This paper focuses on top-k query in cluster-based multi-hop wireless sensor networks (WSNs) employing wake-up receivers. We aim to design wake-up control that enables a sink to collect top-k data set, i.e., k highest readings of sensor nodes within a network, efficiently in terms of energy consumption and delay. Considering a tree-based clustered WSN, we propose a cluster-based wake-up control, which conducts activations and data collections of different clusters sequentially while the results of data collections at a cluster, i.e., the information on provisional top-k data set, are exploited for reducing unnecessary data transmissions at the other clusters. As a wake-up control employed in each cluster, we consider two different types of control: countdown content-based wake-up (CDCoWu) and identity-based wake-up (IDWu). CDCoWu selectively activates sensor nodes storing data belonging to top-k dataset while IDWu individually wakes up all sensor nodes within a cluster. Based on the observation that the best control depends on the number of cluster members, we introduce a hybrid mechanism of wake-up control, where a wake-up control employed at each cluster is selected between CDCoWu and IDWu based on its number of cluster members. Our simulation results show that the proposed hybrid wake-up control achieves smaller energy consumption and data collection delay than the control solely employing conventional CDCoWu or IDWu.

Wireless Full-Duplex (FD) communication can double the point-to-point throughput. To obtain the full benefits of the FD technique in multi-hop networks, its potential throughput performance in multi-hop networks should be clarified qualitatively and quantitatively. Developing an analytical model for FD multi-hop networks is effective and useful for not only clarifying such network dynamics but also developing the optimal protocol design. However, generalized analytical expression for the end-to-end throughput of FD multi-hop networks has not been proposed. This paper proposes analytical expressions for the end-to-end throughput of string-topology wireless FD multi-hop networks. Our approach is to integrate with the analytical model of the airtime expression, which is an effective analytical approach of the throughput analysis for Half-Duplex (HD) multi-hop networks, and the Markov-chain model considering the FD MAC operation. The proposed model clarify the detailed effect of the FD MAC operation on the throughput performance in multi-hop networks. In particular, it can obtain the end-to-end throughput of FD multi-hop networks for arbitrary number of hops, arbitrary payload size and arbitrary value of the minimum contention window. The analytical expressions verified by comparisons with the simulation results. From the comparisons with the results in HD multi-hop networks, we confirm the effectiveness of the FD communication in multi-hop networks.

In this paper, we first evaluate Breadcrumbs in wireless multi-hop networks and reveal that they brings throughput improvement of not only popular content but also less popular content. Breadcrumbs can distribute popular content traffic towards edges of a wireless network, which enables low-popularity content to be downloaded from the gateway node. We also propose a new caching decision, called receiver caching. In receiver caching, only the receiver node caches the transmitted content. Our simulation results show that receiver caching prevents frequent replacement of cached content, which reduces invalid Breadcrumbs trails to be remained. And they also show that receiver caching significantly improves the total throughput performance of Breadcrumbs.

Applying Software Defined Network (SDN) technology to wireless networks are attracting much attention. Our previous study proposed a channel utilization method based on SDN/OpenFlow technology to improve the channel utilization efficiency of the multi-channel wireless backhaul network (WBN). However, since control messages are inherently transmitted with data traffic on a same channel in WBN, it inevitably degrades the network capacity. Specifically, the amount of control messages for collecting statistical information of each flow (FlowStats) linearly increases with the number of ongoing flows, thereby being the dominant overhead for backhaul networks. In this paper, we propose a new method that prevents the increase of control traffic while retaining the network performance of the previous method. Our proposed method uses statistical information of each interface (PortStats) instead of per-flow information (FlowStats), and handles multiple flows on the interface together if possible. Otherwise, to handle individual flow, we propose a way to estimate per-flow information without introducing extra control messages. Finally, we show that the proposed method offers the same performance with the previous method, while greatly reducing the amount of control traffic.

This paper aims to establish expressions for IEEE 802.11 string-topology multi-hop networks with transmission control protocol (TCP) traffic flow. The relationship between the throughput and transport-layer function in string-topology multi-hop network is investigated. From the investigations, we obtain an analysis policy that the TCP throughput under the TCP functions is obtained by deriving the throughput of the network with simplified into two asymmetric user datagram protocol flows. To express the asymmetry, analytical expressions in medium access control-, network-, and transport layers are obtained based on the airtime expression. The expressions of the network layer and those of transport layer are linked using the “delayed ACK constraint,” which is a new concept for TCP analysis. The analytical predictions agree well with the simulation results, which prove the validity of the obtained analytical expressions and the analysis policy in this paper.

