Masato Tanaka

A new method to evaluate blocking probability on high elevation satellites viewed from land vehicles

In this paper, we propose a new method for evaluating the probability of interruptions in communication links between a vehicle in different geographic areas and a satellite at a certain elevation-azimuth angle with respect to the orientation of the vehicle. This method uses the Global Positioning System. The results suggests that EFSAT is more suitable for land-mobile satellite communications than a geostationary satellite in terms of blocking by features on the ground in both cities, expressways and rural areas.

An effective method to evaluate intermittent blocking on land vehicle satellite communications

In this paper, we propose an effective method to evaluate intermittent blocking on land-mobile satellite communications. This method uses the Global Positioning System. The results suggest that EFSAT, which provides higher elevation angles to areas in middle latitudes, is more suitable for land-mobile satellite communications in urban areas than a geostationary satellite in terms of blockage by features on the ground.

A novel evaluation method of blockage by ground features on land vehicle satellite communications

We propose an effective method to evaluate intermittent blocking on land-mobile satellite communications. This method uses the Global Positioning System. The result suggests that EFSAT (Eight-Figure SATellite) which provides higher elevation angles to areas in middle latitudes, is more suitable for land-mobile satellite communications in urban areas than a geostationary satellite in terms of blockage by features on the ground.

COMETS for Ka-band and millimeter-wave advanced mobile satellite communications and 21 GHz advanced satellite broadcasting experiments

COMETS (Communications and Broadcasting Engineering Test Satellite), which was developed to evaluate Ka-band (31/21 GHz) and millimeter-wave (47/44 GHz) advanced mobile satellite communications and 21-GHz advanced satellite broadcasting systems, is presented as well as the developed ground terminals. COMETS carries an SCPC/TDM regenerative transponder for direct mobile-to-mobile communications, and IF-filterbanks for interconnection between multibeams. For mobile and personal applications, a portable terminal for regenerative transponder experiments, and several antennas such as an active phased array antenna, a waveguide slot array antenna, and a torus reflector antenna were developed. For satellite broadcasting experiments, trellis-coded modems for HDTV transmission at 60/140 Mbps and 155 Mbps were developed.

On-orbit measurement of phased arrays in satellites by rotating element electric field vector method

This paper discusses the measurement of the excitation amplitude and phase of each element antenna of phased arrays in satellite orbit. In a phased array, the excitation amplitude and the phase of each element antenna deviate from the desired values, due to the nearby satellite structure, the error of attachment to the satellite, and thermal deformation in the orbit. The errors in the amplitude and the phase must be known for beam scanning and the synthesis of various antenna patterns. The rotating element electric field vector method is useful in measuring the amplitude and the phase of phased arrays. In this method, the amplitude and the phase of the element antenna can be determined simply by varying the phase of the element antenna by a phase-shifter and measuring the amplitude change of the electric field as a result of composition by the array. This is suited to the measurement of phased arrays in satellite orbit, where direct measurement of the phase is difficult. In this study, the above method is used to measure the excitation amplitude and phase of the phased array installed on Engineering Test Satellite VI in orbit. Based on the measured phase, the phase is corrected to realize the designed value. The accuracy of the beam directivity is examined and the validity of the measurements is evaluated.

Block-coded modulation and multiple block-coded modulation with Viterbi decoding for fading channels

This paper describes how block-coded modulation (BCM) and multiple BCM (MBCM) with Viterbi decoding can be designed for use in Rayleigh fading and severe Rician fading channels. New codes are developed by modifying known codes to increase the minimum symbol distance, which is one of the distances that has a strong effect on the bit error rate (BER) performance under fading channels. Combined with anti-fading techniques such as fading compensation, interleaving, and branch weighting, the new codes significantly improve BER performance. Computer simulations were used to confirm the code performance.

Development of a Ka-band active phased array antenna for mobile SATCOM stations

This paper describes a Ka-band active phased array antenna for mobile SATCOM stations. The active phased array is a fully electronic beam-scanning antenna system and is the most technically challenging component in the system development of the Japanese engineering test satellite, COMETS. The hardware components of the antenna, such as antenna element, LNA, and MMIC phase shifter, are described. Antenna tracking performances were measured and analyzed using a land mobile station and an aeronautical mobile station.

ARRAY ELEMENT AND BFN DESIGN FOR PIIASED-ARRAY-FED SATELLITE ANTENNAS

A lightweight, high-efficiency feed array element and a new architecture for the beamforming network (BFN) of phased-array- fed satellite antennas are presented. The array element is a circular microstrip antenna with a metal cup (cupped MSA). which has very suitable mechanical and electrical characteristics especially for phased-array-fed antennas with a large number of elements. The BFN architecture reduces the mass and the complexity of the BFN hardware through the sharing of variable phase shifters for beamsteering.

A study of multimedia CDMA system for personal satellite communication

A variable data rate CDMA system with constant envelope modulation is studied by hardware simulation for personal multimedia random access satellite communications in the Ka-band and millimeter-wave region. 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 handle a variable data rate on demand. A proof of concept hardware system for a 6 MHz bandwidth transponder is developed for hardware simulation, which uses MSK-, GMSK-, and OQPSK-type constant envelope direct sequence spread spectrum modulation and handles data rates of 4 to 64 kbps. The receiver is designed with a coherent matched filter technique to achieve fast code acquisition, AFC and coherent detection in a single matched filter circuit. This receiver structure facilitates a variable data rate 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 Ka-band (30/20 GHz). Both the IF loop back hardware simulation and satellite link test performances of the prototype equipment prove it has the potential for personal multimedia satellite applications.

A class-coded modulation method using orthogonal wavelets

Researchers have studied two types of digital multi-carrier modulation, wavelet packet modulation (WPM), and fractal modulation. The advantage of WPM is that it allows signal time and frequency to be divided and multiplexed. Therefore the time and frequency of noise signals, e.g., tone and impulse noise, can be identified and effectively partitioned in packets. Using this advantage, we propose a class-coded modulation method for WPM that has good bit error rate (BER) performance when the length of the code constraint is extended and can select time and frequency noise signals simultaneously. This report describes the proposed method and the computer simulations carried out to test its effectiveness.