Jin Mitsugi

Phased array fed reflector antennas with interpolation network for next generation mobile satellite communication systems

We propose a modified DCMP method that considers the influence of the interpolation network. An onboard array-fed-reflector antenna with the interpolation network is designed using the modified DCMP method. We confirmed the validity of the method by calculating the resulting antenna patterns. The antenna patterns formed by the array feeder with the interpolation network satisfy the required antenna performance.

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.

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.

An excitation weight determination method for onboard phased array antennas with weight interpolation network

In order to realize lightweight onboard satellite antennas, we proposed a technique that uses linear interpolation to reduce the number of control circuits. Compared to the conventional approach, the reduction is about 70%. To apply the technique to practical multi-beam systems with frequency reuse, it is necessary to meet the requirement in term of beam isolation. This paper presents a method for determining the excitation weights so as to meet the requirement of multi-beam systems with frequency reuse. We confirm the validity of the method by calculating the antenna patterns generated by the excitation weights output.

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.

A NOVEL TECHNIQUE FOR SUPPRESSING HEAT IN ONBOARD HIGH- POWER AMPLIFIERS

Satellite communication systems have entered the mobile multimedia communication era. To support small earth terminals, the satellites must have high levels of effective isotropic radiated power. Onboard high-power amplifier not only need to generate high RF output power, but also to generate as little heat as possible. To address this issue, we present a new technique that reduces the amount of heat generated in high power amplifiers on a satellite. The technique makes use of heat suppression signals so as to maintain the amplifier’s power efficiency. The potential impact on satellite systems is presented. To minimize the interference of the heat suppression signals on the carrier, some techniques are proposed using a multi-port amplifier and an antenna array and a reflector.

IP NETWORK PERFORMANCE OF A Ku BAND MOBILE MULTIMEDIA SATELLTE SYSTEM

We have proposed a mobile multimedia satellite communication system designed to realize high-speed multimedia communications. This system uses a mobile network for the return link and a newly developed tracking antenna that receives high-speed satellite signals for the forward link. This paper describes the system configuration, the tracking antenna performance and the IP network’s performance in mobile environments. The tracking antenna was accurate to within 0.80 degree rms and 0.25 degree rms in azimuth and elevation, respectively. These accuracies meet the pointing loss requirement, 1 dB, in the link analysis. The network performance of the system was evaluated both in stationary and mobile environments by measuring the round trip time and the throughput. These characteristics were measured for several return link implementations, e.g., PDC (Japanese Cellular Standard), PDC-Packet (Packet communication service of PDC) and Satellite phone. Even in mobile environments, 1 Mbit/s of throughput, which is limited by the system round trip time, can be achieved for file downloading with TCP as transport protocol. This throughput can be increased to almost the network limit when XTP is applied as the transport protocol.