The Advanced PHS Committee, subordinate of the Telecommunications Council (an advisory body to the Japanese Government), recently compiled the key findings of its study on advancing the PHS systems as a report. The committee had been deliberating on measures for advancing the PHS systems for coexistence with the IMT-2000 since August 2000.


[Background Requirements for the Report]

Since the inauguration of the PHS service in 1995, PHS systems have penetrated mainly into urban areas as simple and convenient mobile communications means; now the systems, in parallel with the cellular telephone systems, have become very popular information and communications tools closely involved in national daily lives.
In response to a report OMeasures for Introducing the Technology contributing to the Promotion of Advanced Use of the PHSO from the Telecommunications Technology Council in July 1998, the quality of speech while moving and indoors, level of convenience etc. have significantly been improved, resulting in increased data communications traffic mainly for Internet access.
For further advancement of the PHS service, itOs needed to be studied for meeting various and increasing user demands properly.
  In addition, because the frequencies allocated to the PHS systems are adjacent to those to the third-generation (3G) mobile communications systems (IMT-2000), for advancing the PHS systems, measures for reducing interference are also required to be taken into consideration.


[Measures for the Advancement]

Technical requirements compiled this time for advancement of the PHS, based on its study of various measures for the advancement of the PHS coexisting with the IMT-2000 are listed in Table 1 and an example of optimum combination of those are as follows.

An example of optimum combination of measures

Adoption of the 16QAM: 2 times faster
Carrier frequency band multiplied by 3 and the improvement of the roll-off rate : 3.3 times faster
To increase the number of slots per frame to 4: 2 times faster
Efficient slot configuration : 1.2 times faster

Total : 16 times faster

This example shows the possibility that the PHS data transmission speed can be increased up to 1Mbit/s, 16 times faster than the existing PHS systems (64kbit/s) through various optimum combination of measures for the advancement.
Further, coexistence with the IMT-2000 system can be realized through an introduction of the filter for suppressing interferences to the IMT-2000 and gradual shift of the PHS control channel to eliminate the IMT-2000Os guard band.



[Technical Requirements]

In deliberations on advanced PHS systems, measures for advancing the PHS systems are examined, on the assumption that advanced PHS systems coexist with the existing PHS systems in the same frequency band, namely, specifications for radio frequency band, number of TDMA multiplexing and wireless access system remained intact.
Technical requirements as a result of the deliberations are listed in Table 1.

Table1 : Measures for the Advancement

Measures	Effect to be expected	Remarks
Addition of modulation systems	Improvement in efficiency of frequency use High-speed data transmission	/4-QPSK (currently used) Added for public system BPSK, QPSK, 8PSK, 12QAM, 24QAM, 32QAM
Introduction of adaptive modulation system (see Figs.1 and 2)	Improved quality of speech Improved throughput of data communications	Adaptive modulation system adaptively selects optimum modulation system among systems listed above according to the conditions of radio propagation
Introduction of asymmetric communications (see Fig. 3)	Improved throughput of data communications	Adoption of different frequency width, modulation system, time slots for up-link and down-link
Speed-up of symbol speed (including lowering of roll-off rate) (see Fig. 4)	High-speed data transmission Improvement in efficiency of frequency us	Realization of high-speed data communications through setting bandwidth: 900kHzRoll-off rate: 0.38Symbol speed (max.): 640 symbol/s
Introduction of slot linked communications	Improved throughput of data communications	Delete overhead part by linking slots
Realization of packet communications	Improvement in efficiency of frequency use	Efficiency of frequency use is improved by introducing wireless packet system that allows multiple users to share resources. However, compatibility with existing systems is ensured through adoption of wireless packet system that adds the dormant function to the circuit switching system.
Introduction of error correcting codes	mproved quality of speech	mproved quality of speech by introducing error correcting codes
Introduction of path division multiple access technology(see Fig. 5)	Improvement in efficiency of frequency use	Advanced technology with adaptive array antenna enables to use multiple information channels with one single frequency and one slot

Fig.1 : Adaptive Modulation System



Fig.2 : Service Area Employing Adaptive Modulation System



Fig.3 : Asymmetric Communications



Fig.4 : Speed-up of the Symbol Speed