Wamberto J. L. Queiroz

Spatial Correlation for DoA Characterization Using Von Mises, Cosine, and Gaussian Distributions

This paper presents mathematical expressions for the spatial correlation between elements of linear and circular antenna arrays, considering cosine, Gaussian, and Von Mises distributions, for the direction of arrival (DoA) of the electromagnetic waves at the receiver antenna. The expressions obtained for the Von Mises distribution can include or not the mutual coupling effect between the elements and are simpler than those obtained for the cosine and the Gaussian distributions of the angle of arrival. The Von Mises distribution produces spatial correlation expressions in terms of Bessel and trigonometric functions. An exact expression for the spatial correlation, taking into account the mutual coupling, for the circular and linear arrays and an arbitrary number of elements are presented. It can be verified, by numerical evaluation of the expressions, that the coupling between the elements correlates the electromagnetic field, and a separation of half wavelength could not be enough to decorrelate them.

Exact bit error probability of M-QAM modulation over flat rayleigh fading channels

In this paper we derive a general and closed- form expression for the bit error probability of square M-ary quadrature amplitude modulation (M-QAM) for a Rayleigh fading channel.

An alternative method to compute the bit error probability of modulation schemes subject to Nakagami-m fading

This paper presents an alternative method for determining exact expressions for the bit error probability (BEP) of modulation schemes subject to Nakagami- fading. In this method, the Nakagami- fading channel is seen as an additive noise channel whose noise is modeled as the ratio between Gaussian and Nakagami- random variables. The method consists of using the cumulative density function of the resulting noise to obtain closed-form expressions for the BEP of modulation schemes subject to Nakagami- fading. In particular, the proposed method is used to obtain closed-form expressions for the BEP of -ary quadrature amplitude modulation (-QAM), -ary pulse amplitude modulation (-PAM), and rectangular quadrature amplitude modulation (-QAM) under Nakagami- fading. The main contribution of this paper is to show that this alternative method can be used to reduce the computational complexity for detecting signals in the presence of fading.

Bit error probability of M-QAM and I × J-QAM modulation schemes in Nakagami fading

In this paper closed-form expressions for the bit error probability of M-QAM and I times J-QAM modulation schemes in Nakagami fading are derived. The classical optimum detector for signals under additive white Gaussian noise and the bit mapping consistency of QAM signals submitted to Gray mapping are considered.

Localization in IEEE 802.11 networks by using the nelder-mead method

This papers addresses the problem of localization of mobile devices in WiFi IEEE 802.11 networks considering indoor applications. The key idea of this work is estimate the distance between a mobile receiver and an access point based on the signal propagation losses. Five prediction models for the propagation losses are used: free-space, Recommendation ITU-R P.1238-1, WPS, exponential and potential regression. The Nelder-Mead Method was used to determine the mobile position from its distances to three access points. Experimental results shows that the best localization performance is obtained by using potential regression.

Performance of the modulation diversity technique for κ-μ fading channels

The performance of wireless communication systems can be significantly improved using the modulation diversity technique, which is based on the combination of a suitable choice of the reference angle of a signal constellation with independent interleaving of the symbol components. This technique has been evaluated considering different fading channel models, such as Rayleigh, Rice and Nakagami-m. However, in some specific scenarios, the tails of those fading distributions do not properly fit the experimental measured data, which demands the use of more general channel distributions. This article presents a performance evaluation of the modulation diversity technique for κ-μ fading channels. New expressions for the PEP (Pairwise Error Probability) are obtained using numerical integration, series representation and upper/lower bounds. The evaluation, based on Monte Carlo simulation, demonstrates that the performance gain of the modulation diversity increases as the fading becomes more severe. Communications channels exhibit some degree of time correlation, which cannot be perfectly estimated, affecting the performance of the modulation diversity system. Thus, a performance evaluation of the system, concerning the presence of temporal correlation and estimation errors in the channel is also presented in the article.

Performance analysis of generalized QAM modulation under η − μ and κ − μ fading

This paper presents new closed-form expressions for the symbol error probability (SEP) of θ-QAM modulation with maximum ratio combining (MRC) receiver under η−μ and κ−μ fading. The SEP formulae, obtained from the definite integrals of the moment generating function (MGF) of the signal-to-noise ratio (SNR) at the input of the MRC receiver, are written in terms of Lauricella functions. The numerical evaluation of the expressions is carried out for the η−μ distribution, which includes important distributions as special cases, such as Hoyt, Nakagami-m, Rayleigh, and one-sided Gaussian, as well as for the κ−μ distribution, which includes Rice, Nakagami-m, Rayleigh, and one-sided Gaussian as special cases.

Unified Analysis of the Local Scatters Channel Model

This article shows a simple mathematical treatment to model and simulate the local scatters channel using a Gaussian probability density for arrival angle distributions, time correlation functions and power spectral density. The correlation envelope is related to the channel parameters and is used in many applications where second order statistics are needed. The channel temporal analysis uses the WSS-US (Wide-Sense Stationary and Uncorrelated Scattering) model for modeling the directional components, considering parameters as angular spread, channel directional component and Doppler frequency.

Project of antenna arrays with random parameters

This paper presents a new way of projecting linear arrays structures using random excitation coefficients and random spacing between sensors. The results obtained show that these configurations can produce good radiation patterns in terms of side lobes level and other project specifications. Depending upon chosen parameters the radiation pattern can be optimized as compared to the one obtained using binomial coefficients. It can be as good as the patterns obtained using the Dolph-Tschebyscheff algorithm. This method can be used in order to get a smoother radiation pattern and can be useful to control the radiation pattern in response to user mobility. Another advantage is related to the numerical processing involved in the computation of excitation coefficients. They are chosen randomly from a convenient set, while in the other cases they are computed in real time and depend upon antenna dimensions, a task which can be computer intensive.

Closed-Form Expression for the Bit Error Probability of the -QAM for a Channel Subjected to Impulsive Noise and Nakagami Fading

In this paper, new exact expressions for evaluating the bit error probability (BEP) of the -ary quadrature amplitude modulation scheme ( -QAM) for a channel model characterized by double gated additive white Gaussian noise (G2AWGN) and Nakagami fading are presented. The derivation of the BEP is performed considering a method in which the multiplicative fading is transformed in an additive noise obtained by dividing the received signal by the estimated fading envelope. In addition, the probability density function (PDF) and cumulative density function (CDF) of the random variable that represents the aforementioned noise are obtained for the G2AWGN. The BEP curves as a function of the signal to permanent noise ratio for several values of the signal to impulsive noise ratio, modulation order, and fading parameters are also presented.