Perfect link routing for energy efficient forwarding in geographic routing

Geographic routing has been widely advocated for use with multihop ad hoc and sensor networks because of its scalability and use of only local information. These types of networks typically have lossy links where the instantaneous quality of a wireless link can vary significantly presenting a trade-off between hop length and link quality. In this paper we revisit the question of energy efficient geographic routing for such networks and argue in favour of Perfect Link Routing, an extreme form of blacklisting with a fall-back option. Existing research has favoured cost-based methods where all links are considered for routing. We argue, however, that a discontinuity exists between the cost of perfect links (those with virtually guaranteed delivery) and other links. This is based on a more careful use of acknowledgements which we suggest ought to be considered a function of individual links. Revisiting the original analysis we find that for energy efficiency, perfect links should be favoured except in low-density networks where such a scheme leads to very poor delivery rates. A hybrid approach is proposed which we call Perfect Link Routing and this method is shown to outperform alternatives for a number of ARQ schemes

Distributed Load Balancing in Many-To-One Wireless Sensor Networks

A typical sensor network is conceived as being a very large collection of lowpowered, homogeneous nodes that remain static post-deployment and forward sensed data to a single sink via multi-hop communication. For these types of networks there is an inherent funnelling effect whereby the nodes that can communicate directly with the sink must collectively forward the traffic of the entire network and therefore these nodes use more energy than the other nodes. This is known as the energy hole problem because after some time, these nodes deplete their batteries and leave an energy hole cutting the sink off from the network. In this thesis two new routing protocols are proposed that aim to maximise load balancing among these most critical nodes in order to maximise lifetime. They are the first fully distributed routing protocols that are designed to generate a load balanced routing tree to mitigate the energy hole problem. The results show that the better performing of the two is capable of creating a highly balanced tree at the cost of a small increase in latency. Although there have been other fully distributed protocols that aim at a similar form of load balancing, it is proven that the approach they take cannot guarantee perfect balance among the most critical nodes even in unrealistically generous scenarios. This suggests that they are not well suited to that task and the simulation results show that the novel protocols proposed in this thesis outperform the best of the alternatives. Before these protocols are proposed, the absolute reception-based blacklisting routing strategy is shown to be more energy efficient than previously thought and indeed more efficient than the strategy that has previously been considered optimal. This result is used to strongly justify the use of the unit disk graph model in simulations of sensor networks. Additionally, the relay hole problem in sensor networks is analysed for the first time

DECOR: Distributed construction of load balanced routing trees for many to one sensor networks

Many sensor networks suffer from the energy hole problem which is a special case of load imbalance caused by the funnelling effect of many sensor nodes transmitting their data to a single, central sink. In order to mitigate the problem, a balanced routing tree is often required and this can be constructed with either a centralised or distributed algorithm. Distributed solutions are typically less effective but are significantly cheaper than centralised solutions in terms of communication overhead and they scale better for the same reason. In this paper we propose a novel distributed algorithm for the construction of a load balanced routing tree. Our proposed solution, Degree Constrained Routing, is unique in that it aims to maximise global balance during construction rather that relying on rebalancing an arbitrary tree or only maximising local balance. The underlying principle is that if all nodes adopt the same number of children as each other while the routing tree grows, then the final tree will be globally balanced. Simulation results show that our algorithm can produce trees with improved balance which results in lifetimes increased by up to 80% compared to the next best distributed algorithm