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29
Consensus and collision detectors in wireless ad hoc networks
 In PODC
, 2005
"... Abstract In this study, we consider the faulttolerant consensus problem in wireless ad hoc networks with crashprone nodes. Specifically, we develop lower bounds and matching upper bounds for this problem in singlehop wireless networks, where all nodes are located within broadcast range of each oth ..."
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Cited by 46 (21 self)
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Abstract In this study, we consider the faulttolerant consensus problem in wireless ad hoc networks with crashprone nodes. Specifically, we develop lower bounds and matching upper bounds for this problem in singlehop wireless networks, where all nodes are located within broadcast range of each other. In a novel break from existing work, we introduce a highly unpredictable communication model in which each node may lose an arbitrary subset of the messages sent by its neighbors during each round. We argue that this model better matches behavior observed in empirical studies of these networks. To cope with this communication unreliability we augment nodes with receiverside collision detectors and present a new classification of these detectors in terms of accuracy and completeness. This classification is motivated by practical realities and allows us to determine, roughly speaking, how much collision detection capability is enough to solve the consensus problem efficiently in this setting. We consider ten different combinations of completeness and accuracy properties in total, determining for each whether consensus is solvable, and, if it is, a lower bound on the number of rounds required. Furthermore, we distinguish anonymous and nonanonymous protocolswhere &quot;anonymous &quot; implies that devices do not have unique identifiersdetermining what effect (if any) this extra information has on the complexity of the problem. In all relevant cases, we provide matching upper bounds. Our contention is that the introduction of (possibly weak) receiverside collision detection is an important approach to reliably solving problems in unreliable networks. Our results, derived in a realistic network model, provide important feedback to ad hoc network practitioners regarding what hardware (and lowlayer software) collision detection capability is sufficient to facilitate the construction of reliable and faulttolerant agreement protocols for use in realworld deployments.
Maximal Independent Sets in Radio Networks
"... We study the distributed complexity of computing a maximal independent set (MIS) in radio networks with completely unknown topology, asynchronous wakeup, and no collision detection mechanism available. Specifically, we propose a novel randomized algorithm that computes a MIS in time O(log 2 n) with ..."
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Cited by 45 (8 self)
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We study the distributed complexity of computing a maximal independent set (MIS) in radio networks with completely unknown topology, asynchronous wakeup, and no collision detection mechanism available. Specifically, we propose a novel randomized algorithm that computes a MIS in time O(log 2 n) with high probability, where n is the number of nodes in the network. This significantly improving on the best previously known solutions. A lower bound of Ω(log 2 n / log log n) given in [11] implies that our algorithm’s running time is close to optimal. Our result shows that the harsh radio network model imposes merely an additional O(log n) factor compared to Luby’s MIS algorithm in the message passing model. This has important implications in the context of ad hoc and sensor networks whose characteristics are closely captured by the radio network model.
Faster Deterministic Broadcasting in ad hoc Radio Networks
 Proc. 20th Ann. Symp. on Theor. Aspects of Comp. Sci. (STACS’2003), LNCS 2607
, 2003
"... We consider radio networks modeled as directed graphs. In ad hoc radio networks, every node knows only its own label and a linear bound on the size of the network but is unaware of the topology of the network, or even of its own neighborhood. The fastest currently known deterministic broadcastin ..."
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Cited by 27 (7 self)
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We consider radio networks modeled as directed graphs. In ad hoc radio networks, every node knows only its own label and a linear bound on the size of the network but is unaware of the topology of the network, or even of its own neighborhood. The fastest currently known deterministic broadcasting algorithm working for arbitrary nnode ad hoc radio networks, has running time O(n log n). Our main result is a broadcasting algorithm working in time O(n log n log D) for arbitrary n node ad hoc radio networks of eccentricity D. The best currently known lower bound on broadcasting time in ad hoc radio networks is hence our algorithm is the rst to shrink the gap between bounds on broadcasting time in radio networks of arbitrary eccentricity to a logarithmic factor. We also show a broadcasting algorithm working in time O(n log D) for complete layered nnode ad hoc radio networks of eccentricity D. The latter complexity is optimal.
