A comparative investigation on various channel estimation algorithms for OFDM system in the mobile communication environment is presented and analyzed in terms of computational complexity, mean square error, and bit e...
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A comparative investigation on various channel estimation algorithms for OFDM system in the mobile communication environment is presented and analyzed in terms of computational complexity, mean square error, and bit error rate in this paper. As a result, Wiener filter estimation shows the best error performance. Concerning the computational complexity as well as the performance, however, the piecewise linear estimator is considered as a proper choice when the reference signal spacing is relatively narrow. And the cubic-spline estimator is a good alternative to the Wiener filter estimation if the reference signal spacing is wider than the coherent bandwidth of transmission channel.
Memorization is a technique which allows to speed up exponential recursive algorithms at the cost of an exponential space complexity. This technique already leads to the currently fastest algorithm for fixed-parameter...
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Memorization is a technique which allows to speed up exponential recursive algorithms at the cost of an exponential space complexity. This technique already leads to the currently fastest algorithm for fixed-parameter vertex cover, whose time complexity is O(1.2832(k)k(1.5) + kn), where it is the number of nodes and k is the size of the vertex cover. Via a refined use of memorization, we obtain an C(1.2759(k)k(1.5) + kn) algorithm for the same problem. We moreover Show how to further reduce the complexity to O(1.2745(k)k(4) + kn). 2004 Elsevier B.V. All rights reserved.
Although zero-forcing ( ZF) detection is well-known for its low computational complexity in multiple-input multiple-output ( MIMO) communication systems, it suffers from significantly poor performance. The sphere deco...
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Although zero-forcing ( ZF) detection is well-known for its low computational complexity in multiple-input multiple-output ( MIMO) communication systems, it suffers from significantly poor performance. The sphere decoder ( SD) method, on the other hand, achieves the maximum likelihood ( ML) performance yet imposes a high computational complexity. We propose a low-complexity detection scheme, concatenated with the SD method, which verifies the reliability of the ZF equalized observations via some predefined regions and thresholds obtained by the channel realization. We design the threshold analytically, such that the method achieves the ML performance. With the designed threshold, we prove that the method achieves the ML performance and the ZF computational complexity at the same time with probability one, at high signal-to-noise ratio ( SNR). The theoretical analysis is corroborated with numerical simulations. The simulation results also show that the proposed method achieves the ML performance very rapidly as the SNR increases.
We prove a superlinear lower bound on the size of a bounded depth bilinear arithmetical circuit computing cyclic convolution. Our proof uses the strengthening of the Donoho-Stark uncertainty principle [D.L. Donoho, P....
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We prove a superlinear lower bound on the size of a bounded depth bilinear arithmetical circuit computing cyclic convolution. Our proof uses the strengthening of the Donoho-Stark uncertainty principle [D.L. Donoho, P.B. Stark, Uncertainty principles and signal recovery, SIAM journal of Applied Mathematics 49 (1989) 906-931] given by [Tao IT. Tao, An uncertainty principle for cyclic groups of prime order, Mathematical Research Letters 12 (2005) 121-127], and a combinatorial lemma by Raz and Shpilka [R. Raz, A. Shpilka, Lower bounds for matrix product, in arbitrary circuits with bounded gates, SIAM Journal of Computing 32 (2003) 488-513]. This combination and an observation on ranks of circulant matrices, which we use to give a much shorter proof of the Donoho-Stark principle, may have other applications. (C) 2008 Elsevier B.V. All rights reserved.
A subset S of the vertex set of a hypergraph H is called a dominating set of H if for every vertex v not in S there exists u is an element of S such that u and v are contained in an edge in H. The minimum cardinality ...
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A subset S of the vertex set of a hypergraph H is called a dominating set of H if for every vertex v not in S there exists u is an element of S such that u and v are contained in an edge in H. The minimum cardinality of a dominating set in H is called the domination number of H and is denoted by gamma (H). A transversal of a hypergraph H is defined to be a subset T of the vertex set such that T boolean AND E not equal empty set for every edge E of H. The transversal number of H, denoted by tau (H), is the minimum number of vertices in a transversal. A hypergraph is of rank k if each of its edges contains at most k vertices. The inequality tau (H) >= gamma (H) is valid for every hypergraph H without isolated vertices. In this paper, we investigate the hypergraphs satisfying tau (H) = gamma (H), and prove that their recognition problem is NP-hard already on the class of linear hypergraphs of rank 3, while on unrestricted problem instances it lies inside the complexity class Theta(p)(2). Structurally we focus our attention on hypergraphs in which each subhypergraph without isolated vertices fulfills the equality tau (H') = gamma (H'). We show that if each induced subhypergraph satisfies the equality then it holds for the non-induced ones as well. Moreover, we prove that for every positive integer k, there are only a finite number of forbidden subhypergraphs of rank k, and each of them has domination number at most k. (c) 2013 Elsevier B.V. All rights reserved.
We provide new non-approximability results for the restrictions of the MIN VERTEX COVER problem to bounded-degree, sparse and dense graphs. We show that for a sufficiently large B, the recent 1.16 lower bound proved b...
