Óscar Fernández

Empirical analysis of a 2 x 2 MIMO channel in outdoor-indoor scenarios for BFWA applications

The unquestionable advantages of multiple-input multiple-output (MIMO) systems are having a strong influence on the development of new wireless systems, both in wireless local-area networks (WLANs), and in those designed to offer broadband fixed wireless access (BFWA) services in wireless metropolitan-area networks (WMANs). The MIMO channel characterization in different environments and for different operating frequency bands is a crucial factor in the design of new systems and standards, and for adequate planning of existing systems. This article makes two main contributions. First, the experimental characterization of a 2 times 2 MIMO channel at a frequency of 2.4 GHz in a canonical outdoor-indoor scenario is presented. The channel characterization performed includes the analysis of the spatial correlation between the MIMO system subchannels and its impact on the channel capacity. Second, on the basis of the capacity results obtained, a proposal is made for the use of a 2 times 2 MIMO system in outdoor-indoor scenarios for BFWA applications in metropolitan environments. The proposal is based on the experimentally verified hypothesis that the path loss due to building penetration can be practically compensated for by the diversity gain of 2 times 2 systems

Experimental analysis of wireless data transmission systems in space platforms

This paper presents an experimental analysis of the use of wireless data-transmission systems in manned space platforms. Previous studies have analyzed the general advantages of substituting radio systems for some of the harnesses in the platforms. This paper presents a detailed experimental characterization of the radio channel in the environment of a space platform at frequency bands of 2.5 GHz and 17 GHz. For this purpose, a mockup, based on the Columbus Space Laboratory, was built. The probability distribution functions of the fading have been obtained for narrow-band as well as wideband parameters, such as the mean square delay and the coherence bandwidth of the channel. Moreover, a study of the operating mode of a commercial wireless system, based on the IEEE 802.11b standard, has been performed, by monitoring the bit-error rate. The error rates of the IEEE 802.11b system in the typical environment of a small or medium-sized office are compared with those of a space-platform environment. The results and conclusions can be extended to other environments that present geometrical and structural characteristics similar to those of a space platform, such as ships and submarines.

Characterization and Modeling of BFWA Channels in Outdoor--Indoor Environments

This letter presents the experimental characterization and modeling of the radio channel for outdoor-indoor communications, within the framework of broadband fixed wireless access (BFWA) systems. Five models based on tapped delay lines have been proposed. These models provide a good fit of the measured rms delay spread. The time delay values are considerably lower than the typical values for outdoor channels in urban and suburban environments. In quasi-line-of-sight (LOS) situations, it is not necessary to distinguish between open and closed environments, while this is necessary in the case of NLOS and hard-NLOS situations

A MIMO-OFDM testbed, channel measurements, and system considerations for outdoor-indoor wimax

The design, implementation, and test of a real-time flexible (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) MIMO-OFDM IEEE 802.16 prototype are presented. For the design, a channel measurement campaign on the 3.5 GHz band has been carried out, focusing on outdoor-indoor scenarios. The analysis of measured channels showed that higher capacity can be achieved in case of obstructed scenarios and that (Channel Distribution Information at the Transmitter) CDIT capacity is close to (Channel State Information at the Transmitter) CSIT with much lower complexity and requirements in terms of channel estimation and feedback. The baseband prototype used an (Field Programmable Gate Array) FPGA where enhanced signal processing algorithms are implemented in order to improve system performance. We have shown that for MIMO-OFDM systems, extra signal processing such as enhanced joint channel and frequency offset estimation is needed to obtain a good performance and approach in practice the theoretical capacity improvements.

