The PARCTAB transceiver (aka “deathstar”) pictured above, serves as a communication hub for any PARCTABs located in its particular cell. Typically its communication radius is about 20 feet—less if limited by the walls of an office. The transceiver hardware performs numerous functions in addition to transmission and reception, including:
Coding and decoding infrared packets;
Executing link-level protocol checks (e.g., format or checksum);
Providing a serial interface to a workstation’s RS-232 port;
Indicating visually its communication status.
We designed the transceiver conservatively to ensure reliable communication. For transmission, two dozen IR emitters are placed at 15 degree intervals on a circular printed circuit board. For reception, two detectors provide a total viewing angle of 360 degrees (shown above). The transceiver is designed to be attached to a ceiling, preferably in the middle of a room as this usually gives an unobscured communication path over the required area. But since transceivers and PARCTABs can sense infrared light reflected from surfaces, it is not necessary that there be a line of sight between the two for them to communicate.
The PARCTAB system is a research prototype developed at Xerox PARC to explore the capabilities and impact of mobile computers in an office setting. This research is part of PARC’s Ubiquitous Computing research program.
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