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Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) is a multicarrier signaling technique which trades off robustness for spectral efficiency when compared to conventional OFDM with a cyclic prefix. In this paper, a novel matrix model for passband OFDM-OQAM signaling with a small number of subcarriers over a multipath frequency selective fading channel is presented. Specifically, in OFDM-OQAM a frequency selective channel is divided into many smaller but still frequency selective overlapping channels, so approximating the frequency response of a subchannel by the channel frequency response sampled at the subcarrier frequency may be inadequate. Channel effects may be better characterized if the frequency response of each subchannel is represented as a Taylor expansion at the subcarrier frequency. Simulation results show how the matrix model implemented by means of this approximation is a suitable model for OFDM-OQAM with a small number of subcarriers

Abstract:Energy efficiency is a fundamental requirement for a wireless protocol to be suitable for use within the Internet of Things. New technologies are emerging aiming at an energy-efficient communication. Among them, Bluetooth Low Energy is an appealing solution. Recently, the specifications of Bluetooth 5 have been presented with the purpose to offer significant enhancements compared to the earlier versions of the protocol. Bluetooth 5 comes with new communication modes that differ in range, speed, and energy consumption. This paper proposes a fuzzy-based solution to cope with the selection of the communication mode, among those introduced with Bluetooth 5, that allows the best energy efficiency. This communication mode, used by mobile devices, is dynamically regulated by varying the transmission power, returned as the output of a Fuzzy Logic Controller (FLC). A Particle Swarm Optimization (PSO) algorithm is presented to achieve the optimal parameters of the proposed FLC, i.e., optimizing the triangular membership functions, by varying their range, to reach the best results concerning the battery life of mobile devices. The proposed FLC is based on triangular membership functions because they represent a good trade-off between computation cost and efficiency. The paper presents a detailed description of the FLC design, a logical analysis of the PSO algorithm for the derivation of best performance conditions values, and experimental assessments, obtained through testbed scenarios.

The search of routes with multiple Quality of Service (QoS) constraints from sources to destinations connected by networks is a Non Polynomial (NP) problem, which can be approached using Genetic Algorithms (GAs). These are heuristic algorithms that simulate the natural evolution process to solve optimization problems. In this paper we elaborate on tree-based GAs which represent the set of paths from source to destination as a tree. While existing GA applications use m-ary or binary encoding representing single paths and classes of paths in chromosomes, respectively, we propose a GA application with hybrid encoding which uses both of them. This application uses binary encoding from the first iteration until good classes of paths are found and later encodes the best paths of these classes with m-ary encoding. Its objective is taking advantage of the fast convergence due to the per class-processing of binary chromosomes and the lower computational cost of the single path processing of m-ary chromosomes. Simulation results show the performance, in terms of convergence speed, of the proposed GA application with hybrid encoding.

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