During and immediately after their deployment, ad hoc and sensor networks lack an efficient communication scheme rendering even the most basic network coordination problems difficult. Before any reasonable communication can take place, nodes must come up with an initial structure that can serve as a foundation for more sophisticated algorithms. In this paper, we consider the problem of obtaining a vertex coloring as such an initial structure. We propose an algorithm that works in the unstructured radio network model. This model captures the characteristics of newly deployed ad hoc and sensor networks, i.e. asynchronous wake-up, no collision-detection, and scarce knowledge about the network topology. When modeling the network as a graph with bounded independence, our algorithm produces a correct coloring with O(∆) colors in time O( ∆ log n) with high probability, where n and ∆ are the number of nodes in the network and the maximum degree, respectively. Also, the number of locally used colors depends only on the local node density. Graphs with bounded independence generalize unit disk graphs as well as many other well-known models for

An algorithm for time division multiple access (TDMA) is found to be applicable in converting existing distributed algorithms into a model that is consistent with sensor networks. Such a TDMA service needs to be self-stabilizing so that in the event of corruption of assigned slots and clock drift, it recovers to states from where TDMA slots are consistent. Previous self-stabilizing solutions for TDMA are either randomized or assume that the topology is known upfront and cannot change. Thus, the question of feasibility of self-stabilizing deterministic TDMA algorithm where topology is unknown remains open. In this paper, we present a self-stabilizing, deterministic algorithm for TDMA in networks where a sensor is aware of only its neighbors. This is the first such algorithm that achieves these properties. Moreover, this is the first algorithm that demonstrates the feasibility of stabilization-preserving, deterministic transformation of a shared memory distributed program on an arbitrary topology into a program that is consistent with the sensor network model.

Abstract. We propose a new data dissemination protocol for wireless sensor networks, that basically pulls some additional knowledge about the network in order to subsequently improve data forwarding towards the sink. This extra information is still local, limited and obtained in a distributed manner. This extra knowledge is acquired by only a small fraction of sensors thus the extra energy cost only marginally affects the overall protocol efficiency. The new protocol has low latency and manages to propagate data successfully even in the case of low densities. Furthermore, we study in detail the effect of failures and show that our protocol is very robust. In particular, we implement and evaluate the protocol using large scale simulation, showing that it significantly outperforms well known relevant solutions in the state of the art. 1

Abstract This paper shows that TDMA slot assignment for unicast com-munication in a wireless network can be distributively computed for an n-node acyclic network in O(polylog(n)) time, with highprobability. The best previous distributed algorithm for this problem requires O(n) time and obtains a TDMA schedule using 2\Delta time slots. The new algorithm uses (1 + e) * 2\Delta time slots where e is a tunable fraction.

Event-driven programming platforms for sensor networks require the programmers to deal with several challenges including buffer management, stack management, and flow control. To simplify the design of sensor network protocols, several high-level primitives are proposed. However, these primitives have to be implemented in an existing event-driven programming platform and most of them still require the pro-grammers to use the same platform (though some intricate details of the platform are hidden). In this dissertation, we develop tools and protocols that enable the programmers to rapidly prototype and quickly deploy sensor network protocols. We propose to reuse existing abstract models from distributed computing literature (e.g., read/write model, shared-memory model). Since these models hide several low-level challenges of the target system, programs written in these models are simple, easy to under-stand, and concise. These abstract programs must then be transformed into a model consistent with sensor networks. The main contributions of this dissertation are as follows.

Abstract—STDMA emerges as a promising channel access technique for providing QoS guarantees in multi-hop ad hoc networks such as community mesh and sensor networks. The contention-free channel access combined with spatial reuse of the channel provide signi cant bene ts in the energy/throughput trade-off. On the other hand, the time-multiplexed communication introduces extra delay on the packets when relayed by intermediate nodes. Hence in large wireless sensor networks or mesh networks, where data is routed over several hops before reaching the data sink, STDMA protocols may introduce high end-to-end latency due to the reservation-based access policy. We argue that a suitable routing protocol speci cally designed for reservation-based MAC protocols can alleviate their highlatency drawback. Following this argument, we propose rst such routing algorithms working on top of a generic STDMA MAC protocol. First, we consider routing with data fusion and present our GreenWave routing idea. We show that our algorithm signi cantly reduces the end-toend delay when compared to routing over the shortest-hop paths. Second, we consider routing without data fusion, by taking into account the effect of congestion along the paths on the end-to-end delays. We provide a QIP formulation of the problem, and present a lower bound and a heuristic algorithm to bound the optimal solution. Based on the centralized heuristic algorithm, we propose a distributed, dynamic routing protocol GWCF (GreenWave routing with Congestion and Flow control), which uses a novel congestion and ow control technique utilizing the underlying contention-free protocol. We show by simulations that GWCF routing signi cantly improves the end-to-end delay while increasing the network throughput when compared to routing over shortest paths.

