ALBERT

Description: It is generally accepted that populations are useful for the global exploration of multi-modal optimisation problems. Indeed, several theoretical results are available showing such advantages over single-trajectory search heuristics. In this paper we provide evidence that evolving populations via crossover and mutation may also benefit the optimisation time for hillclimbing unimodal functions. In particular, we prove bounds on the expected runtime of the standard ($$mu +1$$ μ + 1 ) GA for OneMax that are lower than its unary black box complexity and decrease in the leading constant with the population size up to $$mu =oleft( sqrt{log n} ight) $$ μ = o log n . Our analysis suggests that the optimal mutation strategy is to flip two bits most of the time. To achieve the results we provide two interesting contributions to the theory of randomised search heuristics: (1) A novel application of drift analysis which compares absorption times of different Markov chains without defining an explicit potential function. (2) The inversion of fundamental matrices to calculate the absorption times of the Markov chains. The latter strategy was previously proposed in the literature but to the best of our knowledge this is the first time is has been used to show non-trivial bounds on expected runtimes.

Description: Given two strings S and T, each of length at most n, the longest common substring (LCS) problem is to find a longest substring common to S and T. This is a classical problem in computer science with an $$mathcal {O}(n)$$ O ( n ) -time solution. In the fully dynamic setting, edit operations are allowed in either of the two strings, and the problem is to find an LCS after each edit. We present the first solution to the fully dynamic LCS problem requiring sublinear time in n per edit operation. In particular, we show how to find an LCS after each edit operation in $$ilde{mathcal {O}}(n^{2/3})$$ O ~ ( n 2 / 3 ) time, after $$ilde{mathcal {O}}(n)$$ O ~ ( n ) -time and space preprocessing. This line of research has been recently initiated in a somewhat restricted dynamic variant by Amir et al. [SPIRE 2017]. More specifically, the authors presented an $$ilde{mathcal {O}}(n)$$ O ~ ( n ) -sized data structure that returns an LCS of the two strings after a single edit operation (that is reverted afterwards) in $$ilde{mathcal {O}}(1)$$ O ~ ( 1 ) time. At CPM 2018, three papers (Abedin et al., Funakoshi et al., and Urabe et al.) studied analogously restricted dynamic variants of problems on strings; specifically, computing the longest palindrome and the Lyndon factorization of a string after a single edit operation. We develop dynamic sublinear-time algorithms for both of these problems as well. We also consider internal LCS queries, that is, queries in which we are to return an LCS of a pair of substrings of S and T. We show that answering such queries is hard in general and propose efficient data structures for several restricted cases.

Description: In the classic k -center problem, we are given a metric graph, and the objective is to select k nodes as centers such that the maximum distance from any vertex to its closest center is minimized. In this paper, we consider two important generalizations of k -center, the matroid center problem and the knapsack center problem. Both problems are motivated by recent content distribution network applications. Our contributions can be summarized as follows: (1) We consider the matroid center problem in which the centers are required to form an independent set of a given matroid. We show this problem is NP-hard even on a line. We present a 3-approximation algorithm for the problem on general metrics. We also consider the outlier version of the problem where a given number of vertices can be excluded as outliers from the solution. We present a 7-approximation for the outlier version. (2) We consider the (multi-)knapsack center problem in which the centers are required to satisfy one (or more) knapsack constraint(s). It is known that the knapsack center problem with a single knapsack constraint admits a 3-approximation. However, when there are at least two knapsack constraints, we show this problem is not approximable at all. To complement the hardness result, we present a polynomial time algorithm that gives a 3-approximate solution such that one knapsack constraint is satisfied and the others may be violated by at most a factor of \(1+\epsilon \) . We also obtain a 3-approximation for the outlier version that may violate the knapsack constraint by \(1+\epsilon \) .

Description: We design a succinct data structure for representing a poset that, given two elements, can report whether one precedes the other in constant time. This is equivalent to succinctly representing the transitive closure graph of the poset, and we note that the same method can also be used to succinctly represent the transitive reduction graph. For an n element poset, the data structure occupies \(n^2/4 + o(n^2)\) bits in the worst case. Furthermore, a slight extension to this data structure yields a succinct oracle for reachability in arbitrary directed graphs. Thus, using no more than a quarter of the space required to represent an arbitrary directed graph, reachability queries can be supported in constant time. We also consider the operation of listing all the successors or predecessors of a given element, and show how to do this in constant time per element reported using a slightly modified version of our succinct data structure.

Description: We consider a graph observability problem: how many edge colors are needed for an unlabeled graph so that an agent, walking from node to node, can uniquely determine its location from just the observed color sequence of the walk? Specifically, let G ( n ,  d ) be an edge-colored subgraph of d -dimensional (directed or undirected) lattice of size \(n^d = n \times n \times \cdots \times n\) . We say that G ( n ,  d ) is t -observable if an agent can uniquely determine its current position in the graph from the color sequence of any t -dimensional walk, where the dimension is the number of different directions spanned by the edges of the walk. A walk in an undirected lattice G ( n ,  d ) has dimension between 1 and d , but a directed walk can have dimension between 1 and 2 d because of two different orientations for each axis. We derive bounds on the number of colors needed for t -observability. Our main result is that \(\varTheta (n^{d/t})\) colors are both necessary and sufficient for t -observability of G ( n ,  d ), where d is considered a constant. This shows an interesting dependence of graph observability on the ratio between the dimension of the lattice and that of the walk. In particular, the number of colors for full-dimensional walks is \(\varTheta (n^{1/2})\) in the directed case, and \(\varTheta (n)\) in the undirected case, independent of the lattice dimension. All of our results extend easily to non-square lattices: given a lattice graph of size \(N = n_1 \times n_2 \times \cdots \times n_d\) , the number of colors for t -observability is \(\varTheta (\root t \of {N})\) .

Description: In this paper, a comprehensive comparison analysis in terms of outage probability and average symbol error ratio (SER) is presented for cooperative cognitive multiple-input and multiple-output (CC-MIMO) multiuser systems with amplify-and-forward (AF) protocol. Specially, we consider two scenarios where the CC-MIMO multiuser systems have the perfect and imperfect channel state information (CSI). The CC-MIMO multiuser systems consist of one multi-antenna source, one single-antenna relay, and multiple multi-antenna destinations. At the secondary source and destinations, the maximal ratio transmission (MRT) and maximal ratio combining (MRC) are employed, respectively. For such CC-MIMO multiuser systems, we first obtain the exact closed-form expressions of outage probability under the two cases where the CC-MIMO multiuser systems have the perfect and imperfect CSI. Then, to reduce the implementation complexity, the tight lower bounds of outage probability and average SER are derived. Finally, to obtain insight, by using the high signal-to-noise ratio (SNR) approximation, the asymptotic estimations of outage probability are achieved. The numerical results show that the derivations are agreed with the simulations, which validate our derivations. At the same time, the results show that, for the systems without perfect CSI, the achievable diversity order reduces to one, regardless of the number of antennas at the cognitive source and destinations as well as the number of the cognitive destinations. Nevertheless, these key parameters affect the coding gain of the CC-MIMO multiuser systems. When the systems have the perfect CSI (or without feedback delay), the achievable diversity gain is determined by the minimum between the number of source’s antennas and the product of the number of destinations and the number of destination’s antennas. For the effect of PU’s parameters, our results indicate that primary systems only affect the coding gain but not the diversity gain.

Description: We revisit the matrix problems sparse null space and matrix sparsification , and show that they are equivalent. We then proceed to seek algorithms for these problems: we prove the hardness of approximation of these problems, and also give a powerful tool to extend algorithms and heuristics for sparse approximation theory to these problems.

Description: We introduce Planar Disjoint Paths Completion , a completion counterpart of the Disjoint Paths problem, and study its parameterized complexity. The problem can be stated as follows: given a, not necessarily connected, plane graph G ,  k pairs of terminals, and a face F of G ,  find a minimum-size set of edges, if one exists, to be added inside F so that the embedding remains planar and the pairs become connected by k disjoint paths in the augmented network. Our results are twofold: first, we give an upper bound on the number of necessary additional edges when a solution exists. This bound is a function of k , independent of the size of G . Second, we show that the problem is fixed-parameter tractable, in particular, it can be solved in time \(f(k)\cdot n^{2}\) .

