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© 2013 IEEE. This paper gives analytical waveform equations of the class-E/ {\text{F } }_{n} rectifier. By using the analytical waveforms, we investigate performances of the class-E/F and E/F rectifiers at any quality factor of the harmonic-resonant and output filters. From the investigations, the rectifier performances, such as the power output capability and the AC-DC current transfer function, are clarified. Besides, the design parameters of the class-E/ {\text{F } }_{n} rectifier with no input reactance, which is called the class- \Phi _{n} rectifier, are obtained. Four types of rectifiers, namely, class-E/F, E/F, \Phi _{2} , and \Phi _{3} rectifiers, were designed and implemented as a part of the resonant DC-DC converters. The experimental and PSpice-simulation results verified the analytical waveform equations and the performance investigation.

Copyright © 2020 The Institute of Electronics, Information and Communication Engineers. In a dense wireless network, concurrent transmissions normally increase interference and reduce network performance. In such an environment, however, there is a possibility that a frame can be decoded correctly if its receive power is higher than that of another frame by some predefined value (i.e., the so-called capture effect). As a result, the unfairness of throughputs among network nodes likely occurs in that context. This research aims to quantify the throughput performance of only one access point Wireless Local Area Networks (WLANs) with dense network nodes in the presence of the capture effect. We first propose a new analytical model, which can express not only WLANs' throughputs but also WLANs' unfairness transmission. The validity of the proposed model is confirmed by simulation results. Second, relying on the model, we present a novel Medium Access Control (MAC) protocol-based solution, which realizes throughput fairness between network nodes induced by the capture effect.

This paper presents an analytic expression of the class-E rectifier with low output-filter inductance. Compared with the traditional rectifiers, the larger power output capability can be obtained by varying the output-filter inductance. Also, the validity of the analytical expression and design strategy are presented by implementation of the class-E resonant DC-DC converter. The converter with low output-filter inductance achieved 11 % power output capability than the traditional class-E rectifier. 2

Millimeter-Wave (mmWave) communication in ultra-dense networks (UDNs) has been considered as a promising technology for future wireless communication systems. Exploiting the benefits of mmWave and UDNs, we introduce a new approach for jointly optimizing small-cell base station (SBS)-user (UE) association and power allocation to maximize the system energy efficiency (EE) while guaranteeing the quality of service (QoS) constraints for each UE. The SBS-UE association problem poses a new challenge since it reflects as a complex mixed-integer non-convex problem. On the other hand, the power allocation problem is in non-convexity structure, which is impossible to handle with the association problem concurrently. An alternating descent method is thus introduced to divide the primal optimization problem into two sub-problems and handle one-by-one at each iteration, where the SBS-UE association problem is reformulated using the penalty approach. Then, path-following algorithms are developed to convert non-convex problem into the simple convex quadratic functions at each iteration. Numerical results are provided to demonstrate the convergence and low-complexity of our proposed schemes.

Multipath TCP (MPTCP), which enables the use of multiple wireless links (e.g., Wi-Fi and LTE) for data transmissions, is an excellent technology for evolving multi-homing devices in mobile wireless networks. This paper explores concepts and feasibility of realizing MPTCP with path awareness (PA), in which the path-aware information is leveraged to reinforce the MPTCP transmissions. In particular, when aware of a network situation, a device can facilitate a mechanism that dynamically shifts the MPTCP traffic to a single path and vice versa. As a result, MPTCP with PA could solve the significant problem of negative aggregation benefit when the MPTCP throughput over divergent paths is worse than the best one of single-path TCP. We illustrate the feasibility of the proposed concept through our new implementation of a so-called MPTCP-LA (i.e., MPTCP with Loss Awareness). MPTCP-LA keeps the aggregation benefits non-negative by temporarily switching an MPTCP transmission on a path to a standby condition when the on-device observed loss reaches a threshold. We extensively evaluate MPTCP-LA in comparison to the standard MPTCP in an emulated environment. The results show that MPTCP-LA has better performance regarding enhancing throughput and saving networking resources.

