Cooperative Energy-efficient Management of Federated WiFi Networks

The proliferation of overlapping, always-on IEEE 802.11 access points (APs) in urban areas, can cause inefficient bandwidth usage and energy waste. Cooperation among APs could address these problems by allowing underused devices to hand over their wireless stations to nearby APs and temporarily switch off, while avoiding to overload a BSS and thus offloading congested APs. The federated house model provides an appealing backdrop to implement cooperation among APs. In this paper, we outline a distributed framework that assumes the presence of a multipurpose gateway with AP capabilities in every household. Our framework allows cooperation through the monitoring of local wireless resources and the triggering of offloading requests toward other federated gateways. Our simulation results show that, in realistic residential settings, the proposed framework yields an energy saving between 45 and 86 percent under typical usage patterns, while avoiding congestion and meeting user expectations in terms of throughput. Furthermore, we show the feasibility and the benefits of our framework with a real test-bed deployed on commodity hardware

Future Trends and Challenges for Mobile and Convergent Networks

Some traffic characteristics like real-time, location-based, and community-inspired, as well as the exponential increase on the data traffic in mobile networks, are challenging the academia and standardization communities to manage these networks in completely novel and intelligent ways, otherwise, current network infrastructures can not offer a connection service with an acceptable quality for both emergent traffic demand and application requisites. In this way, a very relevant research problem that needs to be addressed is how a heterogeneous wireless access infrastructure should be controlled to offer a network access with a proper level of quality for diverse flows ending at multi-mode devices in mobile scenarios. The current chapter reviews recent research and standardization work developed under the most used wireless access technologies and mobile access proposals. It comprehensively outlines the impact on the deployment of those technologies in future networking environments, not only on the network performance but also in how the most important requirements of several relevant players, such as, content providers, network operators, and users/terminals can be addressed. Finally, the chapter concludes referring the most notable aspects in how the environment of future networks are expected to evolve like technology convergence, service convergence, terminal convergence, market convergence, environmental awareness, energy-efficiency, self-organized and intelligent infrastructure, as well as the most important functional requisites to be addressed through that infrastructure such as flow mobility, data offloading, load balancing and vertical multihoming.Comment: In book 4G & Beyond: The Convergence of Networks, Devices and Services, Nova Science Publishers, 201

Heterogeneous integration of optical wireless communications within next generation networks

Unprecedented traffic growth is expected in future wireless networks and new technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing the RF cell for highly mobile devices and devices that lack a reliable OW connection. Visible light communication (VLC) is considered as a potential OW technology due to the increasing adoption of solid state lighting for indoor illumination. Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF small cell implementations is evaluated. A media independent model is developed and results are presented that provide motivation for the adoption of hyper dense small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are evaluated in order to define methods for fair comparison when user-centric channel selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated to show errors in excess of 100x when dominant interferers are present. Finally, dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model is presented to predict device motion for improved channel selection and a novel OW range expansion technique is presented that dynamically alters coverage regions of OW cells by 50%. In addition to analytical results, the dissertation describes two tools that have been created for evaluation of RF/OW HetNets. A communication and lighting simulation toolkit has been developed for modeling and evaluation of environments with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse response simulator model to utilize GPU acceleration and achieves 10x speedup over the previous model. A software defined testbed for OW has also been proposed and applied. The testbed implements a VLC link and a heterogeneous RF/VLC connection that demonstrates the RF/OW HetNet concept as proof of concept

A comparative investigation on the application and performance of Femtocell against Wi-Fi networks in an indoor environment

Due to the strenuous demands on the available spectrum and bandwidth, alongside the ever increasing rate at which data traffic is growing and the poor quality of experience QoE) faced with indoor communications, in order for cellular networks to remain dominant in areas pertaining to voice and data services, cellular service providers have to reform their marketing and service delivery strategies together with their overall network rchitecture. To accomplish this leap forward in performance, cellular service operators need to employ a network topology, which makes use of a mix of macrocells and small cells, effectively evolving the network, bringing it closer to the end-­‐user. This investigation explores the use of small cell technology, specifically Femtocell technology in comparison to the already employed Wi-­‐Fi technology as a viable solution to poor indoor communications.The performance evolution is done by comparing key areas in the every day use of Internet communications. These include HTTP testing, RTP testing and VoIP testing. Results are explained and the modes of operation of both technologies are compared

Exploiting user contention to optimize proactive resource allocation in future networks

