733 research outputs found
On Information and Energy Cooperation in Energy Harvesting Cognitive Radio
This paper considers the cooperation between primary and secondary users at
information and energy levels when both users are energy harvesting nodes. In
particular, a secondary transmitter helps relaying the primary message, and in
turn, gains the spectrum access as a reward. Also, the primary transmitter
supplies energy to the secondary transmitter if the latter is
energy-constrained, which facilitates an uninterrupted cooperation. We address
this two-level cooperation over a finite horizon with the finite battery
constraint at the secondary transmitter. While promising the rate-guaranteed
service to both primary and secondary users, we aim to maximize the primary
rate. We develop an iterative algorithm that obtains the optimal offline power
policies for primary and secondary users. To acquire insights about the
structure of the optimal solution, we examine specific scenarios. Furthermore,
we investigate the effects of the secondary rate constraint and finite battery
on the primary rate and the probability of cooperation. We show that the joint
information and energy cooperation increases the chances of cooperation and
achieves significant rate gains over only information cooperation.Comment: 6 pages, 4 figures, to be presented in IEEE PIMRC 201
Performance and structure of single-mode bosonic codes
The early Gottesman, Kitaev, and Preskill (GKP) proposal for encoding a qubit
in an oscillator has recently been followed by cat- and binomial-code
proposals. Numerically optimized codes have also been proposed, and we
introduce new codes of this type here. These codes have yet to be compared
using the same error model; we provide such a comparison by determining the
entanglement fidelity of all codes with respect to the bosonic pure-loss
channel (i.e., photon loss) after the optimal recovery operation. We then
compare achievable communication rates of the combined encoding-error-recovery
channel by calculating the channel's hashing bound for each code. Cat and
binomial codes perform similarly, with binomial codes outperforming cat codes
at small loss rates. Despite not being designed to protect against the
pure-loss channel, GKP codes significantly outperform all other codes for most
values of the loss rate. We show that the performance of GKP and some binomial
codes increases monotonically with increasing average photon number of the
codes. In order to corroborate our numerical evidence of the cat/binomial/GKP
order of performance occurring at small loss rates, we analytically evaluate
the quantum error-correction conditions of those codes. For GKP codes, we find
an essential singularity in the entanglement fidelity in the limit of vanishing
loss rate. In addition to comparing the codes, we draw parallels between
binomial codes and discrete-variable systems. First, we characterize one- and
two-mode binomial as well as multi-qubit permutation-invariant codes in terms
of spin-coherent states. Such a characterization allows us to introduce check
operators and error-correction procedures for binomial codes. Second, we
introduce a generalization of spin-coherent states, extending our
characterization to qudit binomial codes and yielding a new multi-qudit code.Comment: 34 pages, 11 figures, 4 tables. v3: published version. See related
talk at https://absuploads.aps.org/presentation.cfm?pid=1351
To be or not to be : firm decision making regarding social media presence
While Social Media (SM) is becoming even more relevant for consumers, managers are seeking to understand how they can improve brand’s SM performance while dealing with different external and internal constraints.
This dissertation describes the Decision-Making Processes (DMP) of Portuguese firms when managing their brand’s presence in different SM platforms, resulting in developing a normative, theory-driven framework that supports SM management. To this end, primary data resulting from eight interviews with key informants from seven different firms and two natural observations of DMP from two different companies were analysed. Then, data was interpreted under the light of existing theories about DMP in marketing management. Subsequently, secondary data depicting the cases of four firms deciding about their SM presence was analysed in line with the final framework, resulting on different possible firms’ behaviours characterization when developing their SM strategy.
It was concluded that although SM platforms business model suit current firms and marketing needs, managers have difficulties to integrated SM on marketing strategies. Plus, managers should be aware about firm’s external and internal constraints that are influencing firm’s SM performance. Moreover, it was found that firms still rely a lot in organic SM possibilities and their Investment capacity definition is strategically poor, which leads to a weak SM performance.
In brief, SM positive contribution to firm’s performance requires strong analytical skills, development of Marketing, Branding and Communication strategies, a solid SM budget definition and SM platforms’ business model, audiences and advertising offers appropriate to firm’s goals.As Redes Sociais (RS) são cada vez mais relevantes para os consumidores, enquanto isso, gestores procuram perceber como podem melhorar a performance das marcas nas RS, enquanto lidam com constrangimentos externos e internos.
Esta dissertação descreve o Processo de Tomada de Decisão (PTD) das empresas portuguesas, aquando à gestão da presença das marcas; resultando na criação de um esquema teórico que apoia o PTD no âmbito das RS.
Para este fim, foram recolhidos dados primários de oito entrevistas a key informants de sete empresas e de duas observações naturais de duas empresas. Os dados foram analisados e interpretados em linha com as teorias existentes sobre o tema principal. Posteriormente, dados secundários de quatro empresas foram analisados com base no esquema teórico final; o que resultou na caracterização de diferentes comportamentos que as empresas podem ter quando gerem as suas RS.
