PHS Terminal

The PHS terminals have to provide four modes of service, that is, public, PBX cordless, home cordless and transceiver (walkie-talkie), and two types of terminals are defined, public use and public with private use. PHS terminals must not only be small and lightweight as public cordless telephones but also operate in various modes such as home cordless phones. The PHS system was designed to save its terminal power consumption to extend standby waiting time and talking time, by limiting its peak & average output power and adopting simple logic in its control process. Furthermore, the system was designed to provide terminals with room to expand their functions and services. Following describes the system design, hardware configuration and the prospect of the PHS terminals.

Design Policy

• Advancing common design of parts and modular configuration, taking into account multiple service models
• Promoting low power consumption
• Adopting user-friendly human-machine interfaces

Since all four modes of service are likely to be mixed on wireless channels, the design parameters of the wireless system must be suitable for all four modes, taking into account interference, disturbances and other potential problems. Moreover, from the standpoint of shared use of resources, the original design of each wireless system should be adapted to the parameters of the public network system, keeping changes to the minimum necessary.
In order to meet diverse user needs efficiently, applicable services should be clearly identified by modelling, and the system interfaces and modules for the system should be designed on the basis of this modelling. Further, the adoption of a modular structure for the system will enable efficient use of development resources.
PHS system parameters have been developed to meet the demand in enabling extraordinarily small and lightweight terminals with extremely lower power consumption compared with those of cellulars. This is realized through adoption of micro cell (100 -- 500 m radius) for the PHS system enable the lower output power (10 mW average and 80 mW peak) for the terminals as well as for the cell stations (20 mW, 100 mW and 500 mW). Also, the simple logic protocol which has been established for dynamic channel allocation and other control processes by use of dedicated control channel has helped to realize these impressive PHS terminals.
Further, in realization, the use of custom LSIs that allows a reduced part count and a more compact circuit board is effective in achieving smaller and lighter terminals. In order to extend talking time and standby waiting time, a power-saving design is needed, including a slower clock speed during standby and a reduced driving voltage. In consideration of lithium ion battery operation, characterized by its light weight, compact size and high energy density, LSIs that can be driven with around 3 V are used with the aim of achieving power savings.
Efforts should be made to develop user-friendly human-machine interfaces, including appearances of battery charger and terminals as well as additional functions such as abbreviated dialing, directory assistance and modems, keeping in mind the various applications envisioned for PHS terminals and trends toward more compact designs. Personal computer and PDA manufactures are developing products which interface with PHS as well as those which have built-in PHS.

Hardware Configuration

A PHS terminal mainly consists of an antenna, RF unit, modulator, demodulator, TDMA/TDD processing unit, speech quality monitoring unit and speech processing unit, including a 32 kb/s ADPCM codec (Fig. 1).
These components are composed of individual LSIs and are divided into four function blocks: the wireless block (antenna, RF section, modulator and demodulator), channel codec block (TDMA/TDD processing unit), speech codec block (speech processing unit, speaker and microphone) and operation/control block (CPU, keyboard and display). Each block is designed to operate on around 3 V. Moreover, power consumption is reduced by operating the CPU of the operation/control block intermittently during waiting time and also by cutting off power supply to the transmitter and receiver when the terminal is on standby status.

Recent trends and expectations for multimedia terminals

Even at this very first stage of the service, terminals have been successfully developed that offer both portability and operating ease. A compact size has been achieved by using LSIs to form each function block. As a result of reducing the driving voltage and applying power supply control during waiting time, terminals now provide a calling time of around five hours and a continuous standby waiting time of around 400 hours. In the near future, second-generation PHS terminals, which are much smaller, lightweight and multifunctional, are expected to hit the market as a consequence of continuous efforts devoted to developing next-generation terminals.
The Association of Radio Industries and Businesses (ARIB) has formulated a standard concerning the interface (private standard interface) between the private cell stations and PHS terminals for private use, in addition to a standard for the wireless air interface between cell stations and terminals for public use.
If terminals incorporate this private standard interface, one PHS terminal can provide basic calling functions for making and receiving calls in outdoor, office and home use. This capability is expected to promote further personalization of communications.
PHS terminals are expected to be much more than just inexpensive phones with good speech quality. Because PHS terminals support high-speed digital communications at 32 kb/s over the wireless common air interface, there are large expectations that they will serve as the core infrastructure for mobile computing. ARIB has also formulated a standard concerning the 32 kb/s unrestricted digital data communications and the terminals installed with this function are expected to come up in the market within a year. PHS terminals incorporating this function are strongly expected to be used as portable terminals that can transmit data at markedly higher speeds. In private use, such as at home or in the office, PHS terminals could serve as ISDN mobile terminals which support 64 kb/s high-speed data communications by use of two 32 kb/s slots. At present, videophone prototypes using 64 kb/s data communications are already available and practical use of 28.8 kb/s data communications has been proven as the prototype level.