Radios Waves and Piconets

Bluetooth does all this by embedding a small, low-powered radio-on-a-chip into a traditional

electronic device. This radio—and the chip-based software associated with it—is capable of

transmitting and receiving both data and voice communications from other such devices.

Bluetooth radios use a radio band (called the industrial, scientific, and medical band—or ISM,

for short) between 2.4 and 2.48 gigahertz (GHz). Because the radios are incorporated into

small computer chips, they have a very small form factor and can, eventually, be produced at

relatively low cost. The combination of small size and low cost should help to make

Bluetooth technology ubiquitous in a variety of electronic devices—especially in those with

portable applications.

Note The ISM band is unlicensed, and thus available for use at no charge. (It is also shared

with other types of non-Bluetooth communications.)

When one Bluetooth device senses another Bluetooth device (within about a 30-foot range),

they automatically set up a connection between themselves. This connection is called piconet,

and is a kind of mini-network—a personal area network (PAN), to be specific. In a piconet,

one Bluetooth device is assigned the role of master, while the other device—and any

and is a kind of mini-network—a personal area network (PAN), to be specific. In a piconet,

one Bluetooth device is assigned the role of master, while the other device—and any

one Bluetooth device is assigned the role of master, while the other device—and any

subsequent devices, up to eight in total—is assigned the role of slave. The master device

controls the communications, including any necessary transfer of data between the devices.

Since Bluetooth signals are sent via radio waves, walls and other physical barriers do not

present the same problem that they do for infrared signals, which must operate within a

narrow line-of-sight window. Bluetooth’s radio frequency (RF) signals can travel through

most solid objects, so Bluetooth devices can be used in a small office (walls and cubicles are

invisible) or from inside a contained space (such as a briefcase or shirt pocket). As long as

two Bluetooth-enabled devices are no more than 30 feet apart, they’ll always be able to talk to

each other.

Let’s look at an example of how Bluetooth technology might be employed in a network of

devices within your home. As you can see in Figure 1.1, in this home of the not-too-distant

future, every electronic device is enabled with Bluetooth technology—a desktop PC, printer,

future, every electronic device is enabled with Bluetooth technology—a desktop PC, printer,

scanner, PDA, cordless telephone, and all the components in the home theater system.

Figure 1.1: Bluetooth technology can connect all your household electronics.

Each of these devices is assigned a specific electronic address by its manufacturer. In

addition, each device is programmed to automatically look for other devices within a

predefined range, so that all similar devices automatically recognize each other—and

automatically establish their own private piconet. This is done when each device, as it powers

up, sends out a signal asking for responses from other devices within the predefined range;

any responding devices are automatically added to the first device’s piconet.

Note Each type of Bluetooth device is assigned a particular range of addresses—so that all

cordless phones, for example, have addresses that fall within a predefined range.

As each device in our home of the future is powered on, three separate piconets are

established. The home theater components establish one piconet, the personal computer and

accessories (printer, scanner, etc.) establish a second piconet, and the cordless phone

establishes a third piconet (between the handset and the base station—both of which include

Bluetooth radios). Data (and voice, in the case of the cordless phone) are then routinely

exchanged between all the devices within each individual piconet—the DVD player beams a

movie to the A/V receiver, the computer sends formatted data to the printer, and so on. And

all this happens without any data being inadvertently sent to the wrong device or network.

Of course, some devices can be instructed to work across different piconets. In our wireless

home example, let’s say that we’ve programmed the PDA to function not only with the

computer piconet (automatically synchronizing key data) but also with the home theater

piconet. Programmed in this fashion, the PDA can function not only as a personal digital

assistant, but also as a wireless remote control unit for the home theater system, essentially

bridging the two individual networks.

Note In Bluetooth terminology, when you connect two or more piconets together, you create a

One can also imagine the desktop PC operating across piconets. There is no reason why your

PC, which might contain thousands of songs encoded in the MP3 format, can’t use Bluetooth

to beam the MP3 playback directly to your audio/video receiver—and also connect your home

theater system directly to the huge database of audio files available on the Internet.

The neat thing about this type of Bluetooth-enabled home is that all this interaction—and

more that we can’t even imagine today—will take place relatively invisibly, and without

messy cables strung around and across the room.

Note Of course, Bluetooth isn’t the only technology available for short-range wireless

communications. HomeRF and IEEE 802.11 (both discussed in Chapter 9, “Competitive

and Complementary Technologies”) are two competing standards for wireless

and Complementary Technologies”) are two competing standards for wireless

networking that can be used either beside or in place of Bluetooth. While it’s probably a

good bet to assume that the combined industry might assembled behind Bluetooth bodes

well for its ultimate acceptance as the de facto industry standard, there are no guarantees

that a better or cheaper solution won’t come along and steal Bluetooth’s thunder—and

market potential.