The Experts below are selected from a list of 93150 Experts worldwide ranked by ideXlab platform
Ramin Khalili - One of the best experts on this subject based on the ideXlab platform.
-
neighbor discovery in wireless networks and the coupon collector s problem
ACM IEEE International Conference on Mobile Computing and Networking, 2009Co-Authors: Sudarshan Vasudevan, Don Towsley, Dennis Goeckel, Ramin KhaliliAbstract:Neighbor discovery is one of the first steps in the initialization of a wireless ad hoc network. In this paper, we design and analyze practical algorithms for neighbor discovery in wireless networks. We first consider an ALOHA-like neighbor discovery algorithm in a Synchronous System, proposed in an earlier work. When nodes do not have a collision detection mechanism, we show that this algorithm reduces to the classical {\em Coupon Collector's Problem}. Consequently, we show that each node discovers all its $n$ neighbors in an expected time equal to $ne (\ln n + c)$, for some constant $c$. When nodes have a collision detection mechanism, we propose an algorithm based on receiver status feedback which yields a $\ln n$ improvement over the ALOHA-like algorithm. Our algorithms do not require nodes to have any estimate of the number of neighbors. In particular, we show that not knowing $n$ results in no more than a factor of two slowdown in the algorithm performance. In the absence of node synchronization, we develop aSynchronous neighbor discovery algorithms that are only a factor of two slower than their Synchronous counterparts. We show that our algorithms can achieve neighbor discovery despite allowing nodes to begin execution at different time instants. Furthermore, our algorithms allow each node to detect when to terminate the neighbor discovery phase.
Nitin H Vaidya - One of the best experts on this subject based on the ideXlab platform.
-
exact byzantine consensus on arbitrary directed graphs under local broadcast model
arXiv: Distributed Parallel and Cluster Computing, 2019Co-Authors: Muhammad Samir Khan, Lewis Tseng, Nitin H VaidyaAbstract:We consider Byzantine consensus in a Synchronous System where nodes are connected by a network modeled as a directed graph, i.e., communication links between neighboring nodes are not necessarily bi-directional. The directed graph model is motivated by wireless networks wherein asymmetric communication links can occur. In the classical point-to-point communication model, a message sent on a communication link is private between the two nodes on the link. This allows a Byzantine faulty node to equivocate, i.e., send inconsistent information to its neighbors. This paper considers the local broadcast model of communication, wherein transmission by a node is received identically by all of its outgoing neighbors. This allows such neighbors to detect a faulty node's attempt to equivocate, effectively depriving the faulty nodes of the ability to send conflicting information to different neighbors. Prior work has obtained sufficient and necessary conditions on undirected graphs to be able to achieve Byzantine consensus under the local broadcast model. In this paper, we obtain tight conditions on directed graphs to be able to achieve Byzantine consensus with binary inputs under the local broadcast model. The results obtained in the paper provide insights into the trade-off between directionality of communication and the ability to achieve consensus.
-
byzantine fault tolerant parallelized stochastic gradient descent for linear regression
Allerton Conference on Communication Control and Computing, 2019Co-Authors: Nirupam Gupta, Nitin H VaidyaAbstract:This paper addresses the problem of Byzantine fault-tolerance in parallelized stochastic gradient descent (SGD) method solving for a linear regression problem. We consider a Synchronous System comprising of a master and multiple workers, where up to a (known) constant number of workers are Byzantine faulty. Byzantine faulty workers may send incorrect information to the master during an execution of the parallelized SGD method. To mitigate the detrimental impact of Byzantine faulty workers, we replace the averaging of gradients in the traditional parallelized SGD method by a provably more robust gradient aggregation rule. The crux of the proposed gradient aggregation rule is a gradient-filter, named comparative gradient clipping(CGC) filter. We show that the resultant parallelized SGD method obtains a good estimate of the regression parameter even in presence of bounded fraction of Byzantine faulty workers. The upper bound derived for the asymptotic estimation error only grows linearly with the fraction of Byzantine faulty workers.
Venugopal V Veeravalli - One of the best experts on this subject based on the ideXlab platform.
-
mmse detection in aSynchronous cdma Systems an equivalence result
IEEE Transactions on Information Theory, 2002Co-Authors: A Mantravadi, Venugopal V VeeravalliAbstract:The analysis of linear minimum mean-square error (MMSE) detection in a band-limited code-division multiple-access (CDMA) System that employs random spreading sequences is considered. The key features of the analysis are that the users are allowed to be completely aSynchronous, and that the chip waveform is assumed to be the ideal Nyquist sinc function. It is shown that the asymptotic signal-to-interference ratio (SIR) at the detector output is the same as that in an equivalent chip-Synchronous System. It is hence been established that Synchronous analyses of linear MMSE detection can provide useful guidelines for the performance in aSynchronous band-limited Systems.
