Bandai Masaki

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.

Wireless LAN has been dramatically evolving in performance and coming into wide use. Mesh network, which access points are deployed in mesh structure, extends the coverage of the networks. That has a lot of benefits, simplicity of building network, wide coverage, load balancing of access points and so forth. The paper proposes a new mesh network structure, which consists of access points with longer wireless range and terminal nodes with shorter one. We also define a zone from a viewpoint of asymmetry of wireless range. In order to save battery consumption, a new algorithm of routing for ad hoc mesh network is proposed and discussed.

Wireless LAN has been dramatically evolving in performance and coming into wide use. Mesh network, which access points are deployed in mesh structure, extends the coverage of the networks. That has a lot of benefits, simplicity of building network, wide coverage, load balancing of access points and so forth. The paper proposes a new mesh network structure, which consists of access points with longer wireless range and terminal nodes with shorter one. We also define a zone from a viewpoint of asymmetry of wireless range. In order to save battery consumption, a new algorithm of routing for ad hoc mesh network is proposed and discussed.

When sensing data generation is disproportionate geographically, battery depletion partially occurs. As a result, network lifetime degrades significantly. In order to improve network lifetime we have proposed a scheme with data dispersal transmission for wireless sensor networks with multiple-sinks, and have improved network lifetime. In this paper, in order to improve network lifetime more, we improve the dispersal rate of node for each sink in our proposed. We evaluate the performance of the proposed scheme for several pattern of data generation is by using computer simulations. We show that the improvement of proposed scheme is effective to improve network lifetime more.

In the conventional multi-channel Medium Access Control protocols of ad-hoc networks, a channel allocation problem for collision avoidance occurs if nodes cannot make carrier sensing for different channels simultaneously. In this paper, a novel multi-channel MAC protocol with dynamic channel allocation is proposed to solve the problem. Specifically, in the proposed protocol, nodes make carrier sensing by channel-hopping method. With the information of channel usage, the protocol can allocate a channel to the nodes dynamically. Furthermore, by adjusting the data transmission probability enables. the proposed protocol to also realize high throughput for different number of nodes and data sizes. A theoretical protocol analysis is also described.

We propose Media Access Control (MAC) protocol that applies the transmission power control and the bit-rate control to improve the electric power efficiency in the data transmission. In the proposal protocol, An appropriate sequence is selected according to the received power obtained by exchanging the control frames. Moreover, each node makes a table for the transmission power and the bit-rate in own wireless interface. The data is transmitted with high power efficiency by acquiring appropriate transmission power and the bit-rate corresponding to the change in a peripheral wireless situation. The performance of the proposal protocol is shown by the computer simulation.

RFID systems with plural readers have a problem that communications of readers and tags collide when they are located physically near positions. For this problem, Waldrop, Engels, Sarm proposed DCS and VDCS and showed that they achieve higher probability of communication than slotted aloha in case of high probability between readers and tags through simulation. However, the mathematical structure of the protocols are still unclear. This paper analyses the performance of RFID systems with plural readers. First of all, the paper formals DCS and analyzes state transition probabilities, stationary state probabilities, and communication success rates. The theoretical result shows that there is an optimal load which maximizes the communication success rate, and so forth. We also points out the defects of DCS.

In this paper, we propose a novel routing algorithm constructing a power efficient route called PERFECT (Power-efficient routing based on the Function of Energy Computing Time) in ad hoc networks. In PERFECT, the standby time to forward RREQ (Route REQest) is calculated by the received power of RREQ. PERFECT does not need additional control packets such as position information etc.. Even if some nodes equipped with different characteristic antenna exist together, PERFECT can construct a power efficient route. In addition, we also propose the extended version of PERFECT called D-PERFECT (Discrete-PERFECT) for discrete power control environment. Theoretical and Simulated results show the effectiveness of PERFECT and D-PERFECT.

In conventional multi-channel Medium Access Control protocol of ad-hoc networks, there is a channel allocation problem for collision avoidance because node cannot make carrier sensing for different channels simultaneously. In this paper a novel multi-channel MAC protocol with dynamic channel allocation is proposed to solve the problem. Specifically, in the protocol, nodes make carrier sensing by channel-hopping methods. With the information of channel usage, we can allocate a channel to the nodes dynamically. Furthermore, by adjusting the data transmission probability, proposed protocol can also realize high performance throughput n different number of nodes and data sizes. A theoretically protocol analysis is also described.

Smart antennas are expected to enhance scalability in ad hoc networks. This paper at first evaluates three directional MAC protocols, DMAC, MMAC and SWAMP as well as the omni-directional protocol IEEE 802.11 DCF in multi-hop transmission environment. The evaluations address the problem that the performance strongly depends on the topology of routes between sources and destinations, referred to as a directional hidden terminal problem. After analyzing the problem, we propose three solutions. The solutions are NAV indicators which are high gain CTS (HCTS), backward RTS (BRTS) and relayed CTS (RCTS) indicating on-going communications to a directional hidden terminal to set NAV. Among those we show that the solutions have the improvement of the throughput.