Description: We prove that in a graph with n vertices, induced chordal and interval subgraphs with the maximum number of vertices can be found in time \(\mathcal {O}(2^{\lambda n})\) for some \(\lambda 〈1\) . These are the first algorithms breaking the trivial \(2^n n^{\mathcal {O}(1)}\) bound of the brute-force search for these problems.

Description: We investigate the effect of limiting the number of reserve prices on the revenue in a probabilistic single item auction. In the model considered, bidders compete for an impression drawn from a known distribution of possible types. The auction mechanism sets up to \(\ell \) reserve prices, and each impression type is assigned the highest reserve price lower than the valuation of some bidder for it. The bidder proposing the highest bid for an arriving impression gets it provided his bid is at least the corresponding reserve price, and pays the maximum between the reserve price and the second highest bid. Since the number of impression types may be huge, we consider the revenue \(R_{\ell }\) that can be ensured using only \(\ell \) reserve prices. Our main results are tight lower bounds on \(R_{\ell }\) for the cases where the impressions are drawn from the uniform or a general probability distribution.

Description: To reduce the energy cost of underwater acoustic sensor networks (UWSNs), the duty cycle (i.e., periodic wake-up and sleep) concept has been used in several medium access control (MAC) protocols. Although these protocols are energy efficient, they sacrifice bandwidth utilization, which leads to lower transmission rate. In order to solve this problem, asynchronous duty cycle with network-coding Asynchronous Duty Cycle with Network-Coding MAC (ADCNC-MAC) is proposed. It contains initialization of the MAC protocol phase and data transmission phase. In the first phase, we use an asynchronous duty cycle to find a rendezvous time for exchanging data. A strategy to select network coder nodes is presented to confirm the number of network coder nodes and distribution in the network coder layer. In the data transmission phase, the network coder nodes transmit using the proposed network-coding-based algorithm and a higher volume of packet will be transmitted to the Sink with the same number of transmissions. Simulation results show that ADCNC-MAC achieves higher power efficiency, improves packet delivery ratio (PDR), and network throughput.

Description: The possibility of having information access anytime and anywhere has caused a huge increase of the popularity of wireless networks. Requirements of users and owners have been ever-increasing. However, concerns about the potential health impact of exposure to radio frequency (RF) sources have arisen and are getting accounted for in wireless network planning. In addition to adequate coverage and reduced human exposure, the installation cost of the wireless network is also an important criterion in the planning process. In this paper, a hybrid algorithm is used to optimize indoor wireless network planning while satisfying three demands: maximum coverage, minimal full installation cost (cabling, cable gutters, drilling holes, labor, etc.), and minimal human exposure. For the first time, wireless indoor networks are being optimized based on these advanced and realistic conditions. The algorithm is investigated for three scenarios and for different configurations. The impact of different exposure requirements and cost scenarios is assessed.

Description: Physical transceiver implementations for wireless communication systems usually suffer from transmit-radio frequency (Tx-RF) and receiver-RF (Rx-RF) impairments. In this paper, we aim to design efficient coordinated beamforming for multicell multiuser multi-antenna systems by fully taking into account the residual transceiver impairments. Our design objectives include both spectral efficiency and energy efficiency. In particular, we first derive the closed-form expression of the mean square error (MSE) which includes the impact of transceiver impairments. Based on that, we propose an alternating optimization algorithm to solve the coordinated multicell beamforming problems with the goal of minimizing the worst user MSE, and the sum MSE. Then, by exploiting the relationship between the minimum mean square error (MMSE) and the achievable rate, we develop a new algorithm to address the sum rate maximization problem. This approach is further generalized to solve the more intractable energy efficiency optimization problem. We prove that all the proposed iterative algorithms guarantee to converge to a stationary point. Numerical results show that our proposed schemes achieve a better performance than conventional coordinated beamforming algorithms that were designed ignoring the transceiver impairments.

Description: The new dual-pivot Quicksort by Vladimir Yaroslavskiy—used in Oracle’s Java runtime library since version 7—features intriguing asymmetries. They make a basic variant of this algorithm use less comparisons than classic single-pivot Quicksort. In this paper, we extend the analysis to the case where the two pivots are chosen as fixed order statistics of a random sample. Surprisingly, dual-pivot Quicksort then needs more comparisons than a corresponding version of classic Quicksort, so it is clear that counting comparisons is not sufficient to explain the running time advantages observed for Yaroslavskiy’s algorithm in practice. Consequently, we take a more holistic approach and give also the precise leading term of the average number of swaps, the number of executed Java Bytecode instructions and the number of scanned elements, a new simple cost measure that approximates I/O costs in the memory hierarchy. We determine optimal order statistics for each of the cost measures. It turns out that the asymmetries in Yaroslavskiy’s algorithm render pivots with a systematic skew more efficient than the symmetric choice. Moreover, we finally have a convincing explanation for the success of Yaroslavskiy’s algorithm in practice: compared with corresponding versions of classic single-pivot Quicksort, dual-pivot Quicksort needs significantly less I/Os, both with and without pivot sampling.

Description: In this paper, we consider the Unsplittable (hard) Capacitated Facility Location Problem (UCFLP) with uniform capacities and present new approximation algorithms for it. This problem is a generalization of the classical facility location problem where each facility can serve at most u units of demand and each client must be served by exactly one facility. This problem is motivated by its applications in many practical problems including supply chain problems of indivisible goods (Verter in Foundations of location analysis, chapter 2. International series in operations research and management science. Springer, Berlin, 2011 ) and the assignment problem in the content distribution networks (Bateni and Hajiaghayi in Proceedings of the nineteenth annual ACM-SIAM symposium on discrete algorithms, pp 805–814, 2009 ). While there are several approximation algorithms for the soft capacitated version of this problem (in which one can open multiple copies of each facility) or the splittable version (in which the demand of each client can be divided to be served by multiple open facilities), there are very few results for the UCFLP. It is known that it is NP-hard to approximate this problem within any factor without violating the capacities. So we consider bicriteria \((\alpha ,\beta )\) -approximations where the algorithm returns a solution whose cost is within factor \(\alpha \) of the optimum and violates the capacity constraints within factor \(\beta \) . Shmoys et al. (Proceedings of the twenty-ninth annual ACM symposium on theory of computing, pp 265–274, 1997 ) were the first to consider this problem and gave a (9, 4)-approximation. Later results imply ( O (1), 2)-approximations, however, no constant factor approximation is known with capacity violation of less than 2. We present a framework for designing bicriteria approximation algorithms for this problem and show two new approximation algorithms with factors (9, 3 / 2) and (29.315, 4 / 3). These are the first algorithms with constant approximation in which the violation of capacities is below 2. The heart of our algorithm is a reduction from the UCFLP to a restricted version of the problem. One feature of this reduction is that any \((O(1),1+{\epsilon })\) -approximation for the restricted version implies an \((O(1),1+{\epsilon })\) -approximation for the UCFLP and we believe our techniques might be useful towards finding such approximations or perhaps \((f({\epsilon }),1+{\epsilon })\) -approximation for the UCFLP for some function f . In addition, we present a quasi-polynomial time \((1+\epsilon ,1+\epsilon )\) -approximation for the (uniform) UCFLP in Euclidean metrics, for any constant \({\epsilon }〉0\) .

