Hideki Tode

A study on power saving using RTS/CTS handshake and burst transmission in wireless LAN

Recently, buttery-powered portable devices, which can use wireless LAN (WLAN), such as smart phones and tablet computers, are increasing. However, these devices consume more energy when using WLAN interfaces, and the battery lifetime is shorten. In order to reduce the power consumption of wireless stations, IEEE 802.11 specifies PSM (Power Saving Mode). However, PSM cannot save the energy optimally and it increases the transfer delay of packets severely. In this paper, to reduce the power consumption and suppress the transfer delay, we propose a power saving method using RTS/CTS handshake and burst transmission. Wireless stations save energy by sleeping for NAV (Network Allocation Vector) duration. In addition, we extend NAV duration with burst transmission. The number of packets transmitted per burst is decided so that the acceptable transfer delay of each packet is preserved. Finally, we show the effectiveness of the proposed method by computer simulation.

Robust data gathering method using controlled mobility in underwater sensor network

These days, underwater exploration demand is increasing in the field of industry, science, military, and so on. Hence, Underwater Sensor Network to collect data by scattering sensors in water has been attracted attention. However, there are various problems specific to underwater environments including the communication medium. In this paper, we focus on some problems on broken or degrading link between two neighboring nodes moving away from each other along with water current. To recover such links, we propose to introduce and control mobile nodes to relay communication between such two nodes. Existing studies dealing with the controlled mobility focused on the movement from the sea bed towards the water surface in order to avoid broken links caused by a shadow zone. On the other hand, the proposed method recovers broken and degrading links caused by movement of sensors by the water flow. Different from exiting works, limited number of smart mobile nodes move in any directions. In addition, because the cost of node movement in UWSN is higher than that of terrestrial network, this method also aims at reducing the movement distance of mobile nodes. Furthermore, the proposed method can measure and deal with the link disconnection proactively because the movement of mobile nodes is controlled while grasping the network condition. Finally, we show the effectiveness of the proposed method by computer simulation.

Packet transmission scheduling for enhancing total throughput against channel fading in wireless LAN

Inefficient channel utilization is still a serious problem in wireless LANs. One of effective solutions is to decrease the frequency of packet loss. While the backoff algorithm in IEEE 802.11 avoids only the packet loss caused by collision, other previous works that prevent the packet loss caused by channel fading improve channel utilization with transmission at a lower rate. However, utilizing lower transmission rate degrades transmission efficiency because the channel is occupied for a longer time. In this paper, we avoid decreasing transmission rate with a novel transmission scheduling. Specifically, transmission to stations under fading channel condition is interrupted until the condition improves, and other transmission is processed on ahead. Moreover, we propose an extended RTS/CTS handshake which quickly detects the improvement of channel condition and minimizes the wasted time even if fading loss occurs. Evaluation results demonstrate that network throughput is improved without degrading the throughput fairness between stations.

Adaptive channel selection control saving its redundant usage based on hidden stations in wireless access networks

Recently, wireless networks are utilized in various situations. However, the characteristic of wireless environment causes many problems like limited bandwidth, collisions and interferences among transferred frames. It is required to enhance bandwidth with efficient channel utilization. In this paper, in wireless access networks where a base station and wireless stations communicate directly, we achieve higher network bandwidth by introducing multi-channel environment and utilizing each channel efficiently. Though wireless networking with multiple channels is well explored, the most of the related works focus on wireless multihop networks. However, the topology of wireless access networks we assume is completely different from multihop networks. Hence, a new multi-channel protocol, with different architecture and algorithm, is required to increase network bandwidth. In this paper, we propose a new protocol suited to the target environment. Specifically, the proposed method controls operation channel of each wireless station to minimize collisions and interferences caused by hidden station problem, and to balance data transfer load on every channel. Moreover, the proposed method minimizes the number of utilized channels by suppressing redundant usage of channels according to total data transfer load. This alleviates channel interferences among neighboring wireless access networks and restricts power consumption at base station. Finally, we show the effectiveness of the proposed method by computer simulation.

QoS-Aware Retransmission with Network Coding Based on Adaptive Cooperation with IEEE 802.11e EDCA

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve scarce wireless capacity. In wireless LANs, NC can be applied to packet retransmission in which multiple packets can be equivalently transmitted by a single retransmission trial at base station (BS). In this paper, retransmission based on NC cooperates with IEEE 802.11e EDCA. In EDCA, when network load is high, QoS is significantly degraded even in high priority class. To solve this, existing methods improve backoff control, and decrease packet loss caused by collision. However, backoff control cannot prevent packet loss caused by multipath channel fading. In the proposed cooperation between NC and EDCA, QoS of high priority class is improved from the aspect of efficient loss recovery. Unlike NC method with no QoS control, we encounter transmission scheduling problem among NC packet, single lost packet, and new packet. Moreover, in the constitution of packets encoded into NC packet, priority and traffic load of each priority class should be considered. Therefore, we propose how to determine the packet to be transmitted at next transmission opportunity in BS and how to constitute NC packets encoded by adequate set of lost packets. Finally, we show the effectiveness of the proposed method by extensive computer simulation.