To make WiGig/IEEE 802.11ad backward compatible with the legacy Wi-Fi, a multi-band device that is capable of WiGig and Wi-Fi is necessarily equipped a function of fast switchover between the WiGig and Wi-Fi link. It is expected that the switching action is done as quickly as possible in order to minimize negative effects on an ongoing application. The IEEE 802.11ad standard defines the switching operation within the scope of fast session transfer (FST) protocol. To properly run FST, the device needs extra layer-2 entities that simultaneously manage the PHY/MAC states of multiple radios. Although introducing WiGig radios is a trivial task, installing those entities on an existing legacyWi-Fi network is unfortunately a challenging one. This work presents an experimental feasibility study of achieving the backward compatibility without FST. We initially analyze the feasible capability of multipath transmission control protocol (MPTCP). We then setup a real-world testbed and evaluate different operational modes of MPTCP, aiming to find the most suitable one. Our experimental results show that the fast switchover between a multi-Gigabit WiGig and a legacy Wi-Fi link is achievable with the MPTCP's backup mode.

Small cells deployment is one of the most significant long-term strategic policies of the mobile network operators. In heterogeneous networks (HetNets), small cells serve as offloading spots in the radio access network to offload macro users (MUs) and their associated traffic from congested macrocells. In this paper, we perform analytical analysis and investigate how the radio channel propagation impairments such as multipath fading, shadowing, and small cell base station density affect MUs' offloading to small cells network (SCN). In particular, we exploit composite fading channels in our evaluation when an MU is offloaded to SCN with varying small cell base station density in the stochastic geometry HetNets framework. We derive the expressions for service outage probability (equivalently service coverage probability) of the MU in macro cell network and SCN under two different composite fading scenarios, viz., Nakagami-Lognormal channel fading and time-shared (combined) shadowed/unshadowed channel fading. We propose efficient approximations for the probability density functions of the channel fading (power) for the aforementioned composite fading distributions that do not have closed-form expressions employing Gauss-Hermite integration and finite exponential series, respectively. Finally, the service outage probability performance of MU with and without offloading services is analyzed under various system parameters and channel fading conditions.

In this paper, we conceive an advanced small cells wireless network deployment framework within a managed space under shared spectrum access paradigm. We also conceive a complementary business model, referred to as neutral host micro operator (NH-mu O), that leverages a single shared wireless infrastructure to mutually benefit mu O (a third party service provider), the owner of the space/facility, and mobile network operators (MNOs). The model is composed of a mu O slice, which delivers a venue with customized wireless services tailored to the its local service requirements, and an MNO slice, which facilitates improved wireless coverage to visitors/end-users with subscriptions to several different MNOs. The NH-mu O is not biased to favor any specific client, which can be enforced through a concrete commercial agreement. A radio access network slicing concept is exploited to support and optimize both the slice instances (SIs) efficiently in a shared manner on a single physical network infrastructure. In addition, we devise an efficient architecture for the NH-mu O small cell base station and dynamic spectrum assignment control unit, and their required functionalities supporting sustainable coexistence of different SIs in shared spectrum. We also devise both inter-SI and intra-SI dynamic spectrum allocation policies considering time-varying requirements of different SIs. These policies take care of application level priority by providing a proper mixture of users with guaranteed quality of service and best-effort users, while ensuring a healthy SI competition. The advantages of the proposed framework are twofold. It enables the venue owner to manage its wireless networks and consider its very specific requirements while capitalizing from the MNO slice. This, in turn, reduces the need for deployment of new infrastructure while providing improved wireless coverage and savings to MNOs. Finally, our proposed framework leverages efficient utilization of spectrum, physical infrastructure, and computational resources. The simulation results exhibit various important features of the proposed shared spectrum access policies.

The IEEE 802.11ad standard allows wireless devices to operate in the unlicensed spectrum band of 60 GHz. By utilizing the channel with 2.16 GHz width, the devices are able to transmit at multi-Gigabit data rates that potentially satisfy demanding requirements of quality of services. Additionally, the advent of off-the-shelf IEEE 802.11ad device motivates research efforts to exploit this 60 GHz opportunity for applications. Although much has been understood from the previous works, there is still a lack of insight into building IEEE 802.11ad networks, especially the ones with multi-Gigabit links. Address the issue, this work investigates the feasibility of multi-Gigabit IEEE 802.11ad networks, as well as, the factors that influence network performance in a typical office environment. By experimental study with off-the-shelf IEEE 802.11ad hardware, we can identify the conditions that the TCP and UDP throughput of IEEE 802.11ad link reach multi-Gigabit levels. Moreover, we show and discuss the negative effects of both co-channel and adjacent channel interference on the IEEE 802.11ad network's performance.

