| 单词 | Bluetooth |
| 释义 | Bluetooth A specification to standardize wireless transmission and synchronize data among a wide vari- ety of devices such as PCs, cordless telephones, headsets, printers, and PDAs.The initial effort (April, 1998) was in the form of a consortium of Intel, Microsoft, IBM,Toshiba, Nokia, Ericsson, and Puma Technology and was code-named Bluetooth after Harald Blaatand, the tenth-century Danish king who brought warring tribes together and unified Denmark. Bluetooth is now formalized in IEEE 802.15.1 (2002) as the specification for a wireless personal area network (WPAN) operating in the 2.45 GHz range of the ISM frequency band. Bluetooth employs frequency-hopping spread spectrum (FHSS), with devices stepping through a carefully choreographed pseudorandom hop sequence that makes data collisions highly unlikely even though large numbers of transmissions share the same frequency band. Devices hop through a set of 79 (United States and Europe) or 23 (Spain, France, and Japan) channels spaced 1 MHz apart at a rate of about 1600 hops per second, with each hop lasting 62.5 µs.The baseband signal is modulated using Gaussian frequency shift keying (GFSK). Bluetooth devices are organized into three classes based on transmit power and range: • Class 1 radios (maximum 100 mW) have a nominal link range of 100 meters, or 300 feet. Class 1 radios generally are employed in industrial applications. • Class 2 radios (maximum 2.5 mW) have a nominal range of 10 meters, or 3 feet, and are the most common. • Class 3 radios (maximum 1 mW) have a nominal range of 1 meter, or 3 feet. Bluetooth technology supports both synchronous connection-oriented (SCO) links for packet voice and asynchronous connectionless links (ACLs) for packet data. Bluetooth supports an asynchronous data channel in asymmetric mode of up to 721 Kbps in either direction and 57.6 Kbps in the reverse direction. 74570c02.qxd 9/11/07 12:18 PM Page 65 |
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