1,721,113 research outputs found
Channel hardening, favorable equalization and propagation in wideband massive MIMO
No full textThis paper analyzes the channel hardening and favorable propagation behavior of frequency-selective massive MIMO channels. To this purpose the concept of favorable equalization is introduced to characterize the property of the channel to become frequency flat as the number of antennas grows when proper pre-filtering is adopted. It is shown that classic OFDM-based massive MIMO and time-reversal schemes, usually considered and analyzed as different technologies, are particular cases of the same framework. Their generalization leads to the concept of massive waveforming, which allows the creation of parallel wideband AWGN-like links between the base station and the users
MCM systems with waveform shaping in multi-user environments: effects of fading, interference and timing errors
No full textA unified procedure to characterize the effect of interchannel and intersymbol interference, Doppler and fading in MCM systems, is presented. The effect of different waveform shapes is considered in order to check the possibility of utilizing MCM as a multiple access technique. The degradation of system performance due to time and frequency offsets typical of multi-user environments is evaluated. In order to compare in a concise way different schemes, graphs showing time-frequency signatures, are introduced. The effect of the number of subcarriers and sampling frequency offsets in FFT-based implementation is also taken into account
Reconfigurable Electromagnetic Environments: A Signal Processing Approach
No full textThe emergence of smart radio environments (SREs) and holographic radio paradigms, which rely on reconfigurable intelligent surfaces (RISs), has highlighted the importance of developing physically consistent models and design tools for communication systems [1, 2]. As we move towards a future characterized by reconfigurable electromagnetic (EM) environments, the primary objective will be to optimize the system response in real time by adjusting the parameters of the electromagnetic objects (EMOs) composing the system, such as the reflection properties of metasurface-based RISs. Achieving this goal requires a holistic system view that emphasizes the need for tractable and physically consistent design tools that integrate both signal processing and EM theory [3]. In this perspective, starting from rigorous EM arguments, we have developed a comprehensive framework for the characterization and design of programmable EM environments that is valid in both the far-field and near-field regimes (radiative and reactive). This framework is designed to provide a system-theoretic and physically-consistent interpretation of reconfigurable EM environments. Our approach reveals that any system involving linear EMOs can be viewed as a space-variant feedback filter (see Fig. 1). Specifically, we demonstrate that boundary conditions applied to a generic EMO can be represented as a feedback system. Analyzing and designing space-variant feedback systems can be challenging, so we developed an approach that incorporates linear algebra operations over a graph to design and characterize EM systems with reconfigurable EMOs. We also establish a relationship between the EM transfer function and the linear algebra representation of the system, with a focus on characterizing intelligent surfaces
Communicating with Large Intelligent Surfaces: Fundamental Limits and Models
Full text linkThis paper analyzes the optimal communication involving large intelligent surfaces (LIS) starting from electromagnetic arguments. Since the numerical solution of the corresponding eigenfunction problems is in general computationally prohibitive, simple but accurate analytical expressions for the link gain and available spatial degrees-of-freedom (DoF) are derived. It is shown that the achievable DoF and gain offered by the wireless link are determined only by geometric factors, and that the classical Friis' formula is no longer valid in this scenario where the transmitter and receiver could operate in the near-field regime. Furthermore, results indicate that, contrarily to classical MIMO systems, when using LIS-based antennas DoF larger than 1 can be exploited even in strong line-of-sight (LOS) channel conditions, which corresponds to a significant increase in spatial capacity density, especially when working at millimeter waves
Communicating with Intelligent Surfaces
Full text linkThis paper analyzes the fundamental communication problem involving large intelligent surfaces (LIS) starting from electromagnetic (e.m.) arguments. Since the numerical solution of the corresponding optimal eigenfunction problem is in general computationally prohibitive, simple but accurate analytical expressions for the link gain and available degrees-of-freedom (DoF) are derived. It is shown that the achievable DoF and gain offered by the wireless link are determined only by geometric factors, and that the classic Friis' formula is no longer valid in this scenario where the transmitter and receiver could operate in the near-field regime. Furthermore, results indicate that, contrarily to classic MIMO systems, when using LIS more than one DoF might be available in strong line-of-sight (LOS) channel conditions, which corresponds to a significant increase of spatial capacity density
Introduction to Selected Extended Papers from PIMRC’2018
No full textIntroduction to Selected Extended Papers from PIMRC’201
Holographic Communication Using Intelligent Surfaces
No full textHolographic communication is intended as a holistic way to manipulate, with unprecedented flexibility, the electromagnetic field generated or sensed by an antenna. This is of particular interest when using large antennas at high frequency (e.g., at millimeter-wave or terahertz), whose operating condition may easily fall in the Fresnel region (radiating near-field), where the classical plane wave propagation assumption is no longer valid. This article analyzes the optimal communication involving large intelligent surfaces realized, for example, with metamaterials as possible enabling technology for holographic communication. It is shown that traditional propagation models must be revised and that, when exploiting spherical wave propagation in the near-field region, new opportunities are opened, for example, in terms of feasible orthogonal communication channels
High-Speed Indoor Wireless Communications at 60 GHz with coded OFDM
No full textA high-speed indoor wireless communication system using coded orthogonal frequency-division multiplexing (OFDM) and working at 60 GHz is proposed and analyzed. An actual propagation environment consisting of a medium sized research laboratory, characterized by means of a ray-tracing technique, is considered for the analysis. In this contest the paper investigates and discusses the effects of frequency diversity, antenna sectorization, OFDM clustering, and different block coding strategies. Moreover, to characterize the communication between stationary indoor terminals at millimeter waves, a new definition of coverage is introduced. In order to evaluate the performance of the coded system in the actual environment, a suitable semianalytical algorithm is defined and applied. In the results the feasibility of a coded OFDM system for 155 Mbit/s packet transmission is checked. It is shown that all the line-of-sight (LOS) positions and 70% of the no LOS points can be covered in the scenario considered with a transmitted power of 10 dB
Analytical Evaluation of Total Degradation in OFDM Systems with TWTA or SSPA
No full textIn this paper an analytical parametric formulation of
total degradation in Orthogonal Frequency Division Multiplexing
(OFDM) systems including High Power Amplifiers (HPA) is
presented. Two classes of non-linear devices are considered:
Traveling Wave Tube Amplifiers (TWTA) and Solid State Power
Amplifiers (SSPA). In the results the accuracy of the proposed
method is checked and the impact of coding to mitigate non-linear
distortion is easily assessed
Experimental DSP-based CDMA modem for Ka-band satellite systems: low complexity code acquisition and tracking scheme
No full textThis paper presents a reliable and low complexity acquisition and tracking technique for a DSP-based satellite CDMA modem. An analysis of the performance, in terms of false alarm probability, detection probability and mean acquisition time, is carried out as a function of the complexity and the level of interference. The proposed scheme, based on a dedicated frame format, appears able to cope with the DSP complexity constraint and high levels of interference. The signal structure can be also used for frequency tracking. A DSP implementation and numerical results, obtained by means of analytical evaluations and measurements on a real test-bed, are given
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