Naoko Yoshimura

Toward Optimized Traffic Distribution for Efficient Network Capacity Utilization in Two-Layered Satellite Networks

A multi-layered satellite network (MLSN) appears to be a promising network for providing global ubiquitous broadband communication. To utilize the abundant network resources of the MLSNs, fair traffic distribution among its satellite layers is, indeed, important. In this paper, we propose a routing method to optimally distribute traffic load among the layers (i.e., the satellite layers in the MLSN). The load balancing scheme of the proposed routing method is developed by adopting a traffic distribution model, which is based upon network capacity estimation and theoretical analysis of the congestion rate in each layer. The performance of the proposed routing method has been validated through extensive computer simulations, which demonstrate that our traffic distribution model is reliable enough to characterize the traffic behavior in the MLSN. Furthermore, in contrast with the basic routing approach, our proposed routing method is more effective in terms of improved throughput and lower packet drops, which are optimized by the theoretical parameter setting.

Assessing packet delivery delay in multi-layered satellite networks

Non-Geostationary satellite networks have many advantages to enable ubiquitous wireless environments such as, extensive coverage, disaster-resistance, and efficient power consumption. Furthermore, to use these networks more efficiently, multi-layered satellite networks are a promising approach, due to their ability to achieve increases in network capacity and to detour traffic efficiently, while maintaining the advantages of each layer. However, they suffer from high delay. In this paper, we focus on constellation design of two-layered satellite networks, in particular on the satellite altitude that minimizes the total packet delivery delay of the network. We express the relationship between the total packet delivery delay and the satellite altitude in mathematical form and develop an expression for determining the altitude to minimize total packet delivery delay. Simulation results validate our analyses.

A delay-based traffic distribution technique for Multi-Layered Satellite Networks

Recently, Non-Geostationary Earth Orbit (NGEO) satellite networks have gained research attention. Since they offer many features, e.g., extensive coverage, disaster-resistance, and efficient power consumption, they are considered as a good candidate for providing global communication services. Moreover, Multi-Layered Satellite Networks (MLSNs), which consist of layered NGEO satellite networks, have attracted much attention since they achieve excellent load distribution through bypassing traffic from the lower layer to upper layer. However, there is a possibility that traffic congestion may exist at a satellite on the upper layer because each satellite on the upper layer usually covers more than one satellite on lower layers in MLSNs. In this paper, we focus on traffic control in two-layered networks, especially on distributing the packet flow between the two layers in order to minimize the transfer delay of the network. Simulation results demonstrate the correctness of our analyses about delay in the network.

On real-time data gathering in next generation satellite-routed sensor system (SRSS)

Recently, satellite-routed sensor systems are expected to be used as early disaster detection systems. The networks efficiently provide data collected from wide areas with small sensor terminals and satellites. In this system, each sensor terminal collects and sends data to monitoring stations on the ground via satellites. Although the future major disaster detection systems require high capacity to manage numerous sensor terminals, it is difficult to collect data from a large number of sensor terminals simultaneously since the bandwidth of each satellite is limited. Hence, an efficient system to allocate the bandwidth to each sensor terminals is required. Moreover, for early disaster detection, the real-time performance is very important. Therefore, in this paper, we discuss an appropriate bandwidth allocation model to construct a next generation satellite-routed sensor system while considering the real-time performance. In the new model, we particularly focus on the relationship between throughput of each sensor terminal and real-time performance, and introduce a method to allocate bandwidth. A numerical analysis is used to validate the new system model.

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.

Packet Transfer Delay Minimization by Network-Wide Equalization of Unbalanced Traffic Load in Multi-Layered Satellite Networks

Multi-Layered Satellite Networks (MLSNs) have many advantages such as extensive coverage, lower delay performance, and disaster resistance. Moreover, the networks permit load distribution by bypassing traffic efficiently from lower layers to upper layers. In the future, the MLSNs should play an important role to provide global communication services. However, sometimes traffic congestion happens in these networks since the distribution of users is unbalanced heavily depending on geographical restrictions, which causes bad effects on the networks such as increasing delay. Therefore, we focus on network design to avoid traffic congestion. There are many constitution elements to design these networks. One of the most significant elements is the altitude of satellites because it affects propagation distance and number of links between layers in MLSNs, and thus the packet transfer delay of the networks. Therefore, we analyze the relationship between the altitude of satellites and the packet transfer delay with network-wide equalization. Furthermore, the existence of the optimal altitude of satellites is denoted in this paper. Our analyses are validated by simulation experiments.

A centralized multiple access scheme for data gathering in Satellite-Routed Sensor System (SRSS)

Satellite-Routed Sensor System (SRSS) has attracted attentions as a next generation sensor network system to realize data gathering from a large scale sensors deployment. In this system, a large number of sensor terminals send sensed data to the monitoring stations which are located in the different area via a satellite. With the help of satellite, it is possible to collect data from sensor terminals that are located in an area that has no physical infrastructure. Thus, SRSS is expected to provide many services such as real-time traffic control system and disaster detection systems by utilizing gathered data from large area. However, an efficient access control method is required to accommodate a large number of sensor terminals trying to transmit their sensed data to the satellite. Therefore, this paper proposes a novel data gathering method that can efficiently allocate bandwidth to the sensor terminals in need to transmit their sensed data. Additionally, an optimization to improve the efficiency of our proposed method is provided with mathematical expressions. The effectiveness of our proposal is evaluated through numerical results.

Development of High -Data -Rate Burst Modem for WINDS

[Abstract] The Wideband Internetworking Engineering Test and Demonstration Satellite (WINDS) is an engineering test satellite for research and development of technology for future satellite communication networks. The National Institute of Information and Communication Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA) are jointly developing the WINDS, and it is scheduled for launch in FY 2007. NICT has developed a high-data-rate burst modem for the WINDS network. The data rate of the modem is 622 Mbps. During the WINDS proto-flight test in October 2006, the modem’s BER was measured through the satellite transponder with a high-data-rate communication system of an earth station that consists of the modem and RF components. The measurement was conducted using the transponder in bent-pipe mode over six of its typical routes.

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.

The Tele-Operation Experiment of the Hybrid Remotely Operated Vehicle Using Satellite Link

Communication via satellite is the only method for communicating between the ocean and land. However, present commercial satellites cannot provide sufficient bandwidth to transmit the requisite volume of data. The National Institute of Information and Communications Technology (NICT) and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted broadband satellite communication experiments with the Wideband Inter-Networking engineering test and Demonstration Satellite (WINDS). Using WINDS, the tele-operation of a hybrid remotely operated vehicle (HROV), Otohime, was also carried out successfully.Copyright