Wireless sensor networks have resources of limited capacity (e.g. bandwidth, processing power, memory and energy). That is why these resources should be efficiently used. Node activity scheduling is a technique that allows nodes to alternate sleep and awake states. This technique spares energy insofar as the sleep state is the state using the smallest power. Moreover, by allowing several nodes to transmit simultaneously without interfering, spatial reuse of the bandwidth is obtained. Furthermore with a smart schedule, data gathering can be done in a single cycle. All these reasons render node activity scheduling very attractive in wireless sensor networks. We propose in this paper a three-hop coloring algorithm for data gathering applications. Simulation results allow us to evaluate the number of colors needed to color all network nodes and hence to determine the reduced size of the activity period in each polling cycle. The complexity of our algorithm is given in terms of number of messages sent per node. We can then determine the network configurations for which coloring brings interesting benefits, namely a more efficient use of the bandwidth and the node energy, as well as a shorter delay to collect data ensuring their time consistency. 1.

Contention-free MAC protocols have the desired energy-saving characteristics for wireless sensor networks by avoiding collisions and minimizing retransmissions in the wireless medium [2] [4] [24] [25] [26]. Most of the contention-free MAC protocols split the channel in the time domain, by assigning each node a time slot for use in transmission, which is unique in its neighborhood. In such protocols, the time-multiplexed communication introduces extra delay on the packets when relayed by intermediate nodes. In this paper, we consider the delay optimal routing problem on sensor networks with such MAC protocols. We propose algorithms which construct routing trees rooted at sink nodes to route data to and from sensor nodes. First, we consider routing with data fusion, and present our GreenWave routing idea. We show that our algorithm significantly reduces the end-to-end delay when compared to routing over the shortest-hop paths. We also present a comparison of GreenWave routing over a contention-free MAC protocol to the shortest-path routing over the IEEE 802.11 MAC protocol, accompanied by an end-to-end delay analysis of 802.11. As a side result, we show that there is roughly a two-fold decrease in 802.11 performance when hidden terminals are taken into account. Moreover, we observe that a contention-free MAC protocol may outperform 802.11 with the help of GreenWave routing. Second, we consider routing without data fusion, by taking into account the effect of congestion along the paths on the end-to-end delays. We provide a quadratic integer programming (QIP) formulation of the problem, and present a lower bound and a heuristic algorithm to bound the optimal solution. Numerical results show that the results obtained by the heuristic are close to the lower bounds.

apport de recherche ISSN 0249-6399 ISRN INRIA/RR--6388--FR+ENGinria-00196094, version 2- 13 Dec 2007SERENA: an energy-efficient strategy to schedule nodes activity in wireless ad hoc and sensor networks

Abstract–This paper presents CMAC, a fully desynchronized MAC protocol that is designed to exploit the existing multi-channel support in sensor nodes. The hardware requirements of our protocol are minimal, requiring a single half-duplex transceiver and a lowpower wake-up radio. CMAC takes into account the fundamental energy constraint in sensor nodes by placing them in a default sleep mode and waking them up only when necessary. As a contrast to other dual radio wake-up schemes, our protocol focuses on how communication and its preceding control message exchange mechanism can be undertaken in a multi-channel scenario without assuming a separate control channel. CMAC enables spatial channel re-use, nearly collision free communication, and addresses the deafness problem without incurring a tradeoff in fairness or latency. When compared with a recent MAC protocol SMAC, results show that CMAC obtains nearly 200 % reduction in energy consumption, significantly improved throughput, and end-to-end delay values that are 50-150 % better than SMAC for our simulated topologies.