Log-moment estimators of the Nakagami-lognormal distribution

[EN] In this paper, estimators of the Nakagami-lognormal (NL) distribution based on the method of log-moments have been derived and thoroughly analyzed. Unlike maximum likelihood (ML) estimators, the log-moment estimators of the NL distribution are obtained using straightforward equations with a unique solution. Also, their performance has been evaluated using the sample mean, confidence regions and normalized mean square error (NMSE). The NL distribution has been extensively used to model composite small-scale fading and shadowing in wireless communication channels. This distribution is of interest in scenarios where the small-scale fading and the shadowing processes cannot be easily separated such as the vehicular environment.This work has been funded in part by the Programa de Estancias de Movilidad de Profesores e Investigadores en Centros Extranjeros de Ensenanza Superior e Investigacion of the Ministerio de Educacion, Cultura y Deporte, Spain, PR2015-00151 and by the Ministerio de Economia, Industria y Competitividad of the Spanish Government under the national project TEC2017-86779-C2-2-R, through the Agencia Estatal de Investigacion (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER).Reig, J.; Brennan, C.; Rodrigo Peñarrocha, VM.; Rubio Arjona, L. (2019). Log-moment estimators of the Nakagami-lognormal distribution. EURASIP Journal on Wireless Communications and Networking. 1-10. https://doi.org/10.1186/s13638-018-1328-6S110J. M. Ho, G. L. 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Estimation of the composite fast fading and shadowing distribution using the log-moments in wireless communications

In this work, we propose a framework to obtain estimators from a variety of distributions used in composite fast fading and shadowing modeling with applications in wireless communications: the Suzuki (Rayleigh-lognormal), Nakagami-lognormal, K (Rayleigh-gamma), generalized-K (Nakagami-gamma) and alpha-mu; (generalized gamma) distributions. These estimators are derived from the method of moments of these distributions in logarithmic units, usually known as log-moments. The goodness-of-fit of these estimators to experimental distributions has been checked from a measurement campaign carried out in an urban environment. Moreover a new method to separate fast fading and shadowing based on the Rathgeber procedure is proposed. The results conclude that the best-fitting distribution to the measurements is the Nakagami-lognormal. Also, the alpha-mu; distribution provides an acceptable matching with the advantage of its simplicity.The authors would like to thank the editor and reviewers their valuable comments which have enriched the quality of this paper. We would also express our gratitude to Dr. C. S. Withers, retired research statistician from the Applied Maths Group at Industrial Research Ltd, Lower Hutt, New Zealand, for his revision of the paper and his estimable remarks. This work has been funded in part by the Spanish Ministerio de Ciencia e Innovacion (TEC-2010-20841-C04-1).Reig, J.; Rubio Arjona, L. (2013). Estimation of the composite fast fading and shadowing distribution using the log-moments in wireless communications. IEEE Transactions on Wireless Communications. 12(8):3672-3681. https://doi.org/10.1109/TWC.2013.050713.120054S3672368112

On the Sum of Order Statistics and Applications to Wireless Communication Systems Performances

We consider the problem of evaluating the cumulative distribution function (CDF) of the sum of order statistics, which serves to compute outage probability (OP) values at the output of generalized selection combining receivers. Generally, closed-form expressions of the CDF of the sum of order statistics are unavailable for many practical distributions. Moreover, the naive Monte Carlo (MC) method requires a substantial computational effort when the probability of interest is sufficiently small. In the region of small OP values, we propose instead two effective variance reduction techniques that yield a reliable estimate of the CDF with small computing cost. The first estimator, which can be viewed as an importance sampling estimator, has bounded relative error under a certain assumption that is shown to hold for most of the challenging distributions. An improvement of this estimator is then proposed for the Pareto and the Weibull cases. The second is a conditional MC estimator that achieves the bounded relative error property for the Generalized Gamma case and the logarithmic efficiency in the Log-normal case. Finally, the efficiency of these estimators is compared via various numerical experiments

Multi-RIS-aided Wireless Systems: Statistical Characterization and Performance Analysis

