Energy-efficient wireless communication

In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

Approximating minimum power covers of intersecting families and directed edge-connectivity problems

AbstractGiven a (directed) graph with costs on the edges, the power of a node is the maximum cost of an edge leaving it, and the power of the graph is the sum of the powers of its nodes. Let G=(V,E) be a graph with edge costs {c(e):e∈E} and let k be an integer. We consider problems that seek to find a min-power spanning subgraph G of G that satisfies a prescribed edge-connectivity property. In the Min-Powerk-Edge-Outconnected Subgraph problem we are given a root r∈V, and require that G contains k pairwise edge-disjoint rv-paths for all v∈V−r. In the Min-Powerk-Edge-Connected Subgraph problem G is required to be k-edge-connected. For k=1, these problems are at least as hard as the Set-Cover problem and thus have an Ω(ln|V|) approximation threshold. For k=Ω(nε), they are unlikely to admit a polylogarithmic approximation ratio [15]. We give approximation algorithms with ratio O(kln|V|). Our algorithms are based on a more general O(ln|V|)-approximation algorithm for the problem of finding a min-power directed edge-cover of an intersecting set-family; a set-family F is intersecting if X∩Y,X∪Y∈F for any intersecting X,Y∈F, and an edge set I covers F if for every X∈F there is an edge in I entering X

Complex Signal Mapping for Improving Spectral Efficiency of Li-Fi Systems, Journal of Telecommunications and Information Technology, 2019, nr 3

Light fidelity (Li-Fi) systems based on the orthogonal frequency division multiplexing (OFDM) scheme have gained more attention in the communications circles, as a means to provide high spectral efficiency and ensure stricter data rate requirements for visible light communication (VLC) systems. However, common OFDM schemes employ Hermitian symmetry to obtain a real-valued signal which is necessary in intensity modulation and direct detection (IM/DD) optical systems, at the expense of doubling the required bandwidth. In this paper, a novel transmission scheme for an OFDM-based Li-Fi system is proposed to tackle the issue in question. A new approach to complex signal mapping (CSM), based on the pairing function method, has been developed for Li-Fi systems. It does not require Hermitian symmetry and, hence, saves about 50% of the required bandwidth. Unlike existing OFDM-based VLC approaches, the proposed scheme employs CSM to ensure a real and positive signal without Hermitian symmetry in order to fully utilize the bandwidth available to Li-Fi networks. Simulation results show that the proposed scheme significantly outperforms other systems in terms of spectral efficiency. The CSM-OFDM based Li-Fi system also achieves a good peak-to-average power ratio (PAPR) reduction with acceptable bit-error-rate (BER) performance, compared to conventional approaches

Assessment of Area Energy Efficiency of LTE Macro Base Stations in Different Environments, Journal of Telecommunications and Information Technology, 2015, nr 1

Energy efficiency (EE) of wireless telecommunications has become a new challenge for the research community, governments and industries in order to reduce CO2 emission and operational costs. EE of base stations (BSs) in cellular net- works is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall negative impact to the environment and economic issues for wireless network operators. In this paper, a framework focuses on the Area Energy Efficiency (AEE) evaluation of LTE BSs is presented. The parameters affect on the AEE and the coverage area of LTE BS in different scenarios are investigated. AEE analysis has been done using a few key performance indicators including transmit power, bandwidth, load factor with the assumption of different scenarios (urban, suburban and rural). The simulation results show that the LTE BSs have better AEE in an urban environment for cell radius less than 750 m compare with the suburban and rural environments. Furthermore, it is obvious that there is a strong influence of traffic load, BW and transmission power on AEE of LTE network. On the other hand, AEE increases significantly as the BW size increases. Finally, it has been shown that the AEE of LTE macro BS decreases with increasing the percentage of traffic load for all scenarios

Diseño de la topología de una red ad-hoc

Las redes ad-hoc de comunicación están formadas por diferentes dispositivos, normalmente inalámbricos, que pueden situarse en cualquier punto del espacio. Para poder comunicarse se han de definir enlaces entre los diferentes nodos de manera que exista conectividad entre todos los nodos de la red. Este proyecto, continuación de trabajos anteriores, tiene como objetivo el diseño de la topología de una red ad-hoc con un doble requerimiento. Por un lado, se ha de garantizar conectividad entre todos los nodos de la red (y ello bajo la posibilidad de utilizar cualquier dispositivo como nodo intermedio de conmutación). Por otro lado, se ha de conseguir que el consumo total de las baterías de los dispositivos sea mínimo. El problema presentado por los anteriores proyectos, conocido como subgrafo de difusión de energía mínima (MECBS), fue resuelto mediante la utilización de algoritmos probabilistas –simulated annealing y hormigas– y un algoritmo determinista basado en la obtención de árboles generadores mínimos mediante Kruskal. En ese caso, un único nodo raíz debe mandar información al resto de la red. El presente proyecto trata de añadir pequeñas variaciones a los algoritmos de simulated annealing y hormigas para mejorar sus resultados y generaliza el problema para el caso en que todos los nodos deban enviar información al resto de nodos (problema que hemos denominado subgrafo de gossiping de energía mínima, MECGS), lo que ha de dar como resultado –en comparación con el caso en que sólo un nodo manda información al resto de la red– topologías ligeramente distintas y de mayor densidad de enlaces

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