Contributions to the routing of traffic flows in multi-hop IEEE 802.11 wireless networks

Resumen

The IEEE 802.11 standard was not initially designed to provide multi-hop capabilities. Therefore, providing a proper traffic performance in Multi-Hop IEEE 802.11 Wireless Networks (MIWNs) becomes a significant challenge. The approach followed in this thesis has been focused on the routing layer in order to obtain applicable solutions not dependent on a specific hardware or driver. Nevertheless, as is the case of most of the research on this field, a cross-layer design has been adopted. Therefore, one of the first tasks of this work was devoted to the study of the phenomena which affect the performance of the flows in MIWNs. Different estimation methodologies and models are presented and analyzed. The first main contribution of this thesis is related to route creation procedures. First, FB-AODV is introduced, which creates routes and forwards packets according to the flows on the contrary to basic AODV which is destination-based. This enhancement permits to balance the load through the network and gives a finer granularity in the control and monitoring of the flows. Results showed that it clearly benefits the performance of the flows. Secondly, a novel routing metric called Weighted Contention and Interference routing Metric (WCIM) is presented. In all analyzed scenarios, WCIM outperformed the other analyzed state-of-the-art routing metrics due to a proper leveraging of the number of hops, the link quality and the suffered contention and interference. The second main contribution of this thesis is focused on route maintenance. Generally, route recovery procedures are devoted to the detection of link breaks due to mobility or fading. However, other phenomena like the arrival of new flows can degrade the performance of active flows. DEMON, which is designed as an enhancement of FB-AODV, allows the preemptive recovery of degraded routes by passively monitoring the performance of active flows. Results showed that DEMON obtains similar or better results than other published solutions in mobile scenarios, while it clearly outperforms the performance of default AODV under congestion Finally, the last chapter of this thesis deals with channel assignment in multi-radio solutions. The main challenge of this research area relies on the circular relationship between channel assignment and routing; channel assignment determines the routes that can be created, while the created routes decide the real channel diversity of the network and the level of interference between the links. Therefore, proposals which join routing and channel assignment are generally complex, centralized and based on traffic patterns, limiting their practical implementation. On the contrary, the mechanisms presented in this thesis are distributed and readily applicable. First, the Interference-based Dynamic Channel Assignment (IDCA) algorithm is introduced. IDCA is a distributed and dynamic channel assignment based on the interference caused by active flows which uses a common channel in order to assure connectivity. In general, IDCA leads to an interesting trade-off between connectivity preservation and channel diversity. Secondly, MR-DEMON is introduced as way of joining channel assignment and route maintenance. As DEMON, MR-DEMON monitors the performance of the active flows traversing the links, but, instead of alerting the source when noticing degradation, it permits reallocating the flows to less interfered channels. Joining route recovery instead of route creation simplifies its application, since traffic patterns are not needed and channel reassignments can be locally decided. The evaluation of MR-DEMON proved that it clearly benefits the performance of IDCA. Also, it improves DEMON functionality by decreasing the number of route recoveries from the source, leading to a lower overhead.