Bandai Masaki

Multipath TCP (MPTCP) has been standardized as a TCP extension protocol. MPTCP enables multihomed devices to use several communication pathes through multiple network interfaces simultaneously. One typical scenario for MPTCP is used on mobile devices, such as smartphones or tablets, which have Wi-Fi and 3G/LTE interfaces. However, the different characteristics of each link block packet sending mechanism and decrease the throughput performance of MPTCP. In this paper, we propose a MPTCP-ACK extention method for using in heterogeneous communication links. Through simulations, the proposed method decreases the duration of blocking and improves the throughput performance.

In order to extend transmission distance in ambient backscatter, this paper proposes a data transmission method. In the proposed method, a transmitter tag shares a data to neighbour tags for simultaneous data transmission. We evaluate the performance of the proposed data transmission method via computer simulations, and show that the proposed data transmission method is effective to extend transmission distance and bit error rate (BER) performance.

In this paper, we propose two route selection schemes for content oriented networks (CON), called Proactive CON and Reactive CON, for shortening content arrival delay for users. In the proposed Proactive CON, a content router (CR) informs a cache completion to its neighbor CRS when the CR caches a content. On the other hand, in the proposed Reactive CON, when a CR receives a query (interest) for a content, the CR inquires the cache of the content to its neighbor CRs. Performance evaluation via computer simulation shows that the proposed schemes can improve the content arrival delay performance compared to the conventional content oriented networks.

In this paper, we propose a virtual server migration algorithm for green data centers. The proposed algorithm reduces the energy consumption of physical machines satisfying a predefined service level agreement (SLA) by means of switching off redundant physical servers. This paper considers the server response time as the SLA criteria. The server response time is defined as the latency from a user's service request until the user receives the service response. The proposed algorithm migrates virtual servers based on a threshold on the output queue length of a physical server. Computer simulated evaluations show that the proposed algorithm can reduce the energy consumption satisfying some preset SLA criteria.

無線センサーネットワークとは、無線通信技術を内蔵した複数の<br />センサーノードが観測した情報をシンクで収集するネットワークである。<br />無線センサーネットワークでは省電力化が重要な課題であり、<br />解決方法の1つとしてデータ集約が提案されている。<br />データ集約は伝送する総パケット数を削減する方法であるが、<br />中継ノードでは集約対象の複数のパケットを待つ必要があるため、<br />遅延が増加する問題点がある。<br />本研究では、中継ノードでパケットを待つ時間に上限を設定し、<br />これを超えた場合は集約せずに送信する方式を提案する。<br />評価により、省電力効果と遅延時間の改善を示す。

Recently, multi-view video that is taken by multiple cameras from different positions and angles to provide the real world experience has attracted more attentions. It allows the users freely change their viewpoints. On the other hand, the traffic of multi-view video is several times larger than traditional multimedia, which brings much more increment in the bandwidth requirement. Compression technologies, such as MPEG and MVC, can greatly decrease the traffic of multi-view video. However, as all the views should be encoded and transmitted, even with MVC bit-rate of multi-view video is still high. In this paper, we analyze users' switch models which are classified into random access model and successive motion model. We find that in the successive motion model only part of frames are possible to be displayed in a period of time. According to the analytical result, we propose a user-driven scheme which can significantly decrease the traffic of multi-view video. In the proposed scheme, only those frames that are possible to be displayed are encoded and transmitted. In order to support this scheme, we also propose a prediction structure as a substitute of the prediction structure in MVC. Evaluation proves that this proposed scheme reduces the average bit-rate for the transmission of multi-view video.

In general, LANs are enhanced by cascade connections of switching hubs. In a LAN with the cascade connection, the communication concentrates at the port of connected points; congestion is subject to occur at the point. For the problem IEEE 802.3x has been already proposed for a congestion control in full duplex Ethernet. In addition, the eXplicit Control Protocol (XCP) and the Variable-structure congestion Control Protocol (VCP), which are the router-supported active congestion control based on congestion controls of the window control of TCP, was proposed. However, throughput degrades due to controlling the transmission rate in these methods. On the other hand, the network coding is attracted attention as a technology that improves the bandwidth efficiency. In this paper, we propose a congestion control method that enables the throughput improvement and the congestion reduction at the same time. We adopt the network coding for congestion reductions. We implement the proposal method on application layer to prove the effectiveness of the proposal method.

Recently, wireless sensor networks attract researcher's attention due to its applicability to many fields for effective collection of sensing data with less cost. In wireless sensor networks, due to battery-powered nodes, energy saving is important issue. As one of techniques for energy saving, the data aggregation has been proposed. In this paper, we discuss the trade off between communication delay and energy consumption of the technique. At first, we analyze the full aggregation, non-aggregation and partial aggregation with Markovian chain. Analytical results show that non-aggregation method suffers large energy consumption while full aggregation suffers large transmitting delay. And our proposed partial aggregation method called WRP (Waterfalls Random partial aggregation) can trade off the energy and delay. For getting the better balance of energy and delay, we get several groups of random pushing vectors and investigate them on two criteria based on delay energy products. We find that less arrival data should be aggregated for small data generation rate at nodes to minimize both criteria, and vice versa. For moderate generation rate we must choose a sophisticated random pushing vector depending on the criterion.

When using random access method, such as CSMA/CA (Career Sense Multiple Access/Collision Avoidance) scheme with BEB (binary exponential backoff algorithm), which is defined for IEEE802.11 DCF (Distributed Coordination Function), a large bandwidth capacity is wasted due to collisions, which affects the severe performance of throughput and so on. We propose a backoff algorithm due to the numbers of neighbor terminals related to the information of RSSI (Received Signal Strength Indicator) or PER (Packet Error Rate). We evaluate the backoff algorithm in the actual environments and consider the optimal value of CW (Contention Window) for higher throughput in the experiments. The experimental process is the measurement of throughput related to variable RSSI or PER in both cases of 2way (DATA/ACK) and 4way (RTS/CTS/DATA/ACK). We show the experimental results, which has a smaller CW for the peak throughput with PER in not good propagation conditions compared to that in good propagation conditions besides slot competition due to CW especially in 2way mode with hidden terminal problem rather than 4way mode at small numbers of neighbor terminals with frequent slot competition, that make a little bit sensitive setup in an adaptation of CW for the higher throughput acquisition.

In this paper, we investigate throughput performance of a star-topology wireless network when wireless network coding (WNC) is applied to uni-cast packet forwarding at a relay node. We focus on two WNC schemes: (1) XOR based WNC (XOR-WNC) where a relay node performs XOR operation for received packets, and broadcasts it to neighbors, and (2) physical layer WNC (PL-WNC) where two neighbors simultaneously transmit packets to a relay, followed by the amplification and forwarding of the received signal by the relay. We define scheduling strategies for XOR-WNC and PL-WNC to be applied to uni-cast transport over a star-topology network, and evaluate their achievable throughput by computer simulation. We show that the WNC scheme offering the best throughput differs depending on the network parameters such as channel conditions, traffic pattern and number of nodes in a network. We also show that scheduling strategies play an important role in order to improve throughput of a star-topology network with WNC.