their laptop computer can appreciate the value of Bluetooth. Bluetooth is an emerging standard and a spec for (in the words of the Bluetooth SIG [special interest group]): "small-form factor, low-cost, short range radio links between mobile PCs, mobile phones and other portable devices." In other words, it's a wireless connection between PCs, peripherals, and portables that will let the devices share and synch information, without having to make a physical connection.

Bluetooth's original backer is the Swedish mobile phone maker, Ericsson, which named the technology for a 10th-century king of Denmark, Harald Blåtland, who unified the Danes and Norwegians. The spec's origins date back to 1994, when four companies joined Ericsson to develop the technology: Nokia, Toshiba, Intel, and IBM. Today, the Bluetooth SIG includes nearly 2,000 companies, and prototype devices are beginning to make their way into the marketplace.

Although the idea behind Bluetooth (wireless communication between devices) has been around, it's the momentum behind this standard and the agreement among hundreds of vendors and manufacturers that has brought it to the verge of becoming a reality. The power of the Bluetooth vision begins to really emerge when you consider a world of devices intelligently connected and carrying much of their communication load automatically.

Imagine having a Bluetooth-enabled phone or PDA on you. As you approach your home, you're able to control lighting, heating, even locks with your PDA. As you enter your home, you can use the same device to turn on the television set or the stereo system. Meanwhile, your refrigerator takes the initiative to update your shopping list. As you can see, the full picture includes a whole new level of automation where devices and appliances are programmed to communicate important information to each other, with or without human intervention.

How it works

Bluetooth uses the radio waves located in the frequency band of 2.4 GHz (2400 to 2483.5 MHz), an increasingly popular (and crowded) slice of the spectrum. In this band, Bluetooth transmits voice and data at flows lower than 1 megabit per second.

Bluetooth devices can function in two modes:

  • circuit switched (the most common mode for voice communications, on land and wireless digital networks), and
  • packet switched (the mode for Internet data, as well as for higher bandwidth mobile communication systems on the horizon, like GPRS [General Packet Radio Service]).

A device can use either one or both of these modes. In packet switched mode, connection is asynchronous with a rising flow of 57.6 Kbps to 721 Kbps. In the second case, connection is synchronous with a flow of 64 Kbps.

Piconet and Scatternet

A Bluetooth network (known as Piconet) can allow the interconnection of eight devices in a radius of 10 meters. This network can be fixed or provisional (a mobile or transitory network). In a Piconet, the Master seeks the devices in its entourage by emitting requests (broadcast). The slave answers with its identification number.

As many as 10 Piconets can overlap to form a Scatternet, linking up to 80 Bluetooth appliances. Beyond this, the network saturates. Indeed, only 79 transmission channels are employed by the Bluetooth protocol, a limit based on the frequency.

By default, Piconets transmit up to 10 meters (about 30 feet). However, you can increase it to 100 meters by increasing the power output of 100 mW (milliwatts), as opposed to the 1 mW of default Bluetooth. However, compared to GSM (Global System for Mobile communications), which consumes between 1.5 and 2 Watts, this is still a weak signal. Manufacturers are working to make Bluetooth devices that adapt to the necessary proximity, so as not to consume more energy than is necessary.

Bluetooth Sources

Bluetooth SIG
This site has details about the Bluetooth special interest group, its meetings, and its members. There's also a cartoony Flash animation on the history of Harald Blåtland and the Vikings.

Ericsson's T36 is the first Bluetooth-enabled phone.

Hung Up On Gadgetry
ZDNet's eWeek

The Personal Area Network

Bluetooth isn't designed to compete with wireless local area networks. Even its close-range throughput of 1 Mbps doesn't compare with the 11 Mbps that the emerging standard for wireless LAN, IEEE 802.11, offers.

Instead, Bluetooth's promoters are positioning it as the technology for the Personal Area Network (PAN), and are targeting appliances that don't require large flows -- like printers, personal computers, and mobile phones. One concept that's been put forward is the mobile PAN: a communication device clipped to your belt could contain a GSM transceiver that communicates with the wider world. Meanwhile, the same device has a Bluetooth transceiver that communicates with your headset (replacing your mobile phone), your PDA, your MP3 player, allowing all these devices to communicate with each other and the larger world.

Since it is not a very expensive technology (between $5 and $20 per chip), it can easily be placed in many devices. Also, Bluetooth doesn't require an access point, unlike the traditional radio operator networks. It's well suited for mobile devices, since it can join a local Piconet quickly, as soon as the two devices are in a sufficient perimeter.

And unlike infrared networks (like two Palm computers beaming each other), Bluetooth doesn't require you to align objects for them to communicate.

Towards the intelligent whole

Although most Bluetooth devices are still at the prototype stage, Ericsson has delivered the first Bluetooth-enabled phone, the Ericsson T36. This GSM phone uses Bluetooth to communicate with the handset. Thus, a user could wear the headset and chat away while the handset was stashed away in a briefcase. Of course, since the power of the technology is in the network, a single Bluetooth device without others to communicate with is ... well, a start at least.

Still, the momentum behind this de facto standard suggests a ripe market ahead: Cahners In-Stat Group predicts 1.4 billion Bluetooth-compatible devices by 2005. That's a conquest King Harald could be proud of.

Albert Proust is co-authoring a book on WAP for O'Reilly Media, Inc..


An Introduction to Lucent's Wavelan Wireless LAN Card

Connecting PCs to Apple's Wireless Airport

Affordable Wireless LAN Using Airport

Wireless News - from Meerkat

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