In this paper, we study the statistical characterization and modeling of distributed multi-reconfigurable intelligent surface (RIS)-aided wireless systems. Specifically, we consider a practical system model where the RISs with different geometric sizes are distributively deployed, and wireless channels associated to different RISs are assumed to be independent but not identically distributed (i.n.i.d.). We propose two purpose-oriented multi-RIS-aided schemes, namely, the exhaustive RIS-aided (ERA) and opportunistic RIS-aided (ORA) schemes. In the ERA scheme, all RISs participate in assisting the communication of a pair of transceivers, whereas in the ORA scheme, only the most appropriate RIS participates and the remaining RISs are utilized for other purposes. A mathematical framework, which relies on the method of moments, is proposed to statistically characterize the end-to-end (e2e) channels of these schemes. It is shown that either a Gamma distribution or a LogNormal distribution can be used to approximate the distribution of the magnitude of the e2e channel coefficients in both schemes. With these findings, we evaluate the performance of the two schemes in terms of outage probability (OP) and ergodic capacity (EC), where tight approximate closed-form expressions for the OP and EC are derived. Representative results show that the ERA scheme outperforms the ORA scheme in terms of OP and EC. Nevertheless, the ORA scheme gives a better energy efficiency (EE) in a specific range of the target spectral efficiency (SE). In addition, under i.n.i.d. fading channels, the reflecting element setting and location setting of RISs have a significant impact on the overall system performance of both the ERA or ORA schemes. A centralized large-RIS-aided scheme might achieve higher EC than the distributed ERA scheme when the large-RIS is located near a transmitter or a receiver, and vise-versa

Experimental statistical channel modelling for advanced wireless communication systems in indoor environments

Draadloze communicatiesystemen voor mobiele telefonie en draadloos internet zijn onmisbaar geworden in het dagelijkse leven. De grootste troef van draadloze communicatie over bedrade communicatie is de toegenomen mobiliteit. Draadloze communicatie heeft evenwel ook één groot nadeel, namelijk de onzekerheid over de kwaliteit van de link tussen zender en ontvanger. Waar bedrade communicatie een doorgedreven ontwerp van het kanaal tussen zender en ontvanger (d.i. de kabel) toelaat, is het ontwerp van het draadloze kanaal (d.i. de omgeving) bijna onmogelijk. Desondanks kunnen wel modellen van de propagatie van draadloze signalen opgesteld worden voor verschillende types omgevingen. Deze modellen laten toe om de betrouwbaarheid en de performantie van een draadloze link in te schatten. Modellering van draadloze propagatie voor indooromgevingen is het algemeen onderwerp van dit proefschrift. De propagatiemodellering in dit proefschrift betreft drie types indooromgevingen, nl. industriële en kantooromgevingen, en de omgeving binnen in een voertuig. De modellering bestaat uit statistische modellen gebaseerd op veldmetingen in deze omgevingen. Verschillende parameters van draadloze signalen worden onderzocht, zoals de variabiliteit van het signaalvermogen met de afstand en in de tijd, het signaalbereik, de dispersie in het tijdsdomein, de dispersie in het spatiaal domein en het vermogensverlies bij propagatie van buiten naar binnen een voertuig

Fading Evaluation in the 60GHz Band in Line-of-Sight Conditions

An exhaustive analysis of the small-scale fading amplitude in the 60GHz band is addressed for line-of-sight conditions (LOS). From a measurement campaign carried out in a laboratory, we have estimated the distribution of the small-scale fading amplitude over a bandwidth of 9GHz. From the measured data, we have estimated the parameters of the Rayleigh, Rice, Nakagami-m, Weibull, and \alpha-\mu distributions for the small-scale amplitudes. The test of Kolmogorov-Smirnov (K-S) for each frequency bin is used to evaluate the performance of such statistical distributions. Moreover, the distributions of the main estimated parameters for such distributions are calculated and approximated for lognormal statistics in some cases. The matching of the above distributions to the experimental distribution has also been analyzed for the lower tail of the cumulative distribution function (CDF).These parameters offer information about the narrowband channel behavior that is useful for a better knowledge of the propagation characteristics at 60GHz.This work was supported in part by the Spanish Ministerio de Ciencia e Innovacion TEC-2010-20841-C04-1 and by the Universitat Politecnica de Valencia, PAID 05-11 ref. 2702. The authors thank the anonymous reviewers for their valuable remarks and suggestions which have considerably enriched the final paper.Reig, J.; Martínez Inglés, M.; Rubio Arjona, L.; Rodrigo Peñarrocha, VM.; Molina-García-Pardo, J. (2014). Fading Evaluation in the 60GHz Band in Line-of-Sight Conditions. International Journal of Antennas and Propagation. 2014:1-12. https://doi.org/10.1155/2014/984102S1122014Smulders, P. (2002). 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