Bulletin Spring‧Summer 1997

The mobile unit itself has a liquid crystal display unit, a small keyboard for text input, a small audio-speaker for audio output, and a microphone for voice input. Each mobile unit has a system identity number similar to a telephone number. A VIP Net user can, with his mobile unit, send messages to and receive messages from other users of the system. Efficient Spectrum Usage Perhaps the mos t impo r t an t distinguishing feature of the VIP Net is the manner in which it broadens its spectrum usage by repeatedly usin g the same frequency spectrum i n a number o f different zones. This is done by dividing the area in which the Net is active into honeycomb-like zones; the same frequency (e.g. 900 MHz) can be used by a number of non-adjacent zones, while another set of similar non-adjacent zones can use another frequency (e.g. 901 MHz). The fact that the zones that share the same frequency are not close neighbours is what makes the frequency sharing feasible and devoid of disturbance. Ample User Services VIP Net users have no need for telephones and human intermediaries when they send out messages. And , through gateways connected to wire-based computer networks such as the Internet, they can also send and receive electronic mails to and from these networks. The VIP Net provides several modes of messaging services: priority messages, scheduled delivery, and acknowledgment service. It also supports special services like multicast, voice-to-text translation, directory information, and user-defined applications such as quotations of stock market prices, direct placements of sales orders, banking and reservation services. Each special service provider is given a system identity number. Users can request these services by sending messages to the corresponding numbers. The mobile unit also has buffers (i.e. functions) for text and voice messages. To request text-to-voice translation, a user need onl y send a message containing the text and the type of translation requested to the translation service provider in the CSPU. Three Phases of Research In the first phase of the research, which was completed by the end of 1993, a simple one cell system consisting of one base station and three mobile units was successfully implemented to demonstrate the basic concepts. The mobile un it prototype used for test purposes is shown on page 32. I n the second phase, wh i ch was completed by the end of 1995, the investigators were partially supported by a grant of HK$257,000 from the Research Grants Council. A network o f three cells was implemented along w i t h a more sophisticated version of the mobile units. In the final phase, which is being supported by the Hong Kong Industry Department and should be completed by Chinese University Bulletin Spring • Summer 1997 3 4