Description: Network coding is an emerging technique known to improve the network performance in many aspects. In Vehicular Ad-hoc Networks (VANET), the bandwidth is considered to be one of the most important network resources. In this paper, we propose a network coding technique to improve the bandwidth utilization for non-safety applications in VANET. In a scenario where there are two sources broadcasting the data into the same area at the same time, the relay will use the network coding technique to decrease the number of rebroadcasting events and the consumption of the bandwidth, However, a fundamental problem for the relay when it receives a packet, is whether to wait for a coding opportunity and save the bandwidth or send the packet directly and reduce the delay. In order to address such tradeoff, we introduce two versions of our protocol, namely buffer size control scheme (BSCS) and time control scheme (TCS); by both versions we aim to control the delay that is experienced by the packet at each hop, while achieving better bandwidth utilization.Up to 38 % improvement in the bandwidth utilization has been recorded, and both schemes have shown a considerable amount of control on the imposed delay.

Description: Long-Term Evolution (LTE) was implemented to fulfill and satisfy users’ needs as well as their demands for an improvised, fast and efficient Quality of service (QoS). A minimal aggregate of waiting time in return would give users a better Quality of experience (QoE). Real-time service packet scheduling is an important process in allocating resources to users. An efficient packet scheduling scheme will be able to cater fairly and efficiently to its users in the LTE network. Hence, studies are performed focusing on real-time traffic which includes video as well as Voice over Internet Protocol (VoIP) transmissions. In this work, the existing exponential rule (EXP rule) is utilized to benchmark our proposed packet scheduling techniques so that we are able to further evaluate the scheduling performance. In response to the increasing likelihood of losing packets in the EXP rule’s algorithm and maximizing the throughput rate, several schemes have been experimented with. The proposed schemes include 1) simplified EXP rule (sEXP Rule), 2) modified EXP rule (mEXP Rule), 3) EXP rule with maximum throughput (MT) (EXP_MT Rule), and 4) enhanced EXP rule with MT (E2M). By adding MT as a weight to the EXP rule, the throughput is maximized, thus providing higher throughput rates for real-time and non-real-time traffic. The simulation results show that the sEXP rule has a better performance in throughput, packet loss rate (PLR), and spectral efficiency for video traffic. Aside from this, our proposed E2M rule performs better than the benchmark EXP rule and outperforms the other proposed schemes, as well. It is observed that the E2M rule has better QoS support for real-time transmission in terms of delay, packet loss, throughput and spectral efficiency, within the LTE network. Hence, our proposed E2M rule is an enhancement of the benchmark EXP rule, which is commonly used in LTE packet scheduling.

Description: A commonly studied means of parameterizing graph problems is the deletion distance from triviality (Guo et al., Parameterized and exact computation, Springer, Berlin, pp. 162–173, 2004 ), which counts vertices that need to be deleted from a graph to place it in some class for which efficient algorithms are known. In the context of graph isomorphism, we define triviality to mean a graph with maximum degree bounded by a constant, as such graph classes admit polynomial-time isomorphism tests. We generalise deletion distance to a measure we call elimination distance to triviality, based on elimination trees or tree-depth decompositions. We establish that graph canonisation, and thus graph isomorphism, is \(\mathsf {FPT}\) when parameterized by elimination distance to bounded degree, extending results of Bouland et al. (Parameterized and exact computation, Springer, Berlin, pp. 218–230, 2012 ).

Description: Recent advances in drift analysis have given us better and better tools for understanding random processes, including the run time of randomized search heuristics. In the setting of multiplicative drift we do not only have excellent bounds on the expected run time, but also more general results showing the strong concentration of the run time. In this paper we investigate the setting of additive drift under the assumption of strong concentration of the “step size” of the process. Under sufficiently strong drift towards the goal we show a strong concentration of the hitting time. In contrast to this, we show that in the presence of small drift a Gambler’s-Ruin-like behavior of the process overrides the influence of the drift, leading to a maximal movement of about \(\sqrt{t}\) steps within t iterations. Finally, in the presence of sufficiently strong negative drift the hitting time is superpolynomial with high probability; this corresponds to the well-known Negative Drift Theorem.

Description: In delay tolerant networks (DTNs), the network may not be fully connected at any instant of time, but connections occurring between nodes at different times make the network connected through the entire time continuum. In such a case, traditional routing methods fail to operate because there are no contemporaneous end-to-end paths between sources and destinations. This study examines the routing in DTNs where connections arise in a periodic nature. We analyze various levels of periodicity in order to meet the requirements of different network models. We propose different routing algorithms for different kinds of periodic connections. Our proposed routing methods guarantee the earliest delivery time and minimum hop-count, simultaneously. We evaluate our routing schemes via extensive simulation experiments and compare them to some other popular routing approaches proposed for DTNs. Our evaluations show the feasibility and effectiveness of our schemes as viable routing methods for delay tolerant networks.

Description: Due to rapid developments in mobile technology as well as various multimedia features like messaging, browsing, and streaming, user-created mobile contents are increasing, both in terms of quantity and quality, and at the same time are shared in real time. To get into step with such movements, new content-centric networking (CCN) has appeared. However, CCN has not taken the effect of consumer device movements into consideration. So, this paper proposes a partial path extension scheme to provide lower communication overhead, shorter download time, and lower network resource consumption in mobile consumer environments.

Description: Binets and trinets are phylogenetic networks with two and three leaves, respectively. Here we consider the problem of deciding if there exists a binary level-1 phylogenetic network displaying a given set  \(\mathbb {T}\) of binary binets or trinets over a taxon set  X , and constructing such a network whenever it exists. We show that this is NP-hard for trinets but polynomial-time solvable for binets. Moreover, we show that the problem is still polynomial-time solvable for inputs consisting of binets and trinets as long as the cycles in the trinets have size three. Finally, we present an  \(O(3^{|X|} poly(|X|))\) time algorithm for general sets of binets and trinets. The latter two algorithms generalise to instances containing level-1 networks with arbitrarily many leaves, and thus provide some of the first supernetwork algorithms for computing networks from a set of rooted phylogenetic networks.

Description: We consider stochastic versions of OneMax and LeadingOnes and analyze the performance of evolutionary algorithms with and without populations on these problems. It is known that the ( \(1+1\) ) EA on OneMax performs well in the presence of very small noise, but poorly for higher noise levels. We extend these results to LeadingOnes and to many different noise models, showing how the application of drift theory can significantly simplify and generalize previous analyses. Most surprisingly, even small populations (of size \(\varTheta (\log n)\) ) can make evolutionary algorithms perform well for high noise levels, well outside the abilities of the ( \(1+1\) ) EA. Larger population sizes are even more beneficial; we consider both parent and offspring populations. In this sense, populations are robust in these stochastic settings.

Description: Since Tinhofer proposed the MinGreedy algorithm for maximum cardinality matching in 1984, several experimental studies found the randomized algorithm to perform excellently for various classes of random graphs and benchmark instances. In contrast, only few analytical results are known. We show that MinGreedy cannot improve on the trivial approximation ratio of  \(\frac{1}{2}\) whp., even for bipartite graphs. Our hard inputs seem to require a small number of high-degree nodes. This motivates an investigation of greedy algorithms on graphs with maximum degree  \(\varDelta \) : we show that  MinGreedy achieves a  \({\frac{{\varDelta }-1}{2{\varDelta }-3}} \) -approximation for graphs with  \({\varDelta } {=} 3\) and for \(\varDelta \) -regular graphs, and a guarantee of  \({\frac{{\varDelta }-1/2}{2{\varDelta }-2}} \) for graphs with maximum degree  \({\varDelta } \) . Interestingly, our bounds even hold for the deterministic MinGreedy that breaks all ties arbitrarily. Moreover, we investigate the limitations of the greedy paradigm, using the model of priority algorithms introduced by Borodin, Nielsen, and Rackoff. We study deterministic priority algorithms and prove a  \({\frac{{\varDelta }-1}{2{\varDelta }-3}}\) -inapproximability result for graphs with maximum degree  \({\varDelta } \) ; thus, these greedy algorithms do not achieve a  \(\frac{1}{2} {+} \varepsilon \) -approximation and in particular the  \(\frac{2}{3}\) -approximation obtained by the deterministic MinGreedy for  \({\varDelta } {=} 3\) is optimal in this class. For  k -uniform hypergraphs we show a tight  \(\frac{1}{k}\) -inapproximability bound. We also study fully randomized priority algorithms and give a  \(\frac{5}{6}\) -inapproximability bound. Thus, they cannot compete with matching algorithms of other paradigms.

