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16
Sensor networks continue to puzzle: Selected open problems
 In Proc. 9th Internat. Conf. Distributed Computing and Networking (ICDCN
, 2008
"... Abstract. While several important problems in the field of sensor networks have already been tackled, there is still a wide range of challenging, open problems that merit further attention. We present five theoretical problems that we believe to be essential to understanding sensor networks. The goa ..."
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Cited by 14 (0 self)
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Abstract. While several important problems in the field of sensor networks have already been tackled, there is still a wide range of challenging, open problems that merit further attention. We present five theoretical problems that we believe to be essential to understanding sensor networks. The goal of this work is both to summarize the current state of research and, by calling attention to these fundamental problems, to spark interest in the networking community to attend to these and related problems in sensor networks.
Broadcasting in Unreliable Radio Networks
"... Practitioners agree that unreliable links, which sometimes deliver messages and sometime do not, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set of links and assume that these links work reliably throughout an execution. T ..."
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Cited by 12 (6 self)
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Practitioners agree that unreliable links, which sometimes deliver messages and sometime do not, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set of links and assume that these links work reliably throughout an execution. This gap between theory and practice motivates us to investigate how unreliable links affect theoretical bounds on broadcast in radio networks. To that end we consider a model that includes two types of links: reliable links, which always deliver messages, and unreliable links, which sometimes fail to deliver messages. We assume that the reliable links induce a connected graph, and that unreliable links are controlled by a worstcase adversary. In the new model we show an Ω(
Decomposing Broadcast Algorithms Using Abstract MAC Layers ABSTRACT
"... In much of the theoretical literature on wireless algorithms, issues of message dissemination are considered together with issues of contention management. This combination leads to complicated algorithms and analysis, and makes it difficult to extend the work to harder communication problems. In th ..."
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Cited by 11 (7 self)
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In much of the theoretical literature on wireless algorithms, issues of message dissemination are considered together with issues of contention management. This combination leads to complicated algorithms and analysis, and makes it difficult to extend the work to harder communication problems. In this paper, we present results of a current project aimed at simplifying such algorithms and analysis by decomposing the treatment into two levels, using abstract “MAC layer ” specifications to encapsulate the contention management. We use two different abstract MAC layers: the basic one of [14, 15] and a new probabilistic layer. We first present a typical randomized contentionmanageent algorithm for a standard graphbased radio network model We show that it implements both abstract MAC layers. We combine this algorithm with greedy algorithms for singlemessage and multimessage global broadcast and analyze the combination, using both abstract MAC layers as intermediate layers. Using the basic MAC layer, we prove a bound of O(D log ( n) log ∆) for the time to deliver a single message ɛ everywhere with probability 1 − ɛ, where D is the network diameter, n is the number of nodes, and ∆ is the maximum node degree. Using the probabilistic layer, we prove a bound of O((D + log ( n)) log ∆), which matches the best ɛ previouslyknown bound for singlemessage broadcast over the physical network model. For multimessage broadcast,) log ∆) using the we obtain bounds of O((D + k∆) log ( n ɛ
Broadcast in radio networks with collision detection
 In Proceedings of the ACM Symposium on Principles of Distributed Computing (PODC
, 2013
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Minimal Time Broadcasting in Cognitive Radio Networks *
"... Abstract. This paper addresses timeefficient broadcast scheduling problem in Cognitive Radio (CR) Networks. Cognitive Radio is a promising technology that enables the use of unused spectrum in an opportunistic manner. Because of the unique characteristics of CR technology, the broadcast scheduling ..."
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Abstract. This paper addresses timeefficient broadcast scheduling problem in Cognitive Radio (CR) Networks. Cognitive Radio is a promising technology that enables the use of unused spectrum in an opportunistic manner. Because of the unique characteristics of CR technology, the broadcast scheduling problem in CR networks needs unique solutions. Even for single channel wireless networks, finding a minimumlength broadcast schedule is an NPhard problem. In addition, the multichannel nature of the CR networks, especially the nonuniform channel availability, makes it a more complex problem to solve. In this paper, we first present an Integer Linear Programming formulation (ILP) to determine the minimum broadcast schedule length for a CR network. We then present two heuristics to construct minimal length broadcast schedules. Comparison of optimal results (found by solving the ILP formulation) with the result of the heuristics through simulation shows that both heuristics produce schedules of either optimal or very closer to optimal lengths.
Boundedcontention coding for wireless networks
 in the high SNR regime,” in Distributed Computing
, 2012
"... Abstract Efficient communication in wireless networks is typically challenged by the possibility of interference among several transmitting nodes. Much important research has been invested in decreasing the number of collisions in order to obtain faster algorithms for communication in such networks ..."
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Cited by 4 (1 self)
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Abstract Efficient communication in wireless networks is typically challenged by the possibility of interference among several transmitting nodes. Much important research has been invested in decreasing the number of collisions in order to obtain faster algorithms for communication in such networks. This paper proposes a novel approach for wireless communication, which embraces collisions rather than avoiding them, over an additive channel. It introduces a coding technique called BoundedContention Coding (BCC) that allows collisions to be successfully decoded by the receiving nodes into the original transmissions and whose complexity depends on a bound on the contention among the transmitters. BCC enables deterministic local broadcast in a network with n nodes and at most a transmitters with information of bits each within O(a log n + a ) bits of communication with fullduplex radios, and O((a log n + a )(log n)) bits, with high probability, with halfduplex radios. When combined with random linear network coding, BCC gives global broadcast within O((D + a + log n)(a log n + )) bits, with high probability. This also holds in dynamic networks that can change arbitrarily over time by a worstcase adversary. When no bound on the contention is given, it is shown how to probabilistically estimate it and obtain global broadcast that is adaptive to the true contention in the network.
