Eye On Electronics

Motor, Jan 2004 by Dale, Mike

Technology marches on! It's time to cut your teeth on yet another electronics communication standard with automotive applications: Bluetooth.

It seems that every model year brings something new, especially to upscale vehicles. This year the something new is called Bluetooth, a feature that makes it possible for a vehicle to answer that cell phone in your pocket when you get a call. Without your doing anything, the radio is turned down and the call comes in over the vehicle's sound system. A microphone in the sun visor or rear-view mirror picks up your half of the conversation.

Bluetooth is an open standard for a small, cheap, two-way radio chip set that can be made a part of the vehicle for the purpose of wireless communication. It offers a data rate of about 1 megabit per second and allows up to three high-quality voice channels to operate at the same time. When a vehicle is so equipped, it can link up to a variety of devices, such as laptop computers, personal digital assistants (PDAs) and cell phones that are also equipped with the chip set. Bluetooth is a multilayered standard that defines how the transmitters will work and how the digital exchange of information will be formatted.

With this system, up to seven different products can be linked together to form a Piconet. Like the Local Area Networks (LANs), in your office, the Piconet allows the sharing and transferring of data among devices that are linked. The difference is that the Piconet is a wireless system that searches for and links up to compatible devices without your being aware of it.

Because Bluetooth is the type of wireless system that's moving into vehicles, we'll focus our attention on it. But you should know that there are other wireless protocols out there that are enjoying widespread use. Wi-Fi is a type of wireless system with a larger range (1000 ft. or more) that's used to connect computers to the Internet without wires. When you see someone on park bench surfing the web on his laptop, he's probably linked up to a Wi-Fi site called a hotspot. Within range of the hotspot, anyone can link up to the web and surf for free. The town of Cerritos, California, recently announced that all 8.4 sq. mi. of it will become a web-enabled hotspot this year.

Another type of wireless system is GPRS/GSM. Its main use is for wireless voice and data transmission. Yet another is ZigBee, a wireless system used for monitoring and control purposes. Its something that might be used to control chemical or mechanical processes.

Ericsson, the Swedish cell phone maker, first came up with what would evolve into Bluetooth in 1994. They named it after the Danish King Harald Bluetooth, who brought Christianity to Scandinavia and who united Norway and Denmark in the early 900s A.D. (thus the inspiration for the name: uniting devices through Bluetooth).

A computer protocol is a structured method of how data to be exchanged is organized. The purpose of organizations such as SAE (Society of Automotive Engineers) and IEEE (Institute of Electrical and Electronic Engineers) is to set standards so many different companies can handle data in the same way. It's much the same as establishing standards for how bolts are to be made or materials are to be tested. With more than 2000 companies signed up to the Bluetooth standard, this dream of interconnectedness and compatibility is realized.

The overall IEEE standard that defines wireless communications is called IEEE 802.11. Variations of this standard, from 802.11a through 802.1Ig, exist to define different data exchange rates. The subset of IEEE specifications that cover Bluetooth is IEEE 802.15.1.

In the case of Bluetooth, the radio transmitter and receiver operate in the frequency range of 2.4 gigahertz (GHz), a band that requires no license and is designated worldwide for industrial, scientific and medical purposes (called the ISM band). This is the band garage door openers and baby monitors use.

These radios use a spread-spectrum, frequency-hopping, full duplex signal. Spread spectrum means that instead of transmitting on a single frequency, the information is transmitted by hopping randomly among 79 different channels, spaced IMHz apart in the 2.4GHz band. The frequency being used changes 1600 times per second. By doing this, a high degree of noise immunity and signal security is achieved. Full (Zuplex means that both sides of the conversation can be transmitted simultaneously. This device works like a telephone, not like a walkie-talkie.

The transmitter itself has an output power of only .1 watt and a planned range of 10 meters. Because the frequency is so high, the signal bounces around or propagates throughout this 10-meter radius. Unlike the channel changer for a television, line-of-sight reception of the signal is not necessary.

The beginning of a Bluetooth link-up starts with an interrogation signal. The transmitter sends out a signal asking any compatible piece of equipment within range to respond. When something does, a series of signals go back and forth, establishing the validity of the link. Once that occurs, the two units sync up, and the random frequency-hopping that the units are following begins.