Unlike Wi-Fi, Broadband Wireless Access (BWA) technology provides a high-speed communication in a wide area. The IEEE 802.16 (WiMAX) standard of wireless mesh networks is one of the widely used BWA standards. WiMAX mesh mode achieves data transmission in conflict-free manner in multihop networks by using the control messages (three way handshake messages or MSH-DSCH messages) to reserve channel for sending data. Concurrently, the coordination of three way handshake messages depends on the mechanism named Election based Transmission Timing (EBTT). However, IEEE 802.16 mesh mode uses a static holdoff algorithm, which leads to a low performance in the majority of cases. In this paper, after analyzing the IEEE 802.16 mesh mode with coordinated distributed scheduling, we propose a novel method to improve the throughput by a dynamic holdoff algorithm. The simulation results show that our proposal gets a better throughput performance.

In this paper, we propose an IEEE 802.15.10-based layer 2 routing (L2R) method with a load balancing algorithm; the proposal considers fairness in terms of the cumulative number of sending packets at each terminal to resolve the packet concentration problem for the IEEE 802.15.4-based low-power consumption wireless smart utility network (Wi-SUN) systems. The proposal uses the accumulated sending times of each terminal as a weight in calculating each path quality metric (PQM) to decide multi-hopping routes with load balancing in the network. Computer simulation of the mesh network with 256 terminals shows that the proposed routing method can improve the maximum sending ratio (MSR), defined as the ratio of the maximum sending times to the average number of sending times in the network, by 56% with no degradation of the end-to-end communication success ratio (E2E-SR). The proposed algorithm is also experimentally evaluated by using actual Wi-SUN modules. The proposed routing method also improves the MSR by 84% with 70 terminals. Computer simulations and experiments prove the effectiveness of the proposed method in terms of load balancing.

In this paper, we study Wi-Fi mesh networks (WMNs) as a promising candidate for wireless networking infrastructure that interconnects a variety of access networks. The main performance bottleneck of a WMN is their limited capacity due to the packet collision from the contention-based IEEE 802.11s MAC. To mitigate this problem, we present the distributed link-activation (DLA) protocol which activates a set of collision-free links for a fixed amount of time by exchanging a few control packets between neighboring MRs. Through the rigorous proof, it is shown that the upper bound of the DLA rounds is O(Smax), where Smax is the maximum number of (simultaneous) interference-free links in a WMN topology. Based on the DLA, we also design the distributed throughput-maximal scheduling (D-TMS) scheme which overlays the DLA protocol on a new frame architecture based on the IEEE 802.11 power saving mode. To mitigate its high latency, we propose the D-TMS adaptive data-period control (D-TMS-ADPC) that adjusts the data period depending on the traffic load of a WMN. Numerical results show that the D-TMS-ADPC scheme achieves much higher throughput performance than the IEEE 802.11s MAC.

Wireless engineers and business planners commonly raise the question on where, when, and how millimeter-wave (mmWave) will be used in 5G and beyond. Since the next generation network is not just a new radio access standard, but also an integration of networks for vertical markets with diverse applications, answers to the question depend on scenarios and use cases to be deployed. This paper gives four 5G mmWave deployment examples and describes in chronological order the scenarios and use cases of their probable deployment, including expected system architectures and hardware prototypes. The first example is a 28 GHz outdoor backhauling for fixed wireless access and moving hotspots, which will be demonstrated at the PyeongChang Winter Olympic Games in 2018. The second deployment example is a 60 GHz unlicensed indoor access system at the Tokyo-Narita airport, which is combined with Mobile Edge Computing (MEC) to enable ultra-high speed content download with low latency. The third example is mmWave mesh network to be used as a micro Radio Access Network (µ-RAN), for cost-effective backhauling of small-cell Base Stations (BSs) in dense urban scenarios. The last example is mmWave based Vehicular-to-Vehicular (V2V) and Vehicular-to-Everything (V2X) communications system, which enables automated driving by exchanging High Definition (HD) dynamic map information between cars and Roadside Units (RSUs). For 5G and beyond, mmWave and MEC will play important roles for a diverse set of applications that require both ultra-high data rate and low latency communications.

