Bluetooth technology

Named after a tenth-century Danish king, Bluetooth is a specification for a small form-factor, low-cost radio solution providing links between mobile computers, mobile phones and other portable handheld devices, and connectivity to the internet which it is hoped will revolutionize mobile computing and communications by providing freedom from wired connections. The initiative is backed by leaders in the telecommunications, computing, and network industries – including 3Com, Ericsson, IBM, Intel, Lucent, Motorola, Nokia and Toshiba – and more than 1300 adopter companies. Microsoft’s decision to join the group driving the standard at the end of 1999 significantly increased hopes that one of the problems that had afflicted Bluetooth hitherto – namely that the standard had yet to extend beyond hardware compatibility to encompass the software that runs across it – would not be allowed to undermine the standard to the extent that it had its forerunner, infrared.

Bluetooth’s chief advantage over infrared is that Bluetooth does not require line of sight. Its backers hope the component costs will be so low that it will ultimately replace infrared. Others believe that, although there are clear areas of overlap, IrDA and Bluetooth are complementary with either being the most appropriate for certain applications and intended usage models.

Bluetooth operates in the unlicensed Industrial Scientific and Medical (ISM) 2.4GHz band, ranging from 2.4 to 2.4835 GHz in the US, Japan and Europe. Parts of this band are also available in France and Spain. By using the 2.4 GHz band, Bluetooth Wireless Technology promises to be a universal wireless solution. Essentially, it is the same kind of microwave radio technology that has given us wireless door chimes and automatic garage door openers. It draws heavily on existing wireless LAN technology since it is based around the IEEE’s 802.11 – the existing standard for wireless Ethernet. The main differences are that in order to consume less power, Bluetooth is initially restricted to an operating distance of just 10 metres and a speed of approximately 1 Mbit/s.

Bluetooth isn’t being touted as a replacement for high-speed wired connections like USB or IEEE 1394 but rather as a technology of convenience. The technology will work much like cordless home phone handsets where there are transceivers (portable devices) and base stations. It’ll be possible to operate between eight and ten devices within the same cell, with seven offering data services and three offering voice comms. The catch is that an individual Bluetooth device will actually enjoy an asymmetric data connection – 721 Kbit/s in total, with the up channel running at 56 Kbit/s.

Bluetooth modules have transceivers that transmit or receive data using radio waves. These modules scan for and detect other Bluetooth devices with which to either send or receive data. When Bluetooth devices come within range of each other, they establish contact and form a temporary network called a Personal Area Network (PAN). A network session must be established before any data will be transmitted among devices; for security reasons the user must grant manual networking approval to devices that have not been authorised as companion devices belonging to the same PAN.

In order for two Bluetooth devices to communicate, they must first acknowledge and identify each other. If both devices belong to the same Personal Area Network (PAN) and have been authorized by their user to automatically communicate, then communication is instant. If the devices do not belong to the same PAN, the user must manually approve and initiate the communication. When within range of unrecognized Bluetooth modules, the devices will prompt the user to permit a networking session with the new device. The user can approve or deny the network request. The owner must manually approve communication with a Bluetooth device that has not been approved for communication in that particular PAN.

Bluetooth modules use Frequency-Hopping Spread Spectrum (FHSS) techniques for voice and data transmission. Spread Spectrum communication techniques have been used for many years by the military because of their security capabilities. FHSS uses packet-switching to send data from the transmitter of one Bluetooth module to the receiver of another. Unlike circuit-switching, which establishes a communication link on a certain frequency (channel), FHSS breaks the data down into small packets and transfers it on a wide range of frequencies across the available frequency band. Bluetooth transceivers switch or hop among 79 hop frequencies in the 2.4 GHz band at a rate of 1,600 frequency hops per second. This technique trades off bandwidth, in order to be robust and secure.

A Bluetooth device will contain one or more profiles that will inform other Bluetooth-compliant devices what it is and what it can do. This mechanism allows devices to attempt to synchronize their databases as soon as they recognize each other. The result is that a Bluetooth phone, for example, could automatically create a link to a Bluetooth-enabled PC and Bluetooth wireless earphone. Users would then be able to use the earphone to talk on the phone or use their PC to connect to the Internet through the digital phone – all without wires or setup effort.

Originally slated for availability in Mid-1999, it wasn’t until late 2000 that the first Bluetooth-enabled devices began to emerge. Initial impressions were favourable, with earlier fears that Bluetooth and 802.11 may interfere with each other apparently unfounded and the level of software support appearing to be good. Typically, a Windows Explorer extension – Bluetooth Neighbourhood – shows all of the Bluetooth devices within range, along with a list of services available from the remote devices. The creation of a connection between two Bluetooth PCs involves the dragging of a service icon onto the remote computer’s icon and file-transfer is simply a matter dragging and dropping files from one machine to another within the Bluetooth Neighborhood.