IEEE 802.11ax: challenges and requirements for future high efficiency wifi

The popularity of IEEE 802.11 based wireless local area networks (WLANs) has increased significantly in recent years because of their ability to provide increased mobility, flexibility, and ease of use, with reduced cost of installation and maintenance. This has resulted in massive WLAN deployment in geographically limited environments that encompass multiple overlapping basic service sets (OBSSs). In this article, we introduce IEEE 802.11ax, a new standard being developed by the IEEE 802.11 Working Group, which will enable efficient usage of spectrum along with an enhanced user experience. We expose advanced technological enhancements proposed to improve the efficiency within high density WLAN networks and explore the key challenges to the upcoming amendment.Peer ReviewedPostprint (author's final draft

A novel cheater and jammer detection scheme for IEEE 802.11-based wireless LANs

The proliferation of IEEE 802.11 networks has made them an easy and attractive target for malicious devices/adversaries which intend to misuse the available network. In this paper, we introduce a novel malicious entity detection method for IEEE 802.11 networks. We propose a new metric, the Beacon Access Time (BAT), which is employed in the detection process and inherits its characteristics from the fact that beacon frames are always given preference in IEEE 802.11 networks. An analytical model to define the aforementioned metric is presented and evaluated with experiments and simulations. Furthermore, we evaluate the adversary detection capabilities of our scheme by means of simulations and experiments over a real testbed. The simulation and experimental results indicate consistency and both are found to follow the trends indicated in the analytical model. Measurement results indicate that our scheme is able to correctly detect a malicious entity at a distance of, at least, 120 m. Analytical, simulation and experimental results signify the validity of our scheme and highlight the fact that our scheme is both efficient and successful in detecting an adversary (either a jammer or a cheating device). As a proof of concept, we developed an application that when deployed at the IEEE 802.11 Access Point, is able to effectively detect an adversary. (C) 2015 Elsevier B.V. All rights reserved.Postprint (author's final draft

