Leandro Juan-Llacer

An accurate radio channel model for wireless sensor networks simulation

Simulations are currently an essential tool to develop and test wireless sensor networks (WSNs) protocols and to analyze future WSNs applications performance. Researchers often simulate their proposals rather than deploying high-cost test-beds or develop complex mathematical analysis. However, simulation results rely on physical layer assumptions, which are not usually accurate enough to capture the real behavior of a WSN. Such an issue can lead to mistaken or questionable results. Besides, most of the envisioned applications for WSNs consider the nodes to be at the ground level. However, there is a lack of radio propagation characterization and validation by measurements with nodes at ground level for actual sensor hardware. In this paper, we propose to use a low-computational cost, two slope, log-normal path-loss near ground outdoor channel model at 868 MHz in WSN simulations. The model is validated by extensive real hardware measurements obtained in different scenarios. In addition, accurate model parameters are provided. This model is compared with the well-known one slope path-loss model. We demonstrate that the two slope log-normal model provides more accurate WSN simulations at almost the same computational cost as the single slope one. It is also shown that the radio propagation characterization heavily depends on the adjusted model parameters for a target deployment scenario: The model parameters have a considerable impact on the average number of neighbors and on the network connectivity.

A Broadband Pattern Diversity Annular Slot Antenna

An annular slot antenna suitable for pattern diversity in wideband applications is presented. Pattern diversity is obtained by feeding the antenna simultaneously with two microstrip lines printed on the back of the substrate, which generate orthogonal radiation patterns. Two shorts placed at 45 degrees between the microstrip lines and in the opposite direction ensure an isolation above 15 dB according to measurements. The antenna operates in the range of frequencies from 3 GHz to 12 GHz (1:4 bandwidth) and covers many different standards (Wireless-LAN, HIPERLAN2, WIMAX, UWB). Simulations and measurements for return loss, isolation and radiation patterns are presented. Furthermore, measurements have been carried out in a real multipath environment in order to evaluate pattern diversity performance. Results of measurements of the correlation coefficient and diversity gain over the entire operating bandwidth show that the antenna is suitable for antenna diversity systems.

Polarized Indoor MIMO Channel Measurements at 2.45 GHz

In this paper, a 4 times 4 indoor multiple-input multiple-output (MIMO) measurement campaign at a frequency of 2.45 GHz is presented. The main contribution of this work is the analysis of the impact of radio-wave polarization in MIMO systems operating at a typical indoor scenario through the calculation-from the measurements carried out-of a great deal of parameters such as the mean path loss, the cross polarization discrimination (XPD), and the RMS delay spread, which are all essential to estimate the performance of real MIMO systems. In this sense, some path loss models-which have been adjusted according to the measurements-are given, taking into account polarization, attenuation through walls, and the effect of T-junctions existing in the considered indoor scenario. Moreover, additional parameters such as the K-factor and statistical distribution, as well as spatial parameters, are discussed.

Interpretation of MIMO Channel Characteristics in Rectangular Tunnels From Modal Theory

We develop a modal approach for analyzing multiple-input-multiple-output (MIMO) wireless channel propagation in a tunnel with lossy walls. We use parametric methods to study the effects of the number of modes and of the separation among antennas. We evaluate the performance of the MIMO channel in terms of capacity as a function of range and tunnel size.

Wide-band measurements and characterization at 2.1 GHz while entering in a small tunnel

The wide-band complex transfer function and propagation characteristics in a small passageway tunnel for nonline-of-sight are studied in this paper. A two-dimensional wide-band model based on the uniform theory of diffraction (UTD) and geometric optics (GO) is implemented and a network analyzer is used to perform measurements. In order to obtain the power delay profile, a correction factor is used, which adjusts the deviation caused by the windowing and zero padding performed in frequency domain. The UTD model predicts quite well the averaged path loss, power delay profile, root-mean-square (rms) delay spread and coherence bandwidth, even when the curved tunnel is approximated to two straight lines. Furthermore, it is shown that the position of the transmitter is crucial in the performance of the system: the path loss slope and rms delay spread are increased when the inclination of the transmitter is increased. In all cases, the rms delay spread is lower than 40 ns, where the coherence bandwidth decreases to 20 MHz. This parameter is proposed to estimate the excitation zone inside a tunnel.

Comparison Between Measurements and Simulations of Conventional and Distributed MIMO System

In this work two different implementations of multiple-inputmultiple-output (MIMO) indoor systems are studied: distributed systems (DS) and conventional systems (CS). First a theoretical 3D ray tracing approach, and later an experimental study using a MIMO channel sounder based on a multiport network analyzer (MNA), are used to respectively predict and to measure the MIMO channel response. Results show that, when using DS, capacities are similar to an independent and identically distributed (i.i.d.) fading channel, and they are higher than those obtained by CS, too. They also reveal that ray tracing accurately predicts the results obtained in the measurements for both implementations.

A UTD-PO solution for diffraction of plane waves by an array of perfectly conducting wedges

In this paper, a formulation for plane wave incidence by an array of perfectly conducting wedges is proposed. The solution takes the advantages of the uniform theory of diffraction (UTD) and physical optics (PO), and allows for numerical evaluation of a large number of perfectly conducting wedges. The solution has the major advantage of shortening the computing time over existing formulation when the number of wedges is very large. The source is assumed to be above, below, or level with the edge height. The technique proposed is validated with numerical results from technical literature. Results for cases not previously reported in the technical literature are also presented.

An improved solution expressed in terms of UTD coefficients for the multiple-building diffraction of plane waves

A new formulation expressed in terms of uniform theory of diffraction (UTD) coefficients for the prediction of the multiple diffraction produced by an array of finitely conducting buildings considering plane-wave incidence is presented. The solution considers the building cross sections to be rectangular as well as the source to be above or level with the buildings height and, due to the fact that only single diffractions over finitely conducting wedges are involved in the calculations, an easier final formulation is achieved. Furthermore, the computing time is reduced over existing solutions especially when the number of buildings is large. The proposed formulation can find application in the development of theoretical models to predict more realistic path loss in urban environments when multiple-building diffraction has to be considered.

MIMO Channel Sounder Based on Two Network Analyzers

Different channel sounders are reported in the literature to measure the multiple-input-multiple-output (MIMO) wireless channel, most of them being dedicated systems. In this paper, a MIMO channel sounder that is based on two network analyzers is presented. The measurement process is totally controlled by a PC via a wireless local area network (WLAN), a local area network (LAN), and a general-purpose interface bus, and they are synchronized by using two global positioning systems (GPSs). The system is restricted to static propagation environments. An advantage of this system is its configurability, thanks to which it is not wireless system dependent. Last, initial measurements in a laboratory of a university at 900 MHz for a 4times4 MIMO system are also presented.

Frequency Dependence of 2–5 GHz Polarized UWB Channel Parameters in Office Environment

The ultrawideband (UWB) propagation channel is analyzed by means of measurements carried out in the 2-5 GHz frequency band in an office environment for different scenarios. Measurements were performed for different polarizations on the transmitting and receiving arrays so the effect of the signal polarization can be also taken into account in the analysis. The main contribution of this paper is not only the analysis of path loss and RMS delay spread in a bandwidth of 3 GHz, but also the influence of frequency on such parameters. The relationship between the path loss for copolar configurations and the cross-polarization discrimination (XPD), both in space and frequency domain, is also addressed.