3,930 research outputs found
np-CECADA: Enhancing Ubiquitous Connectivity of LoRa Networks
No full textLong Range Wide Area Networks (LoRaWAN) offer ubiquitous communications for The Internet of Things (IoT). However, there are many challenges in rolling out LoRaWAN - mainly scalability, energy efficiency, Packet Reception Ratio (PRR), and keeping the channel access as simple as unslotted ALOHA. To this end, we design non-persistent Capture Effect Channel Activity Detection Algorithm (np-CECADA), which is a novel, distributed protocol for the MAC layer of LoRaWAN. It utilizes Channel Activity Detection (CAD), which is a built-in imperfect mechanism for channel sensing and minimal feedback from the gateways. In np-CECADA each device independently adapts backoff times based on the traffic in its vicinity and the transmission power based on the heuristically inferred probability of capturing the channel. To achieve this, first, we carried out an extensive on-field evaluation to measure the effectiveness of CAD and capture effect in LoRa. Using them we designed np CECADA and developed ns-3 modules. Packet Reception Ratio of np-CECADA is 15.74× and 5.13× higher than vanilla LoRaWAN and p-CARMA, respectively. Channel utilization is 11.24× higher compared to LMAC. Further, on a testbed of 30 LoRa devices np-CECADA outperforms LoRaWAN up to 5 times.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Embedded System
Dominating Set, Independent Set, Discrete k-Center, Dispersion, and Related Problems for Planar Points in Convex Position
No full textGiven a set P of n points in the plane, its unit-disk graph G(P) is a graph with P as its vertex set such that two points of P are connected by an edge if their (Euclidean) distance is at most 1. We consider several classical problems on G(P) in a special setting when points of P are in convex position. These problems are all NP-hard in the general case. We present efficient algorithms for these problems under the convex position assumption.
● For the problem of finding the smallest dominating set of G(P), we present an O(knlog n) time algorithm, where k is the smallest dominating set size. We also consider the weighted case in which each point of P has a weight and the goal is to find a dominating set in G(P) with minimum total weight; our algorithm runs in O(n³log² n) time. In particular, for a given k, our algorithm can compute in O(kn²log² n) time a minimum weight dominating set of size at most k (if it exists).
● For the discrete k-center problem, which is to find a subset of k points in P (called centers) for a given k, such that the maximum distance between any point in P and its nearest center is minimized. We present an algorithm that solves the problem in O(min{n^{4/3}log n+knlog² n,k² nlog²n}) time, which is O(n²log² n) in the worst case when k = Θ(n). For comparison, the runtime of the current best algorithm for the continuous version of the problem where centers can be anywhere in the plane is O(n³ log n).
● For the problem of finding a maximum independent set in G(P), we give an algorithm of O(n^{7/2}) time and another randomized algorithm of O(n^{37/11}) expected time, which improve the previous best result of O(n⁶log n) time. Our algorithms can be extended to compute a maximum-weight independent set in G(P) with the same time complexities when points of P have weights.
- If we are looking for an (unweighted) independent set of size 3, we derive an algorithm of O(nlog n) time; the previous best algorithm runs in O(n^{4/3}log² n) time (which works for the general case where points of P are not necessarily in convex position).
- If points of P have weights and are not necessarily in convex position, we present an algorithm that can find a maximum-weight independent set of size 3 in O(n^{5/3+δ}) time for an arbitrarily small constant δ > 0. By slightly modifying the algorithm, a maximum-weight clique of size 3 can also be found within the same time complexity.
● For the dispersion problem, which is to find a subset of k points from P for a given k, such that the minimum pairwise distance of the points in the subset is maximized. We present an algorithm of O(n^{7/2}log n) time and another randomized algorithm of O(n^{37/11}log n) expected time, which improve the previous best result of O(n⁶) time.
- If k = 3, we present an algorithm of O(nlog² n) time and another randomized algorithm of O(nlog n) expected time; the previous best algorithm runs in O(n^{4/3}log² n) time (which works for the general case where points of P are not necessarily in convex position)
P≠NP
No full textHere, the author tries to build the structure of the Theory of computation based on considering time as a fuzzy concept.
In fact, there are reasons to consider time as a fuzzy concept. In this article, the author doesn’t go to this side but note that Brower and Husserl views on the concept of time were similar [8]. Some reasons have been given for it in [3].
Throughout this article, the author presents the Theory of Computation with Fuzzy Time. Given the classic definition of Turing Machine, the concept of Time is modified to Fuzzy time. This new term calls as Theory TC* [2] and this type of computation “Fuzzy time Computation”. We have relatively large number of fundamental unsolved problems in Complexity Theory. In the new theory, some of the major obstacles and unsolved problems have been solved [2]. It should be noted that in this article, the writer considers fuzzy number associated to instants of time as a symmetric one. The point about the symmetry is in the proof of Lemma 3, although it is generalizable.
