Tetsushi Ikegami

A slot‐array antenna on a coaxial cylinder with a circularly polarized conical beam

In mobile communication, omnidirectional directivity and circular polarization are convenient properties because when they are used, acquisition and track operations for direction and polarization are not needed. As an antenna which has such properties, we developed a slot-array antenna on an oversize coaxial cylinder. This array antenna has less loss than microstrip arrays because energy is transported to each slot in the oversize coaxial waveguide. Also we can shape the beam in the vertical plane by controlling the size and position of slots. We developed cosecant and conical beam antennas. They are scale model antennas for respectively indoor communication by millimeter waves and mobile satellite communications. We show the performance of these antennas.

Throughput performance of CDMA-ALOHA in S-band land mobile satellite channel

The throughput performance of mobile satellite communications using the unslotted-CDMA-ALOHA system is examined. Computer simulation is carried out using measured propagation data, and throughput performance for the different propagation characteristics are compared. The simulation result shows that the short packet length raises the efficiency of mobile satellite communications. The difference of the propagation characteristic appears in the performance in the longer packet. The throughput performance of the communication channel of the urban city is worse than the suburb, when the traffic is small. The characteristics improve, when the traffic increases.

Variable data rate CDMA experiment with non-geostationary ETS-VI satellite

A variable data rate CDMA system is tested for mobile and personal multimedia random access satellite communications. This system utilizes a constant occupied bandwidth, and has variable data rates and processing gains to mitigate communication link impairments such as fading, rain attenuation, and interference as well as to provide variable data rates on demand. A conceptual hardware system is developed, which uses MSK-type constant envelope direct sequence spread spectrum modulation and handles data rates from 4-64 kbps with FEC. The receiver structure provides variable data rates on demand during a call without the aid of system control earth stations. The proposed system is described, along with the CDMA performance of the prototype equipment with the non-geostationary ETS-VI satellite at the S-band (2.3/2.1 GHz) with Ka-band (30/20 GHz) feeder link. The use of FEC reduces the effect of multiple access interference, and enhances the bit error performance under CDMA conditions. Both the IF loop back and satellite link test performances of the prototype equipment prove it has the potential for personal and mobile satellite applications.

Japan's activities for realizing satellite-based high data rate communications networks

Recently, several activities relating high data rate satellite communications systems have been conducted by CRL in Japan. As the first step of implementation of high data rate (HDR) satellite communications network, CRL starts 155 Mbps ATM/SDH transmission experiment using NTTs new operational satellite N-STAR in December 1995 and the trans-Pacific HDR satellite communications experiment is to be started in April 1996 using Intelsat and NASAs Advanced Communications Technology Satellite (ACTS). To play a major role in the Global Information Infrastructure, satellite communications systems are required to have much higher capacity than 155 Mbps. For realizing gigabit satellite communications systems, CRL already started a study relating to required transponder technology, communications systems and networking technologies. This paper describes detail of these experiments and research project for realizing gigabit satellite communications systems.

Experimental investigation of CDMA mobile satellite communication system

The performance of a direct sequence spread spectrum CDMA communication system in an actual land mobile satellite channel is experimentally evaluated. Field test results using the ETS-V satellite in urban and suburban environments at L-band frequency show that this land mobile satellite channel of 3 MHz bandwidth can be seen as a non-frequency selective Rician fading channel as well as a shadowing channel. The bit error performance can be estimated using signal power measurements as if they were narrow band modulation signals. Based on the experimental results of the ETS-V, a prototype system for the personal satellite communication is proposed and field tests are planned on the S-band frequency using the ETS-VI satellite which will be launched in August 1994.<<ETX>>

Field tests of a spread spectrum land mobile satellite communicationsystem using ETS-V satellite

The performance of a Direct Sequence Spread Spectrum Communication system in actual land mobile satellite channel is evaluated with experiments. Field test results in L-band with the ETS-V satellite are presented, in which the use of a multi-bitquantized Coherent Matched Filter receiver improves the initial acquisition and the bit error rate performances. The BER characteristics in urban and suburban environments are found to agree with that of nonSS BPSK on a non-selective Rician fading channel.