Resumen de Contribution to the evolution of next generation wlans
Muhammad Shahwaiz Iqbal Afaqui
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.