This paper presents a novel multipath communication-based OpenFlow channel for Software Defined Wireless Access Networks (SDWANs), namely mOpenFlow. The advantageous features of mOpenFlow include the following: (i) resilience and scalability in wireless environments, (ii) evolvability of the existing access networks and the OpenFlow standard, (iii) a novel network calculus-based model for performance analysis of mOpenFlow. By lever-aging the multipath communication for conveying OpenFlow traffic, mOpenFlow enhances both robustness (i.e., resilience) and throughput (i.e., scalability) of the control channel. To achieve the evolvability, mOpenFlow adopts the multipath transport control protocol, which conforms to SDWANs and the OpenFlow standard. We evaluate mOpenFlow in an emulated SDWAN in relation to the standard channel. The results show that mOpenFlow outperforms the standard channel, both in terms of robustness and scalability. Additionally, the numerical results indicate that the model provides a fast and reliable way for analyzing the end-to-end delay on mOpenFlow. (C) 2016 The Authors. Published by Elsevier Ltd.

We investigate an advanced two-phase shared spectrum access communication scheme as an efficient approach to enhance the spectral utilization of a network. In the first phase, we devise a spectrum-sharing policy based on demands, fairness, and so on, which utilizes a priority scheme in fulfilling operators' demands, and envision a secure operator-specific information sharing policy where no critical information is exchanged between the operators. In the second phase, a macro cell network (MCN) benefits through offloading services offered by small cell network (SCN). This allows the MCN to satisfy its users' capacity demands, improve its quality of services and coverage under Nakagami fading channel. As a repayment, the SCN is rewarded with licenses to share and operate on the spectrum originally owned by the MCN. We devise a density division-based shared spectrum access model, where the density of the licensee's SCN deployment is exploited as network resources. A fair division of the densities of the licensee operator's small cell base stations into fractions of licensed small cell base stations serving its own users and offloading small cells is presented. Unlike most of the previous research works that considered Poisson point process (PPP) to model the distribution of the network entities even when PPP modeling is not accurate for the networks, where the number of MCN/SCN base stations is definite and the number of MCN/SCN base stations in disjoint areas is not independent, we employ a more realistic network model known as binomial point process to perform an analytical analysis of the cumulative interference and performance of the system. Furthermore, we analyze the rate coverage and outage performances considering a wide range of values for path-loss exponent and fading severity parameter of Nakagami fading.

The Internet may get catastrophic impacts when unexpected disasters such as earthquakes, tsunami, etc. happen. Therefore, it is necessary to equip resilient technologies for the Internet backbones in order to face challenges (e.g., link, device failures, rerouting traffic, etc.) in the disasters. The emerging software-defined networking (SDN) technology, which logically centralizes network function on a controller and remotely manages distributed SDN devices, shows a lot of potential. This paper presents an experimental feasibility study on applying SDN to wide area backbones for the disaster-resilient purpose. To show the efficiency of SDN technology in responding fast to the network situation changes, we conduct three evaluations on real SDN devices and large-scale SDN-based wide area networks (WANs) assuming disaster scenarios. In the first evaluation, we explore the proactive recovery mechanism using the fast failover on SDN devices. In the second one, we investigate the communication latency between controllers and SDN devices, which is one of the most important factors in the reactive recovery in the software-defined backbone. In the last one, we experiment the fast end-to-end reactive recovery behavior of a TCP flow in a disaster scenario. The evaluation results clearly indicate that the SDN-based WAN is technically feasible and effective for fast recovery from disasters.

Multipath TCP (MPTCP) is an evolvable technology for bandwidth aggregation on a mobile device. MPTCP naturally and concurrently exploits wireless links via different interfaces (i.e., Wi-Fi and cellular) for data transferring. Theoretically, the MPTCP's aggregated throughput is better or at least equals to the TCP throughput over a link. However, our investigation of MPTCP performance in a lossy wireless environment shows that the theoretical statement does not always hold. Specifically, the aggregation benefit of MPTCP (i.e., in a comparison to TCP) becomes negative when the loss over a link surpasses specific levels. In this paper, we focus on finding the negative region of MPTCP's aggregation benefit by experimental study. Additionally, we propose a loss-aware disabling mechanism to bypass the negativity. The mechanism temporarily switches a wireless link to a backup mode when an observed loss value reaches a threshold. We integrate the mechanism with a state-of-the-art MPTCP implementation and compare the two MPTCPs in various lossy conditions. The evaluation results confirm the effectiveness of the newly proposed mechanism in terms of enhancing goodput and saving resources.