Description: We discuss how string sorting algorithms can be parallelized on modern multi-core shared memory machines. As a synthesis of the best sequential string sorting algorithms and successful parallel sorting algorithms for atomic objects, we first propose string sample sort. The algorithm makes effective use of the memory hierarchy, uses additional word level parallelism, and largely avoids branch mispredictions. Then we focus on NUMA architectures, and develop parallel multiway LCP-merge and -mergesort to reduce the number of random memory accesses to remote nodes. Additionally, we parallelize variants of multikey quicksort and radix sort that are also useful in certain situations. As base-case sorter for LCP-aware string sorting we describe sequential LCP-insertion sort which calculates the LCP array and accelerates its insertions using it. Comprehensive experiments on five current multi-core platforms are then reported and discussed. The experiments show that our parallel string sorting implementations scale very well on real-world inputs and modern machines.

Description: In modern mobile telecommunications, shadow fading has to be modeled by a two-dimensional (2D) correlated random variable since shadow fading may present both cross-correlation and spatial correlation due to the presence of similar obstacles during the propagation. In this paper, 2D correlated random shadowing is generated based on the multi-resolution frequency domain ParFlow (MR-FDPF) model. The MR-FDPF model is a 2D deterministic radio propagation model, so a 2D deterministic shadowing can be firstly extracted from it. Then, a 2D correlated random shadowing can be generated by considering the extracted 2D deterministic shadowing to be a realization of it. Moreover, based on the generated 2D correlated random shadowing, a complete 2D semi-deterministic path loss model can be proposed. The proposed methodology of this paper can be implemented into system-level simulators where it will be very useful due to its ability to generate realistic shadow fading.

Description: Stochastic boolean function evaluation (SBFE) is the problem of determining the value of a given boolean function f on an unknown input x , when each bit \(x_i\) of x can only be determined by paying a given associated cost \(c_i\) . Further, x is drawn from a given product distribution: for each \(x_i\) , \(\mathbf{Pr}[x_i=1] = p_i\) and the bits are independent. The goal is to minimize the expected cost of evaluation. In this paper, we study the complexity of the SBFE problem for classes of DNF formulas. We consider both exact and approximate versions of the problem for subclasses of DNF, for arbitrary costs and product distributions, and for unit costs and/or the uniform distribution.

Description: The basis of vehicular ad hoc networks (VANETs) is the exchange of data between entities, and making a decision on received data/event is usually based on information provided by other entities. Many researchers utilize the concept of trust to assess the trustworthiness of the received data. Nevertheless, the lack of a review to sum up the best available research on specific questions on trust management in vehicular ad hoc networks is sensible. This paper presents a systematic literature review to provide comprehensive and unbiased information about various current trust conceptions, proposals, problems, and solutions in VANETs to increase quality of data in transportation. For the purpose of the writing of this paper, a total of 111 articles related to the trust model in VANETs published between 2005 and 2014 were extracted from the most relevant scientific sources (IEEE Computer Society, ACM Digital Library, Springer Link, Science Direct, and Wiley Online Library). Finally, ten articles were eventually analyzed due to several reasons such as relevancy and comprehensiveness of discussion presented in the articles. Using the systematic method of review, this paper succeeds to reveal the main challenges and requirements for trust in VANETs and future research within this scope.

Description: Hardware imperfections can significantly reduce the performance of full-duplex wireless systems by introducing non-idealities and random effects that make it challenging to fully suppress self-interference. Previous research has mostly focused on analysing the impact of hardware imperfections on full-duplex systems, based on simulations and theoretical models. In this paper, we follow a measurement-based approach to experimentally identify and isolate these hardware imperfections leading to residual self-interference in full-duplex nodes. Our measurements show the important role of images arising from in-phase and quadrature (IQ) imbalance in the transmitter and receiver mixers. We also observe baseband non-linearities in the digital-to-analog converters (DAC), which can introduce strong harmonic components in the transmitted signal that have not been considered previously. A corresponding general mathematical model to suppress these components of the self-interference signal arising from the hardware non-idealities is developed from the observations and measurements. Results from a 10 MHz bandwidth full-duplex system, operating at 2.48 GHz, show that up to 13 dB additional suppression, relative to state-of-the-art implementations, can be achieved by jointly compensating for IQ imbalance and DAC non-linearities.

Description: Recent years have witnessed the increasing efforts toward making architecture standardization for the secured wireless mobile ad hoc networks. In this scenario when a node actively utilizes the other node resources for communicating and refuses to help other nodes in their transmission or reception of data, it is called a selfish node. As the entire mobile ad hoc network (MANETs) depends on cooperation from neighboring nodes, it is very important to detect and eliminate selfish nodes from being part of the network. In this paper, token-based umpiring technique (TBUT) is proposed, where every node needs a token to participate in the network and the neighboring nodes act as umpire. This proposed TBUT is found to be very efficient with a reduced detection time and less overhead. The security analysis and experimental results have shown that TBUT is feasible for enhancing the security and network performance of real applications.

Description: In this paper, multiple device-to-device (D2D) communication underlaying cellular multiuser multiple inputs multiple outputs (MU-MIMO) systems is investigated. This type of communication can improve spectral efficiency to address future demand, but interference management, user clustering, and resource allocation are three key problems related to resource sharing. Interference alignment (IA) is proposed to better mitigate in-cluster interference compared with a multiplex scheme, and user clustering and resource allocation are jointly investigated using binary-integer programming. In addition to an exhaustive search for a maximum throughput, we propose a two-step suboptimal algorithm by reducing the search space and applying branch-and-bound searching (BBS). To further obtain a good trade-off between performance and complexity, we propose a novel algorithm based on distance-constrained criteria for user clustering. The simulation results show that the IA and multiplex schemes acquiring user clustering gains outperform the orthogonal scheme without user clustering. Besides, the proposed two-step and location-based algorithms achieve little losses compared with the optimal algorithm under low complexities.

Description: When a wireless sensor network (WSN) is employed to monitor environmental data, efficient energy usage is demanded so that the WSN lifetime can be extended. In this context, we propose a distributed energy con...

Description: Recent years, information spreading under the environment of wireless communication has attracted increasing interest. Microblog platform on mobile terminals, as one product of wireless communication, facilita...

Description: Internet of Thing (IoT) or also referred to as IP-enabled wireless sensor network (IP-WSN) has become a rich area of research. This is due to the rapid growth in a wide spectrum of critical application domains...

Description: Throughput imbalances among contending flows are known to occur when any carrier sense multiple access (CSMA)-based protocol is employed in multi-hop wireless networks. These imbalances may vary from slight di...

Description: Interval graphs are intersection graphs of closed intervals of the real-line. The well-known computational problem, called recognition , asks whether an input graph G can be represented by closed intervals, i.e., whether G is an interval graph. There are several linear-time algorithms known for recognizing interval graphs, the oldest one is by Booth and Lueker (J Comput Syst Sci 13:335–379, 1976 ) based on PQ-trees. In this paper, we study a generalization of recognition, called partial representation extension . The input of this problem consists of a graph G with a partial representation \({{{\mathcal {R}}}}'\) fixing the positions of some intervals. The problem asks whether it is possible to place the remaining interval and create an interval representation \({{{\mathcal {R}}}}\) of the entire graph G extending \({{{\mathcal {R}}}}'\) . We generalize the characterization of interval graphs by Fulkerson and Gross (Pac J Math 15:835–855, 1965 ) to extendible partial representations. Using it, we give a linear-time algorithm for partial representation extension based on a reordering problem of PQ-trees.

Description: In this paper, we investigate the coexistence of two technologies that have been put forward for the fifth generation (5G) of cellular networks, namely, network-assisted device-to-device (D2D) communications a...

