On the impact of the radiation pattern of the antenna element on MU-MIMO indoor channels

This paper presents an analysis of the effect that the radiation pattern of the antenna element that makes up the base station array has on the structure of multi-user multiple-input multiple-output (MU-MIMO) channels. In this paper, the analysis focuses on the uplink. It is well known that the antennas are an inseparable part of the radio channel. The use of more or less directional antennas as elements of the base station array of a MIMO system influences the channel in two fundamental parameters that affect the performance of MU-MIMO systems: on the one hand, the coherence bandwidth, which determines the necessary overhead in the channel estimation; and, on the other hand, the orthogonality of the subchannels between the multiple users and the base station, which influences the degree with which the condition of "favorable propagation" is fulfilled. Based on an experimental analysis using both omnidirectional and directional antennas, conclusions are drawn about how these two parameters are affected and their influence on the spectral efficiency obtainable. The measurement campaign was carried out in an indoor environment in the 3 to 4 GHz band.This work was supported by the Spanish Ministerio de Economía, Industria y Competitividad, under the project TEC2017-86779-C2-1-R

A lower bound for the coherence block length in mobile radio channels

A lower bound for the coherence block (ChB) length in mobile radio channels is derived in this paper. The ChB length, associated with a certain mobile radio channel, is of great practical importance in future wireless systems, mainly those based on massive multiple input and multiple output (M-MIMO) technology. In fact, it is one of the factors that determines the achievable spectral efficiency. Firstly, theoretical aspects regarding the mobile radio channels are summarized, focusing on the rigorous definition of coherence bandwidth (BC) and coherence time (TC) parameters. Secondly, the uncertainty relations developed by B. H. Fleury, involving both BC and TC, are presented. Afterwards, a lower bound for the product BCTC is derived, i.e., the ChB length. The obtained bound is an explicit function of easily measurable parameters, such as the delay spread, mobile speed and carrier frequency. Furthermore, and especially important, this bound is also a function of the degree of coherence with which we define both BC and TC. Finally, an application example that illustrates the practical possibilities of the bound obtained is presented. As a further conclusion, the need to determine what degree of correlation is required to consider mobile channels as effectively flat-fading and stationary is highlighted.This work has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (TEC2017-86779-C2-1-R)

Characterisation of indoor massive MIMO channels using ray-tracing: A case study in the 3.2-4.0 GHz 5G band

In this paper, research results on the applicability of ray-tracing (RT) techniques to model massive MIMO (MaMi) channels are presented and discussed. The main goal is to show the possibilities that site-specific models based on rigorous RT techniques, along with measurement campaigns considered for verification or calibration purposes where appropriate, can contribute to the development and deployment of 5G systems and beyond using the MaMi technique. For this purpose, starting from the measurements and verification of the simulator in a symmetric, rectangular and accessible scenario used as the testbed, the analysis of a specific case involving channel characterisation in a large, difficult access and measurement scenario was carried out using the simulation tool. Both the measurement system and the simulations emulated the up-link in an indoor cell in the framework of a MaMi-TDD-OFDM system, considering that the base station was equipped with an array consisting of 10 × 10 antennas. The comparison of the simulations with the measurements in the testbed environment allowed us to affirm that the accuracy of the simulator was high, both for determining the parameters of temporal dispersion and frequency selectivity, and for assessing the expected capacity in a specific environment. The subsequent analysis of the target environment showed the high capacities that a MaMi system can achieve in indoor picocells with a relatively high number of simultaneously active users.This work has been supported by the Spanish Ministry of the Economy, Industry and Competitiveness (TEC2017-86779-C2-1-R

Variaciones temporales del canal radio de interiores en la banda de 1.8 GHz

This communication presents the results of a measurement campaign carried out with the aim of analyzing the impact of people movement and activities on the indoor radio propagation channel at the frequency of 1.8 GHz. For that, the temporal variations of the channel between fixed terminals are measured in several propagation environments, in which usually different degrees of activity take place, allowing the definition of different canonical environments. From the measured data, the figures and statistical parameters that characterize each of the environments are analyzed, in order to be able to associate the results obtained with the density of motion

Resultados experimentales de correlación espacial de un sistema MIMO en un entorno exterior-interior a 2.4 GHz