From past experience of the large-scale cutoff of existing networks as a result of the East Japan Great Earthquake and tsunamis, and from previous research on stabilizing ad hoc networks that lack control mechanisms, we have strengthened the resilience of NerveNet. NerveNet was originally designed and developed as an access network for providing context-aware services with the use of sensors and actuators. Thus, at present, it has the capability to enable resilient information sharing and communications in a region even if access to the Internet is impossible in emergency situations. NerveNet is composed of single or multiple base stations interconnected by a variety of Ethernet-based wired or wireless transmission systems. A network is formed using line, star, tree, or mesh topology. Network and data management works in each base station in a distributed manner, resulting in the resilience of this system. In collaboration with the town of Shirahama in Wakayama prefecture in Japan, we have been conducting a pilot test with the NerveNet testbed. The test includes nine base stations interconnected by 5.6-GHz Wi-Fi and Fixed Wireless Access (FWA), providing tourists and residents with Internet access. In the future, we expect that not only NerveNet but also other novel technologies will contribute to solving social problems and enriching people's lives.

Wireless LAN (WLAN) roaming systems, such as eduroam, enable the mutual use of WLAN facilities among multiple organizations. As a consequence of the strong demand for WLAN roaming, it is utilized not only at universities and schools but also at the venues of large events such as concerts, conferences, and sports events. Moreover, it has also been reported that WLAN roaming is useful in areas afflicted by natural disasters. This paper presents a novel WLAN roaming system over Wireless Mesh Networks (WMNs) that is useful for the use cases shown above. The proposed system is based on two methods as follows: 1) Automatic authentication path generation method decreases the WLAN roaming system deployment costs including the wiring cost and configuration cost. Although the wiring cost can be reduced by using WMN technologies, some additional configurations are still required if we want to deploy a secure user authentication mechanism (e.g. IEEE 802.1X) on WLAN systems. In the proposed system, the Access Points (APs) can act as authenticators automatically using RadSec instead of RADIUS. Therefore, the network administrators can deploy 802.1X-based authentication systems over WMNs without additional configurations on-site. 2) Local authentication method makes the system deployable in times of natural disasters, in particular when the upper network is unavailable or some authentication servers or proxies are down. In the local authentication method, users and APs can be authenticated at the WMN by locally verifying the digital certificates as the authentication credentials.

We proposed to apply compressed sensing to realize information sharing of link quality for wireless mesh networks (WMNs) with grid topology. In this paper, we extend the link quality sharing method to be applied for WMNs with arbitrary topology. For arbitrary topology WMNs, we introduce a link quality matrix and a matrix formula for compressed sensing. By employing a diffusion wavelets basis, the link quality matrix is converted to its sparse equivalent. Based on the sparse matrix, information sharing is achieved by compressed sensing. In addition, we propose compressed transmission for arbitrary topology WMNs, in which only the compressed link quality information is transmitted. Experiments and simulations clarify that the proposed methods can reduce the amount of data transmitted for information sharing and maintain the quality of the shared information.

An information flow problem is a graph-theoretical formalization of the transportation of information over a complicated network. It is known that a linear network code plays an essential role in a certain type of information flow problems, but it is not understood clearly how contributing linear network codes are for other types of information flow problems. One basic problem concerning this aspect is the linear solvability of information flow problems, which is to decide if there is a linear network code that is a solution to the given information flow problem. Lehman et al. characterize the linear solvability of information flow problems in terms of constraints on the sets of source and sink nodes. As an extension of Lehman's investigation, this study introduces a hierarchy constraint of messages, and discusses the computational complexity of the linear solvability of information flow problems with the hierarchy constraints. Nine classes of problems are newly defined, and classified to one of three categories that were discovered by Lehman et al.

