Masazumi Ueba

Broadband multiple satellite MIMO system

This paper proposes a multiple satellite MIMO system for broadband mobile services. It also proposes a MIMO receiver that can handle the large spatial correlation and the different propagation delay of paths created by the use of multiple satellites. The receiver is characterized by multi-stage interference cancellation and maximal ratio combining. Several simulations are conducted assuming two satellites on the same GEO stationary orbit that are separated by about one degree. The simulation results show that the proposed receiver can typically obtain the diversity gain of about 1.0 dB at BER=10 -5 from the theoretical SISO BER curve due to its use of Even in the worst propagation case, the BER degradation is suppressed to about 1.5 dB.

Network performance evaluations for Ku band mobile satellite communications system based on Shinkansen railroad's propagation conditions

This paper presents the network performance of our Ku band mobile satellite communications system under actual Shinkansen railroad propagation conditions. First, satellite visibility were judged by examining the obstacles obscuring the satellite in video taken by a small CCD camera with a fish-eye lens that was placed under the roof window of the Shinkansen High-Speed Multiple Inspection Train. After obtaining satellite visibility data, the statistical features of the obstacles affecting satellite visibility were analyzed. Based on these data, we clarified the optimum design parameter of layer-3 diversity, which is a diversity reception scheme for selecting IP packets (layer 3) as a shadowing countermeasure technology. The network throughput for all Tokaido Shinkansen routes was simulated on the test bed by using the satellite visibility data. The effectiveness of the shadowing countermeasure technology is discussed in relation to these throughput results.

Highly Accurate Inclinometer Robust to Ultralow-Frequency Acceleration Disturbances and Applications to Autotracking Antenna Systems for Vessels

This paper describes a new inclinometer that compensates for ultralow-frequency acceleration disturbances. This inclinometer consists of a low-cost accelerometer, pendulum, and rotary encoder. The key feature of this inclinometer is the estimation method used to calculate the pendulums inertial angle. We propose two algorithms to estimate the pendulums angle. Algorithm I uses time-averaged accelerations and some assumptions. Algorithm II applies the pendulums equation of motion. The results of simulations and experiments confirm that both algorithms can achieve highly accurate level/angle estimations under acceleration disturbance conditions. We apply this inclinometer to an autotracking antenna system for vessels. Time simulations verify its effectiveness.

Communication Capacity Enhancement with Adaptive Resource Assignment for Multi-beam Mobile Satellite Communication Systems

Mobile satellite communication systems are attracting much attention as an effective way to provide broadband communications in planes, ships, and long-haul trains in which economical services are not effectively provided by terrestrial systems. Such a system usually requires a wide frequency bandwidth and a satellite with high electrical output power, but these resources are severely restricted. A multi-beam system with frequency reuse is able to spread the usable bandwidth virtually. Applying an adaptive modulation method to the system achieves efficient use of resources. In this system, optimally assigning resources to beams is indispensable in enhancing the system capacity. However, this optimization method becomes complex since it is necessary to consider the influence of inter-beam interference which may depend on the variation in the communication traffic distribution. We propose a new adaptive resource assignment method in order to overcome this complexity and to enhance the system capacity. In the proposed method, a bandwidth vector and an approximate curve of the spectrum efficiency are introduced. Based on case studies assuming 19 beams, we show that the proposed method achieves 4.2 times higher system capacity than that of a system in which resources of each beam are fixed.

High Accuracy Auto-Tracking Antenna System Using H-infinity Control for Earth Stations on Board Vessels

Broadband communication services are expected in all mobile environments. A satellite communication system is only way to provide access in many cases. Because the frequency bandwidth allocated to mobile satellite services (MSS) is insufficient, use of the frequency band for fixed satellite services (FSS) is considered. In this case, mobile antennas must have the same pointing accuracy as fixed earth stations. The constraints placed on the pointing error and other antenna attributes have been discussed in ITU-R. The provisional required pointing accuracy is 0.2 degrees. This level of accuracy is usually achieved only with expensive gyro systems and monopulse antennas. This paper describes a cost-effective antenna system that uses practical sensors and a step-track-like tracking technique. The key points described in this paper are the stable platform configuration, H-infinity digital controller, and dithering antenna pointing technique. Simulation results show that this antenna system meets the ITU-R requirements.

Forward link multiple access scheme for broadband and scalable mobile satellite communication system

The paper proposes and evaluates a forward link multiple access scheme for a next generation broadband and scalable mobile satellite communication system that offers transmission capacity of 1 Gbps and the maximum bit rate of 100 Mbps. Two major evaluation items are considered. (1) Capacity comparison is made among frequency reuse schemes: single frequency (SF); multiple frequency (MF); variable boundary multiple frequency (VMF). (2) Bit error rates are evaluated among four multiplexing schemes (FDM, OFDM, OCDM and TDM) in terms of required E/sub b//N/sub 0/ through nonlinear and frequency selective Rician fading channels. Evaluation results show that the proposed multiple access scheme, which combines VMF reuse with FDM or OFDM multiplexing, is the optimal solution.

Shadowing countermeasure technology with layer 3 diversity reception for Ku band mobile satellite communication systems

A layer 3 diversity reception scheme that enhances the transmission characteristics of Ku band mobile satellite communication systems is presented. The initial thrust for developing this scheme is to realize high-speed communication for trains that experience shadowing caused by terrestrial obstacles such as tunnels, buildings, bridges and structures that support trolley wires. Layer 3 diversity was chosen for long distance diversity to prevent signal shadowing caused by terrestrial obstacles and to yield packets in the same order as in the original packet stream while minimizing the alterations of existing receivers. The technology enables high-speed communication under simulated shadowing conditions in a running train environment while assuring correct packet order.

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.

Deformed Antenna Pattern Compensation Method for onboard Multi-beam Antennas

To create a next-generation mobile satellite communication system that offers large communication capacity, the onboard antenna system must be a multi-beam system consisting of a light weight 20-m class reflector and a light weight 100-beam class antenna feed system. We clarified that the antenna patterns were deformed by a thermal distortion of the reflector surface and that the antenna gain decrease is relatively large. Our studies confirmed that all of the deformed antenna patterns could be compensated using variable phase-shifters connected to each feed element. This paper proposes a deformed antenna pattern compensation method as an extension of our previous study and describes the results of experiments on a fabricated array-fed reflector antenna that possesses the proposed compensation function.

AFC CONFIGURATION APPLICABLE TO A WIDE RANGE OF FREQUENCY OFFSET

This paper presents a new automatic-frequency control (AFC) configuration capable of removing a large amount of frequency offset (up to about +/- 0.625 fs, where fs means symbol rate of signals). The new AFC consists of the AFC that removes frequency offsets between +/- 0.125 fs and another AFC that detects the frequency offset range coarsely between +/- 0.625 fs. First, the principle of the new AFC configuration is described. Then, the performance of the new AFC is confirmed via computer simulation. It is shown that the proposed AFC configuration can accommodate wide range frequency offsets as well as reduce the acquisition time.