Assim, conclui-se que embora os modelos de negócio das RS se adequam às necessidades das empresas, ainda há dificuldade em integra-las nas estratégias de marketing. É necessário ter consciência de quais são os possíveis constrangimentos que podem influenciar a performance nas RS. Também foi descoberto que as empresas se baseiam nos resultados orgânicos, ignorando que uma fraca capacidade de investimento resulta numa má performance.
Resumindo, para que a atividade nas RS contribua positivamente para a empresa são necessárias fortes capacidades analíticas, desenvolvimento das estratégias de marketing, branding e de comunicação, definição de orçamento e, com base nos modelos de negócio, audiências e publicidade, escolher as RS mais adequadas
Joint Coverage and Power Control in Highly Dynamic and Massive UAV Networks: An Aggregative Game-theoretic Learning Approach
Unmanned aerial vehicles (UAV) ad-hoc network is a significant contingency
plan for communication after a natural disaster, such as typhoon and
earthquake. To achieve efficient and rapid networks deployment, we employ
noncooperative game theory and amended binary log-linear algorithm (BLLA)
seeking for the Nash equilibrium which achieves the optimal network
performance. We not only take channel overlap and power control into account
but also consider coverage and the complexity of interference. However,
extensive UAV game theoretical models show limitations in post-disaster
scenarios which require large-scale UAV network deployments. Besides, the
highly dynamic post-disaster scenarios cause strategies updating constraint and
strategy-deciding error on UAV ad-hoc networks. To handle these problems, we
employ aggregative game which could capture and cover those characteristics.
Moreover, we propose a novel synchronous payoff-based binary log-linear
learning algorithm (SPBLLA) to lessen information exchange and reduce time
consumption. Ultimately, the experiments indicate that, under the same
strategy-deciding error rate, SPBLLA's learning rate is manifestly faster than
that of the revised BLLA. Hence, the new model and algorithm are more suitable
and promising for large-scale highly dynamic scenarios
Beyond Transmitting Bits: Context, Semantics, and Task-Oriented Communications
Communication systems to date primarily aim at reliably communicating bit
sequences. Such an approach provides efficient engineering designs that are
agnostic to the meanings of the messages or to the goal that the message
exchange aims to achieve. Next generation systems, however, can be potentially
enriched by folding message semantics and goals of communication into their
design. Further, these systems can be made cognizant of the context in which
communication exchange takes place, providing avenues for novel design
insights. This tutorial summarizes the efforts to date, starting from its early
adaptations, semantic-aware and task-oriented communications, covering the
foundations, algorithms and potential implementations. The focus is on
approaches that utilize information theory to provide the foundations, as well
as the significant role of learning in semantics and task-aware communications.Comment: 28 pages, 14 figure
Link Scheduling in UAV-Aided Networks
Unmanned Aerial Vehicles (UAVs) or drones are a type of low altitude aerial mobile vehicles. They can be integrated into existing networks; e.g., cellular, Internet of Things (IoT) and satellite networks. Moreover, they can leverage existing cellular or Wi-Fi infrastructures to communicate with one another. A popular application of UAVs is to deploy them as mobile base stations and/or relays to assist terrestrial wireless communications. Another application is data collection, whereby they act as mobile sinks for wireless sensor networks or sensor devices operating in IoT networks. Advantageously, UAVs are cost-effective and they are able to establish line-of-sight links, which help improve data rate. A key concern, however, is that the uplink communications to a UAV may be limited, where it is only able to receive from one device at a time. Further, ground devices, such as those in IoT networks, may have limited energy, which limit their transmit power. To this end, there are three promising approaches to address these concerns, including (i) trajectory optimization, (ii) link scheduling, and (iii) equipping UAVs with a Successive Interference Cancellation (SIC) radio.
Henceforth, this thesis considers data collection in UAV-aided, TDMA and SICequipped wireless networks. Its main aim is to develop novel link schedulers to schedule uplink communications to a SIC-capable UAV. In particular, it considers two types of networks: (i) one-tier UAV communications networks, where a SIC-enabled rotary-wing UAV collects data from multiple ground devices, and (ii) Space-Air-Ground Integrated Networks (SAGINs), where a SIC-enabled rotary-wing UAV offloads collected data from ground devices to a swarm of CubeSats. A CubeSat then downloads its data to a terrestrial gateway. Compared to one-tier UAV communications networks, SAGINs are able to provide wide coverage and seamless connectivity to ground devices in remote and/or sparsely populated areas
Beyond Transmitting Bits: Context, Semantics, and Task-Oriented Communications
Communication systems to date primarily aim at reliably communicating bit sequences. Such an approach provides efficient engineering designs that are agnostic to the meanings of the messages or to the goal that the message exchange aims to achieve. Next generation systems, however, can be potentially enriched by folding message semantics and goals of communication into their design. Further, these systems can be made cognizant of the context in which communication exchange takes place, thereby providing avenues for novel design insights. This tutorial summarizes the efforts to date, starting from its early adaptations, semantic-aware and task-oriented communications, covering the foundations, algorithms and potential implementations. The focus is on approaches that utilize information theory to provide the foundations, as well as the significant role of learning in semantics and task-aware communications
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