Bluetooth

27/09/2005

The 2004 GIM International Product Survey on total stations (October issue, page 49) indicates how major manufacturers have begun to apply Bluetooth technology in their instruments. But what is Bluetooth? How does it work?

Henk Key, contributing editor, GIM International

Radio Signals
The components of computers and instruments when connected, make up a system of electronic devices. They communicate with each other through wires, cables, radio signals or infrared using a variety of connectors, plugs and protocols. Bluetooth instead uses radio signals to enable communication between devices. Small built-in transmitters/receivers communicate on a frequency of 2.45 gigahertz, the ISM (Industrial, Scientific and Medical) range. These transmitters avoid interference with other devices in two ways. Firstly, they produce weak signals so that the range of communication is limited to about 10 metres. Secondly, they switch signals 1,600 times a second between 79 channels within the 2.45 gigahertz frequency: so-called spread-spectrum frequency hopping. As a result, any remaining interference will last no more than a fraction of a second. As soon as Bluetooth devices come within range of one another they recognise each other using the programmed address of each device, so creating a Personal Area Network: PAN or piconet. Once a PAN
is established all its members hop frequencies together simul-taneously to stay in touch. A PAN consists of a master and up to seven slaves, transmitting in timeslots and sharing a common communication data channel with a capacity of one mega-bit per second; headers and handshaking procedures consume about 20% per cent of this capacity.

Making Life Easier
The advantages of Bluetooth are:

wireless, requiring no cables or connectors.
inexpensive.
fully automatic, needing no manual connection.

Today’s geomatic instruments are very compact as a result of minimising the size of all components and placing all inside one housing, thus bypassing the necessity for cable connections. Bluetooth technology enables manufacturers to separate parts to further reduce weight and size of the main instrument. Examples are:

using the keyboard section as remote control.
leaving the data storage unit in the instrument-case.
transfer of data from instrument to vehicle laptop.

But it is not only the surveyor in the field who benefits. In the office, Bluetooth enables data transfer from any geomatics instrument to processing computers. Also, information such as digital photos and audio files present on one device may be added to surveyed points on another, cable-free. The amazing and confusing mess of cables necessary to connect printer, scanner, screen, mouse and keyboard in the office is suddenly defunct.
And many more applications will be found. Bluetooth can thus make life much easier for both field surveyor and computer operator.

Name
Harald Bluetooth was king of Denmark in the late 900s. He introduced Christianity and left behind him a large monument, the Jelling rune stone. Bluetooth was killed in 986 during a battle with his son. The choice of his name says little about the way the technology works but does indicate how important to the communications industry are companies from the Baltic region.

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