Thesis defence: Dr. Luis Sanabria
Thesis defence: Dr. Luis Sanabria
21.10.2016
"Collision-free WLANs: from concepts to working protocols"
-Dr. Luis Sanabria
Thesis supervisors: Dr. Boris Bellalta, Dr. Jaume Barceló and Dr. Miquel Oliver
21/10/2016
Brief Description of the Thesis:
Collisions are a main cause of throughput degradation in wireless local area networks. The current contention mechanism used in the IEEE 802.11 networks is called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). It uses a binary exponential backoff technique to randomize each contender attempt of transmitting, effectively reducing the collision probability. Nevertheless, CSMA/CA relies on a random backoff that while effective and fully decentralized, in principle is unable to completely eliminate collisions, therefore degrading the network throughput as more contenders attempt to share the channel. To overcome these situations and face the challenges of today's scenarios (very crowded WiFi environments), Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is able to create a collision-free schedule in a fully decentralized manner using a deterministic backoff after successful transmissions. Hysteresis and Fair Share, introduced in this work, are two extensions of CSMA/ECA that allows it to support a large number of contenders in a collision-free schedule. As a result, CSMA/ECA offers better throughput than CSMA/CA and short-term throughput fairness. This work also describes CSMA/ECA and its extensions. Additionally, it provides the first evaluation results of CSMA/ECA with non-saturated traffic, as well as realistic traffic sources, backwards-compatible collision-free traffic differentiation for many contenders, and evaluates its performance when coexisting with CSMA/CA nodes. Furthermore, it presents a mechanism to leverage the impact of channel errors and the addition/withdrawal of nodes over collision-free schedules. Finally, it provides the first experimental results on throughput and lost frames from a CSMA/ECA implementation using commercial hardware and open-source firmware.
Experience as a PhD student:
Beyond fulfilling. My supervisors's insight into research made me grow as a professional as well as a person. The whole experience of identifying a problem and come up with a competitive solution demands all of your abilities. Not only technical, but also tests your responsibility and work ethics. UPF provided me with all the tools and aid required to achieve my goal. I feel proud to have the opportunity to represent such a professional and high-level institution everywhere I go. I am forever grateful.