In particular, the new classes of complexity Theory, P*, NP*, BPP* in the TC* analogues to the definitions of P, NP, BPP defines as their natural alternative definition. Here, we will see P*≠ NP*, P*= BPP*. Finally, we have Theorem 4
P≠NP
No full textHere, the author tries to build the structure of the Theory of computation based on considering time as a fuzzy concept.
In fact, there are reasons to consider time as a fuzzy concept. In this article, the author doesn’t go to this side but note that Brower and Husserl views on the concept of time were similar [8]. Some reasons have been given for it in [3].
Throughout this article, the author presents the Theory of Computation with Fuzzy Time. Given the classic definition of Turing Machine, the concept of Time is modified to Fuzzy time. This new term calls as Theory TC* [2] and this type of computation “Fuzzy time Computation”. We have relatively large number of fundamental unsolved problems in Complexity Theory. In the new theory, some of the major obstacles and unsolved problems have been solved [2]. It should be noted that in this article, the writer considers fuzzy number associated to instants of time as a symmetric one. The point about the symmetry is in the proof of Lemma 3, although it is generalizable.
In particular, the new classes of complexity Theory, P*, NP*, BPP* in the TC* analogues to the definitions of P, NP, BPP defines as their natural alternative definition. Here, we will see P*≠ NP*, P*= BPP*. Finally, we have Theorem 4
NP vyhledávací problémy
No full textTitle: NP search problems Author: Tomáš Jirotka Department: Department of Algebra Supervisor: Prof. RNDr. Jan Krajíček, DrSc. Abstract: The thesis summarizes known results in the field of NP search pro- blems. We discuss the complexity of integer factoring in detail, and we propose new results which place the problem in known classes and aim to separate it from PLS in some sense. Furthermore, we define several new search problems. Keywords: Computational complexity, TFNP, integer factorization.
Periodic Properties of Cryptographically Strong Pseudorandom Sequences
No full text'Provable' strength generators of pseudo-random sequences have been considered in this paper, whose cryptanalysis problem reduces to solving a well-known and extremely complex mathematical problem related to the NP-complex class. In particular, the generators Blum-Blum-Shub, Rivest-Shamir-Adleman, Dual Elliptic Curve Deterministic Random Bit Generator and Pseudo-Random Generator Provably as Secure as Syndrome Decoding are considered. The periodic properties of generated pseudorandom sequences are investigated. It is shown that the considered generators do not allow forming sequences of the maximum period. In addition, for each generator there are initial states (weak keys), leading to catastrophically small lengths of the periods of generated sequences
NP-MOVEMENT AND THE POSSESSIVE GENITIVE
No full textU članku se raspravlja o mjestu genitiva u izgradnji složenih NP te posebice o
odnosu s drugim konkurentnim sintaktičkim sredstvima. U žarištu istraživanja,
u kojem su primijenjene neke od modularnih sastavnica teorije načela i
paramatera (TNP): X'-teorija, padežna teorija i teorija tematskih uloga, nalazi
se NP-pomicanje posvojnoga genitiva s temeljno generiranog položaja na
mjesto odrednika, odnosno na projekciju gdje se nalazi posvojni sufiks. Autor
smatra kako između DP i NP u objašnjavanju toga fenomena valja uvesti novi
sloj - funkcionalnu kategoriju Poss, a NP–pomicanje objašnjava se težnjom
svake imenice da bude što bolje određena, aktualizirana. Provjerava se i utjecaj
morfosintaktičkog obilježja određenosti kod morfoloških posvojnih oblika na
druge sročne atribute.The paper discusses the place of the genitive in the derivation of complex NPs, particularly
in relation to other, competing syntactic means. The study that relies on some modular
components of the theory or principles and parametres (X' theory, case theory, and the theory
of thematic roles) focuses on the NP-movement of the possessive genitive out of the basegenerated
position into the specifier position or into the projection occupied by the
possessive suffix. The author argues that in order to explan the phenomenon a new level
should be recognized between DP and NP—the functional category Poss. NP-movement is
explained as the tendency of nouns to be as determined and actualised as possible. The
influence of the morphosyntactic property of determination of possessive forms on other
congruent attributes is examined
Minimizing the effective graph resistance by adding links is NP-hard
No full textThe effective graph resistance, also known as the Kirchhoff index, is metric that is used to quantify the robustness of a network. We show that the optimisation problem of minimizing the effective graph resistance of a graph by adding a fixed number of links, is NP-hard.Quantum & Computer EngineeringNetwork Architectures and Service
NP Photonic lasers and a new laser-frequency offset device
No full textAuthor Institution: NP PhotonicsSlides presented at the 5th Annual Photonic Doppler Velocimetry (PDV) Users Conference held at The Ohio State University, Columbus, Ohio, September 8-9, 2010
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