1. Switch from Analog to Digital

In 1988, NTT released its ACTY wireless PBX system which was based on analog cordless telephone technology. That development helped to open up a new field for wireless PBXs targeted at business applications. Japanese communications equipment manufacturers subsequently brought out many such systems. However, analog systems have certain drawbacks with respect to speech quality, security, traffic capacity and extendability to data communications, among other aspects. Work has been under way to switch to digital technology in order to overcome those limitations.
The Technical Standard for Personal Handy-phone System (RCR STD-28) was issued in December 1993. NTT Mobile Communications Network Inc. (NTT DoCoMo) moved quickly to incorporate this technology into its PASSAGE digital wireless PBX system that was put on the market in April 1994.

2. System Overview

This digital wireless PBX system consists of a digital PBX, cell stations and PHS terminals, as shown in Fig. 1. It provides the same capabilities as a public PHS system, including automatic location registration, handover and authentication. In addition, it also allows the use of the many functions inherent in a PBX.

The system capacity depends on the capability of the PBX that is used. It can be adapted to a wide range of PBXs, from a small PBX supporting around 30 lines to a mammoth PBX capable of accommodating several thousand lines. Photo 1 shows the appearance of the cell station and PHS terminal.

3. Demand Trend

Target customers for the PASSAGE system can be inferred from the results of a market survey that was conducted before this product was released (Fig. 2). The types of businesses that are strongly interested in digital wireless PBXs include advanced offices as well as large places of business such as hospitals, department stores and wholesale markets, which have many extension lines and where there is a need to contact directly specific individuals who are moving about in a relatively wide area.
The specific places where the system has been installed so are include factories, hospitals, hotels, theme parks and universities, among others.

4. Future Developments

Over 200 PASSAGE systems are now in operation in Japan. Efforts are under way to improve and expand the system in various ways, such as by providing a roaming function between PBXs, increasing the data transmission capacity, allowing interworking with LANs and other multimedia systems and adopting key telephone system functions. It is expected that digital wireless PBX systems in Japan will continue to advance on the platform provided by PHS technology.