arXiv subjects

H. Alves

Publications and source records attributed to H. Alves.

6 recordsLinked to original sources

arXiv2020

LoRa Performance Analysis with Superposed Signal Decoding

This paper considers the use of successive interference cancellation (SIC) to decode superposed signals in Long Range (LoRa) networks. We build over a known stochastic geometry model for LoRa networks and include the effect of recovering colliding packets through SIC. We derive closed-form expressions for the successful decoding of packets using SIC taking path loss, fading, noise, and interference into account, while we validate the model by means of Monte Carlo simulations. Results show that SIC-enabled LoRa networks improve worst-case reliability by up to 34%. We show that, for at least one test scenario, SIC increases by 159% the number of served users with the same worst-case reliability level.

cs.IT↗

arXiv2019

On the Statistics of the Ratio of Non-Constrained Arbitrary α-μ Random Variables: a General Framework and Applications

In this paper, we derive closed-form exact expressions for the main statistics of the ratio of squared alpha-mu random variables, which are of interest in many scenarios for future wireless networks where generalized distributions are more suitable to fit with field data. Importantly, different from previous proposals, our expressions are general in the sense that are valid for non constrained arbitrary values of the parameters of the alpha-mu distribution. Thus, the probability density function, cumulative distribution function, moment generating function, and higher order moments are given in terms of both (i) theFox H-function for which we provide a portable and efficient Wolfram Mathematica code and (ii) easily computable series expansions. Our expressions can be used straightforwardly in the performance analysis of a number of wireless communication systems, including either interference-limited scenarios, spectrum sharing, full-duplex or physical-layer security networks, for which we present the application of the proposed framework. Moreover, closed-form expressions for some classical distributions, derived as special cases from the alpha-mu distribution, are provided as byproducts. The validity of the proposed expressions is confirmed via Monte Carlo simulations.

cs.IT↗

arXiv2018

Optimal control of the customer dynamics based on marketing policy

We consider an optimal control problem for a non-autonomous model of ODEs that describes the evolution of the number of customers in some firm. Namely we study the best marketing strategy. Considering a $L^2$ cost functional, we establish the existence and uniqueness of optimal solutions, using an inductive argument to obtain uniqueness on the whole interval from local uniqueness. We also present some simulation results, based on our model, and compare them with results we obtain for an $L^1$ cost functional. For the $L^1$ cost functional the optimal solutions are of bang-bang type and thus easier to implement, because at every moment possible actions are chosen from a finite set of possibilities. For the autonomous case of $L^2$ problem, we show the effectiveness of the optimal control strategy against other formulations of the problem with simpler controls.

math.OC↗

arXiv2017

Wireless Powered Communications with Finite Battery and Finite Blocklength

We analyze a wireless communication system with finite block length and finite battery energy, under quasi-static Nakagami-m fading. Wireless energy transfer is carried out in the downlink while information transfer occurs in the uplink. Transmission strategies for scenarios with/without energy accumulation between transmission rounds are characterized in terms of error probability and energy consumption. A power control protocol for the energy accumulation scenario is proposed and results show the enormous impact on improving the system performance, in terms of error probability and energy consumption. The numerical results corroborate the existence and uniqueness of an optimum target error probability, while showing that a relatively small battery could be a limiting factor for some setups, specially when using the energy accumulation strategy.

cs.IT↗

arXiv2010

Small gap semiconducting organic charge-transfer interfaces

We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene (TMTSF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have un-measurably high resistance, the interface exhibits a resistivity of few tens of MegaOhm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band-diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene (TTF)-TCNQ interfaces, these results indicate that single-crystal organic heterostructures create new electronic systems with properties relevant to both fundamental and applied fields.

cond-mat.mtrl-sci↗

arXiv2009

Band-like transport and trapping in TMTSF Single Crystal Transistors

We perform a combined experimental and theoretical study of tetramethyltetraselenafulvalene (TMTSF) single-crystal field-effect transistors, whose electrical characteristics exhibit clear signatures of the intrinsic transport properties of the material. We introduce a simple, well-defined model based on physical parameters and we successfully reproduce quantitatively the device properties as a function of temperature and carrier density. The analysis allows its internal consistency to be checked, and enables the reliable extraction of the density and characteristic energy of shallow and deep traps in the material. Our findings indicate that shallow traps originate from electrostatic potential fluctuations generated by charges fixed in the deep traps.

cond-mat.mtrl-sci↗