In order to provide ubiquitous communication, seamless connectivity is now required in all environments including highly mobile networks. By using vertical handover techniques it is possible to provide uninterrupted communication as connections are dynamically switched between wireless networks as users move around. However, in a highly mobile environment, traditional reactive approaches to handover are inadequate. Therefore, proactive handover techniques, in which mobile nodes attempt to determine the best time and place to handover to local networks, are actively being investigated in the context of next generation mobile networks. The Y-Comm Framework which looks at proactive handover techniques has de�fined two key parameters: Time Before Handover and the Network Dwell Time, for any given network topology. Using this approach, it is possible to enhance resource management in common networks using probabilistic mechanisms because it is now possible to express contention for resources in terms of: No Contention, Partial Contention and Full Contention. As network resources are shared between many users, resource management must be a key part of any communication system as it is needed to provide seamless communication and to ensure that applications and servers receive their required Quality-of-Service. In this thesis, the contention for channel resources being allocated to mobile nodes is analysed. The work presents a new methodology to support proactive resource allocation for emerging future networks such as Vehicular Ad-Hoc Networks (VANETs) by allowing us to calculate the probability of contention based on user demand of network resources. These results are veri�ed using simulation. In addition, this proactive approach is further enhanced by the use of a contention queue to detect contention between incoming requests and those waiting for service. This thesis also presents a new methodology to support proactive resource allocation for future networks such as Vehicular Ad-Hoc Networks. The proposed approach has been applied to a vehicular testbed and results are presented that show that this approach can improve overall network performance in mobile heterogeneous environments. The results show that the analysis of user contention does provide a proactive mechanism to improve the performance of resource allocation in mobile networks

