A unified framework for performance analysis of contention-based wireless MAC: Case studies on QoS, heterogeneity and rate-adaptation in 802.11.

摘要

Performance analysis for IEEE 802.11 based protocols is essential to not only better understand the protocol, but also provide insight in developing protocol improvement schemes. In this dissertation, we propose a unified IEEE 802.11 MAC performance evaluation framework to systematically explore different facets of protocol behavior and the corresponding inherent interactions between different factors of various scenarios and system performance. Our proposed framework differs from the existing performance analysis approaches in that it categorizes the protocol operation parameters that exhibit similar behavior into the same group and uses the categorizations to interconnect the target scenarios with relevant performance affecting parameters. As a result, such weaving interconnections enable us to formulate the unified performance evaluation framework in explaining the similarity or dissimilarity of the performance impacts on different target scenarios, which can not be achieved by any existing performance evaluation models. Additionally, we aim to provide guidelines for various protocol enhancement designs by applying the insight gained from studying the protocol dynamics with the proposed performance evaluation framework.;Using the proposed framework, we are able to conduct a series of systematic evaluations on the performance of various scenarios in which the performance is affected by a mixture of protocol operation parameters and environment factors such as wireless losses, collisions, and different background traffic load levels. In the first case study, we examine the mixed throughput anomaly effects in hybrid IEEE 802.11b and IEEE 802.11g networks, where various settings that are necessary to accommodate the heterogeneous environment all jointly affect the system performance. We demonstrate that our performance framework not only helps predict the aggregate system performance in hybrid 802.11b/g networks, but also clarifies and isolates the mixed effects among different contention window, different backoff stages, and different data rates and frame formats on these two versions of standard. In the second case study, we evaluate the effectiveness of various performance improvement schemes at the physical layer and MAC layer in understanding the performance limitations on throughput and total system delay of IEEE 802.11 MAC with arbitrary competing traffic. By using the proposed framework, we are able to decompose the effects of various performance improvement schemes and the corresponding interactions with the variable amount of network delay incurred by collisions, and the backoff and re-transmission procedures. We further identify a performance bottleneck beyond which the packet delay becomes infinitely high and we pinpoint the exact turning point depends on the packet arrival pattern in consideration.;Furthermore, in the third case study, we first use the framework to analyze the performance rate adaptation algorithms and discover that a good rate adaptation algorithm needs to dynamically adjusting the rate selection decisions with respect to different background traffic levels, in addition to the wireless channel fluctuations that was believed to be the sole key of rate adaptation. We then apply the insight observed from the proposed framework to design a rate adaptation algorithm that accommodate the mixed effects from different background traffic levels and fluctuating wireless channel conditions. While simulation results show promising improvements over the existing rate adaptation schemes, our real-world test-bed implementations also demonstrate that our framework is suitable for being practically incorporated into real hardware to provide superb performance in real-world scenarios. We expect that the proposed framework can be further generalized to evaluate the cross-layer effects such as TCP and routing in wireless mesh networks.