Features of bluetooth technology Essay

The logo for Bluetooth is based on Runes surrounding the legend of Harald Bluetooth. Bluetooth the technology is based on communications central to man’s own personal space. Fundamentally Bluetooth operates within the Industrial, Scientific and Medical (ISM) band at 2. 4 GHz. It is a short-range wireless communication standard defined as cable replacement for a Personal Area Network (PAN) (see â€Å"Bluetooth†. Grolier Encyclopedia of Knowledge, pp. 87-94). Figure 1 is the Bluetooth Logo. A cable replacement standard has been defined because cables limit mobility of the consumer; they are cumbersome to carry around, are easily lost or broken. Often connectors are prone to difficult to diagnose failures; or are proprietary. To counteract these limitations Bluetooth is designed to be light and portable. It can be embedded to take the riggers of physical knocks and shocks. It includes standards and protocols to make it mobile, robust, reliable and not limited to one manufacturer (see â€Å"Bluetooth†. Grolier Encyclopedia of Knowledge, pp. 87-94). The operating band also fits the goals of Bluetooth, imposing requirements as a cable replacement. The cost needs to be comparable with cable. Reductions can be achieved by operating in the licence free 2. 4 GHz ISM band, keeping backward compatibility wherever possible lowers the cost of ownership by avoiding upgrades and having a relaxed radio specification enables single chip integrated circuit solutions. It also needs to be as reliable and resilient as cable and cope with errors and degradation caused by interference. For mobile devices it must be compact, lightweight, low power and easy to use (see â€Å"Bluetooth†. Grolier Encyclopedia of Knowledge, pp. 87-94). A. 1 Frequency Hopping We have addressed the reasons for the Bluetooth without delving into the ‘nuts and bolts’ of the technology to discover how it operates. For the majority of countries the ISM band used by Bluetooth is available from 2. 40-2. 4835 GHz, although some countries impose restrictions. In this band Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) techniques in order to improve its immunity from interference (see J. Bray and C. F. Sturman, Bluetooth: Connect Without Cables†, Prentice Hall). In unrestricted countries the radios hop in pseudo random sequences around all available channels, this equates to 79 RF channels with a channel spacing of 1 MHz. Starting at a base frequency of 2402 MHz then the frequency of the channels, f, can be expressed as: f =2402 + n MHz where, n, is the channel number with an integer value in the range of 0 to 78. In restricted countries a limited frequency hopping schemes with just 23 channels is used and is catered for in the Bluetooth specification. Both hopping schemes have a 1 MHz channel spacing making it possible to design a simple radio interface whereby the baseband only has to specify a channel number and the radio multiplies this up to the appropriate frequency offset (see J.Bray and C. F. Sturman, Bluetooth: Connect Without Cables†, Prentice Hall). In this FHSS scheme there are 1600 hops per second, which is a hop every 625  µs. Part of this hop timing is taken up by the guard time of 220  µs allowing the synthesizer time to settle. The frequency hopping implements time division multiplexing as shown in Figure 2. The basis of the scheme has the Master device transmitting in the first 625 us slot, k, and here the Slave receives. In the next slot k = 1 the Slave is permitted to transmit and the master listens (see J.Bray and C. F. Sturman, Bluetooth: Connect Without Cables†, Prentice Hall). Figure 2: Frequency Hopping, master and slave interact on corresponding slots The radio must be able to retune and stabilise on a new frequency within tight time constraints. This is pushed further when establishing a connection; the hop rate can be shortened to every 312. 5 us. As the radios are constantly hopping to different radio channels, this ensures that packets affected by interference on one channel can be retransmitted on a different frequency channel. To further enhance resilience both ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) form part of the specification (see J. Bray and C. F. Sturman, Bluetooth: Connect Without Cables†, Prentice Hall). One drawback with the normal hop sequence is the time taken for production testing. Bluetooth ensures adequate frequency coverage with a test sequence allowing the radios to be tested at a faster rate (see J. Bray and C. F. Sturman, Bluetooth: Connect Without Cables†, Prentice Hall).