The Cost of Global Broadcast using Abstract MAC Layers
, 2010
"... We analyze greedy algorithms for broadcasting messages throughout a multihop wireless network, using a slotbased model that includes message collisions without collision detection. Our algorithms are split formally into two pieces: a highlevel piece for broadcast and a lowlevel piece for content ..."
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We analyze greedy algorithms for broadcasting messages throughout a multihop wireless network, using a slotbased model that includes message collisions without collision detection. Our algorithms are split formally into two pieces: a highlevel piece for broadcast and a lowlevel piece for contention management. We accomplish the split using abstract versions of the MAC layer to encapsulate the contention management. We use two different abstract MAC layers: a basic nonprobabilistic one, which our contention management algorithm implements with high probability, and a probabilistic one, which our contention management algorithm implements precisely. Using this approach, we obtain the following complexity bounds: Singlemessage broadcast, using the basic abstract MAC layer, takes time O(D log ( n ɛ) log(∆)) to deliver the message everywhere with probability 1 − ɛ, where D is the network diameter, n is the number of nodes, MAC layer, takes time only O((D + log ( n)) log(∆)). For multimessage broadcast, the bounds ɛ are O((D + k ′ ∆) log ( n ɛ) log(∆)) using the basic layer and O((D + k ′ ∆ log ( n ɛ)) log(∆)) using the probabilistic layer, for the time to deliver a single message everywhere in the presence of at most k ′ concurrent messages. 1
Broadcast Throughput in Radio Networks: Routing vs. Network Coding
"... The broadcast throughput in a network is defined as the average number of messages that can be transmitted per unit time from a given source to all other nodes when time goes to infinity. Classical broadcast algorithms treat messages as atomic tokens and route them from the source to the receivers b ..."
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Cited by 3 (3 self)
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The broadcast throughput in a network is defined as the average number of messages that can be transmitted per unit time from a given source to all other nodes when time goes to infinity. Classical broadcast algorithms treat messages as atomic tokens and route them from the source to the receivers by making intermediate nodes store and forward messages. The more recent network coding approach, in contrast, prompts intermediate nodes to mix and code together messages. It has been shown that certain wired networks have an asymptotic network coding gap, that is, they have asymptotically higher broadcast throughput when using network coding compared to routing. Whether such a gap exists for wireless networks has been an open question of great interest. We approach this question by studying the broadcast throughput of the radio network model which has been a standard mathematical model to study wireless communication. We show that there is a family of radio networks with a tight Θ(log log n) network coding gap, that is, networks in which the asymptotic throughput achievable via routing messages is a Θ(log log n) factor smaller than that of the optimal network coding algorithm. We also provide new tight upper and lower bounds showing that the asymptotic worstcase broadcast throughput over all networks with n nodes is Θ ( 1 log n) messagesperround for both routing and network coding. 1
The Cost of Radio Network Broadcast for Different Models of Unreliable Links∗
"... We study upper and lower bounds for the global and local broadcast problems in the dual graph model combined with different strength adversaries. The dual graph model is a generalization of the standard graphbased radio network model that includes unreliable links controlled by an adversary. It i ..."
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We study upper and lower bounds for the global and local broadcast problems in the dual graph model combined with different strength adversaries. The dual graph model is a generalization of the standard graphbased radio network model that includes unreliable links controlled by an adversary. It is motivated by the ubiquity of unreliable links in real wireless networks. Existing results in this model [11, 12, 3, 8] assume an offline adaptive adversary—the strongest type of adversary considered in standard randomized analysis. In this paper, we study the two other standard types of adversaries: online adaptive and oblivious. Our goal is to find a model that captures the unpredictable behavior of real networks while still allowing for efficient broadcast solutions.
Brief Announcement: NearOptimal BFStree Construction in Radio Networks
"... We present the first improved construction of a Breadth First Search tree (BFStree) in the radio network model. Computing a BFStree, or the hopdistance to a source, was one of the first problems solved in the radio network model. Particularly, more than 20 years ago, BarYehuda et al. showed how ..."
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We present the first improved construction of a Breadth First Search tree (BFStree) in the radio network model. Computing a BFStree, or the hopdistance to a source, was one of the first problems solved in the radio network model. Particularly, more than 20 years ago, BarYehuda et al. showed how to compute a BFStree in O(D log2 n) rounds in any nnode network of diameter D. Since then this BFStree algorithm has been used extensively for constructing a substrate over which communications can be coordinated efficiently. However, the O(D log2 n) dependence on the diameter has become a running time bottleneck in many of these applications, and no faster construction was found. Recently, trying to circumvent this barrier, approximate variants of BFStrees were introduced which can be used in a similar manner but be computed faster. Still, the question whether exact BFStree could be computed faster remained open. Here we present a simple randomized distributed algorithm that computes a BFStree in O(D log n log log n + log3 n log logn) rounds, with high probability. This running time is optimal up to an O(log log n) factor for most values of D, in particular for all D ∈ [log2 n, n1−ε] for any constant ε> 0.