Keizo Sugiyama

Broadcast methods for inter-vehicle communications system

This paper presents novel broadcast methods for an inter-vehicle communications system for ITS. During inter-vehicle communications, it is essential that emergency information be broadcast to surrounding vehicles. Emergency information such as emergency-vehicle-approach information and traffic accident information are needed by vehicles in a particular area. By limiting the broadcast direction, the proposed methods can provide broadcasts to a particular area and avoid mistakenly notifying other areas where the information is not needed. We developed a simulation and experimental system for the proposed method and confirmed that the information is broadcast to the desired area.

Dynamic polling scheme based on time variation of network management information values

Network monitoring is one of the most significant functions in network management to understand the state of a network in real-time. In network management, such as SNMP (simple network management protocol), polling is used for this purpose. If the time interval for two consecutive polling requests is too long, then we cannot understand the state of the network in real-time. Conversely, if it is too short, then the polling message traffic increases and imposes a heavy load on the network although we can understand the state of the network in real-time. Many schemes have been proposed for controlling the overheads of dynamic polling by throttling polling rates. Unfortunately, by only considering overheads, these schemes fail to take into account the rate at which information must be obtained in order to achieve management tasks. Examples of these tasks include checking for threshold violations and determining if additional capacity should be allocated dynamically. This paper proposes a new scheme for dynamic polling that considers both the overhead of polling traffic and the message rates required for management tasks. Our scheme examines polling traffic, applying the discrete Fourier transformation to extract the desired polling rate. We demonstrate the availability of this approach through simulations in which polling requests are varied dynamically. Our scheme adjusts polling rates to make them more consistent and to reduce resource overheads.

MAP Multiplexing in IEEE 802.16 Mobile Multi-Hop Relay

In this paper, we propose a new scheme called MAP multiplexing for efficient use of the radio resource in IEEE 802.16-based multi-hop wireless networks. Although IEEE 802.16-based multi-hop wireless networks enable expansion of the service area due to the introduction of relay stations, the efficiency of radio resource utilization could be degraded because the radio resource is shared between the base station and relay stations in a time-division or frequency-division manner, and either the base station or one relay station can only use it at one time. MAP multiplexing can improve the efficiency of radio resource utilization. Computer simulation results show that MAP multiplexing reduces the end-to-end delay as well as enhances the radio resource utilization

Proposed relay method with P-MP structure of IEEE 802.16-2004

This paper presents a relay method with a P-MP (point to multipoint) structure by extending the IEEE 802.16-2004 standard in order to expand the coverage area (2004). In the proposed relay method, a RS (relay station) sends a polling message for the SSs (subscriber station) assigned to the former to forward uplink data in terms of the contention opportunities in the uplink subframe, and obtains a contention request period to communicate between the RS and these SSs. The feature of the proposed relay method is that it can be applied to TDD (time division duplex) and FDD (frequency division duplex), and both BS (base station) and RS operating at the same and at different carrier frequencies respectively. In this paper, we evaluated the basic characteristics of the proposed relay method in terms of throughput and delay time through computer simulations. We show that the introduction of the proposed relay method is effective in expanding the coverage area, and that the proposed relay method has an effect on the increase of the system throughput without affecting the delay time by adjusting the time interval parameter for BW requests of SSs assigned to the RS correctly

Long-range oversea wireless network using 2.4 GHz wireless LAN installation and performance

High-quality 2.4 GHz wireless LAN over long-range oversea paths was installed using a space diversity technique. The installed network consists of five wireless links, including a long-range 11.3 km link. To lower the adverse affect of fluctuation in the tidal level, two wireless LAN devices with different antenna heights were installed at one side of the longest link. The antenna heights were suitably determined on the basis of link profile and gained data at the deployment of the equipment. The measured performance indicates that the link with space diversity achieves 100% operating rate in a measured period of time, while the link without space diversity achieves an approximately 90% operating rate in the same time. This method effectively improves the quality of conventional wireless LAN systems.