Empirical Analysis of Broadband 2×2 MIMO Channels in Outdoor-Indoor Scenarios

This paper presents the experimental characterization of a wideband 2×2 MIMO channel in typical indoor-outdoor scenarios in the 3.5 GHz band. The transmitter array emulates a base station positioned on the terrace of a building, and the receiver array, situated inside a nearby building, represents the end-user terminal. In a previous work, the authors analyzed the advantages attainable with a 2×2 MIMO channel compared to a SISO channel for the case of narrowband wireless systems in these types of environments without line-of-sight (NLOS). The new results for the wideband channel show that as in the narrowband case, the capacity degradation due to penetration losses can be practically compensated for by the gain of a 2×2 MIMO channel. Furthermore, the frequency diversity attainable in the case of wideband systems appears as a new contribution, reinforcing the conclusion obtained for the narrowband case. This paper also presents a stochastic 2×2 MIMO wideband channel-modeling method that represents a novel simplification with respect to other wideband MIMO models. The resulting models are accurate, but also easy to implement and computationally efficient, Using this method, outdoor-indoor channel models are obtained from a measurements campaign on real MIMO channels in different environments. The empirical data and the models presented in the paper will be very useful in the deployment of future and present broadband fixed wireless-access systems (BFWAS).

Outdoor to Indoor 2x2 Wideband MIMO Channel Modelling

This paper presents a stochastic 2x2 MIMO wideband channel modelling method that uses tapped delay lines (TDL) and a single channel spatial correlation matrix that represents a novel simplification with respect to other wideband MIMO models. The resulting models are accurate but also easy to implement and computationally efficient. Using this method, outdoor-indoor channel models are obtained based on a measurements campaign. These models will be very useful in the context of present and future Broadband Fixed Wireless Systems (BFWS), where a great deal of work has been done in recent years in order to develop and standardize new systems incorporating MIMO technology. In particular, the systems of the IEEE 802.16 family have evolved rapidly: version IEEE 802.16d was completed in the year 2004 and version IEEE 802.16e has been finalized recently.

Analysis of Beamforming and Spatial Multiplexing Strategies in WMAN Outdoor-Indoor Scenarios

In this contribution we analyze the performance of several transmission strategies in a MIMO-OFDM system deployed in a wireless metropolitan area network. With this aim, a measurement campaign has statistically characterized a typical outdoor-indoor scenario for wireless metropolitan area networks. The performance is measured in terms of spectral efficiency under several channel knowledge scenarios at the transmitter and power allocation matrices that lead to different transmission strategies. Also two alternatives (averaging in the time or frequency domains) are explored in order to provide the transmitter with the information needed to implement the transmission strategy when it is only possible to get information about the channel statistics.

Analysis of Multipactor RF Breakdown in a Waveguide Containing a Transversely Magnetized Ferrite

In this paper, the multipactor RF breakdown in a parallel-plate waveguide partially filled with a ferrite slab magnetized normal to the metallic plates is studied. An external magnetic field is applied along the vertical direction between the plates in order to magnetize the ferrite. Numerical simulations using an in-house 3-D code are carried out to obtain the multipactor RF voltage threshold in this kind of structures. The presented results show that the multipactor RF voltage threshold at certain frequencies becomes considerably lower than for the corresponding classical metallic parallel-plate waveguide with the same vacuum gap.

Design and fabrication of a W-band linear array of planar antennas and study for the enhancement of its radiation properties with a chiral metamaterial cover

This work presents the design, fabrication and measurements of a W-band linear array of planar antennas. The structure of the antenna, which presents as benefit low cost and easy manufacture, is composed of three planar patches fed by slots. The simulation and the experimental results are compared showing a good agreement. In order to enhance the radiation properties, a chiral metamaterial cover is added to the antenna array. The chiral metamaterial cover is formed by two layers of mutually twisted planar metal rosettes in parallel planes and it is expected to enhance the directivity of the antenna array.

Novel fishnet-like chiral metamaterial structure with negative refractive index and low losses

In this work a composed chiral metamaterial structure constituted by the combination of a composite chiral metamaterial and a modified fishnet structure is presented and numerically analyzed. This new fishnet-like chiral metamaterial features two wide frequency bands wherein the refractive indices are negative and exhibits lower losses than its constituents do.