萬代 雅希

One of the major challenges for the deployment of underwater acoustic sensor networks is the development of a medium access control (MAC) protocol catering for the harsh underwater environment. In particular, an underwater MAC protocol should provide high end-to-end throughput, low channel access delay, and fair share of the scarce network bandwidth. In this paper, a cross-layer MAC protocol is proposed. It interacts with a price-based rate allocation scheme at the network layer. To accurately reflect the clique constraint of the wireless medium, the clique-based price is generalized to act as the congestion signal, which controls the end-to-end rates of multihop flows. The MAC protocol then schedules contention-free packet transmissions of single-hop subflows in each maximum clique. Both the MAC protocol and rate allocation algorithm are simple and direct, thus owning low computational complexity. Through analysis and simulation, we show that the proposed MAC protocol enables multihop flows to acquire the max-min fair share of the network bandwidth from the end-to-end perspective.

Out-of-order packet problem incurs severe degradation of throughput performance of Multipath TCP (MPTCP) with heterogeneous communication links. In this paper, we propose an extended version of MPTCP to solve the out-of-order packet problem. The proposed method defines two types of ACK: Regular ACK and Extended ACK. When a receiver receives a data packet, the receiver sends a Regular ACK to the original path through which the data is transmitted, and Extended ACKs to all the other paths. If the Extended ACK arrives earlier than the Regular ACK, the proposed method solves the out-of-order packet problem. We evaluate the performance of the proposed method via NS-3 computer simulations, and show that the proposed method can improve the throughput performance when RTT of paths is heterogeneous.

In Wireless Sensor Networks (WSNs), saving energy is of critical importance and has attracted much research. Data aggregation is one of the methods to save energy in WSNs by reducing the amount of redundant data transmission. However, data aggregation causes transmission delay and reduces data accuracy, and may not be suitable for some applications where quick transmission or data accuracy is important. Our first contribution in this regard is giving the formulations of energy efficiency, transmission delay and data accuracy from the viewpoint of full data aggregation as well as non-aggregation.Secondly, as a way to overcome the problems, we propose a random partial aggregation, and compare it with non-aggregation as well as full aggregation to verify its effectiveness. Finally,we define and measure a trade-off index as a useful trade-off criterion among energy consumption, transmission delay, and data accuracy.

The recent advent of cognitive radio has made the opportunistic spectrum access scheme (OSA) a suitable approach to deal with the spectrum inefficiency issues. This paper concerns itself with the temporal aspect of the OSA. Over the years, a plethora of works have discussed the optimal access methods for the OSA environment. However, most of them have not considered the possible combination of a faster transmission rate and the assistance of a relay node in temporal spectrum sharing. In this paper, we affirm that the use of a faster transmission rate with the assistance of a relay (or relays) can be greatly beneficial in the temporal OSA environment. We propose a rate-relay adjustment scheme to dynamically exploit the nature of rate-relay. The scheme is composed of a receiver-based auto rate increase (R-ARI) scheme for rate adjustment, a relay selection scheme, and a rate limit scheme. The scheme takes into account the rate-relay adjustment and the PU activity factors. As demonstrated by simulation results, the use of a proper rate-relay adjustment scheme can lead to a gain in the secondary throughput and a lower primary collision percentage, as compared to the one hop optimal transmission rate scheme.

In this paper, we propose a dynamic Quality of Experience (QoE)-aware live streaming algorithm by utilizing client clustering and similarity metrics. Encoding scheme of the proposed system finds a sufficient bitrate of the video and creates quality levels adapted to the distribution of clients' bandwidth to improve overall average of user's QoE. We show that the proposed system can improve structural similarity method (SSIM) performance when the client's bandwidth is distributed in low or middle bandwidth, and decreases the number of clients who stop play back.

In wireless sensor networks, energy depletion of bottleneck nodes which have more data packets to relay than others, dominates the network lifetime referred to as the funnel effect problem. To overcome this problem, multiple sink methods have been proposed where sensor nodes send observed data packets toward several sinks to distribute traffic load of bottleneck nodes. If both of the topology and the traffic pattern are symmetric, bottleneck nodes are located near sinks. However, in a general sensor network with an asymmetric topology and/or an asymmetric traffic pattern, bottleneck nodes may exist any place in the network. In this paper, we propose DCAM (Dispersive Cast of packets to Avoid bottleneck nodes for Multiple sink sensor network), which is a load balancing method to improve lifetime of a sensor network with an asymmetric topology and an asymmetric traffic pattern. DCAM first finds bottleneck nodes, and then balances the load on the bottleneck nodes. Selected nodes send data packets to several sinks dispersively according to some criteria. The criteria classify DCAM into three variations: DCAM with probability (DCAM-P), DCAM with moving boarder (DCAM-MB), and DCAM with round-robin (DCAM-RR). This paper gives details of the DCAM methods, and thereafter evaluates them with asymmetric topologies and asymmetric traffic patterns. To deal with these dynamic asymmetry, the topology is modeled by a grid network with virtual holes that are defined as vacant places of nodes in the network. Asymmetry of traffic pattern is modeled by defining a hot area where nodes have heavier data traffic than the others. The evaluations are conducted as changing hot-area traffic patterns as well as fixing hot-area patterns. The results show that DCAM improves network lifetime up to 1.87 times longer than the conventional schemes, (i.e., nearest sink transmissions and optimal dispersive cast of packet). We also discuss DCAM on several aspects such as overhead, energy consumption, and applications.