Description: Cognitive radio networks (CRN), in their quest to become the preferred next-generation wireless communication paradigm, will depend heavily on their ability to efficiently manage the limited resources at their...

Description: Modern data management systems often need to deal with massive, dynamic and inherently distributed data sources. We collect the data using a distributed network, and at the same time try to maintain a global view of the data at a central coordinator using a minimal amount of communication. Such applications have been captured by the distributed monitoring model which has attracted a lot of attention in recent years. In this paper we investigate the monitoring of the entropy functions, which are very useful in network monitoring applications such as detecting distributed denial-of-service attacks. Our results improve the previous best results by Arackaparambil et al. in ICLP 1: 95–106 ( 2009 ). Our technical contribution also includes implementing the celebrated AMS sampling method (by Alon et al. in J Comput Syst Sci 58(1): 137–147 1999 ) in the distributed monitoring model, which could be of independent interest.

Description: By modulating the electric field induced to a human body, it is possible to transfer data wirelessly using the body as a transmission medium. This method is referred to as human body communication (HBC), which...

Description: In the Boundary Labeling problem, we are given a set of  n points, referred to as sites , inside an axis-parallel rectangle  R , and a set of  n pairwise disjoint rectangular labels that are attached to  R from the outside. The task is to connect the sites to the labels by non-intersecting rectilinear paths, so-called leaders , with at most one bend. In this paper, we study the Multi-Sided Boundary Labeling problem, with labels lying on at least two sides of the enclosing rectangle. We present a polynomial-time algorithm that computes a crossing-free leader layout if one exists. So far, such an algorithm has only been known for the cases in which labels lie on one side or on two opposite sides of  R (here a crossing-free solution always exists). The case where labels may lie on adjacent sides is more difficult. We present efficient algorithms for testing the existence of a crossing-free leader layout that labels all sites and also for maximizing the number of labeled sites in a crossing-free leader layout. For two-sided boundary labeling with adjacent sides, we further show how to minimize the total leader length in a crossing-free layout.

Description: In this paper we consider the problem of the strict self-assembly of infinite fractals within tile self-assembly. In particular, we provide tile assembly algorithms for the assembly of a Sierpinski triangle and the discrete Sierpinski carpet within a class of models we term the h - handed assembly model ( h -HAM), which generalizes the 2-HAM to allow up to h assemblies to combine in a single assembly step. Despite substantial consideration, no purely growth self-assembly model has yet been shown to strictly assemble an infinite fractal without significant modification to the fractal shape. In this paper we not only achieve this, but in the case of the Sierpinski carpet are able to achieve it within the 2-HAM, one of the most well studied tile assembly models in the literature. Our specific results are as follows: We provide a 6-HAM construction for a Sierpinski triangle that works at scale factor 1, 30 tile types, and assembles the fractal in a near perfect way in which all intermediate assemblies are finite-sized iterations of the recursive fractal. We further assemble a Sierpinski triangle within the 3-HAM at scale factor 3 and 990 tile types. For the Sierpinski carpet, we present a 2-HAM result that works at scale factor 3 and uses 1216 tile types. We further include analysis showing that the aTAM is incapable of strictly assembling the Sierpinski triangle considered in this paper, and that multiple hands are needed for the near-perfect assembly of a Sierpinski triangle and the Sierpinski carpet.

Description: We consider k -Facility Location games, where n strategic agents report their locations on the real line and a mechanism maps them to k facilities. Each agent seeks to minimize his connection cost, given by a nonnegative increasing function of his distance to the nearest facility. Departing from previous work, that mostly considers the identity cost function, we are interested in mechanisms without payments that are (group) strategyproof for any given cost function, and achieve a good approximation ratio for the social cost and/or the maximum cost of the agents. We present a randomized mechanism, called Equal Cost , which is group strategyproof and achieves a bounded approximation ratio for all k and n , for any given concave cost function. The approximation ratio is at most 2 for Max Cost and at most n for Social Cost . To the best of our knowledge, this is the first mechanism with a bounded approximation ratio for instances with \(k \ge 3\) facilities and any number of agents. Our result implies an interesting separation between deterministic mechanisms, whose approximation ratio for Max Cost jumps from 2 to unbounded when k increases from 2 to 3, and randomized mechanisms, whose approximation ratio remains at most 2 for all k . On the negative side, we exclude the possibility of a mechanism with the properties of Equal Cost for strictly convex cost functions. We also present a randomized mechanism, called Pick the Loser , which applies to instances with k facilities and only \(n = k+1\) agents. For any given concave cost function, Pick the Loser is strongly group strategyproof and achieves an approximation ratio of 2 for Social Cost .

Description: We give a deterministic #SAT algorithm for de Morgan formulas of size up to \(n^{2.63}\) , which runs in time \(2^{n-n^{{\varOmega }(1)}}\) . This improves upon the deterministic #SAT algorithm of Chen et al. (Proceedings of the twenty-ninth annual IEEE conference on computational complexity, 2014 ), which has similar running time but works only for formulas of size less than \(n^{2.5}\) . Our new algorithm is based on the shrinkage of de Morgan formulas under random restrictions, shown by Paterson and Zwick (Random Struct Algorithms 4(2):135–150, 1993 ). We prove a concentrated and constructive version of their shrinkage result. Namely, we give a deterministic polynomial-time algorithm that selects variables in a given de Morgan formula so that, with high probability over the random assignments to the chosen variables, the original formula shrinks in size, when simplified using a given deterministic polynomial-time formula-simplification algorithm.

Description: We consider Conditional random fields ( CRFs ) with pattern-based potentials defined on a chain. In this model the energy of a string (labeling) \(x_1\ldots x_n\) is the sum of terms over intervals [ i ,  j ] where each term is non-zero only if the substring \(x_i\ldots x_j\) equals a prespecified pattern w . Such CRFs can be naturally applied to many sequence tagging problems. We present efficient algorithms for the three standard inference tasks in a CRF, namely computing (i) the partition function, (ii) marginals, and (iii) computing the MAP. Their complexities are respectively \(O(\textit{nL})\) , \(O(\textit{nL} \ell _{\max })\) and \(O(\textit{nL} \min \{|D|,\log (\ell _{\max }\!+\!1)\})\) where L is the combined length of input patterns, \(\ell _{\max }\) is the maximum length of a pattern, and D is the input alphabet. This improves on the previous algorithms of Ye et al. (NIPS, 2009 ) whose complexities are respectively \(O(\textit{nL} |D|)\) , \(O\left( n |\varGamma | L^2 \ell _{\max }^2\right) \) and \(O(\textit{nL} |D|)\) , where \(|\varGamma |\) is the number of input patterns. In addition, we give an efficient algorithm for sampling, and revisit the case of MAP with non-positive weights.

Description: Estimating the number of triangles in graph streams using a limited amount of memory has become a popular topic in the last decade. Different variations of the problem have been studied, depending on whether the graph edges are provided in an arbitrary order or as incidence lists. However, with a few exceptions, the algorithms have considered insert-only streams. We present a new algorithm estimating the number of triangles in dynamic graph streams where edges can be both inserted and deleted. We show that our algorithm achieves better time and space complexity than previous solutions for various graph classes, for example sparse graphs with a relatively small number of triangles. Also, for graphs with constant transitivity coefficient, a common situation in real graphs, this is the first algorithm achieving constant processing time per edge. The result is achieved by a novel approach combining sampling of vertex triples and sparsification of the input graph. In the course of the analysis of the algorithm we present a lower bound on the number of pairwise independent 2-paths in general graphs which might be of independent interest. At the end of the paper we discuss lower bounds on the space complexity of triangle counting algorithms that make no assumptions on the structure of the graph.

