Ryutaro Suzuki

Demonstration of robust multi-hop wireless packet broadcasts for moving vehicles using aggregated redundancy

We demonstrate a method for improving quality of ad-hoc multihop wireless communications between moving vehicles. This method is designed to overcome problems of high packet loss and route instability common in inter-vehicular communications. We implemented the proposed method as middleware supporting real-time packet transmissions such as VoIP, and evaluated the performance in experimental tests, including a 3-vehicle test on a public road. We obtained measurement results showing maximum packet loss lower than 5 %, compared to more than 80% with existing implementations of the ad hoc routing protocols OLSR and AODV. We also showed that it is possible to support good quality VoIP broadcasts at normal traffic speeds of from 40km/h to 60 km/h on open roads.

CURRENT STATUS OF NeLS PROJECT: R&D OF GLOBAL MULTIMEDIA MOBILE SATELLITE COMMUNICATIONS

The paper presents the recent situation of the research and development on global multimedia mobile satellite communications system using non-geo type satellite constellations. This system is called Next-generation LEO system (NeLS). NeLS research center has carried out the key technology development of the satellite constellation system, which would provide a global mobile satellite service with broadband handheld terminals. The paper presents the development results of key technologies including the digital beam forming (DBF) satellite antenna, optical inter-satellite link system, on-board switching system.

Microstrip antenna with solar cells for microsatellites

In order to install a high-gain antenna on a microsatellite with solar cells on the surface, a newly designed microstrip antenna has been developed. A high-gain antenna requires the large area of the surface of a microsatellite, therefore, reducing the area for the solar cells. A microstrip antenna with solar cells attached to the surface has been designed. By using this technique, a high-gain antenna can be installed on the surface of a microsatellite without reduction of the area for the solar cells.<<ETX>>

Turbo network coding for efficient and reliable relay

A turbo network coding based relay model and its decoding method are proposed for the quasi-static fading multi-access up-link channel. In the model a relay assists two mobile nodes simultaneously by forwarding a network coded version of the two interleaved messages. Access Point (AP) performs joint channel and network decoding with signals received from two mobile nodes and the relay. Compared with existing schemes, the proposed turbo network coding scheme has two main contributions: (i) Only parity check bits of two messages are forwarded by relay and they are further XORed together to improve relay efficiency. (ii) The iterative decoding is used in joint network and channel decoding to salvage packets from erroneous signals in the absence of a priori knowledge. Simulation results indicate that the proposed scheme provides up to 1.8 dB gain to the existing scheme in the case of mutual cooperation among mobile nodes.

Message Dissemination in Inter-Vehicle CDMA Networks for Safety Driving Support

Although the near-far effect has been considered to be the major issue preventing CDMA from being used in ad-hoc networks, in this paper, we show that the near-far effect is not a severe issue in inter-vehicle networks for safety driving support, where packet transmissions are performed in the broadcast manner. Indeed, the near-far effect provides extremely reliable transmissions between near nodes, regardless of node density, which can not be achieved by CSMA/CA. However, CDMA can not be directly applied in realistic traffic accident scenarios, where highly reliable transmissions are required between far nodes as well. This paper proposes to apply packet forwarding and transmission scheduling methods that try to expand the area, where reliable transmissions are achievable. Simulation results show that the proposed scheme achieves approximately 100% of delivery ratio and 4 milliseconds of delay in a realistic traffic accident scenario, where CSMA/CA achieves approximately 60% of delivery ratio and 80 milliseconds of delay.

Bidirectional Packet Aggregation and Coding for VoIP Transmission in Wireless Multi-Hop Networks

This paper proposes bidirectional packet aggregation and coding (BiPAC), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable VoIP sessions in wireless multi-hop networks. BiPAC applies network coding for aggregated VoIP packets by exploiting bidirectional nature of VoIP sessions, and largely reduces the required protocol overhead for transmitting short VoIP packets. We design BiPAC and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by VoIP transmission, such as delay and packet loss rate. Our computer simulation results show that BiPAC can increase the number of supportable VoIP sessions maximum by around 70% as compared with the case when the packet aggregation alone is used, and 450% in comparison to the transmission without aggregation/coding. We also implement BiPAC in a wireless testbed, and run experiments in an actual indoor environment. Our experimental results show that BiPAC is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.

Optical terminal for NeLS in-orbit demonstration

This paper presents outline of the optical terminal for Next-generation LEO System (NeLS) in-orbit demonstration, which will be conducted as part of Phase 2 of NeLS project. Two small satellites are assumed to launch into GTO orbit changing distance between them from 500km to 3000km. Acquisition and tracking experiments with a star or planet and 2.4Gbps data transmission between two SmartSat is also planned. The design of optical terminal is briefly presented.

Mobile TDM/TDMA system with active array antenna

A multicarrier time-division multiple-access (TDMA) system is proposed for future mobile satellite communications systems that include a multisatellite system. This TDMA system uses an active array antenna in which the digital beamforming technique is adopted to control the antenna beam direction. The antenna beamforming is carried out at the baseband frequency by using digital signal processing. In the proposed system, TDM/TDMA with a time-division duplex technique is adopted for the satellite link between the mobile earth station and the HUB station in order to remove the diplexer from each mobile antenna element.<<ETX>>

Variable spot scanning antenna using optically controlled beam forming network

An Optically controlled beam forming network has been developed, which has capacity of steering 2 beams and exciting 64 antenna elements. Using it, beam steering and beam width control is possible in parallel.

A Study of Constellation for LEO Satellite Network

For a LEO constellation system, it is important to optimize the orbit parameters to maximize the quality of communication service. At the Next-generation LEO System (NeLS) Research Center, the LEO parameters were evaluated for a mobile satellite communication system. A 2π constellation was selected to maintain a stable inter-satellite link (ISL). The performance of optical ISL terminals has since improved as a result of key technological developments at the NeLS Research Center. As a consequence, the constellation parameters for ISL have become more flexible. Furthermore, the ability of ground station to access two satellites has improved communication quality. In this paper, we address the optimum constellation parameters for dual-satellite coverage. An equation for determining the optimum inclination angle was derived from the constellation parameters. Moreover, by using the new constellation parameters, we found that the satellite network consists a bidirectional Manhattan Street Network (MSN). Nomenclature N = number of satellites of the Walker Notation P = number of orbital planes of the Walker Notation S = number of satellites in each orbital plane, S = N/P F = phasing factor of the Walker Notation I = inclination angle of the satellite orbit