Quality of service in ad-hoc networks

• Authors: Rajarshi Gupta;Jean Walrand
• Venue: Quality of service in ad-hoc networks
• Year: 2005

The broad problem we address is to support multi-hop flows in a wireless ad-hoc network. In such networks, achieving predictable quality of service is difficult due to interference between links. This thesis approaches this complicated problem by addressing the following three sub-areas. 1. Fairness in distributed MAC. The backoff mechanism used by most distributed ad-hoc MAC protocols (like 802.11) is unfair towards nodes in the middle of the network. We propose the novel Impatient Backoff Algorithm (IBA) that achieves a fairer allocation of the available bandwidth by decreasing the backoff delay upon collision, or a failure to transmit. That is, a node becomes more aggressive after each failure. Nodes maintain stability by resetting, in a distributed way, the average backoff delays when they become too small. We perform a Markov analysis of the system to prove stability and fairness in simple topologies. We also simulate the performance of IBA in random ad-hoc networks and compare with exponential backoff scheme. Results show that IBA achieves comparable mean throughput, while delivering significantly better fairness. 2. Service limits. We address the feasibility of a given set of flows on an arbitrary ad-hoc network, by modeling the interference between links as a conflict graph. We consider cliques in the conflict graph, and propose a distributed polynomial-time approximation algorithm to generate all maximal cliques. We then use these cliques to write constraints that provide sufficient conditions for feasibility, yet are guaranteed to be within a constant bound of the optimal. 3. QoS routing. We propose a distributed Ad-hoc Shortest Widest Path (ASWP) routing algorithm, which transforms the well-known SWP paradigm to the ad-hoc domain by taking interference into account, and addresses its limitations. We further propose IQRouting - a source-based heuristic mechanism that is able to select QoS routed paths in a dynamic manner, using only localized state information. Results show that the admission ratio of IQRouting achieves significant gains over comparable ad-hoc QoS routing algorithms. We also present prior work on algorithms for protection and restoration in networks that require quality guarantees. We propose a novel scheme that shares the protection bandwidth, and even the reserved normal bandwidth during a failure. This allows enhanced accounting of the available resources in the network, thereby supporting more flows.