Contributions to the evolution of next generation WLANs

The explosive growth in usage of IEEE 802.11 based WLAN networks has resulted in dense deployments in diverse environments and has made the concept of anytime - anywhere data connectivity a realm of commercial reality. The IEEE 802.11 standard has evolved as a key enabling technology to cover medium to large scale enterprises, public area hots spots, apartment complexes etc. Such environments are characterized to encompass multiple small cells with many access points and serve large numbers of client stations. Improved coverage and higher data rates are the primary achievements, where many cells coexist to create an environment containing multiple Overlapping Basic Service Sets. This small cell deployment is also considered as a key component of the next generation wireless communication to provide greater end user experience. Adjacent access points can choose different frequency bands (if available) for operations to avoid interference for the client stations placed at the cell edge. However, the interference created by overlapping cells using similar frequency can adversely result in reduced performance. Moreover, the overly protected contention-based medium access mechanism of IEEE 802.11 also limits the possibility of concurrent transmissions. The increased number of access points deployed in complex untrusted network environments can also induce network management challenges that incorporate inconsistent security. The work presented in this thesis originates from the need to understand some of the key challenges affecting legacy IEEE 802.11 protocols under high density scenarios and to design mechanisms that improve network performance within overlapping cells. Through our work, we have contributed to the evolution of IEEE 802.11 standard by demonstrating network enhancements in three important dimensions: availability, capacity and interference management. Throughout the thesis, methods are proposed that require minimum modifications to be made over the exiting IEEE 802.11 protocols. Yet, with the help of extensive evaluation, the proposed schemes have shown considerable performance improvements. The contributions made in this thesis significantly advance the state-of-the-art for IEEE 802.11 WLANs along the lines of the aforementioned three dimensions. To better understand the security threat that a jammer entails, first this thesis demonstrates the impact of a jammer on IEEE 802.11 and proposes a novel malicious entity detection scheme, called Beacon Access Time, that is required before taking appropriate countermeasures to improve the availability of IEEE 802.11. Next, a new IEEE 802.11 standard called IEEE 802.11ah, is evaluated as an alternative to densely deployed overlapping Wi-Fi cells. This amendment aims to improve on legacy IEEE 802.11 by enhancing the coverage as well as supporting increased number of associated stations. Also, recent technological additions to IEEE 802.11 standard with the intent to improve operations within high density environments, in the form of future IEEE 802.11ax amendment, are also explored. To enhance network capacity, a technique named Dynamic Sensitivity Control, is introduced which dynamically adapts carrier sensing and improves the area throughput (spatial reuse) within dense WLAN deployments by limiting the impact of increased interference. Detailed simulation results indicate that this scheme allowed multiple concurrent transmissions to coexist and, thus, increases the overall network throughput and fairness over the cost of increased frame error. Finally, an access point controlled four-way handshake mechanism is proposed that can improve the performance of dense deployments by reducing interference and frame error rate. Different contributions proposed throughout this thesis provide solutions for amicable operations of densely deployed Wi-Fi cells. The importance of the prsented work is also validated through our contributions to the IEEE 802.11ax task group.El creixement en l'ús de xarxes basades en IEEE 802.11 ha donat lloc a desplegaments densos en entorns molt diversos i ha fet que el concepte de connectivitat en qualsevol moment i lloc sigui una realitat. L'estàndard IEEE 802.11 ha evolucionat com una tecnologia clau per oferir connectivitat sense fils en oficines, zones d'interès públic, complexos d'apartaments, etc. Aquests entorns es caracteritzen per abastar múltiples cel·les parcialment solapades i servir a un gran nombre dispositius. Aquest desplegament de "small cells" també es considera un component clau de la comunicació sense fil de propera generació per proporcionar una millor experiència d'usuari. Punts d'accés propers poden triar diferents bandes de freqüències per evitar interferències en les estacions client situades als extrems de la cel·la. No obstant això, la interferència creada pel solapament de múltiples cel·les amb freqüència similar pot resultar en un pobre rendiment de la xarxa. A més, el mecanisme d'accés al medi utilitzat a l'estàndard IEEE 802.11 també limita la possibilitat de transmissions simultànies. El gran nombre de punts d'accés desplegats en entorns de xarxa complexos i poc fiables també implica desafiaments de seguretat. El treball presentat en aquesta tesi s'origina a partir de la necessitat de comprendre alguns dels desafiaments clau que afecten els protocols IEEE 802.11 sota escenaris d'alta densitat i amb l'objectiu de dissenyar mecanismes que millorin el rendiment de la xarxa en entorns amb múltiples cel·les solapades. A través del nostre treball, hem contribuït a l'evolució de l'estàndard IEEE 802.11 demostrant millores a la xarxa en tres aspectes importants: disponibilitat, capacitat i gestió d'interferències. Al llarg de la tesi es proposen mètodes que requereixen modificacions mínimes sobre els protocols d'accés IEEE 802.11, les quals, com s'ha demostrat, són beneficioses. Les contribucions resultants d'aquesta tesi fan avançar significativament l'estat de l'art de les xarxes sense fils IEEE 802.11 al llarg de les tres línies esmentades. En primer lloc, per comprendre millor l'amenaça de seguretat que comporta un dispositiu jammer, aquesta tesi demostra l'impacte d'aquests dispositius sobre un enllaç IEEE 802.11 i proposa un nou esquema de detecció anomenat temps d'accés de Beacon. La detecció és la condició necessària prèvia a la presa de contramesures apropiades per millorar la disponibilitat de IEEE 802.11 i minimitzar l'impacte del jammer. A continuació, s'avalua un nou estàndard, l'IEEE 802.11ah, una alternativa als entorns WLAN densos i amb presència massiva de dispositius de baix consum. Aquesta esmena té com a objectiu millorar IEEE 802.11 mitjançant l'augment de la cobertura, així com el suport a un major nombre d'estacions. També s'exploren les recents incorporacions tecnològiques al futur estàndard IEEE 802.11ax amb la intenció de millorar les operacions dins d'entorns d'alta densitat. Per millorar la capacitat de la xarxa, s'introdueix una tècnica denominada DSC (control dinàmic de sensibilitat), que adapta dinàmicament la detecció del canal i millora el rendiment en desplegaments densos en reduir l'impacte de les interferències (augmenta la reutilització espacial). Els detallats resultats de simulació presentats avalen que aquest esquema permet major nombre de transmissions simultànies i, per tant, augmenta el rendiment i la justícia de la xarxa encara que pagant amb un augment en la taxa d'error de transmissió. Reduir aquests errors, però, és l'objectiu de la darrera contribució, un mecanisme de transmissió de quatre fases controlat centralitzadament pel punt d'accés que millora el rendiment reduint la interferència i la taxa d'error. Les diferents contribucions proposades en aquesta tesi proporcionen solucions per a operacions més eficients en cel·les Wi-Fi en entorns densos. La importància del treball presentat en aquesta tesi també es valida a través de contribucions al grup de treball IEEE 802.11ax.Postprint (published version