IP Network Performance in Mobile Environments over Ku Band Satellite Links

Nagase, Fumiaki,Tanaka, Hiroshi,Ueba, Masazumi 통신위성우주산업연구회 2001 Joint Conference on Satellite Communications Vol.2001 No.-

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 the newly developed tracking antenna that receives high-speed satellite signals for the forward link. This paper describes IP network performance evaluation results of the proposed system in mobile environments. First, we measured round trip time and TCP throughput and confirmed the coincidence between experimental and theoretical TCP throughput that can be obtained from round trip time and TCP window size. Then, in order to make throughput recovered right after a shadowing environment caused by buildings, trees, etc. in which the tracking antenna can not receive satellite signals, the XTP (Xpress Transfer Protocol), which is designed to boost throughput for long latency networks, was incorporated into the proposed system and throughput tests were carried out. We confirmed that the throughput was improved and almost reached the network limit by the tests. We also clarified that the XTP is effective even in a low network quality that includes shadowing environments.

Satellite experiments on Variable Polarization/Frequency Division Multiplexing(VPFDM)

Yamashita, Fumihiro,Kobayashi, Kiyoshi,Ueba, Masazumi,Zakouji, Takaaki 통신위성우주산업연구회 2006 Joint Conference on Satellite Communications Vol.2006 No.-

We report the results of satellite experiments on Variable Polarization/Frequency Division Multiplexing (VPFDM) and its operational principles. VPFDM is a new multiple access method that enables each user to freely utilize dual polarization and frequency resources. No BER degradation was observed in VPFDM satellite experiments, meaning that the VPFDM modem can demodulate received signals as expected regardless of the polarization rotation angle or dynamic polarization rotation. Because of this performance, we expect VPFDM to be applied to the maritime satellite communications service called Earth Station onboard Vessel (ESV)[l][2], to which Ku band is allotted as a primary band in the WRC 2003.

Satellite Link Availability Analysis using 3-Dimensional Map Data

Imaizumi, Yutaka,Ohata, Kohei,Ueba, Masazumi 통신위성우주산업연구회 2006 Joint Conference on Satellite Communications Vol.2006 No.-

We propose a method of simulating satellite link availability that uses three dimensional map data. Our method calculates the satellite signal reception level at a reception point by taking into account diffracted and/or reflected waves as well as direct waves. This paper identifies simulation parameters that enable calculations that show good agreement with measured satellite signal reception levels. Our work further shows the following. 1) To calculate satellite signal levels accurately it is necessary to take into consideration diffracted and reflected waves as well as direct waves. 2) The optimum reflection coefficient of building walls and roads was 10 dB for this evaluation environment. 3) The radius of the observation area where the reflected wave was calculated was about 150 m. This choice of area was made considering CPU time required to calculate one reception point. In future work the optimum radius will be determined by evaluating the accuracy of simulation results. The results confirmed that our satellite link availability analysis can effectively predict link conditions.

A Satellite Resource Allocation for Multi-Beam Satellite Communication System

Sagawa, Yuichi,Ohata, Kohei,Ueba, Masazumi 통신위성우주산업연구회 2003 Joint Conference on Satellite Communications Vol.2003 No.-

A multi-beam system is one solution for enlarging the communication capacity by re-using the limited system frequency band, but system resources should be allocated to each user considering the interferences from vicinity beams(users). In addition, in mobile satellite systems, the resource allocation must consider user mobility and the uneven user distribution in the system and each beam. In this paper, we analyze an FDMA based multi-beam satellite system resource allocation scheme that considers both inter-beam interference and user distribution in the system in controlling both forward link power and frequency simultaneously. We confirm that this scheme enhances system capacity relative to the CDMA system, which uses the entire system frequency band.

A Method of Single-hop Connection between Mobile User Terminals Using a Through Repeater GEO Mobile Satellite

Kataoka, Nobuyuki,Ebina, Kazuhito,Ueba, Masazumi 통신위성우주산업연구회 2001 Joint Conference on Satellite Communications Vol.2001 No.-

In conventional geostationary mobile satellite communication systems, users may experience bad quality of service due to a large propagation delay, which is caused by the double-hop connection link. In a double-hop link, a signal is passed through the satellite twice and the base station once before reaching its destination. To reduce the propagation delay, it is necessary to have single-hop connection link that connects user terminals directly by passing through the satellite only once. The single-hop connection method proposed in this paper uses a through repeater satellite to which future services can be accommodated. The method uses a newly developed common control channel to send the signaling messages to users during the single-hop connection. We evaluate its performance and show its feasibility.

