1,720,963 research outputs found
Optimal radio resources and transmission formats assignment in OFDMA systems
No full textThe problem of assigning radio resources and transmission formats to users in the downlink of an OFDMA network is addressed. In particular, a single cell environment with a realistic interference model and a margin adaptive approach is considered, i.e., the aim is of minimizing the total transmission power while maintaining a certain given rate for each user. The computational complexity issues of the problem are discussed, and an approximation analysis is presented. Heuristic approaches, based on rounding techniques and graph models, are also proposed. Computational experiences show that, in a comparison with a commercial state-of-the-art optimization solver and with alternatives from the literature, the proposed algorithms are effective in terms of solution quality and CPU times
Performance Analysis of a Distributed Resource Allocation Scheme for D2D Communications
No full textDevice-to-device (D2D) communications underlaying a cellular infrastructure has recently been proposed as a means of increasing the cellular capacity, improving the user throughput and extending the battery lifetime of user equipments by facilitating the reuse of spectrum resources between D2D and cellular links. In network assisted D2D communications, when two devices are in the proximity of each other, the network can not only help the devices to set the appropriate transmit power and schedule time and frequency resources but also to determine whether communication should take place via the direct D2D link (D2D mode) or via the cellular base station (cellular mode). In this paper we formulate the joint mode selection, scheduling and power control task as an optimization problem that we first solve assuming the availability of a central entity. We also propose a distributed suboptimal joint mode selection and resource allocation scheme that we benchmark with respect to the centralized optimal solution. We find that the distributed scheme performs close to the optimal scheme both in terms of resource efficiency and user fairness
A min-sum approach for resource allocation in communication systems
No full textThis paper considers distributed protocol design for resource allocation (RA) problems. We propose a fully decentralized RA scheme based on the min-sum message passing (MP) approach in which each message is the solution of small distributed allocation problems. Due to the presence of cycles in the network graph, the MP routine may not converge to a fixed point. To this end, we introduce a reweighted MP (ReMP) algorithm that perturbs the ordinary min-sum algorithm by suitably re-weighting messages. ReMP distributes the computational effort of achieving an optimal RA among nodes. Such feature makes ReMP particularly attractive in wireless networks allowing the convergence to a fixed and provably optimum point without employing any central controller. Numerical results show that ReMP outperforms conventional MP-based algorithms for RA problems in terms of computation time
A message passing approach for multi-cellular OFDMA systems
No full textWe propose a novel distributed and low complexity joint channel and power allocation scheme for the uplink of multi-cellular multi-carrier systems. The algorithm is based on the min-sum message passing (MP) scheme that entails passing messages between the base station (BS) and mobile terminals (MTs) with the aim of achieving a low power consumption resource allocation while respecting rate constraints. MP algorithm is combined with the classical closed loop power control scheme to undertake the effects of multiple access interference. Compared to alternatives, the algorithm rapidly adapts to the channel fluctuations. Besides, it does not require any central controller and distributes the computational load among BSs and MTs, with a significant reduction on the execution time
Message Passing Resource Allocation for the Uplink of Multi-Carrier Multi-Format Systems
No full textWe propose two novel distributed resource allocation (RA) schemes for the uplink of a cellular multi-carrier multi-format system based on the message passing (MP) technique. In the proposed approaches each transmitter iteratively sends and receives information messages to/from the base station with the goal of achieving an optimal RA strategy. The exchanged messages are the solution of small distributed allocation problems. Hence, despite the NP-hardness of the original RA problem, they distribute the computational effort in the cell among all the transmitters and the base station. Specifically, the first algorithm combines MP with a dynamic programming formula solved at each step, while the second method initially solves to optimality a simplified single-format RA via MP, and eventually performs format allocation to satisfy the rate constraints. Compared to alternatives, numerical results assess the validity of MP-based schemes both in terms of efficiency and complexity
Complexity analysis and heuristic algorithms for radio resource allocation in OFDMA networks
No full textIn this paper, we address the problem of allocating users to radio resources (i.e. subcarriers) in the downlink of an OFDMA system. In particular, we consider a multi-format resource allocation problem (MF-RAP) in which the link adaptation adjusts the spectral efficiency for each user-subcarrier pair, i.e. for each radio link, in order to minimize the total transmission power while fulfilling a rate request for each user. We propose an integer linear programming (ILP) formulation of the problem and exhaustively discuss the computational complexity. Specifically, we prove that the problem is NP-hard in the strong sense and demonstrate that it is hard to be approximated in polynomial time within a constant factor. Hence, we present heuristic approaches that achieve reasonably good solutions in the general case. Computational experiences show that, in comparison with a commercial state-of-the-art ILP optimization solver, the proposed algorithms are effective in terms of solution quality and CPU times
A Message Passing Approach for Resource Allocation in Cellular OFDMA Communications
No full textThis paper proposes a distributed and low-complexity resource allocation scheme for cellular OFDMA networks. In particular, we consider ReMP, a reweighted message passing algorithm that perturbs the standard max-sum algorithm by suitably reweighting messages. In a single-cell scenario, such a scheme allows to achieve convergence to a fixed and provably optimum point without employing any central controller. The ReMP algorithm is then adapted to a multi-cell environment. To this aim, we devise X-ReMP, a ReMP-based algorithm that combines cross-cell signaling and the regular ReMP routine that still runs within each cell. The cross-signaling among cells aids ReMP to deal with the inter-cell multiple-access interference, so that X-ReMP allows convergence to a good working point in terms of system throughput even in presence of strong inter-cell interference
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
