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What Is the Use of Collision Detection (in Wireless Networks)?
"... We show that the asymptotic gain in the time complexity when using collision detection depends heavily on the task by investigating three prominent problems for wireless networks, i.e. the maximal independent set (MIS), broadcasting and coloring problem. We present lower and upper bounds for all thr ..."
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We show that the asymptotic gain in the time complexity when using collision detection depends heavily on the task by investigating three prominent problems for wireless networks, i.e. the maximal independent set (MIS), broadcasting and coloring problem. We present lower and upper bounds for all three problems for the GrowthBounded Graph such as the Unit Disk Graph. We prove that the benefit of collision detection ranges from an exponential improvement down to no asymptotic gain at all. In particular, for the broadcasting problem our deterministic algorithm is running in time O(D log n). It is an exponential improvement over prior work, if the diameter D is polylogarithmic in the number of nodes n, i.e. D ∈ O(log c n) for some constant c. 1
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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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.
Communication complexity of consensus in anonymous message passing systems
 In Proc. 15th International Conference on Principles of Distributed Systems (OPODIS 2011), LNCS 7109
"... Abstract. We consider the message complexity of achieving consensus in synchronous anonymous message passing systems. Unlabeled processors (nodes) communicate through links of a network. In each round every processor can exchange messages with all neighbors and the duration of each transmission is o ..."
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Abstract. We consider the message complexity of achieving consensus in synchronous anonymous message passing systems. Unlabeled processors (nodes) communicate through links of a network. In each round every processor can exchange messages with all neighbors and the duration of each transmission is one round. An adversary wakes up some subset of processors at possibly different times and assigns them arbitrary numerical input values. All other processors are dormant and do not have input values. Any message wakes up a dormant processor. The goal of consensus is to wake up all processors and have them agree on one of the input values. We seek deterministic consensus algorithms using as few messages as possible. As opposed to most of the literature on consensus, the difficulty of our scenario are not faults (we assume that the network is faultfree) but the arbitrary network topology combined with the anonymity of nodes. For unknown nnode networks we show a consensus algorithm using
Deterministic MultiChannel Information Exchange ABSTRACT
"... In this paper, we study the information exchange problem on a set of multiple access channels: k arbitrary nodes have information they want to distribute to the entire network via a shared medium partitioned into channels. We present algorithms and lower bounds on the time and channel complexity for ..."
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In this paper, we study the information exchange problem on a set of multiple access channels: k arbitrary nodes have information they want to distribute to the entire network via a shared medium partitioned into channels. We present algorithms and lower bounds on the time and channel complexity for disseminating these k information items in a singlehop network of n nodes. More precisely, we devise a deterministic algorithm running in asymptotically optimal time O(k) using O(n log(k)/k) channels if k ≤ 1 log n 6 and O(log 1+ρ (n/k)) channels otherwise, where ρ> 0 is an arbitrarily small constant. In addition, we show that Ω(n Ω(1/k) + log k n) channels are necessary to achieve this time complexity.
Deterministic recurrent communication and synchronization in restricted sensor networks.
 In Proceedings of the 6th International Workshop on Algorithms for Sensor Systems, Wireless Ad Hoc Networks and Autonomous Mobile Entities (ALGOSENSORS),
, 2010
"... Monitoring physical phenomena in Sensor Networks requires guaranteeing permanent communication between nodes. Moreover, in an effective implementation of such infrastructure, the delay between any two consecutive communications should be minimized. The problem is challenging because, in a restricte ..."
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Monitoring physical phenomena in Sensor Networks requires guaranteeing permanent communication between nodes. Moreover, in an effective implementation of such infrastructure, the delay between any two consecutive communications should be minimized. The problem is challenging because, in a restricted Sensor Network, the communication is carried out through a single and shared radio channel without collision detection. Dealing with collisions is crucial to ensure effective communication between nodes. Additionally, minimizing them yields energy consumption minimization, given that sensing and computational costs in terms of energy are negligible with respect to radio communication. In this work, we present a deterministic recurrentcommunication protocol for Sensor Networks. After an initial negotiation phase of the access pattern to the channel, each node running this protocol reaches a steady state, which is asymptotically optimal in terms of time efficiency, and optimal (0) or constant (for a worstcase adversary) in terms of transmissions overhead, which we use as energy efficiency metric. As a byproduct, a protocol for the synchronization of a Sensor Network is also proposed. Furthermore, the protocols are resilient to an arbitrary node powerup schedule and a general node failure model.
DYNAMIC SHARING OF A MULTIPLE ACCESS CHANNEL
, 2010
"... In this paper we consider the mutual exclusion problem on a multiple access channel. Mutual exclusion is one of the fundamental problems in distributed computing. In the classic version of this problem, n processes perform a concurrent program which occasionally triggers some of them to use shared r ..."
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In this paper we consider the mutual exclusion problem on a multiple access channel. Mutual exclusion is one of the fundamental problems in distributed computing. In the classic version of this problem, n processes perform a concurrent program which occasionally triggers some of them to use shared resources, such as memory, communication channel, device, etc. The goal is to design a distributed algorithm to control entries and exits to/from the shared resource in such a way that in any time there is at most one process accessing it. We consider both the classic and a slightly weaker version of mutual exclusion, called εmutualexclusion, where for each period of a process staying in the critical section the probability that there is some other process in the critical section is at most ε. We show that there are channel settings, where the classic mutual exclusion is not feasible even for randomized algorithms, while εmutualexclusion is. In more relaxed channel settings, we prove an exponential gap between the makespan complexity of the classic mutual exclusion problem and its weaker εexclusion version. We also show how to guarantee fairness of mutual exclusion algorithms, i.e., that each process that wants to enter the critical section will eventually succeed. 1.