Description: We consider the problems of finding optimal identifying codes, (open) locating-dominating sets and resolving sets (denoted Identifying Code , (Open) Open Locating-Dominating Set and Metric Dimension ) of an interval or a permutation graph. In these problems, one asks to distinguish all vertices of a graph by a subset of the vertices, using either the neighbourhood within the solution set or the distances to the solution vertices. Using a general reduction for this class of problems, we prove that the decision problems associated to these four notions are NP-complete, even for interval graphs of diameter 2 and permutation graphs of diameter 2. While Identifying Code and (Open) Locating-Dominating Set are trivially fixed-parameter-tractable when parameterized by solution size, it is known that in the same setting Metric Dimension is W [2]-hard. We show that for interval graphs, this parameterization of Metric Dimension is fixed-parameter-tractable.

Description: In network virtualization, one of its core challenges lies in how to map the virtual networks (VNs) to the shared substrate network (SN) that is managed by an infrastructure provider, termed as the virtual net...

Description: Recent years have witnessed major innovations in mobile crowdsourcing networks. For selfish participants, conventional methods resort to incentive mechanism design for resource utilization, which might overloo...

Description: Given a partition of an n element set into equivalence classes, we study the problem of assigning unique labels to these elements in order to support the query that asks whether the elements corresponding to two given labels belong to the same equivalence class. This has various applications including for testing whether two vertices are in the same connected component in an undirected graph or in the same strongly connected component in a directed graph. We consider the problem in several models. Concerning labeling schemes where we assign labels to elements and the query is to be answered just by examining the labels of the queried elements (without any extra space): if each vertex is required to have a unique label, then we show that a label space of \(\sum _{i=1}^n \lfloor {n \over i} \rfloor \) is necessary and sufficient. In other words, \(\lg n + \lg \lg n + O(1)\) bits of space are necessary and sufficient for representing each of the labels. This slightly strengthens the known lower bound and is in contrast to the known necessary and sufficient bound of \(\lceil \lg n \rceil \) for the label length, if each vertex need not get a unique label. Concerning succinct data structures for the problem when the n elements are to be uniquely assigned labels from label set \(\{1,\ldots , n\}\) , we first show that \(\varTheta (\sqrt{n})\) bits are necessary and sufficient to represent the equivalence class information. This space includes the space for implicitly encoding the vertex labels. We can support the query in such a structure in O (1) time in the standard word RAM model. We also develop a dynamic structure that uses \(O(\sqrt{n} \lg n)\) bits to support equivalence queries and unions in \(O(\lg n/\lg \lg n)\) worst case time or \(O(\alpha (n))\) expected amortized time where \(\alpha (n)\) is the inverse Ackermann function. Concerning succinct data structures for the problem when the n elements are to be uniquely assigned labels from label set \(\{1,\ldots , cn\}\) for any constant \(c 〉 1\) , we show that \(\varTheta (\lg n)\) bits are necessary and sufficient to represent the equivalence class information. Moreover, we can support the query in such a structure in O (1) time in the standard word RAM model. We believe that our work can trigger further work on tradeoffs between label space and auxiliary data structure space for other labeling problems.

Description: We perform a thorough study of various characteristics of the asynchronous push–pull protocol for spreading a rumor on Erdős–Rényi random graphs \(G_{n,p}\) , for any \(p〉c\ln (n)/n\) with \(c〉1\) . In particular, we provide a simple strategy for analyzing the asynchronous push–pull protocol on arbitrary graph topologies and apply this strategy to \(G_{n,p}\) . We prove tight bounds of logarithmic order for the total time that is needed until the information has spread to all nodes. Surprisingly, the time required by the asynchronous push–pull protocol is asymptotically almost unaffected by the average degree of the graph. Similarly tight bounds for Erdős–Rényi random graphs have previously only been obtained for the synchronous push protocol, where it has been observed that the total running time increases significantly for sparse random graphs. Finally, we quantify the robustness of the protocol with respect to transmission and node failures. Our analysis suggests that the asynchronous protocols are particularly robust with respect to these failures compared to their synchronous counterparts.

Description: We propose a one-shot (non-iterative) cooperative beamforming scheme for downlink multicell systems. Unlike previous non-iterative beamforming schemes, the proposed cooperative beamforming strives to balance m...

Description: Intra-vehicular wireless sensor network (IVWSN) enables the integration of the wireless sensor network technology into the vehicle architecture through either eliminating the wires between the existing sensors...

Description: We study connectivity relations among points, where the precise location of each input point lies in a region of uncertainty. We distinguish two fundamental scenarios under which uncertainty arises. In the favorable Best-Case Uncertainty , each input point can be chosen from a given set to yield the best possible objective value. In the unfavorable Worst-Case Uncertainty , the input set has worst possible objective value among all possible point locations, which are uncertain due, for example, to imprecise data. We consider these notions of uncertainty for the bottleneck spanning tree problem, giving rise to the following Best-Case Connectivity with Uncertainty problem: given a family of geometric regions, choose one point per region, such that the longest edge length of an associated geometric spanning tree is minimized. We show that this problem is NP-hard even for very simple scenarios in which the regions are line segments or squares. On the other hand, we give an exact solution for the case in which there are \(n+k\) regions, where k of the regions are line segments and n of the regions are fixed points. We then give approximation algorithms for cases where the regions are either all line segments or all unit discs. We also provide approximation methods for the corresponding Worst-Case Connectivity with Uncertainty problem: Given a set of uncertainty regions, find the minimal distance r such that for any choice of points, one per region, there is a spanning tree among the points with edge length at most r .

Description: We define the modular treewidth of a graph as its treewidth after contraction of modules. This parameter properly generalizes treewidth and is itself properly generalized by clique-width. We show that the number of satisfying assignments can be computed in polynomial time for CNF formulas whose incidence graphs have bounded modular treewidth. Our result generalizes known results for the treewidth of incidence graphs and is incomparable with known results for clique-width (or rank-width) of signed incidence graphs. The contraction of modules is an effective data reduction procedure. Our algorithm is the first one to harness this technique for #SAT. The order of the polynomial bounding the runtime of our algorithm depends on the modular treewidth of the input formula. We show that it is unlikely that this dependency can be avoided by proving that SAT is W[1]-hard when parameterized by the modular incidence treewidth of the given CNF formula.

Description: In a classical online network design problem, traffic requirements are gradually revealed to an algorithm. Each time a new request arrives, the algorithm has to satisfy it by augmenting the network under construction in a proper way (with no possibility of recovery). In this paper we study a natural generalization of online network design problems, where a fraction of the requests (the outliers ) can be disregarded. Now, each time a request arrives, the algorithm first decides whether to satisfy it or not, and only in the first case it acts accordingly. We cast three classical network design problems into this framework: (i) Online Steiner tree with outliers In this case a set of t terminals that belong to an n -node graph is presented, one at a time, to an algorithm. Each time a new terminal arrives, the algorithm can either discard or select it. In the latter case, the algorithm connects it to the Steiner tree under construction (initially consisting of a given root node). At the end of the process, at least k terminals must be selected. (ii) Online TSP with outliers This is the same problem as above, but with the Steiner tree replaced by a TSP tour. (iii) Online facility location with outliers In this case, we are also given a set of facility nodes, each one with an opening cost. Each time a terminal is selected, we have to connect it to some facility (and open that facility, if it is not already open). We focus on the known distribution model, where terminals are independently sampled from a given distribution. For all the above problems, we present bicriteria online algorithms that, for any constant \(\epsilon 〉0\) , select at least \((1-\epsilon )k\) terminals with high probability and pay in expectation \(O(\log ^2n)\) times more than the expected cost of the optimal offline solution (selecting k terminals). These upper bounds are complemented by inapproximability results for the case that one insists on selecting exactly k terminals, and by lower bounds including an \(\varOmega (\log n/\log \log n)\) lower bound for the case that the online algorithm is allowed to select \(\alpha \,k\) terminals only, for a sufficiently large constant \(\alpha \in (0,1)\) .

