The working process of ITU-R BWA Recommendation including Next-generation PHS had already been introduced in the first volume. Besides, the Next-generation PHS is also to appear in other documents of ITU-R. Two of these documents, titled REPORT ITU-R M. <LMS.CHAR-BWA> and Land Mobile Handbook respectively are introduced below.

• The Report ITU-R M. <LMS.CHAR-BWA>



Interference Examination Report − PRELIMINARY DRAFT NEW REPORT ITU-R M. <LMS.CHAR-BWA> “Characteristics of broadband wireless access systems operating in the mobile service to be used in sharing studies” is a report providing necessary information for examining the interference to other systems.

Though this report is draft one now, it would move into official report from now on passing through some approvals. Since the Next-generation PHS which is one of the systems in BWA Recommendation is listed on this report as well as WiMAX and others, PHS MoU Group has the obligation to provide relevant data for the report.

• Land Mobile Handbook



ITU-R publishes Land Mobile Handbook as a mobile system guidebook mainly for developing countries. Volume 1 − Volume 4, four documents have already been completed by now, while Volume 5 for BWA (Broadband Wireless Access Systems) is under compilation.

• Volume 1: Fixed Wireless Access
• Volume 2: Principles and Approaches on Evolution to IMT-2000
• Volume 3: Dispatch and Advanced Messaging Systems
• Volume 4: Intelligent Transport Systems

The Next-generation PHS is to be described in Volume 5 as one BWA system. Some parts of article are introduced below.

Next-generation PHS based on microcellular networks for broadband wireless access systems

1. The background of Next-generation PHS

Next-generation PHS is a new mobile BWA system, which was enhanced from the mature original PHS by introducing latest technologies. The standard of Next-generation PHS was developed by PHS MoU Group as one of the new BWA methods with high data rates for both (up⁄down) links and a high efficiency of spectral utilization.

PHS MoU Group is an open international association established in 1995, which is consisted of companies and organizations involved in or interested in PHS services, such as telecommunications carriers, service providers, equipment manufacturers, technology providers, telecommunications authorities, and public organizations. The main objective of PHS MoU Group is to introduce, operate and spread the PHS on a world-wide basis and thereby to contribute to the improved convenience of telecommunications users and to the consequential benefit of the people in the world.

PHS, “Personal Handy-phone System”, was originally developed as a digital cordless telephone system upon the early concept of fixed⁄mobile convergence (FMC). However, PHS can serve, and actually has been utilized, as an ordinary mobile phone system such as PDC or GSM, because of its handover function and its high-quality voice service. Therefore, PHS is now regarded as one of mobile phone systems, which has some unique concepts such as “micro-cell”. Because of micro-cell, PHS doesn’t need wide frequency bandwidth, and large facility for radio equipment. Therefore, PHS is comparatively easy to introduce because its scale of investments is small at the beginning phase of deployment. PHS has expanded worldwide, especially in Asia after its startup in Japan. Today, the number of PHS subscribers has reached over 100 million in the world.

PHS systems including Next-generation PHS utilize micro-cell concept as a main feature. Generally speaking, a micro-cell system is superior in an efficiency of spectral utilization per one square kilometer to other macro-cell systems. The main causal factor for realizing the micro-cell system is an autonomous decentralized control method for the channel assignment. And because of that, the advantages of PHS are not only the improved efficiency of spectral utilization but also its simplified cell designing while rigorous cell designing is necessary in typical macro-cell systems.

PHS has got evolutions in its own system repeatedly since the original standard decision, and its maximum data rate will be 1Mbps in “Enhanced PHS” commercial service in the near future. The air interface of “Enhanced PHS” actually has functions such as packet switching communication, multi-channel connection, various rate modulation (BPSK - 256QAM), adaptive modulation, half-rate transmission, and multi-slot bundle, most of which were not included in PHS original standard published in 1993. The “Enhanced PHS” is suitable for not only mobile phone systems but also for fixed wireless access (FWA) systems, because PHS was originally started from a digital cordless telephone system based on the network facility for a fixed service and it is not difficult to deploy macro-cell networks (several kilometers in cell radius) for services in suburban area, although the network basically operates on micro-cell design.

The “Enhanced PHS” introduced here is, in a broad sense, included in “Next-generation PHS”. However, “Next-generation PHS”, in a narrow sense, indicates a BWA system which is utilizing orthogonal frequency division multiplexing (OFDM) technology besides basic PHS concepts, and it will realize higher maximum data rate of over 20Mbps, and higher efficiency of spectral utilization.

2. Features of Next-generation PHS in comparison with the Enhanced PHS

As explained above, the term “Next-generation PHS” in a broad sense indicates two systems, one of which is the “Enhanced PHS” based on time division multiple access⁄time division duplex (TDMA⁄TDD), and the other is narrowly-defined “Next-generation PHS” based on orthogonal frequency division multiple access (OFDMA) +TDMA⁄TDD. The comparison of the “Enhanced PHS” and the narrowly-defined “Next-generation PHS” is shown in Table.1. “PHS” had grown up to the “Enhanced PHS”, and also will grow up to the narrowly-defined “Next-generation PHS” by integrating technical improvements.

The term “Next-generation PHS” hereinafter indicates the narrowly-defined “Next-generation PHS” as a new BWA system.




Table 1. The basic elements of Next-generation PHS in comparison with the Enhanced PHS





“Next-generation PHS” achieves high efficiency of spectral utilization by utilizing technologies such as adaptive array antenna (AAA), spatial division multiple access (SDMA) and multiple-input multiple-output (MIMO). It also has, as the preceding systems do, the functions of autonomous decentralized control for dynamic channel assignment in order to make the micro-cell network work efficiently, thereby achieving high efficiency of spectral utilization.

3. Link Access technique

As depicted in Figure 1, the “Next-generation PHS” radio interface has two dimensions for multiple access. One dimension is time domain control realized by TDMA and the other dimension is frequency domain control realized by OFDMA. In the time domain, the time-frame structure is the same as that of the original PHS which is 5 ms symmetric frame. In the frequency domain, one or more sub-channel consisted of OFDM subcarriers would be flexibly allocated to users, depending on conditions such as users’ demand, channel usage, and channel quality. The time-frame has 8 slots of 5 ms each, the consecutive 4 slots are for downlink, and the other consecutive 4 slots are for uplink. Each slot of 4 slots is separately assigned to users and also can be assigned continuously for one user. Moreover, continuous assignment of more than 4 slots is possible when asymmetric frame structure is employed.




Figure 1. TDMA-TDD in original PHS and OFDMA⁄TDMA-TDD in Next-generation PHS





In the frequency domain control employing OFDMA, the radio interface can use several defined classes of effective bandwidth: 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz. As shown in Figure 2, “Next-generation PHS” has multiple sub-channels in its effective channel band-width, and each sub-channel consists of multiple sub-carriers. The sub-carrier spacing in this system is 37.5 kHz which is comparatively wider than typical OFDM systems.




Figure 2. OFDM Structure





Concerning the rest of materials, please find them in the original ITU-R Land Mobile Handbook after publication.

The work for the Next-generation PHS standardization is advanced actively within PHS MoU Group. Meanwhile the field experiment by WILLCOM was carried out and sufficient performance result was obtained. In addition, as was described above, the Next-generation PHS is building a strong international background such as the ITU-R Recommendation, which is indispensable to introduce for various countries.

The Next-generation PHS is different from WiMax and it is the unique BWA system with huge capacity backed up by micro cell technology. And commercial service in several years is sincerely expected.