Real-space and real-time observation of a plasmon-induced chemical reaction of a single molecule

Kazuma, Emiko,Jung, Jaehoon,Ueba, Hiromu,Trenary, Michael,Kim, Yousoo American Association for the Advancement of Scienc 2018 Science Vol.360 No.6388

<P>Plasmon-induced chemical reactions of molecules adsorbed on metal nanostructures are attracting increased attention for photocatalytic reactions. However, the mechanism remains controversial because of the difficulty of direct observation of the chemical reactions in the plasmonic field, which is strongly localized near the metal surface. We used a scanning tunneling microscope (STM) to achieve real-space and real-time observation of a plasmon-induced chemical reaction at the single-molecule level. A single dimethyl disulfide molecule on silver and copper surfaces was dissociated by the optically excited plasmon at the STM junction. The STM study combined with theoretical calculations shows that this plasmon-induced chemical reaction occurred by a direct intramolecular excitation mechanism.</P>

Direct Pathway to Molecular Photodissociation on Metal Surfaces Using Visible Light

Kazuma, Emiko,Jung, Jaehoon,Ueba, Hiromu,Trenary, Michael,Kim, Yousoo American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.8

<P>We demonstrate molecular photodissociation on single-crystalline metal substrates, driven by visible-light irradiation. The visible-light-induced photodissociation on metal substrates has long been thought to never occur, either because visible-light energy is much smaller than the optical energy gap between the frontier electronic states of the molecule or because the molecular excited states have short lifetimes due to the strong hybridization between the adsorbate molecular orbitals (MOs) and metal substrate. The S-S bond in dimethyl disulfide adsorbed on both Cu(111) and Ag(111) surfaces was dissociated through direct electronic excitation from the HOMO-derived MO (the nonbonding lone-pair type orbitals on the S atoms (n(s)))to the LUMOderived MO (the antibonding orbital localized on the S-S bond (sigma*(ss))) by irradiation with visible light. A combination of scanning tunneling microscopy and density functional theory calculations revealed that visible-light-induced photodissociation becomes possible due to the interfacial electronic structures constructed by the hybridization between molecular orbitals and the metal substrate states. The molecule metal hybridization decreases the gap between the HOMO-and LUMO-derived MOs into the visible-light energy region and forms LUMO-derived MOs that have less overlap with the metal substrate, which results in longer excited-state lifetimes.</P>

Fundamental Characteristics of Onboard Bandwidth-Variable FFT Filter Bank

Yamashita, Fumihiro,Kazama, Hiroshi,Nakasuga, Yoshinori,Ueba, Masazumi 통신위성우주산업연구회 2000 Joint Conference on Satellite Communications Vol.2000 No.-

Voice service is currently the main service in mobile satellite communications, but in the future, there will be a demand for high-data rate services offering multimedia contents. Therefore, an onboard processor capable of handling services of various data rates is required. In the present study, it is assumed that a non-regenerative onboard processor will be used. The onboard processor must have functions to filter signals and convert their frequencies in a channel-by-channel manner. An FFT filter bank satisfies these requirements. However, the conventional onboard FFT filter bank is only applicable to signals of constant bit rate. Hence, the onboard bandwidth-variable filter bank that can handle many signals of various bit rates is proposed. The principle of operation of the bandwidth-variable FFT filter bank is described, then the BER performance of an FPGA-implemented design is evaluated.

Multicarrier/Multirate modem providing channel de-assemble and assemble functions

Tanabe, Kazuhiro,Kobayashi, Kiyoshi,Ohata, Kohei,Ueba, Masazumi 통신위성우주산업연구회 2001 Joint Conference on Satellite Communications Vol.2001 No.-

A satellite communication system for enterprise Intranets must be able to support simultaneous multi-point connections among dispersed locations and to allocate satellite channels with the required data rates of each of the connections independently. To meet these requirements, the Multicarrier/Multirate Group Modem (MCMRM) for earth stations is proposed that can process multiple and various rate. MCMRM has the following features. 1. Supports simultaneous communications with hundreds of channels. (Maximum 768) 2. The prototype modem is roughly the same size of as the conventional single carrier modem. 3. To secure flexibility and scalability, the developed modem consists of independent modules. 4. Supports the allocation of bandwidth required over dispersed frequency bands, even if continuous frequency band is not available. MCMRM consists of a multi-rate filter bank and a group modem implemented on several FPGAs controlled by a timesharing system. Evaluations show that MCMRM has even higher BER performance than a conventional single carrier modem. This paper describes the architecture and processing method of MCMRM and performance evaluation results.

A Study on an Optimal Resource Allocation Algorithm for Next Generation Mobile Satellite Communication Systems

Nakahira, Katsuya,Kobayashi, Kiyoshi,Ohata, Kohei,Ueba, Masazumi 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

To yield a large communication capacity in future mobile satellite communication systems, a multi-beam system must be employed that has extremely high levels of frequency reuse. This paper proposes a novel resource allocation algorithm for multi-beam satellite communication systems that can dynamically offer the virtually maximum communication capacity. The algorithm optimizes frequency bandwidth, satellite transmission power, modulation level and coding rate to each beam to deal with the ever changing traffic distribution considering interference between beams. First, the optimal resource allocation is found by evaluating capacities for all possible resource allocation patterns. Although, this primitive search takes a huge amount of computer calculation power, the achieved communication capacities are higher than with conventional ones such as fixed resource system. In addition, the results of analysis clarify the the optimal condition by which all clusters have the same bandwidth allocation ratio. Second, we propose an optimal resource allocation algorithm utilizing the aforementioned condition as a constraint. By using our algorithm, which is based on sequential quadratic programming, the calculation amount can be drastically reduced. It is confirmed that the algorithm allocate the same bandwidth as that by the amount can be drastically reduced. It is confirmed that the algorithm allocate the same bandwidth as that by the primitive search method for varieties of traffic model. This means that the preposed algorithm is applicable for multi-beam satellite resource allocation.