This paper introduces USD, a novel User-centric Software Defined platform for 5G mobile devices, which supports a wide range of users with the diversity of technical experience. Respecting user preferences, USD is able to exploit multiple wireless networks, as well as, to differentiate application traffic. The advantages of USD are realized by using a set of network virtualization (NW) and Software Defined Networking (SDN) technologies. Similar to the state-of-the-art works, USD leverages SDN in the exploitation of multiple networks. However, USD uniquely uses network namespace to isolate an application traffic at a granularity as fine as a process (i. e., each process's traffic belong to one networking stack). Moreover, USD relaxes the dependence on radio hardware by using wireless virtualization. The relaxation aims not only to efficiently utilize 5G networking resources but also to add an usercentric interface. As a proof of concept, we implement a prototype of USD using the Wi-Fi, Open vSwitch, and the network virtualization technologies. We evaluate the performance of USD in a comparison with a legacy platform in an assuming 5G scenario. The evaluation results show that the USD prototype achieves comparable performances to the legacy platform while it introduces the advanced user-centric features.

Small cell deployments are one of the most significant long-term strategic policies of the mobile network operators since small cell architecture delivers not only the required capacity boost but also the flexibility important for immensely-localized deployments in high-traffic environments. In HetNets, small cells serve as offloading spots in the radio access network to offload users and their associated traffic from congested macrocells. In this paper, we perform analytical analysis and investigate how the radio propagation effects such as multipath and shadowing, and small cell base station density affect macro users' offloading to small cell networks. In particular, we exploit composite fading channel in our evaluation when a macro user is offloaded to small cells networks within the stochastic heterogeneous networks framework. We derive the expressions for outage probability (equivalently success probability) of the macro user in macro network and small cells network for Nakagami-lognormal desired and interfering signals. We propose efficient approximation for the probability density functions of the channel fading power for shadowed Nakagami-m fading distribution that does not have closed-form expression employing Gauss-Hermite quadrature. Finally, the outage probability performance of macro user with and without offloading options/services is analyzed for various settings of fading channels.

Disconnection of Internet access in natural disasters may cause serious obstacles for relief works. Immediately providing Internet connection in disaster stricken regions is still a challenge because infrastructure-based networks may have been drastically destroyed. This paper proposes a Group-based Internet Connection Spreading (GICS) architecture for disaster recovery. This architecture supports groups of Internet-unconnected mobile devices to connect to the Internet through still alive infrastructure access points or groups of Internet-connected mobile devices in an effective way. By the support of the Internet-connected Device Discovery mechanism in the proposed GICS, mobile devices can discover nearby devices that have already reached the Internet connection and can share their Internet connectivity. GICS enables mobile devices within a group to collaborate together to bring reasonable Internet connection to all group members. Moreover, GICS can flexibly adapt with changes in the network condition since GICS groups can rearrange the roles of group members to maintain the suitable the Internet connection. In addition, the quality of connections between devices in GICS is reliable since they are based on the IEEE 802.11 (Wi-Fi) standard.

In recent years, there has been an increasing number of Software Defined Wireless Access Network (SDWAN) proposals aiming to cope with the proliferation of mobile devices, as well as, the novel Quality of Service (QoS) demands. One of the most important issues in the SDWANs is to maintain a scalable and robust OpenFlow channel through which the network control and update information (i.e., OpenFlow traffic) are exchanged. However, the standard channel does not well support those characteristics nor does it properly conform to the SDWAN environment. This paper seeks to remedy these problems by analyzing the requirements of SDWAN's OpenFlow channel. We then propose a novel OpenFlow channel named mOpenFlow, which is not only compatible with the SDWANs but also evolved with the OpenFlow standard. The advantage of mOpenFlow is using multipath communication for conveying OpenFlow traffic. Hence, both the robustness and the achievable throughput of the OpenFlow channel is significantly enhanced (i.e., scalable). Combining with the compatibility requirement, the multipath TCP is adopted in the mOpenFlow's design. We extensively evaluate the channel's performance in SDWANs including emulated SDN devices and a real controller. The results show that mOpenFlow outperforms the standard channel both in terms of robustness and scalability.