Multi-view video is attracting extensive interest due to its innovative viewing experience. It allows user to change viewpoints by playing different video sequences. However, the traffic of multi-view video is much larger than that of conventional media, which would greatly decrease the quality of service, i.e., more transmission delay. In this paper, we analyze the successive motion switching model and find that only the frames in a triangle window are possible to be displayed at a subsequent period of time. A live-encoding scheme called UMS (User dependent Multi-view video Streaming) is proposed to reduce transmission bitrate. Instead of all the frames, UMS transmits only these specific frames by the periodic feedback. We also propose a prediction structure as a substitute of the prediction structure of MVC. Performance evaluation proves that UMS reduces the transmission bitrate by 53.64% compared to MVC with periodic feedback. Copyright © 2013 Binary Information Press.

In this paper, we propose and implement a cross layer protocol for ad hoc networks using directional antennas. In the proposed protocol called RSSI-based MAC and routing protocol using directional antennas (RMRP), RSSI is used for computing the direction of the receiver and also used for controlling backoff time. Moreover, the backoff time is weighted according to number of hops from a source node. In addition, simple routing functions are introduced in the proposed RMRP. We implement the proposed RMRP on a testbed with the electronically steerable passive array radiator (ESPAR) antenna and IEEE 802.15.4. From some experimental results, we confirm some throughput improvement and show the effectiveness of the proposed RMRP. Especially, the proposed RMRP can achieve about 2.1 times higher throughput than a conventional random backoff protocol in a multi-hop communication scenario.

Energy harvesting from ambient energy sources including solar and vibration has been studied as a candidate for powering next generation wireless sensor networks. However, energy harvesting is unstable to supply a sensor node with energy, and a node cannot know whether its neighbouring nodes have enough energy to receive a data packet. In this paper, we propose two data collection protocols for energy harvesting wireless sensor networks called the Probabilistic ReTransmission protocol (PRT) and PRT with Collision Consideration (PRT-CC). The idea is to derive the appropriate number of times to retransmit a packet based on the reception probability and the active intervals computed by the receivers themselves while, in PRT-CC, each node computes the reception probability with packet collision consideration. The performance evaluation shows that the proposed protocols are able to achieve higher delivery ratio than the previous work, namely, Geographic Routing with Duplicate Detection (GR-DD) and GR-DD with Retransmission.

In this paper, we propose and implement a cross layer protocol for ad hoc networks using directional antennas. In the proposed protocol called RSSI-based MAC and routing protocol using directional antennas (RMRP), RSSI is used for computing the direction of the receiver and also used for controlling backoff time. Moreover, the backoff time is weighted according to number of hops from a source node. In addition, simple routing functions are introduced in the proposed RMRP. We implement the proposed RMRP on a testbed with the electronically steerable passive array radiator (ESPAR) antenna and IEEE 802.15.4. From some experimental results, we confirm some throughput improvement and show the effectiveness of the proposed RMRP. Especially, the proposed RMRP can achieve about 2.1 times higher throughput than a conventional random backoff protocol in a multi-hop communication scenario. © 2012 Information Processing Society of Japan.

一般にキャンパスネットワークにおける幹線から支線への拡張手段として，スイッチングハブの多段接続が用いられることが多い．このような接続形態では，ハブ間の接続ポート部に通信データが集中し，輻輳が発生しやすいという問題点がある．しかし，輻輳の発生時にはTCPウインドウ制御など通信の抑制による方法がほとんどであり，ネットワークのスループットが低下することは避けられない．一方で通信効率を向上させるために複数のパケットを排他的論理和で多重化するネットワークコーディングが注目されている．本研究では，スイッチングハブの多段接続による潜在的なボトルネック問題をコンシューマ向けの市販実機によって明らかにするとともに，ネットワークの輻輳制御におけるフレーム処理方法にネットワークコーディングを活用し，スループットの向上と輻輳の緩和を同時に可能とする輻輳制御方式を提案する．実験環境として提案方式をアプリケーション層に実装し，提案方式の優位性を立証する．さらにキャンパスネットワークにおける実際の通信環境を分析し，提案方式が有効に機能する環境であることを明らかにした．In general, LANs are enhanced by cascade connection of switching hubs. In a LAN with the cascade connection, the communication at the port of connected points, congestion is subject to occur at the point. For the problem TCP's window control has been already proposed for a congestion control in full duplex Ethernet. 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 clarify a potential problem by the cascade connection of switching hubs, and we propose a congestion control method that enables the throughput improvement and the congestion reduction at the same time. We implement the proposal method on application layer to prove the effectiveness of the proposal method. Furthermore, we analysis real communication data in a campus network and revealed that a proposal method functioned in this environment.