Jesús Gutiérrez

Frequency-Domain Methodology for Measuring MIMO Channels Using a Generic Test Bed

A multiple-input multiple-output (MIMO) frequency-domain channel measurement methodology is presented. This methodology can be implemented in any transmit/receive hardware consisting of radio frequency modules and baseband digital processing units. It involves the transmission and reception of frequency and phase-optimized complex exponentials through antenna arrays, followed by an offline frequency estimation, which makes additional synchronization circuitry unnecessary. To test the feasibility of this method, a series of measurements is presented, employing a 4×4 dual-band (2.4/5 GHz) MIMO test bed.

Building a web platform for learning advanced digital communications using a MIMO testbed

Society demands access to high capacity wireless communications and to the services that can be provided on top of them. To satisfy these demands, engineers are constantly developing new technologies. These developments have to be selectively transferred to the university curricula. The student has to be familiar not only with the basic theory and techniques, but also with those of the more advanced techniques that provide a more profound insight. One of these techniques is based on Multiple-Input Multiple-Output (MIMO) systems. In this paper we show how to build a web platform for learning advanced digital communications based on a MIMO testbed. Using as starting point a 4 × 4 flexible dual band (2.4/5 GHz), we first develop a webservice interface to provide remote access to the services offered by the testbed and then implement a virtual laboratory where the students can parameterize and perform advanced experiments.

Multi-Way ranging with clock offset compensation

This paper presents a new approach for reducing the ranging error due to the crystal clock offset. This approach is applicable in cooperative ranging methods like N-Way or Multi-Way ranging, which are mainly used in Wireless Sensor Networks (WSN). Leaving the crystal clock offset error uncompensated leads to propagation of the ranging error through the WSN. In our approach, the crystal clock offset between the nodes is estimated and used to compensate the ranging error. The main advantage of our approach is the smaller number of transmissions compared to other crystal clock offset mitigation techniques. This reduces the energy consumption and minimizes the wireless medium usage for ranging purposes. The simulation results show that, even when a coarse estimation of the clock offset is performed, it has a significant impact (i.e. two orders of magnitude) on the reduction of the ranging error.

MIMO OTA Testing Based on Transmit Signal Processing

Usually, multiple-input-multiple-output (MIMO) testbeds are combined with channel emulators for testing devices and algorithms under controlled channel conditions. In this work, we propose a simple methodology that allows over-the-air (OTA) MIMO testing using a MIMO testbed solely, avoiding the use of channel emulators. The MIMO channel is emulated by linearly combining the signals at the testbed transmitter. The method is fully flexible, so it is able to emulate any equivalent baseband narrowband MIMO channel by adequately selecting the weights of the linear combination. We derive closed-form expressions for the computation of such weights. To prove its feasibility, the method has been implemented and tested over a commercial MIMO testbed.

Spatial correlation beamforming scheme for MISO channel emulation

Temporal and spatial correlation are inherent mobile wireless channel characteristics that determine multiple-input multiple-output (MIMO) systems performance. Wireless test beds, which are developed to assess MIMO techniques under these realistic conditions, are usually placed in indoor laboratories where wireless channels are intrinsically quasi-static. In this paper we propose a methodology for emulating multiple-input single-output (MISO) channels with arbitrary distributions as well as spatial correlation characteristics. This methodology, based on time-varying beamforming, allow us to evaluate MISO techniques in controlled channel conditions. Moreover, it has been implemented and tested over a commercial MIMO test bed.

Beamforming-based emulation of spatial and temporal correlated MISO channels

Temporal and spatial correlation are inherent mobile wireless channel characteristics that determine multiple-input multiple-output (MIMO) systems performance. It is widely known that in indoor laboratories with fixed conditions, wireless channels are intrinsically quasi-static. In this paper we propose a methodology for emulating multiple-input single-output (MISO) channels with arbitrary distributions as well as spatial and temporal correlation characteristics. This methodology, based on time-varying beamforming, allows us to evaluate MISO techniques in controlled channel conditions. To prove its feasibility, it has been implemented and tested over a commercial MIMO testbed.

Selection schemes for orthogonal tripole antennas

Cross-polarized antenna selection schemes lead to a considerable decrease in overall cost of system and size of the hardware without sacrificing the advantages of multiple-input multiple-output systems. In this work, we present a study of receive antenna selection based on measurements obtained with a tripole antenna pair. From the measurement data we extract the selection gains associated with triple polarized channels for a different number of antenna combinations at the receiver. The obtained results show the effectiveness of dealing with antenna selection schemes along with orthogonal antennas, providing higher gains in most of the cases.

Indoor measurements by dual tripole antennas

We present in this paper indoor measurements at 2.45 GHz of a tripole antenna pair and investigate typical channel characteristics that include the antenna elements. Each of the two antenna arrays consists of three orthogonal co-located dipoles promising high capacity, irrelevant of their orientation. The impact of classic parameters related to polarization, correlation and time dispersion are analyzed in order to get an idea of the performance that this real multiple-input multiple-output (MIMO) system could offer.