-
asymptotic analysis of mmse detection in aSynchronous cdma Systems an equivalence result
International Symposium on Information Theory, 2001Co-Authors: A Mantravadi, Venugopal V VeeravalliAbstract:We consider the analysis of linear MMSE detection in a CDMA System that employs random spreading sequences. The key features of the analysis are that the users are allowed to be completely aSynchronous and the chip waveform is assumed to be the ideal band-limited sine waveform. We show that the asymptotic signal to interference ratio (SIR) at the detector output is the same as that in an equivalent chip Synchronous System. Hence, Synchronous analyses can provide useful guidelines for the performance in aSynchronous band-limited Systems.
Sudarshan Vasudevan - One of the best experts on this subject based on the ideXlab platform.
-
neighbor discovery in wireless networks and the coupon collector s problem
ACM IEEE International Conference on Mobile Computing and Networking, 2009Co-Authors: Sudarshan Vasudevan, Don Towsley, Dennis Goeckel, Ramin KhaliliAbstract:Neighbor discovery is one of the first steps in the initialization of a wireless ad hoc network. In this paper, we design and analyze practical algorithms for neighbor discovery in wireless networks. We first consider an ALOHA-like neighbor discovery algorithm in a Synchronous System, proposed in an earlier work. When nodes do not have a collision detection mechanism, we show that this algorithm reduces to the classical {\em Coupon Collector's Problem}. Consequently, we show that each node discovers all its $n$ neighbors in an expected time equal to $ne (\ln n + c)$, for some constant $c$. When nodes have a collision detection mechanism, we propose an algorithm based on receiver status feedback which yields a $\ln n$ improvement over the ALOHA-like algorithm. Our algorithms do not require nodes to have any estimate of the number of neighbors. In particular, we show that not knowing $n$ results in no more than a factor of two slowdown in the algorithm performance. In the absence of node synchronization, we develop aSynchronous neighbor discovery algorithms that are only a factor of two slower than their Synchronous counterparts. We show that our algorithms can achieve neighbor discovery despite allowing nodes to begin execution at different time instants. Furthermore, our algorithms allow each node to detect when to terminate the neighbor discovery phase.
-
on neighbor discovery in wireless networks with directional antennas
International Conference on Computer Communications, 2005Co-Authors: Sudarshan Vasudevan, Jim Kurose, Don TowsleyAbstract:We consider the problem of neighbor discovery in static wireless ad hoc networks with directional antennas. We propose several probabilistic algorithms in which nodes perform random, independent transmissions to discover their one-hop neighbors. Our neighbor discovery algorithms are classified into two groups, viz. Direct-Discovery Algorithms in which nodes discover their neighbors only upon receiving a transmission from their neighbors and Gossip-based algorithms in which nodes gossip about their neighbors' location information to enable faster discovery. We first consider the operation of these algorithms in a slotted, Synchronous System and mathematically derive their optimal parameter settings. We show how to extend these algorithms for an aSynchronous System and describe their optimal design. Analysis and simulation of the algorithms show that nodes discover their neighbors much faster using gossip-based algorithms than using direct-discovery algorithms. Furthermore, the performance of gossip-based algorithms is insensitive to an increase in node density. The efficiency of a neighbor discovery algorithm also depends on the choice of antenna beamwidth. We discuss in detail how the choice of beamwidth impacts the performance of the discovery process and provide insights into how nodes can configure their beamwidths.
Lin Gui - One of the best experts on this subject based on the ideXlab platform.
-
Practical ASynchronous Neighbor Discovery in Ad Hoc Networks with Directional Antennas
IEEE Transactions on Vehicular Technology, 2016Co-Authors: Bo Liu, Haibo Zhou, Hao Cai, Lin GuiAbstract:Neighbor discovery is a crucial step in the initialization of wireless ad hoc networks. When directional antennas are used, this process becomes more challenging since two neighboring nodes must be in transmit and receive states, respectively, pointing their antennas to each other simultaneously. Most of the proposed neighbor discovery algorithms only consider the Synchronous System and cannot work efficiently in the aSynchronous environment. However, aSynchronous neighbor discovery algorithms are more practical and offer many potential advantages. In this paper, we first analyze a one-way handshake-based aSynchronous neighbor discovery algorithm by introducing a mathematical model named “Problem of Coloring Balls.” Then, we extend it to a hybrid aSynchronous algorithm that leads to a 24.4% decrease in the expected time of neighbor discovery. Compared with the Synchronous algorithms, the aSynchronous algorithms require approximately twice the time to complete the neighbor discovery process. Our proposed hybrid aSynchronous algorithm performs better than both the two-way Synchronous algorithm and the two-way aSynchronous algorithm. We validate the practicality of our proposed aSynchronous algorithms by OPNET simulations.
