Mr. Yoshiki Chika of DDI Pocket Telephone, Inc. delivered a speech, "PHS beyond 3G," at the PHS seminar of the 2000 Annual General Meeting of PHS MoU Group, held in Singapore on June 7. Following is an excerpt of the speech. The presentation material in its entirety can be accessed at http://www.phsmou.org.
PHS was launched as a service with high voice quality and high-speed data communications function. With PHS data communications having achieved the speed at 64 kbit/s and frame synchronization system and with macro-cell having been introduced, PHS has now gained functions comparable with or superior to those of the cellular system in terms of mobility and data transmission speed. Nevertheless, with the 3G system scheduled to be put into service in a few years, it is crucial for us to enhance the PHS features further. Now we are planning these four items: 1) enhancement of P-Mail DX, 2) international roaming, 3) packet data, and, 4) higher Equivalent Isotropic Radiation Power (EIRP).

1) Enhancement of P-Mail DX
Currently, P-Mail DX (PDX) allows users to transmit/receive e-mails as well as to access WWW content of up to 5,000 bytes. There are more than 2 million PDX-enabled terminals today. As a PDX enhancement plan, we are considering making larger-sized content available to users, such as colored content and music downloads. With the 64 kbit/s PHS data communications service, we think we can offer such content service at lower prices not only against today's cellular system but also against the upcoming 3G system.

2) International roaming
The public PHS is presently in service in Japan and Thailand, and is also planned for kick-off in Taiwan at the end of 2000. Toward realization of international roaming, we are developing our proprietary international roaming system. We also intend to negotiate with telecommunications service operators in these countries.>

3) Packet data
As regards the packet data transmission methods, studies are under way for the following two methods: a) the PHS Internet Access Forum Standard (PIAFS)-based packet protocol, and b) the proprietary packet protocol.

a) PIAFS-based packet protocol
This protocol is being developed by the Mobile Internet Access Forum (MITF). As Fig. 1 shows, this protocol enables packet data transmissions only by making changes to software on PCs, PC cards or remote access servers (RAS) but not to PHS terminals nor to the PHS network.

Fig. 1 Mechanism of PIAFS packet

This method, because of the use of packets, allows charging by data volume. This method also ensures improved mobility with its the dormant function (see Fig. 2), which keeps the upper layer connected even when the lower layer has automatically been disconnected upon passing of a time period with no transmissions data handled. With this function, for example, one can continue the call even when passing through a tunnel.

Fig. 2 Improvement of mobility

b) Proprietary packet protocol
The other method is the proprietary packet protocol, which we are developing now. This method enables more efficient packet communications than the PIAFS-based packet protocol, by the use of control channel for packet communications. As the first application of this method, we plan to launch the "Always On/Dynamic ISDN (AO/DI)" service in the second quarter of 2001. In the service, data flow is always monitored; when data is small, the packet switching is chosen, whereas if the data is large, then the circuit switching is chosen (see Fig. 3).

Fig. 3 AO/DI (Always On/Dynamic ISDN)

Thus, this service tactfully manage the balance of packet and line switching charges depending on the data volume, thereby cutting back on communications charges billed to users. This service is suitable for WWW accesses over the Internet, since users can enjoy high-speed PHS data communications without worrying about the time they spend online. We are also planning to achieve higher-speed data transmission such as 128 kbit/s and 512 kbit/s by installing multiple Cell Stations (see Fig. 4).

Fig. 4 Very high-speed

4) Higher EIRP
After three years of R&D, we have found that mobility and penetration can be improved if the antenna gain and transmission power are set higher than the values defined by relevant Japanese laws. For example, the Radio Law stipulates that the transmission power of PHS be lower than 10mW in Japan. We built a PHS terminal with the transmission power of 40mW for trial, and confirmed the results were satisfactory. We also expect that if QAM (quadrature amplitude modulation) is to be chosen as the modulation method, higher-speed data transmission can be achieved. We would like to ask telecommunications service operators of each nation to consider adoption of these methods, according to regulations being observed in each nation. We expect that, with the above mentioned enhancement measures, PHS in the year 2001 will be greatly improved in terms of mobility and transmission speed (see Fig. 5).

Fig. 5 2001-PHS (2.5G)

Moreover, it is necessary for us, the members of PHS MoU Group, to begin extensive studies for the development of next-generation PHS, while being much aware of its importance. It is very certain that such studies will result in MoU specifications superceding the 3G system (see Fig. 6).

Fig. 6 New-generation system (Beyond 3G)