In this paper, we investigate the problems of the established congestion solution and then introduce a self-adjustable rate control that supports quality of service assurances over multi-hop wireless mesh networks. This scheme eliminates two phases of the established congestion solution and works on the MAC layer for congestion control. Each node performs rate control by itself so network congestion is eliminated after it independently collects its vector parameters and network status parameters for rate control. It decides its transmission rate based on a predication model which uses a rate function including a congestion risk level and a passing function. We prove that our scheme works efficiently without any negative effects between the network layer and the data link layer. Simulation results show that the proposed scheme is more effective and has better performance than the existing method.

To solve the problems of the existing trusted network access protocols for Wireless Local Area Network (WLAN) mesh networks, we propose a new trusted network access protocol for WLAN mesh networks, which is abbreviated as WMN-TNAP. This protocol implements mutual user authentication and Platform-Authentication between the supplicant and Mesh Authenticator (MA), and between the supplicant and Authentication Server (AS) of a WLAN mesh network, establishes the key management system for the WLAN mesh network, and effectively prevents the platform configuration information of the supplicant, MA and AS from leaking out. Moreover, this protocol is proved secure based on the extended Strand Space Model (SSM) for trusted network access protocols.

As a flexible and cost-efficient scalable Internet access network, we studied architectures, protocols, and design optimizations of the Wireless Internet-access Mesh NETwork (WIMNET). WIMNET is composed of multiple access points (APs) connected through multihop wireless communications on IEEE 802.11 standards. The increasing popularity of real-time applications such as IP-phones and IP-TV means that they should be supported in WIMNET. However, the contention resolution mechanism using a random backoff-time in the CSMA/CA protocol of 802.11 standards is not sufficient for handling real-time traffic in multihop wireless communications. In this paper, we propose a Fixed Backoff-time Switching (FBS) method for the CSMA/CA protocol to improve the real-time traffic performance in WIMNET by giving the necessary activation chances to each link. We implement our proposal on the QualNet simulator, and verify its effectiveness through simulations on three network topologies with four scenarios.

The contradictions created by the differences in mass P2P data and transfer capability of wireless networks, and mismatch of overlay network topology and physical network topology are the main barriers hindering the implementation of P2P resource sharing in wireless multi-hop networks. This paper investigates the problem of enabling P2P resource sharing in WMNs with two-tier architecture. SpiralChord, the DHT approach implemented through routers in the upper tier, is proposed to address the major problems of wireless resource sharing – how to efficiently find resources currently available and reduce redundant messages as much as possible. SpiralChord uses an ID assignment technique to integrate location awareness with cross-layering. Location awareness aims at alleviating mismatch in physical network topology and overlay network topology, and it is designed to map neighboring routers to close-by IDs in the logical ring. Cross-layering aims at speeding up resource lookup operations in the application layer by exploiting the information that is available at the MAC layer, and it tends to be more effective when physically neighboring routers have faraway IDs in the logical ring. An ID assignment strategy based on spiral curve is proposed to meet the contradictory requirements of location awareness and cross-layering, mapping a peer's neighbors in the overlay network to peers which are its physical neighbors and distributing the remaining physical neighbors as widely as possible in the overlay network. In addition, a mobility management mechanism is proposed to address the adverse effect of the movements of clients in lower tier on resource sharing. A client is assigned a managing router to take the responsibility for the location of the client. Simulations show SpiralChord is more effective in reducing message overhead and increasing lookup performance than Chord, and mobility management for mobile clients performs well at reducing message overhead caused by mobile clients in SpiralChord.

