Personal-area networks


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Most of us use a Personal Area Network (PAN) in our daily routines in front of our desktop and notebook PCs. PANs are technically defined as any network used to communicate with other slave devices located close to a master device. The most common PAN might be the connection between a PC and another device such as a printer or scanner.

PANs are not limited to devices wired to each other; they can also be created through a Wireless Personal Area Network (WPAN.) The most common WPAN technology is Bluetooth. Bluetooth is a common way to connect cell phones to wireless headsets. Many new automobile manufactures include Bluetooth technology in models to integrate cell phones, GPS or digital audio players. The nice thing about Bluetooth-enabled devices is the ease of connection: once the devices are properly configured, they will recognize each other and start communicating once they are in range. Other technologies that support PANs are Ultra-Wideband (UWB), Zigbee and a futuristic application using the human body to pass electrical information. These all have specific industrial applications. Let's look at each of them.

Bluetooth

In 1994, two engineers from Ericsson developed the initial implementation of Bluetooth. The IEEE, under the designation of 802.15.1, subsequently standardized the specification in 1998.

Bluetooth uses the Industrial Scientific and Medical (ISM) band in the 2GHz spectrum. This band is used for a number of applications, including wireless Ethernet technologies such as Wi-fi, as well as many other scientific and medical devices. The rules for operating in this spectrum require that communication be spread over 79 1MHz channels to make more efficient use of the spectrum. Overall, the bandwidth of Bluetooth does not exceed 1Mb/s. There are two primary methods to achieve this spreading across the permitted bandwidth:

  1. Direct Sequence Spread Spectrum (DSSS). The power is spread across the available channels to achieve wide bandwidth and reduce power. DSSS might look familiar as it is typically used for 802.11x wireless Ethernet.
  2. Frequency Hopping Spread Spectrum (FHSS). The carrier is randomly sent on a (single) different channel. This method tends to be more secure due to the random nature of the hopping.

The power level of Bluetooth devices are typically limited to 1mW and yield a range of about 30 feet, however the specifications permit a power level up to a maximum of 100mW, which support communications in excess of 300 feet.

Bluetooth can also operate in either of two modes, circuit switched or packet switched, depending on the type of application for which it is used, i.e. voice or data. This flexibility allows the creation of a small complex network with other devices. As many as eight devices can be networked to form a piconet; additionally, as many as 10 piconets can be linked to form a scatternet.

A Bluetooth network is created by using a master device and as many as seven slave devices. The master polls all the active clients on the network sequentially. One characteristic that makes Bluetooth unique is that any host can become a client and vise versa.




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