A new asynchronous transfer mode adaptation layer (AAL), called AAL2, is being designed mainly for low-bit-rate voice traffic, and nodes that can assemble and disassemble AAL2 cells are being developed to make AAL2 usage efficient. This paper investigates the delay and performance of AAL2 nodes by an analytical method. Then, using the results, it analyzes a network using AAL2 nodes and shows the bandwidth reduction achieved by using AAL2 switching nodes as transit nodes.

The world of mobile communications has undergone dramatic changes in recent years. Since the Personal Digital Cellular (PDC) system of digital mobile communications became commercially available in Japan in 1993, the number of subscribers has increased to the extent that almost 30% of the Japanese population are subscribed. Furthermore, the increasing sophistication of communications, such as the growing popularity of the Internet and expansion of our spheres of existence, have led to demand for new applications, such as use on a global scale. Many new technologies are also being introduced, such as the IMT-2000 system and the IN system which are slated to be introduced at the end of 2000. Based on the above and in view of the increasing scale and sophistication of mobile communications networks, the time has come to reexamine the configuration within networks of SCPs, which perform subscriber data management and service control. This paper focuses on the functions of subscriber data management and service control, classifies data necessary for mobile networks and using the signal number of common networks as a guide considers the optimum arrangement of data and control nodes. The paper also examines reliability measures for SCPs to ensure the reliability of increasingly large-scale networks.

This article clarifies the requirements of VHE (Virtual Home Environment), issues and resolution for realization of VHE, when the environment will use Intelligent Network (IN) within IMT-2000 networks that is targeted to start in the year 2000. The IN aims the applicability of it's architecture to any kind of network. However, the following subjects need to be considered when IN will be used in the IMT-2000 network; The approach of the service related capabilities' extraction and specification; security management; cooperation between the service switching function within a core network and the IN function(s); cooperation between the mobility management function and the IN function(s); and consideration of mobile and fixed network convergence/integration. This article mainly focuses on these subjects. Some open issues like service/feature interaction and their tentative solutions are identified. Main results are; expandability of current IN to supporting IMT-2000 requirements, identification of key issues in providing VHE in IMT-2000, identification of candidate relationships, and associated issues for VHE. The currently available scenarios for VHE are evaluated from these points, and it is proposed that the specification to be common both for mobile and fixed network.

Radio transmission technologies for IMT-2000 are being studied and standardized all over the world. Several national/regional standardization bodies are developing proposals on radio transmission technologies to meet the cut off date of June 30, 1998 set by ITU. This paper shows necessity to develop and standardize IMT-2000 in Japan, principle attitude on IMT-2000 standardization, selection process of W-CDMA, and the current situation of study on IMT-2000 in ARIB (Association of Radio Industries and Businesses).

In this paper, we briefly describe the proposed radio access scheme based on CDMA/FDD for next-generation mobile radio systems, and evaluate its performance through laboratory and field experiments on transmission power control (TPC) and diversity, which are the key technologies to achieve efficient CDMA systems. The design of the practical TPC method is discussed, and a robust method is presented for operation in low signal to interference power ratio (SIR). Laboratory experiments demonstrate that space and path diversity effectively improve the TPC performance in the Doppler frequency range of 40 to 80 Hz, and reduces the required Eb/N0 to achieve the BER of 10-3. The necessary diversity order for multipath fading mitigation in all the Doppler frequency range is also investigated. Through the field experiments in urban area of Tokyo using a developed system at 0. 96 Mcps, a low required Eb/N0 of 2. 8 dB can be obtained because of the effectiveness of the diversity.

ITU (International Telecommunication Union) has issued request for submission of candidate technologies for IMT (International Mobile Telecommunication)-2000/FPLMTS radio interface in April 1997. In order to propose a candidate technology and to contribute to the production of a world wide standard of IMT-2000, ARIB (Association of Radio Industries and Businesses) has studied radio transmission technologies for IMT-2000. This paper shows the recent study results on IMT-2000 radio transmission technologies in ARIB. Now in ARIB detailed study to produce necessary specifications and prepare of a proposal on candidate radio transmission technology to ITU are being conduced based on wide band DS-CDMA technologies.