When Beepers Alone Can't Help
Try the VIP Net -- A High-Tech Messaging System

Limitations of the Existing Paging Networks System

The paging system has recorded phenomenal growth since its introduction and few telecommunication systems can claim to have a similar market penetration rate. It however has one serious drawback in its current form -- it is not an independent system. To send a message, a user has to telephone a paging system operator to broadcast it. This system may also pose a serious bottleneck in areas where telephone services are not readily available.

It is these considerations that motivated Prof. W. S. Wong of the Department of Information Engineering to plan a prototype mobile cellular messaging system with his colleague Prof. Yum Tak Shing. In this project they are aided by Prof. Jiandong Li (Xidian University, Xi'an), Prof. Shihua Zhu (Xi'an Jiaotong University), Dr. On-Ching Yue (Lucent Technology, USA), and Dr. Hong Shen Wang (Mediatech Incorporated, Taiwan). The investigators have come up with a mobile, two-way, store-and-forward, packet-switching system called the Voice Interactive Paging Network (VIP Net) to provide text and voice messaging services. By restricting its application to only messaging services, the researchers hope to not only simplify its design but also reduce the development and production cost of the entire system.

Salient Features of VIP Net

Figure A: VIP Net Architecture
System Architecture

The VIP Net consists of a central switching and processing unit (CSPU) and a number of base station units (BSUs) connected by a backbone network (Figure A) that has access to other wire-based data networks such as the Internet via gateway nodes.

The CSPU is responsible for routing and storing all messages, and provides a computation platform for a variety of information processing services. Each BSU serves as a micro-cell, and covers a geographic area of interest. Users communicate with the BSUs by specially designed mobile units. The fact that all inter-BSU messages are delivered through the CSPU simplifies the control algorithm as well as administration and maintenance problems.

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 most important distinguishing feature of the VIP Net is the manner in which it broadens its spectrum usage by repeatedly using the same frequency spectrum in a number of 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 only 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 unit prototype used for test purposes is shown on the right.

In the second phase, which 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 of three cells was implemented along with 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 mid-1998, advanced application services such as text-to-voice translation and directory information will be incorporated. An extension to this project aims to put advanced data applications onto a standard platform, i.e. a more compact mobile unit. The investigators have chosen the Digital Enhanced Cordless Telephone (DECT) standard in their effort to make the unit ultimately comparable in size to a cellular phone, which will add to the product's market viability.

The researchers have come a long way since they started to improve telecommunications technology for the convenience of users on the street. It is their goal to produce effective and easy-to-use devices that are also commercially viable.

Prof. Wong Wing-shing received his BA and MA degrees from Yale University, and his MS and Ph.D. degrees from Harvard University. He is a senior member of IEEE and a fellow of the HKIE, and has been an associate editor of the IEEE Transactions of Automatic Control.
Prof. Wong had worked for two years for Scientific Systems, Inc., before he joined AT&T Bell Labs, where he worked for 10 years. He joined The Chinese University as a reader in the Department of Information Engineering in 1992, and was appointed professor of information engineering in October 1996.
Prof. Peter Yum Tak-shing received his B.Sc., M.Sc., M.Ph., and Ph.D. degrees from Columbia University in the US. He worked with Bell Telephone Laboratories for two years before taking up a teaching post at the National Chiao-Tung University's Institute of Computer Engineering in Taiwan. He became a senior member of the IEEE in 1986.
Prof. Yum joined The Chinese University as a lecturer in electronics in 1982. He was promoted to senior lecturer rank in 1988, reader in 1991, and professor of information engineering in January 1995.