Support of resource-aware vertical handovers in WLAN hotspots

Endgeräte wie Smartphones oder Tablets bieten häufig eine Vielfalt drahtloser Zugänge zum Internet an. Üblicherweise schließt dies die 802.11 WLANs und auch Technologien drahtloser Weitverkehrsnetze (WWANs) aus dem Bereich LTE oder WiMAX ein. Aufgrund dieser Optionen haben sich die Endanwender daran gewöhnt, überall und zu jeder Zeit auf ihre Internetdienste zuzugreifen. Damit hat auch der Datenverkehr pro Anwender zugenommen, was eine Herausforderung insbesondere für die Betreiber von WWANs ist. Soweit verfügbar, favorisieren Endanwender heutzutage eher einen drahtlosen Zugang zum Internet über WLANs als über WWANs. Des Weiteren haben die 3GPP-Standardisierungsgremien Ansätze erarbeitet, die zusätzlich Verkehr aus WWANs in Netze mit geringerer Abdeckung wie WLAN- oder Femto-Zellen abgeben. Solche Ansätze werden auch als "Traffic Offloading" bezeichnet und haben das Ziel, die WWANs zu entlasten. Dabei werden jedoch eher einfache Strategien verfolgt, die auf der Nutzung zusätzlicher Kapazitäten heterogener Netze beruhen und dann angewendet werden, wenn ein alternatives Zugangsnetz für ein Endgerät verfügbar ist. Im Rahmen dieser Arbeit zeigen wir Gewinne auf, die entstehen, wenn man die Auswahl der Endgeräte für ein WLAN-Netz stattdessen auf Basis der von ihnen belegten Ressourcen durchführt. In diesem Kontext schlagen wir vor, Geräte mit stark negativem Einfluss auf die WLAN-Kapazität wieder zurück in das WWAN zu reichen, was wir als "Onloading" bezeichnen. Ein solches "Onloading" zieht Herausforderungen in unterschiedlichen Richtungen mit sich. Die fortschreitende Miniaturisierung hat in den letzten Jahren zu dem Trend geführt, die Anzahl der Netzwerkkarten (NICs) in Endgeräten zu reduzieren. Wir bezeichnen eine NIC als multimodal, wenn sie mehrere Funktechnologien unterstützt, aber zu einem bestimmten Zeitpunkt immer nur eine davon genutzt werden kann. Deswegen stellt für eine multimodale NIC das "Onloading" während einer laufenden Verbindung eine Herausforderung dar. Wir schlagen einen Ansatz vor, der vorbereitende Mechanismen für ein "Onloading" als auch eine laufende Verbindung im WLAN über eine solche NIC ermöglicht. Des Weiteren ist es wichtig, in einem WLAN Hotspot zu entscheiden, welche Geräte einen negativen Einfluss auf die Kapazität des Netzes haben. Dafür haben wir eine Metrik entwickelt, die eine Entscheidungsgrundlage für das Onloading bildet. Diese Metrik basiert rein auf einer Beobachtung des Netzes und seiner Geräte, ermöglicht jedoch keine Entscheidung für sich neu assoziierende Geräte im WLAN. Erschwerend kommt hinzu, dass viele Eigenschaften der NICs durch herstellerabhängige Implementierungen geprägt werden. Solche Algorithmen bieten eine zusätzliche Herausforderung, da ihre internen Abläufe üblicherweise unbekannt sind. Ein bekanntes Beispiel für solche Algorithmen stellt die Anpassung der WLAN-Link-Datenraten dar. Diese Algorithmen wählen die jeweiligen Modulations- und Kodierungsschemata (MCSs) für die drahtlosen Übertragungen aus. Robuste MCSs resultieren dabei in geringere Link-Datenraten und haben somit einen starken Einfluss auf die Kapazität einer WLAN-Zelle. Aus diesem Grund fokussieren wir uns auf eine Abschätzung der Datenratenwahl eines Endgerätes. Damit lassen sich im Vorfeld Aussagen treffen, ob ein Gerät starken Einfluss auf die WLAN-Kapazität haben wird, so dass es für ein "Onloading" in Frage kommt.End-user devices such as smart phones and tablets have become very popular as they offer a variety of wireless Internet accesses ranging from the WLAN standards to WWAN technologies such as LTE or even WiMAX. Due to these different wireless access options and new emerging applications—e.g., from the areas of video streaming, social networks, as well as Internet clouds—people are increasingly connecting to the Internet with their de- vices while being on the move. In line with this, the number of devices as well as the traffic demand of end users have been reported to increase rapidly over the last years which imposes a strong challenge especially for the operators of WWANs. Thereby, end users frequently tend to use settings that favor a connectivity to the Internet whenever possible rather over WLAN than over WWAN access. Further, the cellular standardization bodies of the 3GPP envision solutions to hand over on-going wireless sessions from cellular to other small cell accesses such as WLANs or femto cells. This is also known as traffic offloading essentially freeing capacity in terms of users with a certain service in the cellular accesses. Nevertheless this offloading follows a rather simple strategy to utilize additional capacity of heterogeneous accesses such as WLANs whenever being available for a given device. This thesis shows that stronger gains can be expected if the selection of devices to be served in WLANs is conducted in a resource-aware fashion including an evaluation of the WLAN traffic in terms of the channel occupation time and MAC overhead as result of contention, interference, and fluctuating channels. In this context, this thesis envisions to onload unfavorable devices negatively affecting the WLAN capacity back to WWAN accesses. A support of such an onloading imposes challenges in different dimensions. From the hardware design of devices, there is a strong trend to limit the number of separate network interface cards (NICs) due to space and cost issues. We refer to a multi-mode NIC if it covers multiple technologies, while at a given time only access to one technology is possible. Thus, smoothly onloading a device with such a NIC is by far not trivial. We present an approach that conducts handover preparation mechanisms, while also allowing a continuous WLAN communication over a multi-mode NIC. Further, it is by far not trivial to judge which subset of associated devices is negatively affecting the capacity of a WLAN hotspot. Thus, a careful evaluation of devices regarding a selection for an onloading back to WWAN accesses imposes a challenge yet. In this direction, we present a performance metric that identifies devices degrading the WLAN capacity. While our performance metric tackles a reactive selection, it falls short to support a predictive evaluation, e.g., of devices which just joined the WLAN cell. Even worse, proprietary algorithms inside a WLAN stack impose a severe challenge as their internal routines are usually not conveyed via typical management interfaces. A well-known example for this category of algorithms are the link data rate adaptation schemes, with which WLAN devices adjust the modulation and coding scheme (MCS) for their transmissions. As MCSs resulting in low link data rates may specifically degrade the capacity of a WLAN cell, we focus on an estimation regarding the data rate selection of a device as a third contribution of this thesis. This estimation enables to select devices that will likely degrade the capacity of the WLAN hotspot for an onloading in advance

Experimenting with commodity 802.11 hardware: overview and future directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.This work has been partly supported by the European Community through the CROWD project (FP7-ICT-318115) and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919).Publicad