In this paper, we reformulate the issue related to wireless mesh networks (WMNs) from the Chief Executive Officer (CEO) problem viewpoint, and provide a practical solution to a simple case of the problem. It is well known that the CEO problem is a theoretical basis for sensor networks. The problem investigated in this paper is described as follows: an originator broadcasts its binary information sequence to several forwarding nodes (relays) over Binary Symmetric Channels (BSC); the originator's information sequence suffers from independent random binary errors; at the forwarding nodes, they just further interleave, encode the received bit sequence, and then forward it, without making heavy efforts for correcting errors that may occur in the originator-relay links, to the final destination (FD) over Additive White Gaussian Noise (AWGN) channels. Hence, this strategy reduces the complexity of the relay significantly. A joint iterative decoding technique at the FD is proposed by utilizing the knowledge of the correlation due to the errors occurring in the link between the originator and forwarding nodes (referred to as intra-link). The bit-error-rate (BER) performances show that the originator's information can be reconstructed at the FD even by using a very simple coding scheme. We provide BER performance comparison between joint decoding and separate decoding strategies. The simulation results show that excellent performance can be achieved by the proposed system. Furthermore, extrinsic information transfer (EXIT) chart analysis is performed to investigate convergence property of the proposed technique, with the aim of, in part, optimizing the code rate at the originator.

This study proposes an efficient identity-based secure routing protocol based on Weil pairing, that considers symmetric and asymmetric links for Wireless Mesh Networks (WMNs). A wireless mesh network is a group of wireless mesh routers and several types of wireless devices (or nodes). Individual nodes cooperate by forwarding packets to each other, allowing nodes to communicate beyond the symmetric or asymmetric links. Asymmetric communication is a special feature of WMNs because of the wireless transmission ranges of different wireless devices may be different. The asymmetric link enhances WMN coverage. Ensuring security in WMNs has become an important issue over the last few years. Existing research on this topic tends to focus on providing security for routing and data content in the symmetric link. However, most studies overlook the asymmetric link in WMNs. This study proposes a novel distributed routing protocol that considers symmetric and asymmetric links. The proposed protocol guarantees the security and high reliability of the established route in a hostile environment, such as WMNs, by avoiding the use of unreliable intermediate nodes. The routes generated by the proposed protocol are shorter than those in prior studies. The major objective of the proposed protocol is to allow trustworthy intermediate nodes to participate in the path construction protocol. Using the proposed protocol, mesh clients out of mesh router wireless transmission range may discover a secure route to securely connect to the mesh router for Internet access. The proposed protocol enhances wireless mesh network coverage and assures security.

We present a novel transmission rate control method for Wireless Mesh Networks, termed Semi-Fixed Rate Control (SFRC), which incorporates the advantages of Fixed Rate Control (FRC) and Adaptive Rate Control (ARC). SFRC has two periods, which are alternately repeated: an autorate period and a fixed-rate period. A unit of an autorate period and the successive fixed-rate period is termed “rate-control period”. The duration of the rate-control period is set considerably longer than that of the autorate period. In the autorate period, RTS/CTS is used with the lowest transmission rate, transmission rate adjustment is only applied to data frames, and loss of CTS frames is not reflected in the transmission rate adjustment. In the fixed-rate period, the transmission rate that was used most frequently in the preceding autorate period (optimum rate) is fixed, and RTS/CTS is not used. Implementation of SFRC is straightforward as it uses conventional IEEE 802.11 DCF and only minor modification of the wireless LAN driver is required. SFRC, which uses a modified SampleRate, an ARC implementation in the Madwifi, (SampleRate+) in the autorate period, termed SFRC-SampleRate+, was developed. The results of real-world experiments indicate that SFRC-SampleRate+ is superior to SampleRate and SampleRate+, and is closer to FRC, which uses optimum rate on each link, in terms of throughput in wireless mesh network environments.

The IEEE has recently released IEEE 802.15.5 standard [3] to provide multi-hop mesh functions for low-rate wireless personal area networks (WPANs). In this paper, we extensively describe a link-layer reliable broadcast protocol referred to as timer-based reliable broadcast (TRB) [3] in the IEEE 802.15.5 standard. The TRB scheme exploits (1) bitmap based implicit ACK to effectively reduce the unnecessary error control messages and (2) randomized timer for ACK transmission to substantially reduce the possibility of contentions. Performance evaluation shows that the TRB scheme achieves 100% reliability compared with other schemes with expense of slightly increased energy consumption.