For a better planning of a MIMO system is necessary a deep knowledge of the propagation channels characteristics and the degree of independence or correlation among them. This work presents the results obtained from the experimental analysis of the spatial correlation of a MIMO system as a function of the separation between receiver elements. The measurements were made at 2.4GHz for wireless applications in ISM band. The results show that the subchannels have a Rayleigh behavior and that the correlation depends on the relative disposition between receiver and transmitter array and on the presence or absence of line of sight. For LOS situations, depending on the receiver and transmitter relative position (in-line, broadside) the correlation distance gets values up to 6λ. Whereas, in NLOS situations the correlation distance is smaller than in LOS case, independently of the relative disposition of the arrays

Modelado de canales MIMO 2x2 de banda ancha en interiores

A stochastic 2x2 MIMO wideband channel modelling method is presented. This channel model uses tapped delay lines (TDL) to model the subchannels and a single channel spatial correlation matrix to introduce the statistical dependence. This model represents a novel simplification with respect to other wideband MIMO models. The channel models obtained from this method are accurate and computationally efficient. Using this method channel models of indoor scenarios are obtained. The results show that the simulated channels provides channel capacity results similar to the measured ones

Análisis de la correlación de canales MIMO en interiores a 2 y 2.4 GHz

This paper presents an experimental analysis of the spatial correlation between MIMO subchannels, analyzing the various factors which affect the correlation, such as the type of scenario, topology of the arrays and the relative position between them. The results show a great variability in the correlation coefficient as a function of the distance between the elements. Thus, a statistical characterization of the correlation coefficient is performed

Modelado del canal MIMO interior mediante trazado de rayos

This communication presents a MIMO (Multiple Input Multiple Output) channel model based on ray-tracing techniques, which uses a full 3D implementation of Geometric Optics and Uniform Theory of Diffraction. Results obtained from measurements and simulation of capacity of a 2x2 system in specific indoor environments at the frequency of 2 GHz are presented. The rigorous and quantitative comparison between measurements and simulations shows that the model accuracy is sufficient for the analysis and design of different aspects of the full MIMO system

Simulación de radares de tráfico marítimo en entornos portuarios

This paper presents a method to predict site-specific radar coverage. The method is based on solving the monostatic scattering problem by using the Physical Optics (PO) or Kirchhoff method, in combination with the use of Geographical Information Systems, to model the specific terrain. The possibility to calculate the radar coverage, the time of arrival of the reflected pulses and the power delay profile allows the effect of clutter and multireflections to be analyzed in detail. Radar parameters, such as its location, antenna types, pulse duration and pulse repetition frequency can be optimized. Also, this information is of great interest in the design and improvement of sensitivity time control (STC) and constant false-alarm rate (CFAR) systems

Analysis of massive MIMO performance in an indoor picocell with high number of users

This paper presents an analysis of the massive multiple input and multiple output (MIMO) channel in an indoor picocell with a high number of active user terminals and a base station consisting of a virtual array with up to one hundred elements. The analysis is based on the results of a measurement campaign carried out in the 3.2 to 4 GHz band in a scenario of reduced size and with a symmetrical geometry, in which users are also placed in an orderly manner. The channel meets the condition of favorable propagation depending on several factors, one of the most important being the spatial distribution of users. Results concerning the inverse condition number as well as the channel sum capacity are included. Another factor that determines the performance of massive MIMO systems when operated in an orthogonal frequency division multiplexing (OFDM) framework is the frequency selectivity of the channel that limits the size of the coherence block (ChB). Focusing on the most significant results achieved, it can be concluded that the channel reaches a capacity of 89% with respect to an i.i.d. Rayleigh channel. Concerning the cumulative distribution function (CDF) of the sum capacity, it can also be observed that the tails are not very pronounced, which indicates that a homogeneous service can be given to all users. Regarding the number of samples that make up the ChB, although it is high in all cases (of the order of tens of thousands), it strongly depends on the degree of correlation used to calculate the coherence bandwidth.This work was supported in part by the Spanish Ministerio de Economía, Industria y Competitividad, under Grant TEC2017-86779-C2-1-R, in part by the European economic community (EEC) through Fondo Europeo de Desarrollo Regional (FEDER) funds, and in part by the Spanish Ministerio de Ciencia e Innovación under Grant UCAN08-4E-010