Ultra densification of the number of antennas combined with the use of large bandwidths in the millimeter wave (mmWave) spectrum is considered one of the main methodologies to achieve the quality of service requirements for future generations of wireless communications. Massive multipleinput multiple-output (mMIMO) cell-free (CF) systems have a large number of access points (APs) distributed in the coverage area, serving simultaneously a smaller number of users consuming the same timefrequency resources. In order to support realistic CF networks designs, this work proposes a performance analysis based on ray tracing simulations. The propagation modeling considers reflection, diffraction, diffuse scattering, atmospheric molecular absorption and foliage and rainfall losses. CF networks with APs equipped with multiple antennas operating in the 26 GHz, 38 GHz and 73 GHz bands are evaluated. From the simulation results, the communication channel is characterized and parameterized. Different performance analysis of CF networks are performed, based on downlink spectral efficiency. In addition, the performance of CF networks in rainy environments is evaluated, and it has been observed that this architecture promotes resistance to the effect of rain attenuation.INDEX TERMS cell-free, massive MIMO, millimeter wave, ray tracing, spectral efficiency.

This paper presents an analysis of the gated Gaussian impulsive noise and its effects on M-ary Quadrature Amplitude Modulation (M-QAM) schemes. In the approach, both amplitude variation and noisy pulse duration can be characterized as a modulation of the impulsive noise component by a discrete (binary or m-ary) random process. New exact expressions are presented for the probability density function, autocorrelation function and power spectral density of the noise, as well as for the bit error probability of M-QAM, considering the maximum a posteriori probability optimum receiver. An important aspect of the proposed approach is the fact that the discrete random process incorporates the main parameters of the impulsive noise, such as amplitude, duration, instants in which the noise is added and time intervals between instants in which the noise is added.

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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.

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