Bandai Masaki

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.

This paper discusses a buffering strategy for a delay-tolerant multimedia sensor network (DTMSN), whose typical application is video surveillance. In DTMSN, a sensor node observes events and stores the data in its own buffer memory. All the data is collected to the sink. Sensor nodes have restrictions on buffer memory as well as battery capacity. In DTMSN, the generated data size is much larger than a node's memory size. Thus, a strategy for buffering satisfying these restrictions should be developed for DTMSN. In this paper, we propose a novel buffering method for DTMSN, called cooperative buffering (CB). In the proposed CB, a sensor node which has a large amount of data cooperates with its neighbor nodes to buffer them in a distributed manner. CB uses mobile sinks. The cooperatively buffered data are transmitted directly to the mobile sink when it arrives. In addition to the existing CB, we propose two buffering methods for easy data collection of mobile sinks. This paper discusses evaluates the power consumption performance and data collection delay of CB using the computer simulations. As a result, we show that it is important for decreasing total cost to select the CB method suitable for mobile sinks or application.

In this paper, we investigate the use of smart antennas in WSNs. In addition, we propose the hierarchical sensor network (HSN) which uses smart antennas together with omni-directional antennas for large-scale sensor networks. The proposed HSN consists of two layers: relay layer and sensing layer. A node in relay layer equips a smart antenna and operates as a cluster head (CH). The smart antenna of CHs extends the transmission range to improve network scalability. Sensor nodes in sensing layer transmits its sensed data to the nearest CH, therefore it does not need to relay data from other SNs to reduce power consumption at SNs. We implement the proposed HSN with UNAGI (Ubiquitous Network testbed with an Adaptively Gain-controlled antenna for Improvement of spatial and temporal efficiency) and MICA Mote. We show the effectiveness of the proposed HSN via the experiment of using the implemented HSN and computer simulation.

In recent years, ad hoc networks have attracted a significant amount of attention. Smart antennas have great potential such as higher spatial reuse and range extension and can improve the network capacity in wireless ad hoc network. However new problems occur in MAC protocols with smart antennas. One of the problems is directional exposed terminal problem. Due to the interference from other communication, channel utilization degrades. In this paper, we propose an on-demand routing protocol called LORA (LOwer interference Routing protocol for Ad hoc networks using smart antennas). Simulation results show LORA outperforms the conventional method to establish the lower interference routes.

Delay tolerant network (DTN) is one of the promising applications of multimedia sensor networks. This paper focuses on delay-tolerant multimedia sensor networks (DTMSNs). A typical example of DTMSNs is a surveillance camera. In DTMSNs, sensor nodes (SNs) need to keep all the recorded data in own memory. Even though the recorded period is short, the data size is large for the SN's memory because SNs cannot have a large memory. Keeping a large size of data at a SN is a critical issue toward DTMSNs. In this paper, we propose a novel buffering scheme for DTMSNs, called cooperative buffering (CB). In the proposed CB, the SN which records a large amount of video data asks its neighbor nodes to buffer them cooperatively. CB is used with mobile sink. The buffered data are transmitted directly to the sink when the sink arrives. SNs can handle large amount of video data energy-efficiently without having a large memory in SNs. We evaluate the power consumption performance of the proposed CB via theoretical analysis and computer simulation. As a result, we show that the proposed CB can handle multimedia data, and can realize low-power operation.

In this paper, we analyze the multihop performance of the geographical forwarding with directional antennas theoretically. We clarify the potential of the use of directional antennas for the geographical forwarding by means of the theoretical analysis. In addition, we propose a novel cross-layer data forwarding protocol called the geographical forwarding with directional antennas (GFDA) to alleviate the disadvantage of the use of directional antennas. By computer simulations, we show that GFDA is effective to improve the energy efficiency.

Physical layer specifications for wireless LANs such as IEEE 802.11 provide multiple channels available for use. We can achieve a higher throughput than using single channel. However, the MAC protocol of IEEE 802.11 DCF is designed for a single channel between hosts. In this paper, a medium access control (MAC) Protocol for ad hoc networks using a single transceiver is proposed. The network we consider is an ad hoc network that does not rely on infrastructure, so proposed protocol operates asynchronously. We evaluate problems of multi-channel communication using single transceiver asynchronously. And the simulation results show that proposed protocol exploits multiple channels to achieve higher throughput because of reduction of problems which occur in multiple channels communication using single transceiver.

Physical layer specifications for wireless LANs such as IEEE 802.11 provide multiple channels available for use. We can achieve a higher throughput than using single channel. However, the MAC protocol of IEEE 802.11 DCF is designed for a single channel between hosts. In this paper, a medium access control (MAC) Protocol for ad hoc networks using a single transceiver is proposed. The network we consider is an ad hoc network that does not rely on infrastructure, so proposed protocol operates asynchronously. We evaluate problems of multi-channel communication using single transceiver asynchronously. And the simulation results show that proposed protocol exploits multiple channels to achieve higher throughput because of reduction of problems which occur in multiple channels communication using single transceiver.