Description: A well known result in graph algorithms, due to Edmonds, states that given a digraph D and a positive integer \(\ell \) , we can test whether D contains \(\ell \) arc-disjoint out-branchings in polynomial time. However, if we ask whether there exists an out-branching and an in-branching which are arc-disjoint, then the problem becomes NP -complete. In fact, even deciding whether a digraph D contains an out-branching which is arc-disjoint from some spanning tree in the underlying undirected graph remains NP -complete. In this paper we formulate some natural optimization questions around these problems and initiate its study in the realm of parameterized complexity. More precisely, the problems we study are the following: Arc - Disjoint Branchings and Non - Disconnecting Out - Branching . In Arc - Disjoint Branchings ( Non - Disconnecting Out - Branching ), a digraph D and a positive integer k are given as input and the goal is to test whether there exist an out-branching and in-branching (respectively, a spanning tree in the underlying undirected graph) that differ on at least k arcs. We obtain the following results for these problems. Non - Disconnecting Out - Branching is fixed parameter tractable (FPT) and admits a linear vertex kernel. Arc - Disjoint Branchings is FPT on strong digraphs. The algorithm for Non - Disconnecting Out - Branching runs in time \(2^{\mathcal {O}(k)}n^{\mathcal {O}(1)}\) and the approach we use to obtain this algorithms seems useful in designing other moderately exponential time algorithms for edge/arc partitioning problems.

Description: We study the stable roommates problem in networks where players are embedded in a social context and may incorporate positive externalities into their decisions. Each player is a node in a social network and strives to form a good match with a neighboring player. We consider the existence, computation, and inefficiency of stable matchings from which no pair of players wants to deviate. We characterize prices of anarchy and stability, which capture the ratio of the total profit in the optimum matching over the total profit of the worst and best stable matching, respectively. When the benefit from a match (which we model by associating a reward with each edge) is the same for both players, we show that externalities can significantly improve the price of stability, while the price of anarchy remains unaffected. Furthermore, a good stable matching achieving the bound on the price of stability can be obtained in polynomial time. We extend these results to more general matching rewards, when players matched to each other may receive different benefits from the match. For this more general case, we show that network externalities (i.e., “caring about your friends”) can make an even larger difference and greatly reduce the price of anarchy. We show a variety of existence results and present upper and lower bounds on the prices of anarchy and stability for various structures of matching benefits. All our results on stable matchings immediately extend to the more general case of fractional stable matchings.

Description: We present the first general bounds on the mixing time of the Markov chain associated to the logit dynamics for wide classes of strategic games. The logit dynamics with inverse noise \(\beta \) describes the behavior of a complex system whose individual components act selfishly according to some partial (“noisy”) knowledge of the system, where the capacity of the agent to know the system and compute her best move is measured by parameter \(\beta \) . In particular, we prove nearly tight bounds for potential games and games with dominant strategies. Our results show that for potential games the mixing time is bounded by an exponential in \(\beta \) and in the maximum potential difference. Instead, for games with dominant strategies the mixing time cannot grow arbitrarily with \(\beta \) . Finally, we refine our analysis for a subclass of potential games called graphical coordination games, often used for modeling the diffusion of new technologies. We prove that the mixing time of the logit dynamics for these games can be upper bounded by a function that is exponential in the cutwidth of the underlying graph and in \(\beta \) . Moreover, we consider two specific and popular network topologies, the clique and the ring. For the clique, we prove an almost matching lower bound on the mixing time of the logit dynamics that is exponential in \(\beta \) and in the maximum potential difference, while for the ring we prove that the time of convergence of the logit dynamics to its stationary distribution is significantly shorter.

Description: Given a plane graph G (i.e., a planar graph with a fixed planar embedding and outer face) and a biconnected subgraph \(G^{\prime }\) with a fixed planar straight-line convex drawing, we consider the question whether this drawing can be extended to a planar straight-line drawing of G . We characterize when this is possible in terms of simple necessary conditions, which we prove to be sufficient. This also leads to a linear-time testing algorithm. If a drawing extension exists, one can be computed in the same running time.

Description: Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct ins...

Description: Cognitive radio sensor networks (CRSNs) are multi-channel-capable networks that inherit some of the challenges of traditional wireless sensor networks (WSNs), such as limited power source and hardware capacity...

Description: In this paper, we study an infrastructure-less public safety network (IPSN) where energy efficiency and reliability are critical requirements in the absence of cellular infrastructure, i.e., base stations and ...

Description: An improved triple-pulse high-power pulse-width modulation (HP-PWM) signal model is proposed to enhance the performance of current underwater sonar transmitter. The presented model is based on reducing the thi...

Description: Stream classification service (SCS) is a novel concept proposed in the newly released IEEE 802.11aa standard for robust audio and video streaming, particularly for graceful degradation of streaming quality dur...

Description: In order to improve the quality of multimedia communication and mobile users, the work efficiency of the cloud platform, the service-oriented mobile multimedia cooperative storing, and the delivery scheme were...

Description: Big data analytics (BDA) applications are a new category of software applications that process large amounts of data using scalable parallel processing infrastructure to obtain hidden value. Hadoop is the most...

Description: The rotor–router model , also called the Propp machine , was first considered as a deterministic alternative to the random walk. The edges adjacent to each node  v (or equivalently, the exit ports at  v ) are arranged in a fixed cyclic order, which does not change during the exploration. Each node  v maintains a port pointer   \(\pi _v\) which indicates the exit port to be adopted by an agent on the conclusion of the next visit to this node (the “next exit port”). The rotor–router mechanism guarantees that after each consecutive visit at the same node, the pointer at this node is moved to the next port in the cyclic order. It is known that, in an undirected graph  G with  m edges, the route adopted by an agent controlled by the rotor–router mechanism eventually forms an Euler tour based on arcs obtained via replacing each edge in  G by two arcs with opposite direction. The process of ushering the agent to an Euler tour is referred to as the lock-in problem . In Yanovski et al. (Algorithmica 37(3):165–186, 2003 ), it was proved that, independently of the initial configuration of the rotor–router mechanism in  G , the agent locks-in in time bounded by  \(2mD\) , where \(D\) is the diameter of  G . In this paper we examine the dependence of the lock-in time on the initial configuration of the rotor–router mechanism. Our analysis is performed in the form of a game between a player \({\mathcal {P}}\) intending to lock-in the agent in an Euler tour as quickly as possible and its adversary \({\mathcal {A}}\) with the counter objective. We consider all cases of who decides the initial cyclic orders and the initial values \(\pi _v\) . We show, for example, that if \({\mathcal {A}}\) provides its own port numbering after the initial setup of pointers by \({\mathcal {P}}\) , the worst-case complexity of the lock-in problem is \({\varTheta }(m\cdot \min \{\log m,D\})\) . We also investigate the robustness of the rotor–router graph exploration in presence of faults in the pointers \(\pi _v\) or dynamic changes in the graph. We show, for example, that after the exploration establishes an Eulerian cycle, if k edges are added to the graph, then a new Eulerian cycle is established within \(\mathcal {O}(km)\) steps.

Description: Owning to the high peak-to-average power ratio problem, the power efficiency of orthogonal-frequency-division-multiplexing (OFDM) systems is usually low. It deteriorates in millimeter wave systems in which the...

Description: Typically, site survey is an inevitable phase for WiFi fingerprint-based localization which is regarded as one of the most promising techniques for indoor localization. However, the site survey can cause poten...

Description: Power control (PC) is a key solution to enable spectrum sharing between secondary users (SUs) and primary users (PUs). However, previous research lacks sensing uncertainties for the status of PUs. In this arti...

Description: With the increasing demands of wireless communication, flexible, complex, and diversified wireless communication applications are required. However, the difficulty of enabling new wireless communication applic...

Description: Developments of wireless body area networks (WBANs) facilitate the pervasive health monitoring with mHealth applications. WBANs can support continuous health monitoring for the human body in convenience and hi...

Description: Wireless personal area networks (WPAN) and wireless local area networks (WLAN) based on IEEE 802.15.4 and 802.11 standards operate in overlapping unlicensed frequency bands; therefore, they create harmful inte...

