Topics: Bluetooth, Wireless, ISM band Pages: 6 (1820 words) Published: October 8, 2007
Bluetooth technology
- a standard for wireless networking of small peripherals

Bluetooth has now established itself in the market place enabling a variety of devices to be connected together using wireless technology. Bluetooth technology has come into its own connecting remote headsets to mobile phones, but it is also used in a huge number of other applications as well.

Beginnings ...
Bluetooth technology originated in 1994 when Ericsson came up with a concept to use a wireless connection to connect items such as an earphone and a cordless headset and the mobile phone. The idea behind Bluetooth (it was not yet called Bluetooth) was developed further as the possibilities of interconnections with a variety of other peripherals such as computers printers, phones and more were realised. Using this technology, the possibility of quick and easy connections between electronic devices should be possible.

It was decided that in order to enable the technology to move forward and be accepted as an industry standard that it needed to be opened up as an industry standard. Accordingly, in Feb 1998, five companies (Ericsson, Nokia, IBM, Toshiba and Intel) formed a Special Interest Group (SIG). Three months later in May 1998, Bluetooth was publicly announced with the first specification following on with the first release of the standard in July 1999. Later more members were added to the group with four new companies, Motorola, Microsoft, Lucent and 3Com, joining the group. Since then more companies have joined and the specification has grown and is now used in a large variety of products.

The name
The name of the Bluetooth standard originates from the Danish king Harald Blåtand who was king of Denmark between 940 and 981 AD. His name translates as "Blue Tooth" and this was used as his nickname. A brave warrior, his main achievement was that of uniting Denmark under the banner of Christianity, and then uniting it with Norway that he had conquered. The Bluetooth standard was named after him because Bluetooth endeavours to unite personal computing and telecommunications devices.

Bluetooth is a wireless data system and can carry data at speeds up to 721 Kbps in its basic form and in addition to this it offers up to three voice channels. Bluetooth technology enables a user to replace cables between devices such as printers, fax machines, desktop computers and peripherals, and a host of other digital devices. Furthermore, it can provide a connection between an ad hoc wireless network and existing wired data networks.

The technology is intended to be placed in a low cost module that can be easily incorporated into electronics devices of all sorts. Bluetooth uses the licence free Industrial, Scientific and Medical (ISM) frequency band for its radio signals and enables communications to be established between devices up to a maximum distance of 100 metres.

RF system
Running in the 2.4 GHz ISM band, Bluetooth employs frequency hopping techniques with the carrier modulated using Gaussian Frequency Shift Keying (GFSK).

With many other users on the ISM band from microwave ovens to Wi-Fi, the hopping carrier enables interference to be avoided by Bluetooth devices. A Bluetooth transmission only remains on a given frequency for a short time, and if any interference is present the data will be re-sent later when the signal has changed to a different channel which is likely to be clear of other interfering signals. The standard uses a hopping rate of 1600 hops per second. These are spread over 79 fixed frequencies and they are chosen in a pseudo-random sequence. The fixed frequencies occur at 2400 + n MHz where the value of n varies from 1 to 79. This gives frequencies of 2402, 2404 ….. 2480 MHz. In some countries the ISM band allocation does not allow the full range of frequencies to be used. In France, Japan and Spain, the hop sequence has to be restricted to only 23 frequencies because of the ISM band allocation is...
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