Higher rate packet transmission scheduling for enhancing TCP performance by smoothing of queuing time in wireless LAN

Recently, wireless LANs are utilized in various situations. However, inefficient channel utilization is still a serious problem. One of effective solutions is to prevent packet loss and to transmit packets at a higher rate. While the backoff algorithm in IEEE 802.11 avoids only the packet loss caused by collision, other existing works tackle the packet loss caused by channel fading by transmitting packets at a lower rate. The authors have proposed a transmission scheduling algorithm which avoids decreasing transmission rate and improves channel utilization. However, these previous methods do not consider influence to TCP performance. In this paper, we propose a novel packet transmission scheduling which enhances TCP performance by effectively utilizing higher channel transmission rate and by keeping TCP congestion window size large. The proposed scheduling at MAC level avoids retransmission time out (RTO) of TCP ACK and duplicate ACK, without modifying TCP itself and adopting complicated cross-layer approaches. Evaluation results demonstrate that total throughput which aggregates all transferred TCP flows and the minimum throughput among the TCP flows are enhanced by explicitly decreasing the frequencies of duplicate ACK and RTO.

Power-saving for wireless stations using RTS/CTS handshake and burst transmission in wireless LANs

Recently, usage of wireless LANs (WLANs) by mobile devices has spread rapidly. However, these devices consume large amounts of electricity when they communicate through WLAN. Although IEEE 802.11 specifies power saving mode (PSM), it cannot let wireless stations (STAs) sleep in an optimal manner and increases packet transfer delay. In this paper, we propose a power saving method that uses a different framework. Specifically, STAs reduce power consumption by sleeping for the network allocation vector duration that is extended by bidirectional burst transmission within the acceptable delay of each downlink packet. In addition, we put forth the combination of the proposed method with PSM to improve performance in the situations for which the amount of traffic is small.

Hop counts reduction of ZigBee nodes by cooperating wireless LAN in ZigBee network

Lately, ZigBee has been attracting attention as a short-range wireless communication standard. In a ZigBee network, it is necessary to suppress the packet transfer load because ZigBee needs to operate with low power consumption and within narrow communication bandwidth. On the other hand, in typical environments in which ZigBee is utilized, such as a smart home network, it generally coexists with WLAN (Wireless LAN), which has relatively long idle periods. Thus, to reduce the communication load in ZigBee, this paper proposes a hop counts reduction method, where some packets in the ZigBee network are transferred via WLAN when the WLAN is not overloaded. Existing studies that assume an environment in which ZigBee and WLAN coexist are only concerned with interference avoidance between the two networks. On the other hand, this paper focuses on adaptive cooperation, which enables more efficient communication with low power consumption and higher channel utilization.

Lightweight data transfer unified with active localization and robust routing in underwater networks

These days, the demand for investigating underwater area by using underwater sensor network is increasing. Compared with terrestrial environment, underwater communication has specific characteristics of low bandwidth and high packet loss rate. Hence, robust data transfer needs to be realized with lower network load by limiting the number of exchanged packets, reducing end-to-end data packet transfer delay, and so on. Moreover, as for network management, localization as well as routing is also required to be done successfully on more sensor nodes with low load. To realize localization and routing with low network load, the authors focus on an integration of localization and routing which saves redundant packet communication. In this paper, based on the integration, we propose an active localization and a robust routing to enhance success ratio of the localization and robustness of the routing, respectively. Moreover, we propose a new integration method where the transfer process of sensed data is also integrated with localization and routing to further enhance robustness of data transfer and reduce end-to-end packet transfer delay. Finally, we demonstrate the effectiveness of the proposed method by computer simulation.

Adaptive channel selection control equalizing sojourn time of sending packets inside wireless stations in wireless access networks

In recent years, wireless networks have been utilized in many situations. However, further increase in network capacity is essential in order to transfer large volume of traffic demanded by many and various clients and applications. By introducing multi-channel environment, network capacity is increased. However, in cases that packet generation rates from wireless stations to a base station are different among wireless stations, all the communication bandwidth over multiple channels is not properly allocated to wireless stations with larger generation rates in particular, even though there is enough available network bandwidth in total. This issue becomes significantly serious in actual wireless access networks where the distance between the base station and each wireless station is different, that means different maximum transmission rate of each station, under the fading condition. Therefore, in this paper, we adaptively allocate proper communication channel, and as a result, adaptive bandwidth to all wireless stations so that they transmit all generated packets by equalizing sojourn time in their sending buffers if there is enough total network bandwidth over all channels. Finally, we show the effectiveness of the proposed method by computer simulation.