Multi-hop networks have been proposed to increase the data transmission rate in wireless mobile networks, and consequently improve the quality of experience of cell-edge users. A successive resource allocation scheme (SAS) has been proposed for a 2-hop virtual cellular network (VCN). In a multi-cell environment, the performance of SAS degrades because of intra-cell and inter-cell interference. In order to alleviate the effect of intra-cell and inter-cell interference and consequently increase the channel capacity of the VCN, this paper proposes the sequential iterative allocation scheme (SIS). Computer simulation results show that, compared to SAS, SIS can improve the fairness, the ergodic, and the outage channel capacity per mobile terminal (MT) of the VCN in a multi-cell environment. This paper also analyzes the performance of the VCN compared to that of the single hop network (SHN) when SIS is applied in a multi-cell environment. Using SIS, VCN can provide higher ergodic channel capacity, and better degree of fairness than SHN in a multi-cell environment. The effect of the number of wireless ports (WPs) in the VCN is also investigated, and the results suggest that adding more WPs per virtual cell in the VCN can enhance the outage channel capacity per MT and the degree of fairness of the VCN.

String-topology multi-hop network is often selected as an analysis object because it is one of the fundamental network topologies. The purpose of this paper is to establish expression for end-to-end delay for IEEE 802.11 string-topology multi-hop networks. For obtaining the analytical expression, the effects of frame collisions and carrier-sensing effect from other nodes under the non-saturated condition are obtained for each node in the network. For expressing the properties in non-saturated condition, a new parameter, which is frame-existence probability, is defined. The end-to-end delay of a string-topology multi-hop network can be derived as the sum of the transmission delays in the network flow. The analytical predictions agree with simulation results well, which show validity of the obtained analytical expressions.

DetF (Detect-and-Forward) is studied as a relay method in multi-hop networks. When an error detection scheme is introduced, DetF is likely to achieve an efficient transmission. In this study, AMI (Alternate Mark Inversion) code is focused on as an error detection scheme. Error detection performances of ternary PSK (Phase Shift Keying) using AMI code and binary PSK using parity check code are examined. It is shown that ternary PSK using AMI code has a good error detection performance.

The rapid variation of wireless channels and feedback delay make the available channel state information (CSI) outdated in dynamic wireless multi-hop networks, which significantly degrades the accuracy of cross-layer resource allocation. To deal with this problem, a cross-layer resource allocation scheme is proposed for wireless multi-hop networks by taking the outdated CSI into account and basing compensation on the results of channel prediction. The cross-layer resource allocation is formulated as a network utility maximization problem, which jointly considers congestion control, channel allocation, power control, scheduling and routing with the compensated CSI. Based on a dual decomposition approach, the problem is solved in a distributed manner. Simulation results show that the proposed algorithm can reasonably allocate the resources, and significantly improve the throughput and energy efficiency in the network.

In wireless single-hop networks, IEEE 802.11e Enhanced Distributed Channel Access (EDCA) is the standard for Quality of Service (QoS) control. However, it is necessary for controlling QoS to modify the currently used IEEE 802.11 Distributed Coordination Function (DCF)-compliant terminals as well as Access Points (APs). In addition, it is necessary to modify the parameter of IEEE 802.11e EDCA when the traffic is heavy. This paper proposes a novel scheme to guarantee QoS of high-priority flow with Receiving Opportunity Control in MAC Frame (ROC) employed adaptive flow control in wireless multi-hop network. In the proposed scheme, the edge APs which are directly connected to user terminals estimate the network capacity, and calculate appropriate ACK prevention probability against low-priority flow according to traffic load. Simulation evaluation results show that the proposed scheme guarantees QoS.