Packet Switch and Its Impact on Dynamic Base Station Relocation in Mesh Networks Using Cognitive Radio

CR (Cognitive Radio) is a technology that can realize more intensive and efficient spectrum use through spatial and temporal utilization. In the context of mesh networks where each base station consists of heterogeneous multi-radio interfaces, packet switch in L2/L3 of each base station selects each radio interface and channel adaptively in order to take full advantage of all multiple heterogeneous interfaces. At first, this paper examines the achievable performance of the new packet switch schemes in mesh topology. Secondly, we investigate the potentiality of dynamic base station relocation approach in order to cope with the change of terminal traffic distribution, and show the impact of packet switch policy on dynamic base station relocation.

Experimental Verification on the Prediction of the Trend in Radio Resource Availability in Cognitive Radio

This paper presents a prediction of the trend in radio resource availability in cognitive radio. In this paper, cognitive radio is defined as the wireless communication technology in which each node communicates via an optimal wireless system based on recognition of the radio resource availability in heterogeneous wireless communication systems. We focused on the prediction of the network allocation vector (NAV) value for radio resource availability in IEEE 802.11, which is one of the candidates for installation in a cognitive radio [1]. We verified the prediction of the future value of the trend in the NAV time series; based on an auto-regressive model (AR model) and using captured data within a real environment. Based on the results of the verification, we show that prediction based on the AR model with suitable parameters is applicable in comparison when the average of the last 10 samples is used as a predicted value and the case where prediction is not applied. Furthermore, it is possible to set up a long update interval for the regression coefficients.

Direction and Communication-Aware Directional Mac Protocol in Ad Hoc Networks Using Directional Antenna

Our major contribution in this paper is to devise a MAC protocol that exploits the advantages of directional antenna in ad hoc networks for improved system performance. In order to implement effective MAC protocol in this context, a node should know how to set its transmission direction to transmit a packet to its neighbors and to avoid transmission in other directions where data communications are already in progress. In this paper, we are proposing a receiver-centric approach for direction and communication-aware MAC (DCA-MAC) protocol, so that, nodes become aware of its neighborhood and also the direction of the nodes for communicating directionally. Our proposed directional MAC protocol can be effective in both ITS (intelligent transportation system), which we simulate in string and parallel topology, and in any community network, which we simulate in random topology. The performance evaluation on QualNet network simulator clearly indicates the efficiency of our protocol. In addition, under the fading channel conditions, its difficult for each node to perceive the status of the neighbors. In AWGN, Ricean and fading environments, we compare and analyze the performance of omnidirectional MAC, conventional directional MAC and our proposed directional MAC

Simulation evaluation on area extension and system capacity of CDMA packet communication system utilizing multihop connection

The objective of this study is to evaluate effectiveness of multihopping technique applied to CDMA packet communication system. The system model is designed so that mobile stations that have no direct connectivity to any base station setup multi-hopped paths by way of neighbor mobile stations. Two policies are addressed in selecting relay stations based on battery usage, minimized usage on relay station and minimized usage on all stations along multihopped path. With these conditions, system characteristic is evaluated in terms of system capacity and coverage area extension. The result of computer simulation shows that multihopping technique does extend the coverage area with effectively equal performance to the conventional single hop system when the system load is relatively light.

Adaptive media switching for future vehicle-to-vehicle communication

Vehicle-to-vehicle (peer-to-peer) communication is expected to play an important role in ITS (intelligent transport systems). This paper proposes an adaptive media switching method for future vehicle-to-vehicle communication. Our method adopts an approach to select the most suitable radio communication media from several possible types based on the vehicle locations, available media and communication quality. Before the network configuration of inter-vehicle and roadside-vehicle communication changes, the vehicle detects it and then initiates the media reselection. During such media switching, our proposed HTTP-based session layer mobility avoids any interruption of communication. We conducted field tests using several experimental vehicles. The results verify that our proposed method is effective in selecting the most suitable media, and disconnection of communication during the media switching is also avoided