Toru Otsu

Multi-hop radio access cellular concept for fourth-generation mobile communications system

This paper proposes a multi-hop radio access cellular (MRAC) scheme for achieving both high speed and high capacity and good area coverage in fourth generation mobile communications systems. In this scheme, we assume two kinds of hop stations, one is a dedicated repeater station installed at a good propagation location such as a rooftop, and the other is a user terminal that temporarily experiences good propagation conditions. For both cases, the path diversity effect can be obtained between single-hop and multi-hop paths. Four propagation models were studied representing the paths among the base station, hop stations, and mobile station. Based on the propagation models, suitable MRAC operation conditions are discussed. For mobile stations located at the cell edge area, MRAC operation is effective in reducing the transmit power. Consequently, MRAC reduces the interference in cellular systems and enhances the area coverage.

Network architecture for mobile communications systems beyond IMT-2000

This article describes a suitable network architecture for the mobile communications system beyond IMT-2000. The rapid developments in mobile communication services have significantly altered the lifestyles of many people. With the increasing demand for access to the Internet, the amount of data traffic in mobile communication networks has significantly increased and will dominate these networks. Therefore, mobile networks beyond IMT-2000 should offer higher bit rate channels and adapt to multimedia traffic more efficiently. This article first forecasts market trends in mobile communications in order to identify requirements of the mobile communications system beyond IMT-2000. Then the article considers the network architecture of the mobile communications system beyond IMT-2000 that will satisfy those requirements.

Area coverage and capacity enhancement by multihop connection of CDMA cellular network

In future broadband communication systems, a multi-hop scheme, in which stations between a mobile terminal and a base station relay signal transmissions, seems a promising approach for wide-area coverage and system capacity enhancement. We apply the multi-hop connection scheme to a code division multiple access (CDMA) cellular system and compare its performance to that of a conventional single-hop cellular system. In computer simulations, we assume a packet-based multi-cell environment considering intercell and intracell interference and that every mobile station is equipped with a function for relaying transmission signals. Simulations are performed for the cases where the area coverage cannot be obtained by using only a single-hop connection, and where full area coverage is obtained by a single-hop connection. In the former case, almost 90% of area coverage is obtained when the area coverage by a single hop is approximately 50%. In the latter case, packet arrival ratio is increased by using a multi-hop connection. The degree of improvement, however, is very slight due to interference between signals from base stations and relay stations.

System architecture for mobile communications systems beyond IMT-2000

This paper presents a system architecture for mobile communications systems beyond IMT-2000 (4G system). Considering the growth of data communications through mobile networks, the 4G system should offer higher bit rate channels and accommodate a significantly larger amount of traffic. To meet these requirements, the 4G system may use higher frequency bands. This paper first considers objectives of the 4G system and it proposes a system architecture that meets the objectives. The architecture proposed in this paper comprises core networks that will accommodate multiple types of radio access networks (RAN). The 4G RAN is constructed by distributed controlled base stations that are connected to each other by a multi-hop wireless network.

Fiber and free-space hybrid optical networking for new generation mobile radio access network

This paper proposes fiber and free-space hybrid optical (FFHO) networking for radio access networks (RANs) in the new generation mobile communication systems. FFHO networking applies technologies that cause fiber transmitted optical signals to be emitted directly into free-space and make free-space transmitted optical signals focus directly onto fibers by using beam size converters such as a lens. This networking provides flexibility to the optical network structure and expands the application areas of the existing optical fiber infrastructure such as dark fiber. Optical signals with 1.55-/spl mu/m band transmission characteristics such as BER and atmosphere attenuation caused by weather conditions through free-space transmission are presented as the basis of the transmission evaluation. The evaluation results show that FFHO transmission incurs a penalty of about 1.5 dB in received power compared to fiber transmission and that FFHO has atmosphere attenuation characteristics comparable to conventional optical free-space transmission systems using the 800-nm wavelength band.

Capacity and transmission power estimation of two-hop CDMA cellular system

This paper describes a novel direct sequence code division multiple access (DS-CDMA) cellular system where a relaying function is introduced to mobile terminals. By using a relay, a considerable transmit power reduction might be achieved. Particularly, those terminals located in the shadowing region or in the cell edge are able to reduce the transmit power by asking a nearby terminal with low propagation loss to the base station to relay its signal. For relaying, the same frequency bands that are already allocated are assumed to be reused. This might cause an excessive interference due to the uncoordinated frequency reuse. To clarify these points, a two-hop DS-CDMA cellular system and a conventional DS-CDMA cellular system without relaying are compared in terms of the user capacity and transmit power. Simulation results reveal that the system capacity can be increased by using a sophisticated routing scheme.

Satellite communication system integrated into terrestrial ISDN

This paper presents an advanced satellite communication system named DYANET II. This system uses satellite channels as subscriber lines for ISDN customers as well as trunk circuits for overflow traffic. The system can offer the same ISDN services to satellite customers as those available to terrestrial subscribers in terms of numbering, signaling, and charging systems as well as user-network interfaces. It can also set up satellite channels on a demand assignment basis to achieve efficient satellite channel utilization, and to connect customers by single-hop satellite connections. A compact, lightweight Earth station has been developed for remote customers and temporary demands such as exhibitions.

Performance evaluation of a time division multi-hop relay scheme in CDMA cellular networks

The multi-hop connection scheme for cellular systems is expected to be an efficient method of expanding the cell size covered by a single base station without the need for additional transmission power at the base or mobile stations. The target of this paper is to propose the time division multi-hop relay scheme in combination with the packet admission control that is applied to the CDMA cellular system forward link. The cell size of CDMA cellular systems has a trade-off relationship with the system capacity and the transmission bit rate. We evaluated enhancing the cell size while trying to maintain the same system capacity and transmission bit rate as that currently achieved. The simulation results clarify that the multi-hop connection scheme applied to the CDMA cellular system has the capability to expand the cell size while maintaining the system capacity and the transmission bit rate.

Asia — Driver of Mobile Communications Markets, a Japanese Perspective

It is my pleasure and honour to present here the DoCoMo’s Business and R&D activities. And first of all please keep it in mind that my presentation encloses some of my personal views although this is based on facts and I use slides which have been used for company’s official presentations.