Hideki Mizuno

Compact six-sector antenna employing patch Yagi-Uda array with common director

A novel compact planar six-sector antenna employing the patch Yagi-Uda array with common directors for mobile terminals is proposed. This antenna has square parasitic director elements that are shared by two sector arrays that face in opposite directions, and has a hexagonal central director element that is shared by all six sectors. These elements form three line arrays, which intersect at 60 degrees to each other. These shared elements enable the sector antenna to be compact. The antenna configuration is described, a numerical analysis of the properties of the front-to-back (F/B) ratio under termination conditions and the number of parasitic elements is given, the validity of the electrical characteristics and the downsizing effect based on the experimental results from a fabricated antenna are shown.

Novel smart antennas for applying SDMA to cellular mobile communication systems

The popularization of mobile communication has necessitated efficient use of the radio spectrum. Space-division-multiple-access (SDMA), which enables several users to use the same communication channel simultaneously by forming individual radiation patterns for the users, is an attractive candidate to reuse the frequency spectrum efficiently. However, there still remain problems for applying SDMA to actual cellular systems. These problems are summarized. Then, as solutions to overcome the problems, a new smart antenna configuration comprising sub-arrays and utilizing a space time coding (STC) technique, and a new smart antenna system utilizing space and polarization control are proposed. The effectiveness of the proposed antennas is presented.

Modified multi-focal paraboloid design for high aperture efficiency multibeam reflector antenna

To meet the growing demand for broadband access and diversification of communication services, for example, satellite communications, a high-gain multibeam antenna that can communicate with two or more stations is desired. There are two basic types of high-gain multibeam antennas using a single reflector. One is the torus reflector antenna, and the other is the multifocal parabola reflector antenna. We propose a modified multi-focal paraboloid design method to develop a highly efficient multibeam antenna for wide angle beam scanning with a simple configuration. This design enables control of the feed points, and we demonstrate the performance of the planar array fed multibeam reflector antenna as an example of this design method. This antenna simplifies the feed configuration of a single reflector multibeam antenna. The results of numerical analysis using a case employing a 16-element array feed shows that the antenna offers homogeneous patterns in a wide scanning range and an aperture efficiency of over 64% (13 beam widths).

Investigation of single-hop connections between user terminals in geostationary mobile satellite communication systems

The number of subscribers in geostationary mobile satellite communication systems has been increasing, as a result of the increase voice communication between user terminals. In this situation, there is a strong demand to improve the communication quality of the double-hop connection between two user terminals. As an means of reducing the voice delay, we developed four single-hop connection methods in traffic channel frames are sent through the satellite only once. After comparing these methods with the conventional one, we found that the method using a through repeater satellite and one using a regenerative transponder on board the satellite were promising single-hop connection methods. In particular, we found that using a newly developed common control channel is promising for the former method, and that using frame decomposition and reassembly for communication frames is promising for the latter.

Simplified polarization assignment method for terminals in SDMA adopting directivity and polarization control

This paper proposes a simplified polarization assignment method for the space division multiple access (SDMA) terminal station that adopts directivity and polarization control by using the spatial correlation and the difference in the spatial correlation. Since the difference in the channel responses among all users is considered in the proposed method, an effective assignment of the polarization for the terminal stations is achieved even if the number of the users is large in SDMA systems. Moreover, we evaluate the effectiveness of the proposed polarization assignment method by computer simulation using the measured data in a cellular environment.

Bi-directional multimedia satellite communication system employing superposed transmission

A bi-directional multimedia satellite communication system has been proposed to support high-speed Internet access. This system utilizes a low-cost user earth station with an ultra-small antenna for easy installation. Since this system utilizes ultra-small antennas, it employs the low-power spread spectrum (SS) scheme in the access link to keep the off-axis equivalent isotropic radiation power below the limit. For efficient use of transponders and frequency, SS signals are superposed on the high-speed TDM forward link signal. To demodulate access link signals under this condition, two novel technologies are introduced. They are the adaptive interference cancellation technique, and the parallel and staggered operation SS demodulation technique. This paper describes system configuration, the new technologies and the results of a system performance evaluation in an experiment. The results of the evaluation demonstrate that superposed transmission over the forward link and low-power access link signals is feasible.

A new portable and economic earth station for ISDN satellite communication

NTT has developed a new compact-size, hand-transportable, user earth station (UES) that provides both of the ISDN user-network interfaces (ITU-T reccomendations I.430 and 1.431), applying the time division multiple access (TDMA) scheme. This user earth station provides a maximum of eight interfaces for I.430 and a maximum of two interfaces for 1.431. The new UES consists of four components. Each component can be readily transported, so an 1157 overall UES has good portability. The total weight of the user earth station is about 100 kg, and the volume has been reduced to one-third that of the former type of earth station. The disassembled station can be loaded into a small sedan. Using newly developed technology, this earth station offers very good economy and high performance, in spite of its small size. These earth stations were used in the Kobe area to restore telecommunications after the Great Hanshin Earthquake. Dozens of lines were activated with 11 UESs, which transmitted more American Institute of Aeronautics and Astronautics than several hundred calls per hour. It proved the effectiveness of the satellite communications and the new earth stations.This paper describes the configuration and characteristics of the newly developed LIES.