Adversarial queuing on the multipleaccess channel
 In Proc. of PODC ’06
, 2006
"... We consider broadcasting on the multipleaccess channel when packets are injected continuously. Multipleaccess channel is a synchronous system with the properties that a single transmission at a round delivers the message to all nodes, while multiple simultaneous transmissions result in a conflict ..."
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Cited by 21 (9 self)
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We consider broadcasting on the multipleaccess channel when packets are injected continuously. Multipleaccess channel is a synchronous system with the properties that a single transmission at a round delivers the message to all nodes, while multiple simultaneous transmissions result in a conflict which prevents delivering messages to any among the recipients. The traditional approach to dynamic broadcasting has been concerned with stability of protocols under suitable stochastic assumptions about injection rates. We study deterministic protocols competing against adversaries restricted by injection rate and burstiness of traffic. Stability means that the number of packets in queues is bounded by a constant in any execution, for a given number of stations, protocol, and adversary. Strong stability denotes the
The Wireless Synchronization Problem
, 2009
"... In this paper, we study the wireless synchronization problem which requires devices activated at different times on a congested singlehop radio network to synchronize their round numbering. We assume a collection of n synchronous devices with access to a shared band of the radio spectrum, divided i ..."
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Cited by 16 (6 self)
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In this paper, we study the wireless synchronization problem which requires devices activated at different times on a congested singlehop radio network to synchronize their round numbering. We assume a collection of n synchronous devices with access to a shared band of the radio spectrum, divided into F narrowband frequencies. We assume that the communication medium suffers from unpredictable, perhaps even malicious interference, which we model by an adversary that can disrupt up to t frequencies per round. Devices begin executing in different rounds and the exact number of participants is not known in advance. “ We first prove a lower bound, demonstrating that at least log Ω
TimeEfficient Broadcast in Radio Networks
, 2010
"... Broadcasting is a basic network communication task, where a message initially held by a source node has to be disseminated to all other nodes in the network. Fast algorithms for broadcasting in radio networks have been studied in a wide variety of different models and under different requirements. S ..."
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Cited by 16 (0 self)
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Broadcasting is a basic network communication task, where a message initially held by a source node has to be disseminated to all other nodes in the network. Fast algorithms for broadcasting in radio networks have been studied in a wide variety of different models and under different requirements. Some of the main parameters giving rise to the different variants of the problem are the accessibility of knowledge about the network topology, the availability of collision detection mechanisms, the wakeup mode, the topology classes considered, and the use of randomness. This chapter introduces the problem, reviews the literature on timeefficient broadcasting algorithms for radio networks under a variety of models and assumptions, and illustrates some of the basic techniques.
Efficient computation of maximal independent sets in unstructured multihop radio network. In: Proc of 1st international conference on mobile ad hoc and sensor systems
"... Abstract — When being deployed, adhoc and sensor networks are unstructured and lack an efficient and reliable communication scheme. Hence, the organization of a MAC layer is the primary goal during and immediately after the deployment of such networks. Computing a good initial clustering facilitat ..."
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Cited by 14 (1 self)
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Abstract — When being deployed, adhoc and sensor networks are unstructured and lack an efficient and reliable communication scheme. Hence, the organization of a MAC layer is the primary goal during and immediately after the deployment of such networks. Computing a good initial clustering facilitates this task and is therefore a vital part of the initialization process. A clustering based on a maximal independent set provides several highly desirable properties. Besides yielding a dominating set of good quality, such a clustering avoids interference between clusterheads, thus allowing efficient communication. We propose a novel algorithm that works under a model capturing the characteristics of the initialization phase of unstructured radio networks, i.e., asynchronous wakeup, scarce knowledge about the topology of the network graph, no collision detection, and the hidden terminal problem. We show that even under these hard conditions, the algorithm computes a maximal independent set in polylogarithmic time. I.