There exists a considerable number of node placement models and algorithms for simulation of wireless multihop networks. However, the topologies created with the existing algorithms do not have properties of real networks. We have developed NPART (Node Placement Algorithm for Realistic Topologies) in order to resolve this fundamental issue in simulation methodology. We compare topologies generated by NPART with open wireless multihop network in Berlin. The NPART generated topologies have almost identical node degree distribution, number of cut-edges and vertices as the real network. Unlike them, topologies generated with the common node placement models have their own characteristics which are considerably different both from NPART and from reality. NPART algorithm has been developed into a tool. We propose a method and present a tool for integration of NPART with various realistic node mobility algorithms and tools, such as Citymob [1] and MOVE [2]. This integrated tool allows easy and time-efficient generation of highly complex, realistic simulation scenarios. We use the tool to evaluate effects of integration between existing open community wireless multi-hop networks and vehicular ad-hoc networks (VANETs). The evaluation shows that despite partial coverage and peculiar topological properties of open networks, they offer high levels of performance and network availability to the mobile end users, virtually identical to performance and availability of planned, dedicatedly deployed networks. Our results indicate that the integration of these networks may bring considerable benefits to all parties involved.

This paper quantitatively analyzes the maximum UDP (User Datagram Protocol) throughput for two-way flows in wireless string multi-hop networks. The validity of the analysis is shown by the comparison with the simulation and the experiment results. The authors also clarify the difference fundamental characteristics between a one-way flow and a two-way flow in detail based on the simulation results. The result shows that collisions at both ends' nodes are decisive in determining the throughput for two-way flows. The analyses are applicable to the estimation of VoIP (Voice over Internet Protocol) capacity for string multi-hop networks represented by WLAN (Wireless Local Area Network) mesh networks.

We propose the use of an invertible code in cooperative multi-hop relaying networks. The effect of the code on the probability that an information block is undelivered to the destination is analyzed at the link level with a simple network topology. Numerical results indicate that significant improvement is feasible by an incorporation of an invertible code, since an information block can be reproduced by correcting channel errors in the received blocks at a relaying node.

In this letter, we propose a network-adaptive video streaming scheme based on cross-layered hop-by-hop video rate control in wireless multi-hop networks. We argue that existing end-to-end network-adaptive video rate control schemes, which utilize end-to-end statistics, exhibit serious performance degradation in severely interfered wireless network condition. To cope with this problem, in the proposed scheme, intermediate wireless nodes adjust video sending rate depending upon wireless channel condition measured at MAC (Medium Access Control) layer. Extensive experimental results from an IEEE 802.11a-based testbed show that the proposed scheme improves the perceptual video quality compared to an end-to-end scheme.

In this paper, we propose a cross-layer design of packet level cooperation for wireless LANs that support rate adaptation. While keeping compatibility with legacy wireless LANs, distributed control of multi-hop packet transmission is enabled without pre-negotiation of routing or pairing. These features are provided by prioritization scheme based on IEEE 802.11e EDCF in which we set the parameters according to the measured link condition at each terminal. Relaying packets with high transmission rate makes much efficient use of radio resource, and it leads not only to improve performance of the total system, but also to overcome the fairness issue known in rate adaptation, where the terminals with good link conditions cannot gain enough resource because of the time consumed by low data rate transmission. These advantages are confirmed through computer simulations considering packet error rate at each transmission which is assumed by receiving power calculated from the distance between source, relay, and destination terminals. Furthermore, we also discuss about the fairness between cooperation-enabled and legacy terminals when they coexist in the same system, in order to make gradual deployment feasible.

Maximizing the throughput of a network while supporting fairness among nodes is one of the most critical issues in designing wireless networks. In single-hop networks, a lot of schemes have been proposed to satisfy this criterion, and efficient protocols like the IEEE 802.11 and the HiperLAN/2 standards have been established for wireless LAN. In multi-hop wireless networks, however, throughput and fairness have different characteristics from those of single-hop networks. In this paper, the tradeoff between throughput and fairness on multi-hop networks is studied by computer simulation, assuming three node distribution models, namely, normal, constant, and uniform distribution and four different bandwidth (channel) scheduling methods, i.e., first-in first-out buffer based, weighted traffic model based, bandwidth reservation based, and maximum throughput based scheduling. Furthermore, as a realistic model, a hybrid scheme is investigated where partial bandwidth is allocated to the bandwidth reservation based scheduling and the remaining to the maximum throughput based one.