Description: Consider the problem of selecting k items that maximize the value of a monotone submodular set function f , where f can be accessed using value queries. It is well known that polynomially many queries suffice in order to obtain an approximation ratio of \(1 - \frac{1}{e}\) . We consider a variation on this problem in which the value queries are required to be of uniform size: each queried set, like the desired solution itself, must contain k items. We show that polynomially many uniform size queries suffice in order to obtain an approximation ratio of \(\frac{1}{2}\) , and that an approximation ratio of \(\frac{1 + \epsilon }{2}\) requires a number of queries that is exponential in \(\epsilon k\) . For the interesting special case of coverage functions, we show that an approximation ratio strictly better than \(\frac{1}{2}\) is attainable with polynomially many uniform size queries. The “uniform size” requirement is motivated by situations in which a firm may offer a menu of exactly k items to its clients, where k is a parameter determined by external considerations. Performing a query corresponds to physically changing the identities of the items offered, and the reply to the query is deduced by observing the behavior of clients in response to the change. Queries that involve a number of items that differs from k may not be desirable due to these external considerations. In such situations it is natural to ask whether the same approximation ratios that can be guaranteed by general value queries can also be obtained by uniform size queries.

Description: In this paper, we study the approximability of the Maximum Labeled Path problem: given a vertex-labeled directed acyclic graph D , find a path in D that collects a maximum number of distinct labels. For any \(\epsilon 〉0\) , we provide a polynomial time approximation algorithm that computes a solution of value at least \(OPT^{1-\epsilon }\) and a self-reduction showing that any constant ratio approximation algorithm for this problem can be converted into a PTAS. This last result, combined with the APX -hardness of the problem, shows that the problem cannot be approximated within any constant ratio unless \(P=NP\) .

Description: We present the first results on the parameterized complexity of reconfiguration problems, where a reconfiguration variant of an optimization problem \(\mathcal {Q}\) takes as input two feasible solutions S and T and determines if there is a sequence of reconfiguration steps, i.e. a reconfiguration sequence, that can be applied to transform S into T such that each step results in a feasible solution to \(\mathcal {Q}\) . For most of the results in this paper, S and T are sets of vertices of a given graph and a reconfiguration step adds or removes a vertex. Our study is motivated by results establishing that for many NP -hard problems, the classical complexity of reconfiguration is PSPACE -complete. We address the question for several important graph properties under two natural parameterizations: k , a bound on the size of solutions, and \(\ell \) , a bound on the length of reconfiguration sequences. Our first general result is an algorithmic paradigm, the reconfiguration kernel, used to obtain fixed-parameter tractable algorithms for reconfiguration variants of Vertex Cover and, more generally, Bounded Hitting Set and Feedback Vertex Set , all parameterized by k . In contrast, we show that reconfiguring Unbounded Hitting Set is W[2] -hard when parameterized by \(k+\ell \) . We also demonstrate the W[1] -hardness of reconfiguration variants of a large class of maximization problems parameterized by \(k+\ell \) , and of their corresponding deletion problems parameterized by \(\ell \) ; in doing so, we show that there exist problems in FPT when parameterized by k , but whose reconfiguration variants are W[1] -hard when parameterized by \(k+\ell \) .

Description: A time domain sub-sampling technique that can be applied to wired or wireless orthogonal frequency division multiplexing systems is described in this paper. Focus is given on the specific conditions that allow...

Description: The greedy spanner is the highest quality geometric spanner (in e.g. edge count and weight, both in theory and practice) known to be computable in polynomial time. Unfortunately, all known algorithms for computing it on n points take \(\varOmega (n^2)\) time, limiting its applicability on large data sets. We propose a novel algorithm design which uses the observation that for many point sets, the greedy spanner has many ‘short’ edges that can be determined locally and usually quickly. To find the usually few remaining ‘long’ edges, we use a combination of already determined local information and the well-separated pair decomposition. We give experimental results showing large to massive performance increases over the state-of-the-art on nearly all tests and real-life data sets. On the theoretical side we prove a near-linear expected time bound on uniform point sets and a near-quadratic worst-case bound. Our bound for point sets drawn uniformly and independently at random in a square follows from a local characterization of t -spanners we give on such point sets. We give a geometric property that holds with high probability, which in turn implies that if an edge set on these points has t -paths between pairs of points ‘close’ to each other, then it has t -paths between all pairs of points. This characterization gives an \(O(n \log ^2 n \log ^2 \log n)\) expected time bound on our greedy spanner algorithm, making it the first subquadratic time algorithm for this problem on any interesting class of points. We also use this characterization to give an \(O((n + |E|) \log ^2 n \log \log n)\) expected time algorithm on uniformly distributed points that determines whether E is a t -spanner, making it the first subquadratic time algorithm for this problem that does not make assumptions on E .

Description: Micro-blog has become an emerging application in the Internet in recent years, and affective computing and sentiment analysis for micro-blog have been a vital research project in computer science, natural ling...

Description: Future wireless communication systems are demanding a more flexible physical layer. GFDM is a block filtered multicarrier modulation scheme proposed to add multiple degrees of freedom and to cover other wavefo...

Description: Let \(\mathcal {D} = \{\mathsf {T}_1,\mathsf {T}_2, \ldots ,\mathsf {T}_D\}\) be a collection of D string documents of n characters in total, that are drawn from an alphabet set \(\varSigma =[\sigma ]\) . The top-k document retrieval problem is to preprocess \(\mathcal{D}\) into a data structure that, given a query \((P[1\ldots p],k)\) , can return the k documents of \(\mathcal{D}\) most relevant to the pattern P . The relevance is captured using a predefined ranking function, which depends on the set of occurrences of P in \(\mathsf {T}_d\) . For example, it can be the term frequency (i.e., the number of occurrences of P in \(\mathsf {T}_d\) ), or it can be the term proximity (i.e., the distance between the closest pair of occurrences of P in \(\mathsf {T}_d\) ), or a pattern-independent importance score of \(\mathsf {T}_d\) such as PageRank. Linear space and optimal query time solutions already exist for the general top- k document retrieval problem. Compressed and compact space solutions are also known, but only for a few ranking functions such as term frequency and importance. However, space efficient data structures for term proximity based retrieval have been evasive. In this paper we present the first sub-linear space data structure for this relevance function, which uses only o ( n ) bits on top of any compressed suffix array of \(\mathcal{D}\) and solves queries in \(O((p+k) {{\mathrm{polylog}}}\,\,n)\) time. We also show that scores that consist of a weighted combination of term proximity, term frequency, and document importance, can be handled using twice the space required to represent the text collection.

Description: We study the parameterized complexity of Geometric Graph Isomorphism (Known as the Point Set Congruence problem in computational geometry): given two sets of n points A and B with rational coordinates in k -dimensional euclidean space, with k as the fixed parameter, the problem is to decide if there is a bijection \(\pi :A \rightarrow B\) such that for all \(x,y \in A\) , \(\Vert x-y\Vert = \Vert \pi (x)-\pi (y)\Vert \) , where \(\Vert \cdot \Vert \) is the euclidean norm. Our main result is the following: We give a \(O^*(k^{O(k)})\) time (The \(O^*(\cdot )\) notation here, as usual, suppresses polynomial factors) FPT algorithm for Geometric Isomorphism. This is substantially faster than the previous best time bound of \(O^*(2^{O(k^4)})\) for the problem (Evdokimov and Ponomarenko in Pure Appl Algebra 117–118:253–276, 1997 ). In fact, we show the stronger result that even canonical forms for finite point sets with rational coordinates can also be computed in \(O^*(k^{O(k)})\) time. We also briefly discuss the isomorphism problem for other \(l_p\) metrics. Specifically, we describe a deterministic polynomial-time algorithm for finite point sets in \(\mathbb {Q}^2\) .

Description: Full duplex (FD) protocol has been widely used in wireless communications, which could transmit and receive signals at the meantime. In this paper, considering the worst-case channel uncertainty, opportunistic...

Description: This paper presents the problem formulation, development, and use of a robust dynamic genetic algorithm (GA) for channel allocation in cognitive radio. This approach offers an efficient way to access available...