Chapter: Network Concepts and Standards
To explore low power design, a portable multimedia terminal, the InfoPad, which supports speech I/O, a pen input, text/graphics output and full-motion video is being implemented. The availability of communications between the terminal and computational resources at a fixed base-station at the other end of the wireless link provides a major degree of freedom for optimizing power; i.e any computation that does not have to be performed on the terminal (such as general purpose computation or application specific tasks such as speech and handwriting recognition) can be removed from the terminal. Other techniques for achieving low-power include optimizing algorithms for minimal switching activity, using parallel architecture that enables slow and low-voltage operation, optimizing memory structures for reduced capacitance, and utilizing low-power cell libraries.
Figure: Schematic of Infopad
wireless computing environment.
See an enlargement.
Hear P.I. Bob Brodersen speak about the project.
Slides describing the project
The portable multi-media terminals will offer access to large commercial databases that contain transitory information such as international and domestic news, financial information, traffic data, transportation schedules, voice and electronic mail, telephone directories, etc. For several years, information such as encyclopedias and data bases have been distributed via CD-ROM in a relatively static form. Not only can these services be provisioned in a more dynamic format via a wireless radio link, but they can be offered in a more physically comfortable setting by minimizing the weight that a user must carry. The multi-media terminal envisioned would also be able to provide a user interface in an X-windows distributed computing environment. The X-functions are presumably best performed in the local base station, where processing power is abundant, while computations and data base searches are done remotely. Intensive task can be performed by supercomputers connected with base stations through a high speed backbone network.
In this approach, almost no error-critical data is sent over the wireless link. Since most of the image processing and X-server functions are performed in the base station, the power consumption in the terminal can be kept small. It implies that the wireless link to the terminal needs to support dynamic screen data at high rate. This requires a downlink (base station to terminal) with relatively high bandwidth, which may however tolerate occasional signal outages during periods of excessive channel load by other users. The tolerance of signal outages substantially reduces the transmission overhead that would be required other- wise to achieve almost error free exchange of data.
The situation in the uplink is quite different: Many existing notebook computers use a key pad for entering data into the system, but simplified entry mechanisms such as voice recognition and hand-writing recognition are likely to be available in the near future. In order to minimize terminal power consumption, speech recognition will be performed in the base station rather than in the terminal itself. Speech compression techniques have been refined and are available for instance for GSM digital telephony. Such schemes are likely to allow power efficient implementation in the near future. These schemes imply that the uplink (terminals-to-base station) only needs to support relatively low bit rates, say up to 10 kbit per second in a burst mode.