Bluetooth Technology

Last week I sprained my ankle due to circumstances beyond human control, or were they? As I got out of my car I was balancing my bag in one hand, my groceries in the other, all while holding the phone up to my ear using my shoulder. I then proceeded in the house where I walked into my room. This is where the disaster took place. I own a stereo, a computer, and a house phone, which are all located in my room. I am an electronic junky so of course they are all connected with cords, and unfortunately the cords run all through the room. As I walked in the room I tripped on one of the many cables going across the room and proceeded to sprain my ankle. Well, you may say, "how could all of this have been avoided?" A simple invention called Bluetooth would have done the trick. Bluetooth eliminates the wires, cords and cables needed for devices to communicate.

So what exactly is Bluetooth Technology? Its how mobile phones, personal digital assistants, computers, and a wide variety of other electronics can inter-connect using short range wireless connectivity.

In today's world Bluetooth makes things flow easier and smoother. Imagine coming home talking on your Bluetooth enabled mobile phone and automatically having the call transferred to your Bluetooth enabled house phone. That Mp3 you downloaded on your phone earlier that day automatically transfers to your Bluetooth enabled stereo. Your home CPU automatically downloads the picture you took on mobile phone and sends it through Bluetooth to your printer, where a beautiful picture prints out. All of this happens with out you pressing a button, or sending a command. This is the type of power that Bluetooth technology enables us to have. With this type of power at our hands, our opportunities for it are endless.

Besides cleaning up the mess of cords and wires, Bluetooth also has many other benefits. One of those benefits is by using Bluetooth you will save power. Bluetooth does not use a lot electricity so it allows you to save battery life on many devices. Another benefit of using Bluetooth devices is that their cost is minimal. When comparing them to the cost of cords and cables, they do not cost much more. This makes them a cost effective and more convenient alternative to using cords and cables.

So how did Bluetooth come about? Bluetooth is a specification for a wireless technology, developed by members of the Bluetooth SIG (Special Interest Group). The SIG was founded in February 1998, and initially consisted of the five companies Ericsson, Intel, Toshiba, Nokia & IBM. These companies worked diligently to come up with the technology we call Bluetooth. Today more than 1800 companies have joined the SIG to work for an open standard for the Bluetooth concept. Today the SIG consists of 9 promoter members Motorola, Lucent, Toshiba, Lucent, Microsoft, 3Com & Panasonic, IBM, Intel, Nokia & Ericsson, and a host of Associate member companies. By signing a zero cost agreement, companies can join the SIG and qualify for a license to build products based on the Bluetooth technology. To avoid different interpretations of the Bluetooth process and how a specific type of application should be applied to Bluetooth, the SIG has defined a number of user models and protocol profiles.

To meet the requirements set by the air interface, a frequency band between 2.400 and 2.500 GHz was selected. This radio frequency band is the Industrial-Scientific-Medical, ISM band and ranges from 2.400 to 2.4835 GHz. As a result, Bluetooth devices must be able to act in the range from2.400 to 2.500 GHz and be able to select a part in the ISM band where they can communicate. The ISM band is open to any radio system. Cordless telephones, garage door openers and microwave ovens operate in this band, with microwave ovens being the strongest source of interference. Bluetooth devices use a technique called frequency hopping to minimize these interferences from other networks that use the ISM band. With frequency hopping Bluetooth devices randomly hop between frequencies up to 1600 times per second which is much faster than other type of device that uses the ISM band is capable of. This means that if another device, such as a 2.4-GHz cordless phone, interferes with a Bluetooth device n at a particular frequency, the interference only lasts for about 1/1600 of a second until the Bluetooth device hops to another frequency. This gives Bluetooth devices less susceptible to interference from other ISM band devices.

Bluetooth units connect to each other forming piconets, consisting of up to eight active Bluetooth units. Any two Bluetooth devices that come within range of another can set up a connection. When a connection is established a piconet is formed. In a piconet there is a master device and the rest of the devices act as slaves. Up to eight active devices can form a piconet, which is defined by the channel these units share. The number of devices in a piconet is actually unlimited even though you can have only eight active devices at the same time. There is no difference in the devices that can be a master and a slave, so any unit can be a master. The first or establishing unit of the piconet becomes the master unit. The roles in a piconet can change but there can never be more than one master of an individual piconet.

The communication process in the piconet allows for only the master device to control the traffic inside of the piconet. Slave units may only send in a slave to master mode. If the master does not have any information to send to the slave, a packet with access code and header only is sent. That way every slave device is addressed in a specific order, and may only send upon being addressed. This eliminates collisions between different sending slave devices.

Before a device has joined a piconet it is in standby mode. In this mode, an unconnected device periodically sends a signal about every two seconds looking for another device to pair with. To pair devices with an unknown addresses an inquiry signal is transmitted initially. This signal is used to inform the master unit of the slave's identity within range. Devices receiving this message respond with their identity and system clock. The inquiry message is typically used for finding Bluetooth devices, including public printers, fax machines and similar devices with an unknown address.

As you can see there are many different Bluetooth enabled devices. Therefore, there may be more than one piconet in an environment. Multiple piconets are called scatternets. Within one scatternet all devices share the same frequency range but each piconet uses different frequency hopping sequences and communicates on different channels. If you have a lot of different Bluetooth devices that you want to connect, your best bet would be to form multiple piconets