1,721,034 research outputs found
Lower bound on training-based channel estimation error for frequency-selective block-fading Rayleigh MIMO channels
No full textLinear and nonlinear preequalization/equalization for MIMO systems with long-term channel state information at the transmitter
No full textMar.2004
Continual Meta-Reinforcement Learning for UAV-Aided Vehicular Wireless Networks
No full textUnmanned aerial base stations (UABSs) can be deployed in vehicular wireless networks to support applications such as extended sensing via vehicle-to-everything (V2X) services. A key problem in such systems is designing algorithms that can efficiently optimize the trajectory of the UABS in order to maximize coverage. In existing solutions, such optimization is carried out from scratch for any new traffic configuration, often by means of conventional reinforcement learning (RL). In this paper, we propose the use of continual meta-RL as a means to transfer information from previously experienced traffic configurations to new conditions, with the goal of reducing the time needed to optimize the UABS's policy. Adopting the Continual Meta Policy Search (CoMPS) strategy, we demonstrate significant efficiency gains as compared to conventional RL, as well as to naive transfer learning methods
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
Cooperation and coordination in cognitive networks with packet retransmission
No full textThe cognitive framework, which fosters an efficient use of the channel resource by granting access to smart and adaptive terminals, has been recently integrated with the cooperative paradigm. Accordingly, following a spectrum-leasing approach, licensed (primary) users may let unlicensed (secondary) users access the owned bandwidth in exchange for an increased performance via cooperation. Nevertheless, assuming that secondary transmission is limited to idle primary slots, as the traffic from the primary sources increases, implementation of spectrum leasing via cooperation becomes more challenging. In fact, the opportunities for secondary transmission reduce and the secondary users may find spectrum leasing not advantageous. In this paper, a solution is proposed that exploits fading temporal correlation and retransmission-based error control in order to increase secondary throughput even in high primary traffic conditions. Focusing on a simple network with a primary and a secondary source transmitting to a common destination, it is shown that the primary source may actively leave part of its channel resource to the secondary source without significant performance loss while greatly improving secondary throughput
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
Spectrum Leasing via Cooperative Opportunistic Routing Techniques
No full textA licensed multihop network that coexists with a set of unlicensed nodes is considered. Coexistence is regulated via a spectrum leasing mechanism that is based on cooperation and opportunistic routing. Specifically, the primary network consists of a source and a destination communicating via a number of primary relay nodes. In each transmission block, the next hop is selected in an on-line fashion based on the channel conditions (and thus the decoding outcome) in the previous transmissions, according to the idea of opportunistic routing. The secondary nodes may serve as extra relays, and hence potential next hops, for the primary network, but only in exchange for spectrum leasing. Namely, in return for their forwarding of primary packets, secondary nodes are awarded spectral resources for transmission of their own traffic. Secondary nodes enforce Quality-of-Service requirements in terms of rate and reliability when deciding whether or not to cooperate. Four policies that exploit spectrum leasing via opportunistic routing in different ways are proposed. These policies are designed to span different operating points in the trade-off between gains in throughput and overall energy expenditure for the primary network. Analysis is carried out for networks with a linear geometry and quasi-static Rayleigh fading statistics by using Markov chain tools. Different multiplexing techniques are considered for multiplexing of the primary and secondary traffic at the secondary nodes, namely orthogonal multiplexing (such as time, frequency or orthogonal code division multiplexing) and superposition coding. The optimality in terms of both throughput and primary energy consumption of superposition coding over all possible multiplexing strategies, for the given routing techniques, is proved. Finally, numerical results demonstrate the advantages of the proposed spectrum leasing solution based on opportunistic routing and illustrate the trade-offs between primary throughput and energy co- - nsumption
Compound relay channel with informed relay and destination
No full textA two-state compound relay channel is considered where the relay and the destination are informed about the channel state while the source is not. Achievable rates and upper bounds are derived for discrete memoryless and Gaussian models, and specialized to a scenario with orthogonal components. It is shown that, apart from some special cases, optimality conditions valid for decode-and-forward (DF)-based solutions on a standard relay channel do not carry over to a compound setting, and more fl exible transmission strategies are generally advantageous. For instance, partial decode-and-forward (PDF) that superimposes transmission of three layers and uses joint decoding at the destination performs better than the standard two-layer PDF with successive decoding, even when the latter is optimal for the regular relay channel. Moreover, the capacity is derived in the special case in which the relay is not active in one state. Extension to the broadcast coding approach, as an alternative to the compound model, is also discussed. ©2009 IEEE
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