Kazuya Tsukamoto

On Spatially-Aware Channel Selection in Dynamic Spectrum Access Multi-Hop Inter-Vehicle Communications

The use of dynamic spectrum access techniques has a great potential in future inter-vehicle communications, while it must cope with (i) temporal and spatial spectrum utilization changes introduced by the primary and secondary users (environmental changes); and (ii) topology changes due to movement of vehicles (spatial movement). In the present paper, along this line, dynamic per-hop channel switching in multi-hop vehicular ad hoc networking is investigated. After defining a set of simple metric-based dynamic channel selection schemes with/without spatial-awareness, the basic performance (the total communication duration and the amount of transmitted data) are evaluated. These spatially-aware schemes estimate the maximum communication period, and tend to select a channel with a large amount of possible data transmission within the period. The simulation results demonstrate the advantages of the proposed spatial-awareness, especially in the multi-hop and highly congested environments with high-speed mobility. Index Terms—Dynamic spectrum access, inter-vehicle commu- nications, multi-hop communication, channel selection metric

Experimental Evaluation of Decision Criteria for WLAN Handover: Signal Strength and Frame Retransmission

In ubiquitous networks, Mobile Nodes (MNs) often suffer from performance degradation due to the following two reasons: (1) reduction of signal strength by the movement of an MN and intervening objects, and (2) radio interference with other WLANs. Therefore, handover initiation based on quick and reliable detection of the deterioration in a wireless link condition arising from the above two reasons is essential for achieving seamless handover. In previous studies, we focused on a handover decision criterion and described the problems related to the two existing decision criteria. Furthermore, we showed the effectiveness of the number of frame retransmissions through simulation experiments. However, a comparison of the signal strength and the number of frame retransmissions could not be examined due to the unreliability of the signal strength in simulations. Therefore, in the present paper, by employing FTP and VoIP applications, we compare the signal strength and the number of frame retransmissions as a handover decision criterion with experiments in terms of (1) and (2) in a real environment. Finally, we clarify the problem of the signal strength in contrast to the effectiveness of the number of frame retransmissions as a handover decision criterion.

Service-oriented mobility management architecture for seamless handover in ubiquitous networks

In ubiquitous wireless LANs, a mobile node is likely to move between many access points while using certain applications. However, in the conventional Internet architecture, an MN can never inherently avoid the degradation in communication quality during handover. To achieve seamless handover, we propose a service-oriented mobility management scheme to address application quality. In this article, we first clarify three requirements for achieving seamless handover. We then describe our concept of the service-oriented mobility management scheme, which satisfies all three requirements. Our main contribution is the proposal of a scheme of how to properly use the number of frame retransmissions as a new handover-decision criterion to accomplish seamless handover. Performance evaluations show that our proposed scheme can maintain application quality during handover

Demonstration of Vehicle to Vehicle Communications over TV White Space

Future vehicular communications systems are expected to utilize the vacant channels (white spaces) of the spectrum, otherwise allocated for specific designated use. One such candidate of white space comes from the TV broadcast band. In this demonstration, we will first present animated results of a TV spectrum measurement campaign along the entire portion of Interstate I-90 located in the US state of Massachusetts. Next, we will demonstrate a cyber-physical proof-of-concept lab implementation of our previously developed control and data channel assignment schemes for vehicle-to-vehicle communications over (TV) white space. Finally we will show a video of actual vehicle to vehicle communications field tests conducted in Japan using TV white space.

New TCP congestion control schemes for multimodal mobile hosts

Two congestion control schemes designed specifically to handle changes in the datalink interface of a mobile host are presented. The future mobile environment is expected to involve multimode connectivity to the Internet and dynamic switching of the connection mode depending on network conditions. The conventional Transmission Control Protocol (TCP), however, is unable to maintain stable and efficient throughput across such interface changes. The two main issues are the handling of the change in host Internet Protocol (IP) address, and the reliability and continuity of TCP flow when the datalink interface changes. Although existing architectures addressing the first issue have already been proposed, the problem of congestion control remains. In this paper, considering a large change in bandwidth when the datalink interface changes, two new schemes to address these issues are proposed. The first scheme, Immediate Expiration of Timeout Timer, detects interface changes and begins retransmission immediately without waiting for a retransmission timeout as in existing architectures. The second scheme, Bandwidth-Aware Slow Start Threshold, detects the interface change and estimates the new bandwidth so as to set an appropriate slow start threshold for retransmission. Through simulations, the proposed schemes are demonstrated to provide marked improvements in performance over existing architectures.