In the software defined networks (SDNs), the OpenFlow protocol is typically used as the southbound API in manipulating OpenFlow switches. However, the OpenFlow control messages are in a low abstraction level. Therefore, even a single application-level operation requires many OpenFlow messages, which consume the bandwidth of the control network and reduce the SDN's scalability. One potential solution is to use high level domain specific northbound APIs in the control network. In this paper, we explore the possibility of adopting this solution by implementing and evaluating a new SDN framework, Ryuo. In Ryuo, we introduce Local Service, which runs directly on each SDN switch (hardware/software). In operations, Local Service provides northbound APIs to the SDN applications while it can use different southbound APIs for different switches. Ryuo eliminates unnecessary control messages, hence it decreases the volume of control traffic. Our evaluation of Ryuo on Mininet with example applications shows that Ryuo reduces the volume of control traffic at least 50% compared to the standard OpenFlow, and up to 40% compared to the local controller approach. We also evaluate the performance of running Local Services directly on physical switches. The results show that we can achieve lower event handling latency in large networks, but with the trade-off of a lower event handling throughput due to the computing power limitation on physical switches. In summary, we have shown that using high level northbound API in the control network can make the control network more efficient, and leads to better scalability.

The Wi-Fi technology has been fast growing and available on a huge number of electronic devices. Moreover, due to the easiness in deployment a Wi-Fi user is normally in the coverage of several surrounding Wi-Fi access points (APs). The Wi-Fi virtualization, which abstracts a Wi-Fi interface to appear as several virtual ones to the user, is one of the most significant current approaches in improving the performance of Wi-Fi networking. The existence of multiple virtual interfaces enables many useful applications such as aggregating APs' backhaul bandwidth, sharing Internet connections, or increasing range of Wi-Fi networks, etc. In the previously mentioned applications, the authors generally show that a Wi-Fi client with several virtual interfaces has better performances than the one with a physical interface under the considered metrics (e.g., throughput, mobility, etc.). However, they have not shown the investigation on the performance bounds of the virtual Wi-Fi links. Therefore, it is worthy to investigate those performance parameters. This work extensively evaluates a real virtual Wi-Fi-based system to reveal the capacity of downlink, uplink of the virtual Wi-Fi interfaces.

This article proposes a novel approach to on-the-fly establishment of multihop wireless access networks (OEMAN) for disaster response. OEMAN extends Internet connectivity from surviving access points to disaster victims using their own mobile devices. OEMAN is set up on demand using wireless virtualization to create virtual access points on mobile devices. Virtual access points greedily form a tree-based topology, configured automatically for naming and addressing, which is then used to provide multihop wireless Internet access to users. Ordinary users can easily connect to the Internet through OEMAN as if they are connected through conventional access points. After connecting, users naturally contribute to the network extension, realizing the self-supporting capability of a disaster's local communities. The proposed scheme establishes a wireless access network quickly, which is essential in emergency relief situations. Furthermore, OEMAN is transparent to users and cost effective as it does not require additional hardware. Experimental evaluations on top of our preliminary prototype over Windows-based laptops confirm OEMAN's feasibility and its effectiveness for multihop paths of up to seven hops, and standard Internet services such as audio and video streaming.

This paper proposed a novel approach to resilient wireless multihop disaster recovery access networks (MDRAN). Both virtual access point (VAP) and wireless virtualization (WV) techniques have been combined in an appropriate way thereby the networks can be automatically setup on-demand using on-site commodity mobile devices (laptops, tablet PCs, smart phones). In the proposed approach, difficulties remained from conventional access network technologies such as the requirements of installing special hardware (e.g. multiple network interface cards - NICs, particular mesh routers, etc.,) and software (e.g. network auto-configuration software including routing protocols) on each mobile node (MN) in advance have been resolved. As a result, users can connect to the proposed MDRAN as easily as connecting to conventional APs. After connecting to the proposed network, users naturally and unconsciously contribute to the network extension. This feature improves the self-supporting capability at the disaster's local communities. Experimental evaluations reveal the feasibility, effectiveness as well as the scalability of the proposed approach. As a result, the proposed scheme is ready to be realized in the actual disaster recovery applications. © Rinton Press.

Wireless multihop access network is an appropriate approach to providing Internet access to applications such as last-mile and rural area communications, disaster recovery, etc. However, the realization of the existing wireless access networks is still limited. The main reasons are that they require particular hardware and software to be installed at pre-defined locations, or it is costly to deploy enough density nodes in a vast area for network formation. This paper proposes a novel approach to automatically set up multihop access networks, bringing Internet connectivity to users by leveraging their commodity mobile devices. In this work, a single Wifi interface equipped mobile device is transformed into a virtual access point (VAP) using wireless virtualization. As a result, each node works in both the station (STA) and the YAP modes to connect with each other forming tree-based networks which extend the Internet connectivity. Users can access Internet through the proposed network easily as if they are connected to the conventional access points (APs) and unconsciously contribute to the network extension. A prototype has been implemented and evaluated to confirm the feasibility as well as the effectiveness of the proposed approach.