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.

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.

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 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.

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.

A proposal on the configuration of AFC applicable to a wide range of frequency offset

Yamashita, Fumihiro,Nakasuga, Yoshinori,Mitsugi, Jin,Ueba, Masazumi 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-

Future mobile satellite communications systems will provide services to fast vehicles. Thus, the signal received by the user terminals may experience a wide frequency shift away from the assigned frequency that is caused by the Doppler shift and insufficient precision of the Oscillator. This paper presents a new auto-frequency control (AFC) configuration that is capable of removing a large amount of frequency offset (about ${\pm}$0.6 fs, where fs means symbol rate of signal). The operational principle of the AFC is described, and its BER performance and initial acquisition time are evaluated via computer simulation.

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.

An Architecture of Group MODEM with Timesharing Processing for Satellite Communication Networks

Tanabe, Kazuhiro,Sagawa, Yuichi,Kobayashi, Kiyoshi,Ohata, Kohei,Ueba, Masazumi 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-

A satellite communication system for a mesh type network must support many multi-point connections simultaneously, and allocate satellite channels with the required data rates to support each connection independently. The conventional approach is excessively expensive since it forces the earth station to have one single carrier modem for each connection. To eliminate this problem, we introduce the Multicarrier/Multirate Group MODEM for earth stations. This new MODEM is implemented as a single LSI chip. The current version supports up to 128 communication channels simultaneously, and the bandwidth of each communication channel can be set individually. This paper describes the architecture and processing method of the modem and proposes an algorithm that decreases buffer circuit so as to reduce circuit size. Performance evaluation results are shown.