Mobility management of transport protocol supporting multiple connections

A mobility management scheme for handling seamless handoffs between appropriate datalink interfaces is presented. The future mobile environment will be characterized by multimodal connectivity to the Internet with dynamic switching based on many factors. Many technologies have been proposed to support host mobility across diverse wireless access networks, and operate in various layers of the network architecture. Our major concern is the transport protocol that recovers packets lost during handoffs and controls transmission speed to achieve efficient communication. In this paper, we first examine the various latencies associated with the handoff mechanism, and discuss the limited performance of existing technologies based on a single transport connection. We then propose a new mobility management scheme that resolves the problems of limited performance by transport protocol supporting multiple connections. We compare the performance of the proposed scheme with existing technologies, and demonstrate that the proposed scheme achieves excellent goodput performance.

Experimental evaluation of decision criteria for WLAN handover: signal strength and frame retransmission

In ubiquitous networks, Mobile Nodes (MNs) may often suffer from performance degradation due to the following two reasons: (1) reduction of signal strength by an MNs movement and intervening objects, and (2) radio interference with other WLANs. Therefore, quick and reliable detection of the deterioration of a wireless link condition is essential for avoiding the degradation of the communication quality during handover. In our previous works, we focused on a handover decision criterion allowing MNs to maintain communication quality and stated the problems of existing decision criteria. Furthermore, we showed the effectiveness of the number of frame retransmissions through simulation experiments. However, a comparison between signal strength and the number of frame retransmissions could not be examined due to the unreliability of signal strength in simulations. Therefore, in this paper, by employing FTP and VoIP applications, we compare signal strength and the number of frame retransmissions as a handover decision criterion with experiments in terms of (1) and (2) in a real environment. Finally, we show the problems of signal strength in contrast to the effectiveness of the number of frame retransmissions as a handover decision criterion.

Network-supported TCP rate control for high-speed power line communications environments

Abstract High-speed power line communications (PLC) technology has great potential to serve as an infrastructure for home networking. To investigate the performance of end-to-end data flows over high definition (HD)-PLC, we have developed a new module on the NS-2 network simulator for HD-PLC that is driven by the particular patterns of the time-varying packet-error-rate as measured by experiments. To solve the problem on coexisting multiple TCP flows, a novel network-supported TCP rate control that appropriately modifies the advertized-window value in a TCP-ACK packet in response to the PLC network condition is presented and is shown to be effective through simulations.

Distributed autonomous multi-hop vehicle-to-vehicle communications over TV white space

This paper presents design and experimental evaluation of a distributed autonomous multi-hop vehicle-to-vehicle (V2V) communication system over TV white space performed in Japan. We propose the two-layer control channel model, which consists of the Zone Aware Control Channel (ZACC) and the Swarm Aware Control Channel (SACC), to establish the multi-hop network. Several vehicles construct a swarm using location and direction information shared through ZACC, and share route and channel information, and available white space information through SACC. To evaluate the system we carried out field experiments with swarm made of three vehicles in a convoy. As the test case application, the leading vehicle sends real-time speed and sudden break information to the rear vehicle, while the vehicle in between acts as the relay. The vehicles observe channel occupancy via energy detection and agree on the control and the data channels autonomously. For coarse synchronization of quiet periods for sensing we use GPS driven oscillators, and introduce a time margin to accommodate for remaining drift. When a primary user is detected in any of the borrowed channels, the vehicles switch to a vacant channel without disrupting the ongoing multi-hop communication. We present results of the experiments in terms of the time to establish control channel, channel switching time, and throughput.

Field tests and indoor emulation of distributed autonomous multi-hop vehicle-to-vehicle communications over TV white space

This paper presents design and experimental evaluation of a distributed autonomous multi-hop vehicle-to-vehicle (V2V) communication system over TV white space performed in Japan. We propose the two-layer control channel model, which consists of the Zone Aware Control Channel (ZACC) and the Swarm Aware Control Channel (SACC), to establish the multi-hop network. Several vehicles construct a swarm using location and direction information shared through ZACC, and share route and channel information, and available white space information through SACC. To evaluate the system we carried out field experiments with swarm made of three vehicles in a convoy. As the test case application, the leading vehicle sends real-time speed and sudden break information to the rear vehicle, while the vehicle in between acts as the relay. The vehicles observe channel occupancy via energy detection and agree on the control and the data channels autonomously. For coarse synchronization of quiet periods for sensing we use GPS driven oscillators, and introduce a time margin to accommodate for remaining drift. When a primary user is detected in any of the borrowed channels, the vehicles switch to a vacant channel without disrupting the ongoing multi-hop communication. We present results of the experiments in terms of the time to establish control channel, channel switching time, and throughput.