In time division multiple access (TDMA)-based wireless mesh networks, interference relationships should be considered when time slots are assigned to links. In graph theory-based time slot assignment algorithms, the protocol interference model is widely used to determine radio interference information, although it is an inaccurate model of actual radio interference. On the other hand, the signal-to-interference-plus-noise-ratio model (SINR model) gives more accurate interference relationships but is difficult to apply to time slot assignment algorithms since the radio interference information cannot be determined before time slot assignment. In this paper, we investigate the effect of the parameters of the protocol interference model on the accuracy of the interference relationships determined using this model. Specifically, after assigning time slots to links based on the protocol interference model with various interference ratios, which is the major parameter of the protocol interference model, we compare the interference relationship among links in the protocol interference and SINR models. Through simulation experiments, we show that accuracy of the protocol interference model is improved by up to 15% by adjusting the interference ratios of the protocol interference model.

We investigate the problem of joint frequency and power allocation in wireless mesh networks, using a self-pricing game based solution. In traditional pricing game models, the price factor is determined from the global information of the network, which causes heavy communication overhead. To overcome this problem, we propose a self-pricing game model, in which the price factor is determined by the distributed access points processing their individual information; moreover, it is implemented in an autonomous and distributed fashion. The existence and the efficiency of Nash equilibrium (NE) of the proposed game are studied. It is shown that the proposed game based solution achieves near cooperative network throughput while it reduces the communication overhead significantly. Also, a forcing convergence algorithm is proposed to counter the vibration of channel selection. Simulation results verify the effectiveness and robustness of the proposed scheme.

To provide convenient wireless access, wireless mesh networks (WMNs) can be rapidly deployed and connected for mobile clients. Although route redirection traffic control schemes and dynamic routing metrics can be used to improve the performance of WMNs, more of the available network bandwidth will be consumed by control message exchange. This paper proposes a capacity-aware and multipath supported traffic control framework in WMNs. The proposed framework can be used to dispatch data traffic in a multipath manner to improve the utilization of wireless links and forwarding latency. A hierarchical queue architecture is proposed to monitor and classify network traffic without the effort of control message exchange. Our traffic control strategy, which is based on local minimization of the forwarding latency, consists of two phases to automatically adapt to the utilization rate of the network links. In the first phase, the incoming packets are dispatched to the lower level queues according to the Internet gateway capacity. In the second phase, the packets are dispatched to the related network links according to the link load. The current study implements the proposed traffic control system on NS2 for simulation and on Linux 2.6 for real traffic analysis. Experimental results show that the proposed framework improves the throughput and reduces forwarding delay with an approximate minimum delay time. The results also show that the behavior of the long-term delay model can be applied to short-term traffic control methods in WMNs.

The aggregate throughput of wireless mesh networks (WMNs) can be significantly improved by equipping the mesh routers with multiple radios tuned to orthogonal channels. Not only the links using orthogonal channels can be activated at a time, but some links in the same channel also can be activated concurrently if the Signal-to-Interference-and-Noise Ratio (SINR) at their receivers is not lower than the threshold, which is the spatial-reuse characteristic. STDMA is considered as one of the medium access schemes that can exploit spatial reuse to improve network throughput. Past studies have shown that optimizing the performance of STDMA is NP-Hard. Therefore, we propose a STDMA-based scheduling algorithm that operates in a greedy fashion for WMNs. We show that the proposed algorithm enhances not only the throughput but also the fairness by capturing the essence of spatial-reuse approach of STDMA and giving medium access opportunities to each network element based on its priority. We furthermore validate our algorithm through theoretical analysis and extensive simulations and the results show that our algorithm can outperform state-of-the-art alternatives.