Broadcasting in UDG radio networks with unknown topology
, 2009
"... The paper considers broadcasting in radio networks, modeled as unit disk graphs (UDG). Such networks occur in wireless communication between sites (e.g., stations or sensors) situated in a terrain. Network stations are represented by points in the Euclidean plane, where a station is connected to al ..."
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Cited by 12 (2 self)
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The paper considers broadcasting in radio networks, modeled as unit disk graphs (UDG). Such networks occur in wireless communication between sites (e.g., stations or sensors) situated in a terrain. Network stations are represented by points in the Euclidean plane, where a station is connected to all stations at distance at most 1 from it. A message transmitted by a station reaches all its neighbors, but a station hears a message (receives the message
On the wakeup problem in radio networks
 In ICALP
, 2005
"... Abstract. Radio networks model wireless communication when processing units communicate using one wave frequency. This is captured by the property that multiple messages arriving simultaneously to a node interfere with one another and none of them can be read reliably. We present improved solutions ..."
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Cited by 11 (3 self)
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Abstract. Radio networks model wireless communication when processing units communicate using one wave frequency. This is captured by the property that multiple messages arriving simultaneously to a node interfere with one another and none of them can be read reliably. We present improved solutions to the problem of waking up such a network. This requires activating all nodes in a scenario when some nodes start to be active spontaneously, while every sleeping node needs to be awaken by receiving successfully a message from a neighbor. Our contributions concern the existence and efficient construction of universal radio synchronizers, which are combinatorial structures introduced in [6] as building blocks of efficient wakeup algorithms. First we show by counting that there are (n, g)universal synchronizers for g(k) = O(k log k log n). Next we show an explicit construction of (n, g)universalsynchronizers for g(k) = O(k 2 polylog n). By way of applications, we obtain an existential wakeup algorithm which works in time O(n log 2 n) and an explicitly instantiated algorithm that works in time O(n ∆ polylog n), where n is the number of nodes and ∆ is the maximum indegree in the network. Algorithms for leaderelection and synchronization can be developed on top of wakeup ones, as shown in [7], such that they work in time slower by a factor of O(log n) than the underlying wakeup ones. 1
Consensus and mutual exclusion in a multiple access channel
 IEEE Transactions on Parallel and Distributed Systems
"... Abstract. We consider deterministic feasibility and time complexity of two fundamental tasks in distributed computing: consensus and mutual exclusion. Processes have different labels and communicate through a multiple access channel. The adversary wakes up some processes in possibly different rounds ..."
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Cited by 9 (3 self)
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Abstract. We consider deterministic feasibility and time complexity of two fundamental tasks in distributed computing: consensus and mutual exclusion. Processes have different labels and communicate through a multiple access channel. The adversary wakes up some processes in possibly different rounds. In any round every awake process either listens or transmits. The message of a process i is heard by all other awake processes, if i is the only process to transmit in a given round. If more than one process transmits simultaneously, there is a collision and no message is heard. We consider three characteristics that may or may not exist in the channel: collision detection (listening processes can distinguish collision from silence), the availablity of a global clock showing the round number, and the knowledge of the number n of all processes. If none of the above three characteristics is available in the channel, we prove that consensus and mutual exclusion are infeasible; if at least one of them is available, both tasks are feasible and we study their time complexity. Collision detection is shown to cause an exponential gap in complexity: if it is available, both tasks can be performed in time logarithmic in n, which is optimal, and without collision detection both tasks require linear time. We then investigate both consensus and mutual exclusion in the absence of collision detection, but under alternative presence of the two other features. With global clock, we give an algorithm whose time complexity linearly depends on n and on the wakeup time, and an algorithm whose complexity does not depend on the wakeup time and differs from the linear lower bound only by a factor O(log 2 n). If n is known, we also show an algorithm whose complexity differs from the linear lower bound only by a factor O(log 2 n).