Search

In modern day communication systems, the massive MIMO architecture plays a pivotal role in enhancing the spatial multiplexing gain, but vice versa the system energy efficiency is compromised. Consequently, resource allocation in-terms of antenna selection becomes inevitable to increase energy efficiency without having any obvious effect or compromising the system spectral efficiency. Optimal antenna selection can be performed using exhaustive search. However, for a massive MIMO architecture, exhaustive search is not a feasible option due to the exponential growth in computational complexity with an increase in the number of antennas. We have proposed a computationally efficient and optimum algorithm based on the probability distribution learning for transmit antenna selection. An estimation of the distribution algorithm is a learning algorithm which learns from the probability distribution of best possible solutions. The proposed solution is computationally efficient and can obtain an optimum solution for the real time antenna selection problem. Since precoding and beamforming are also considered essential techniques to combat path loss incurred due to high frequency communications, so after antenna selection, successive interference cancellation algorithm is adopted for precoding with selected antennas. Simulation results verify that the proposed joint antenna selection and precoding solution is computationally efficient and near optimal in terms of spectral efficiency with respect to exhaustive search scheme. Furthermore, the energy efficiency of the system is also optimized by the proposed algorithm, resulting in performance enhancement of massive MIMO systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose a model for the effect of misalignment of antennas due to mechanical vibrations and experimentally validate its accuracy in a Ka-band (26-40 GHz) transmission link. Our approach provides a valuable tool that is analytically tractable and physically simple to implement. To highlight the applicability of the model, a setup based on a centralized radio access network (C-RAN) transmitting and receiving wireless signals in the Ka-band is implemented. With this tool, the robustness of 5G networks to antenna misalignments can be evaluated in terms of bit-error rate. We show how the presence of misalignment in this type of systems induces an error floor observable in the bit-error-rate performance. A simple static decision threshold is implemented taking into account the amount of displacement and, directly related to that factor, on the expected number of fades per unit time. The closed-form expressions derived through this paper are in perfect agreement with the experimental measurements taken from the implemented system. [ABSTRACT FROM AUTHOR]

Satellite communications require more bandwidth due to the necessity of increasing the capacity of communication channels and bandwidth to end-users. As a result, looking for new bands is required in the electromagnetic spectrum including millimeter and sub-millimeter wavelengths. Recent technological developments made the extremely high frequencies (EHF) above 30 GHz as a candidate for wireless applications such as the fifth generation (5G) of mobile communications, high resolution radars, and remote sensing. The EHF communication systems are becoming more and more commercial, cheap, and compact. However, the fact that the atmospheric medium is not completely transparent to millimeter waves requires considerations of the frequency selective absorption and dispersion effects emerging in this band. These phenomena affect also remote sensing in the millimeter and sub-millimeter waves (the terahertz frequencies). The atmospheric effects on the propagation of millimeter and sub-millimeter wave transmission from land to satellite are discussed. It is shown that not only atmospheric absorption plays a significant role on the received signal strength but also the refraction index of the atmospheric medium. The inhomogeneous refractivity causes the beam to "bend" along the propagation path, and it may even "miss" its destination. This phenomenon should be considered in the design of a link operating in extremely high frequencies involving highly directive antennas. [ABSTRACT FROM AUTHOR]

Attenuation measurements through extreme rain in a climate wind tunnel are carried out to benchmark the possibility of wireless data transmission at 77 GHz during adverse weather conditions. Based on a network analyzer and external E-band mixers, the propagation loss at 77 GHz is obtained over a distance of 180 m using a corner reflector at the end of a 90-m tunnel. Comparing the results to prediction models like the ITU-R P.838, a large deviation of several tens of dB/km was found for high rain rates when the drop size distribution is neglected. In the paper, the authors use known attenuation models based on rain drop distribution functions to explain the high measured attenuation during the testing, demonstrating a large variation of specific attenuation under heavy rain at high microwave frequencies. [ABSTRACT FROM AUTHOR]

This paper contains measured data for desktop propagation path loss at millimeter wave band. Different ratios between transmitting antenna height and receiving antenna height were studied based on a vector network analyzer system. Transmitting and receiving antenna were separated by distances ranging from 5 to 300 cm on a wooden desktop, and the antenna heights were varied from 5 to 25 cm. Average path loss data are coupled with the path loss exponents and the breakpoint locations of piecewise model to provide insight into large scale propagation characteristics of desktop millimeter wave communication systems. These measurement results may aid in the development of future short range wireless propagation in millimeter wave bands. [ABSTRACT FROM AUTHOR]

The theory is presented for one method of determining the effective polarization parameters of the rain medium in the problem of polarization information processing of detecting target. The determination of the effective polarization parameters of the propagation medium is from the data of propagation measurements over a line-of-sight link. The polarization parameters ϕ the effective average value, σ the effective standard deviation and F the effective shape parameter of the propagation medium are obtained by means of the method of inverse scattering, showing a good agreement with the data from direct measurements. [ABSTRACT FROM AUTHOR]

As the operating frequencies of communication systems more higher into the millimeter wave range, and the density of particles in medium is more denser, the effects of multiple scattering in sandstorm become more significant. This paper treats the problems of electromagnetic multiple scattering in strong sandstorm by the Monte Carlo method. Based on the analytical theory of multiple scattering, the millimeter wave propagation and scattering in discrete random media are investigated by means of the particle-tracking technique. The millimeter wave is regarded as a Markov chain of wave particle collisions in a medium in which it is scattered and absorbed. Considering the effect of multiple scattering, millimeter wave attenuation induced by strong sandstorm is simulated numerically. The values of theoretical calculation are in good agreement with the measured results of simulated experiment at 34 and 93 GHz. [ABSTRACT FROM AUTHOR]