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We provide new non-approximability results for the restrictions of the MIN VERTEX COVER problem to bounded-degree, sparse and dense graphs. We show that for a sufficiently large B, the recent 1.16 lower bound proved by Hastad (1997) extends with negligible loss to graphs with bounded degree B. Then, we consider sparse graphs with no dense components (i.e. everywhere sparse graphs), and we show a similar result but with a better trade-off between non-approximability and sparsity, Finally, we observe that the MIN VERTEX COVER problem remains APX-complete when restricted to dense graph and thus recent techniques developed for several MAX SNP problems restricted to "dense" instances introduced by Arora et al. (1995) cannot be applied. (C) 1999 Elsevier Science B.V. All rights reserved.
We prove a number of general theorems about ZK, the class of problems possessing ( computational) zero-knowledge proofs. Our results are unconditional, in contrast to most previous works on ZK, which rely on the assum...
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We prove a number of general theorems about ZK, the class of problems possessing ( computational) zero-knowledge proofs. Our results are unconditional, in contrast to most previous works on ZK, which rely on the assumption that one-way functions exist. We establish several new characterizations of ZK and use these characterizations to prove results such as the following: 1. Honest-verifier ZK equals general ZK. 2. Public-coin ZK equals private-coin ZK. 3. ZK is closed under union. 4. ZK with imperfect completeness equals ZK with perfect completeness. 5. Any problem in ZK boolean AND NP can be proven in computational zero knowledge by a BPPNP prover. 6. ZK with black-box simulators equals ZK with general, non-black-box simulators. The above equalities refer to the resulting class of problems ( and do not necessarily preserve other efficiency measures such as round complexity). Our approach is to combine the conditional techniques previously used in the study of ZK with the unconditional techniques developed in the study of SZK, the class of problems possessing statistical zero-knowledge proofs. To enable this combination, we prove that every problem in ZK can be decomposed into a problem in SZK together with a set of instances from which a one-way function can be constructed.
To resist the adverse effect of shadow interference, illumination changes, indigent texture and scenario jitter in object detection and improve performance, a background modelling method based on local fusion feature ...
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To resist the adverse effect of shadow interference, illumination changes, indigent texture and scenario jitter in object detection and improve performance, a background modelling method based on local fusion feature and variational Bayesian learning is proposed. First, U-LBSP (uniform-local binary similarity patterns) texture feature, lab colour and location feature are used to construct local fusion feature. U-LBSP is modified from local binary patterns in order to reduce computational complexity and better resist the influence of shadow and illumination changes. Joint colour and location feature are introduced to deal with the problem of indigent texture and scenario jitter. Then, LFGMM (Gaussian mixture model based on local fusion feature) is updated and learned by variational Bayes. In order to adapt to dynamic changing scenarios, the variational expectation maximisation algorithm is applied for distribution parameters optimisation. In this way, the optimal number of Gaussian components as well as their parameters can be automatically estimated with less time expended. Experimental results show that the authors' method achieves outstanding detection performance especially under conditions of shadow disturbances, illumination changes, indigent texture and scenario jitter. Strong robustness and high accuracy have been achieved.
The mobile communication system has become increasingly complicated with the dramatic growth of user's requirement in quality of service (QoS). The high fluctuation of traffic data makes conventional cell associat...
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The mobile communication system has become increasingly complicated with the dramatic growth of user's requirement in quality of service (QoS). The high fluctuation of traffic data makes conventional cell association schemes difficult to guarantee satisfactory service in accord with traffic demand. In this study, the authors propose a novel QoS-aware cell association scheme in a heterogeneous network. Utilising traffic prediction achieved by support vector regression, the user can decide the best cell according to the future traffic demand. The authors aim at maximising the total throughput with consideration of channel gains and blocking probability in different cells and formulate the cell association as a binary combinatorial optimisation problem. Since users are selfish for their own benefits without the global information, the authors turn this problem into a game theoretical framework. To obtain the Nash equilibrium with low computation complexity, a heuristic dynamic selection algorithm is proposed by updating selection probability which enables each user to associate with the best cell independently. Numerical simulation results show that the proposed algorithm achieves a remarkable throughput gain. The number of satisfied users increases substantially under the different density of users compared with conventional cell association schemes.
Recently, Lutz [14, 15] introduced a polynomial time bounded version of Lebesgue measure. He and others (see e.g. [11, 13-18,20]) used this concept to investigate the quantitative structure of Exponential Time (E = DT...
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Recently, Lutz [14, 15] introduced a polynomial time bounded version of Lebesgue measure. He and others (see e.g. [11, 13-18,20]) used this concept to investigate the quantitative structure of Exponential Time (E = DTIME(2(lin))). Previously, Ambos-Spies et al. [2,3] introduced polynomial time bounded genericity concepts and used them for the investigation of structural properties of NP (under appropriate assumptions) and E. Here we relate these concepts to each other. We show that, for any c greater than or equal to 1, the class of n(c)-generic sets has p-measure 1. This allows us to simplify and extend certain p-measure I-results. To illustrate the power of generic sets we take the Small Span Theorem of Juedes and Lutz [11] as an example and prove a generalization for bounded query reductions.
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