In recent years, ad hoc networks have attracted a significant amount of attention. Various protocols are proposed since the nodes can construct ad hoc networks without depending on infrastructures. In this paper, especially we focus on the problems of unidirectional links due to heterogeneity of transmission power of nodes, and we evaluate an on-demand protocol called LEX-R (Least EXposed Routing to avoid unidirectional links). LEX-R avoids the interference from unidirectional links to establish routes with bidirectional links. It solves the hidden terminal problems incurred by unidirectional links and improves the packet delivery ratio and route establishment ratio in the power heterogeneous networks. We show via simulations that, especially, LEX-R outperforms AODV-BL with regard to packet delivery ratio, route establishment ratio and any evaluation in random topology.

In recent years, ad hoc networks, sensor networks and mesh networks which do not require any fixed infrastructure have been attracted a great deal of attention. In this paper we call these networks infra-less infrastructure, since they require no fixed infrastructure and they will be important and fundamental technologies to achive ubiquitous society. This paper presents the current status of communication protocols for infra-less infrastructure, especially medium access control (MAC) protcols and routing protocols of ad hoc networks and sensor networks. It also provides a view of the future networks and technical challentes.

In recent years, ad hoc networks have attracted a significant amount of attention. Various protocols are proposed since the nodes can construct ad hoc networks without depending on infrastructures. In this paper, especially we focus on the problems of unidirectional links due to heterogeneity of transmission power of nodes, and we propose an on-demand protocol called LEX-R (Least EXposed Routing to avoid unidirectional links). LEX-R avoids the interference from unidirectional links to establish routes with bidirectional links. It solves the hidden terminal problems incurred by unidirectional links and improves the throughput in the power heterogeneous networks. We show via simulations that, especially, LEX-R outperforms AODV-BL with regard to end-to-end throughput.

Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. In directional MAC protocols, deafness problem is one of the major problems, which are caused by a transmitter repeatedly attempts to communicate with its intended receiver, but it fails because the receiver has its beam pointed away from the transmitter. In this paper, we analyze the deafness problem. In addition, we experiment with the effects of deafness using the testbed. The experimental results show that the deafness problem deteriorates the throughput performance.

In this paper, a medium access control (MAC) protocol with transmission power and data rate control in ad hoc networks is proposed to realize high energy efficient data transmission. In the proposed protocol, each node makes a table including the relation between the combination of transmission power and data rate, and power efficiency. According to the exchange of control frames and looking up the transmission power and data rate table, direct or relay transmission sequences is used arbitrarily. When relay transmission by the intermediate node between sender and receiver is more effective in power consumption, relay sequence is adopted instead of direct transmission. By using computer simulations, it is shown that the proposed protocol can realize high power consumption efficiency.

Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. However, the MAC protocols in the previous studies were evaluated using simulation with ideal antenna forms. When using practical antenna beam forms, side lobes and back lobes exist which may cause new problems. In this paper, we evaluate the performance of the directional MAC protocol in the previous studies with practical antenna beam forms. In addition, we propose a directional MAC protocol that assumes practical antenna beam forms. The proposed MAC protocol mitigates data collisions due to the effects of minor lobes. The simulation results show that the proposed directional MAC protocol improves throughput performance compared to existing directional MAC protocol when using practical antenna beam forms.

In this paper, to realize high throughput route selection in multi-rate ad hoc networks, we propose a novel signal strength aware routing, referred to as Signal Strength aware Routing (SSR). SSR is based on the on-demand routing. In SSR, nodes measure signal strength of the received a route request (RREQ), and calculates the appropriate transmission rate. The node also calculates the standby time for RREQ forwarding proportionally to the medium time at the data transmission rate. This means that a RREQ through higher rate links arrives at the destination earlier. We evaluate the performance of the proposed SSR by means of QualNet network simulator. As result, we show that the proposed SSR can construct higher throughput route than the conventional scheme without increasing overhead in multi-rate ad hoc networks.

Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. However, the MAC protocols in the previous studies were evaluated using simulation with ideal antenna forms. When using practical antenna beam forms, side lobes and back lobes exist which may cause new problems. In this paper, we evaluate the performance of the directional MAC protocol in the previous studies with practical antenna beam forms. In addition, we propose a directional MAC protocol that assumes practical antenna beam forms. The proposed MAC protocol mitigates data collisions due to the effects of minor lobes. The simulation results show that the proposed directional MAC protocol improves throughput performance compared to existing directional MAC protocol when using practical antenna beam forms.

In this paper, we propose a routing protocol which uses a stepwise RREQ spread limitation technique for mobile sensor networks. Since the proposed stepwise RREQ spread limitation technique reduces control messages, the power saving in sensor nodes can be realised. In addition, the transmission timing of sensed data is differentiated and collisions in MAC layer are mitigated. As result, high data arrival ratio can be also realised. Simulation and theoretical analysis results show the effectiveness of the proposed technique is high power efficiency and data arrival ratio.