Haruki Izumikawa

An efficient TCP with explicit handover notification for mobile networks

TCP is a popular Internet protocol for reliable end-to-end data delivery, but it cannot be directly applied to wireless networks in which packet loss may be induced by higher BER or handover than congestion. TCP assumes that such packet loss is caused by network congestion and initiates congestion control procedures. In this paper, we present a novel protocol using explicit handover notification to improve TCP performance over wireless links. Additionally, we execute computer simulations using the network simulator and compare it with the other various protocols.

Novel WLAN Coverage Area Estimation Leveraging Transition of Cellular Signal Using Multi-Mode Mobile Terminal for Heterogeneous Networks

It is necessary to select an appropriate access network out of the several available as well as perform vertical handover, which can be considered to be one of the key features of IMT-Advanced. We now have a dual-mode mobile terminal (MT) which can connect to both wireless LAN (WLAN) and cellular NWs, featuring a high transmission rate and wide coverage area, respectively. Before selecting and switching access NWs, it must detect the coverage areas of the access NWs that are candidates for connection. Since the MT is generally battery powered, it is a mandatory requirement to detect NWs without consuming too much power. Thus, the authors consider the possibility of controlling WLAN interface (I/F) activation solely by monitoring the transition of the signal quality of a cellular system. From some preliminary experiments and based on previous literature, it has been shown that the signal quality tends to rapidly degrade and then become more stable when moving into an indoor space, which is a different signal transition than that under fading circumstances. From the findings, in this paper, the authors introduce a radically new WLAN area estimation approach for such dual-mode MT leveraging the transition. The transition is used for the estimation of the movement from an outdoor cellular area into an indoor space, where the WLAN areas are expected. The MT activates the WLAN I/F only when it is deduced that the user is about to walk indoors. Furthermore, the authors introduce a method of ascertaining the deduction by leveraging the GPS signal. Thus, the proposed approach adopts a completely different concept from existing ones which require changes to existing NWs or keeping the WLAN I/F active for WLAN area detection. Experimental results and analysis show that the proposed approach has huge potential for reducing the amount of power consumed in detecting the coverage area compared to continuous or periodic search of the WLAN area while keeping the I/F active.

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

RoCNet: Spatial mobile data offload with user-behavior prediction through delay tolerant networks

We present a robust cellular network (RoCNet) that combines a cellular and an opportunistic networks for spatial uplink mobile data offloading, which focuses on the spatial difference of the traffic load among areas (e.g., business district and residential area in the daytime). RoCNet realizes the spatial data offload by leveraging the store-carry-forward routing mechanism. In the area where traffic load is high, delay-tolerant data originated from a mobile terminal is directly forwarded to a nearby terminal using Bluetooth or wireless LAN instead of being transmitted to a congested cellular base station. When the data is carried by the nearby terminal to other area where the traffic load is low, the data is forwarded to a cellular base station. To enhance the offload effect, it is necessary for data to be forwarded to a terminal that moves to a low traffic load area. In this paper, we use the particle filter to predict user behavior. Before forwarding data between mobile terminals, the terminals exchange prediction results and decide whether or not the data should be forwarded. We conducted a computer simulation whose result shows RoCNet can spatially offload uplink traffic in a traffic concentration area to non-congested areas. As a result, RoCNet can suppress peak traffic by about 20 percent in a traffic-congested base station by distributing traffic to vicinity base stations.

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

Spatial uplink mobile data offloading leveraging store-carry-forward paradigm

The growing popularity of mobile data communication has been leading a growing lack of radio resource on a cellular network. Therefore, to avoid the data traffic from exceeding the capacity limit of a cellular base station (BS), cellular operators have been trying to install cellular femto cells (local BSs) or wireless LAN access points (APs) in restaurants, cafes, users houses, etc., to divert data traffic from the cellular radio access link to the fixed-line such as x-DSL and FTTH. However, the traffic levels extremely change in a day, even locally, due to the mobility of users. While peak data traffic at certain times of a day appears locally, cellular BSs as well as the femto cells and the APs would sit underutilized for the rest of the day. Thus, we have started designing a robust cellular network (RoCNet) that combines infrastructure-based network (e.g., cellular network) and opportunistic networking for spatial mobile data offloading, which focuses on the difference of the data traffic level among areas (e.g., business district and residential area). The RoCNet facilitates the data traffic offloading leveraging the store-carry-forward feature considering a degree of traffic congestion. In this paper, we give an overview of the RoCNet and show a simulation result. The result shows RoCNet can spatially offload uplink traffic in a traffic concentration area to non-congested areas. In other words, RoCNet can suppress peak traffic in a traffic-congested base station by distributing traffic to vicinity base stations.

Novel multiple path routing technology for multi-hop wireless networks

The novel routing method proposed enables simultaneous utilisation of multiple paths without them interfering with each other, and improves the system throughput of multi-hop wireless networks between base station (BS) and mobile users. The basic concept is that the BS searches and selects the secondary multi-hop path that is located out of the coverage of the primarily selected multi-hop path derived by the conventional AODV scheme. Simulation results show that the proposed scheme improves the system capacity of the conventional multi-hop wireless network.

A hybrid TCP-friendly rate control for multimedia streaming

This paper presents a hybrid congestion control algorithm supporting throughput efficiency, TCP friendliness and RTT fairness, in order to provide highly smart multimedia streaming over the Internet. Recent studies on TCP and TFRC are evolving to achieve better throughput efficiency and RTT fairness. Examples are Hybrid TCP congestion control, VTP and TCP-Libra, where the former two improve throughput efficiency of TCP and TFRC, respectively, and the last one improves RTT fairness of TCP. This paper integrates these ideas and propose a new congestion control algorithm, called Hybrid TFRC, for multimedia streaming. Experiments are carried out and effectiveness of our proposal is verified.

User-Centric Seamless Handover Scheme for Realtime Applications

We bring a new perspective on a vertical handover scheme, a user-centric seamless handover, toward a next generation network where heterogeneous network systems converge. The proposed scheme allows us to provide users with the optimal service quality for real-time applications in respective network systems, as well as sustaining on-going sessions. Firstly we propose SIP-based bi-casting technology using a Handover Assistant Server to provide optimal service quality in respective network systems and avoid packet loss during handover. The delay difference absorption method is also proposed to adjust the service quality smoothly to the newly connected network. Evaluation results show that the scheme works well for the handover between cellular and high speed wireless access via the implementation of a prototype system.

Retarding application idle timer expiration for service resumption in challenged network

In challenged network environments like tunnels, a mobile node can suffer from a sudden disruption in mobile services, e.g., the abrupt ending of an application session, due to factors like coverage holes. To tackle this issue, there is an approach that provides tolerance for disruptions or disconnections in the network architecture, in which proxy functions in the network and the mobile node conceal the disruption of the wireless link from users and application servers. After the wireless link is re-established, the services the user enjoys are resumed. However, even if such a disruption-tolerant function avoids the direct negative effects of a disruption, i.e., the sudden end of an application session, the services could still end due to an application idle timer. In this paper, we propose a dynamic buffering method, named application idle timer retardation buffering (ARB), to deal with the application idle timeout issue. The proxy function in a mobile node has a buffer for incoming data from the network and queues data for only a brief moment before forwarding it to an application. When link connectivity is lost, the proxy function forwards queued data to the end-user application at a very low rate in order to delay application idle timer expiration by repeatedly resetting the timer. We implemented ARB in PCs and conducted field tests. The results of the ARB field test indicate that ARB maintains continuity despite communication interruptions as much as eleven times longer than could be handled without it, without throughput degradation.