Search

A measurement campaign has been designed and developed to test the polarization behavior of different obstacles when a 5 GHz radio wave reaches their surfaces from different angles of incidence, with two orthogonal polarizations in transmission. The measurement outcomes have been analyzed by means of a matrix procedure, which is inspired in the polarimetric matrix formulation. This method allows the computation of depolarization indexes. The results highlight a strong depolarization of waves. A set of depolarization indexes for specular direction is given for several angles of incidence and three different materials, with direct application to wireless local area networks planning. These results are interesting for radio systems planning to double the channel capacity, if orthogonally polarized transmissions are used, or to mitigate the signal fading, if diversity techniques are applied at reception. Index Terms--Cross polarization, dielectric materials, electromagnetic scattering measurements, wireless LAN.

Mitigation of interference among adjacent radio systems is a topic of growing interest as the spectrum occupation increases. Site-shielding techniques appear as a method of improving millimeter-wave wireless communication system design, allowing frequency reuse and reducing cochannel interference. The viability of applying such techniques to systems operating in frequency bands around 40 GHz is the aim of this paper. Several propagation mechanisms are experimentally studied, including transmission across building obstacles, depolarization, reflection, and diffraction. The performance of some theoretical models of the different scattering mechanisms has been compared with measurement results. The measuring and processing procedures have also been improved. Values of the dielectric parameters of the materials in this frequency band have been obtained and are given in this paper. The attenuation results indicate that various materials, such as mortar, brick, and concrete walls, that present large values of attenuation in decibels per centimeter, can be used to shield base stations, reducing the frequency reuse distance in radio cellular networks. It can also be concluded that there is a significant diffracted field in the shadow region of brick corners. Index Terms--Diffraction, materials, millimeter frequencies, scattering, shielding.

In this paper, impulsive noise is simultaneously measured in the horizontal and vertical polarizations of the UHF radio band in order to determine their relationship. The measurements are taken from several environments: an anechoic chamber, an urban traffic, a factory, and an arc-welding workshop, with a bandwidth of 10 MHz. Measurements show that there is always an appreciable degree of positive correlation between the amplitudes of both polarizations. Index Terms--Correlation, electromagnetic interference, impulsive noise, polarization, UHF measurements.

Indoor radio channel planning tools implement different models to simulate propagation mechanisms such as transmission or reflection. The specular reflection formulation is commonly used instead of more complete scattering models. This happens because its coding is less complicated and the software runs faster than when considering reflection in all directions, not yet specular. In this paper, results from measurements are presented, consisting of the effect of constructive walls on an oblique incident wave. These experimental outcomes are modelled by means reflection pattern computations. Physical optics scattering model is used in its classical formulation, and it is then modified to take into account antenna pattern effects in the measurements. The comparison between measurements and simulations is also presented, showing good agreement. Measurements show that low reflective walls produce reflections in several directions across the incidence region. In these situations, the use of algorithms that compute reflection pattern, instead of just specular reflection coefficients, will lead to better agreement with actual results. Index Terms--Dielectric surface, reflection, scattering.

Wideband radio channel sounders based on the correlation of pseudorandom maximal length sequences are a commonly used tool for channel characterization purposes. However, a larger dynamic range can be achieved, and wideband parameter estimation can be improved by using Golay sequences. This is important when dealing with large attenuation, as at millimeter frequencies. The theoretical and experimental improvement of sounder performance by using Golay sequences is analyzed in this paper. Measurements, using both kinds of sequences, have been performed. Channel functions and parameters have been calculated and compared. Index Terms--Land mobile radio, radio propagation, time-domain measurements.

The growing interest in the relation between electromagnetic fields and human health forces the assumption of national and international regulations on emission levels. In order to reduce the risks, restricted access around transmitting antennas have to be defined according with those regulations. This paper offers a guideline to determine the boundary of the potentially risky volumes around radio broadcasting antennas for AM-MF and FM-VHF services. With the proposed method, a complete reference volume is defined by just five parameters. Index Terms--Antenna radiation patterns, biological effects of electro-magnetic radiation, electromagnetic radiation effects, Pollution.

External nonstatic effects on the indoor radio channel can be classified according to their natures; they can be quasistatic, as are those due to the furnishing and decoration of rooms, or clearly dynamic, as are those forced by the movement of people and pets within the propagation environment. So, it can be stated that people acting and walking nearby the antennas of radio-communication systems introduce nondeterministic effects in the radio channel, whereas walls, ceiling, floors, and even doors and windows are structural elements whose influence can be modeled by ray-tracing tools, the activity of people (both movement and variations in the distribution of elements such as furniture or decorative objects) introduces stochastic components in the channel characteristics prediction. Deterministic tools cannot model these effects, but their experimental knowledge will allow radio-network designers to keep guard values for the different design parameters at the same time that they plan the radio network. In this manner, the quality of service provided by these communication systems could be preserved. This paper shows the results and analysis of measurement campaigns performed in static and dynamic conditions, in order to compare the behavior of both narrow and wide-band parameters of the radio channel, including people activity within the environment. Index Terms--High-performance radio-access network (HIPERLAN), people effect, radio-channel characterization, wide-band measurements.

This paper presents results of frequency domain measurements conducted to evaluate the effectiveness of frequency diversity in mitigating the effects of multipath fading in indoor microcellular channels employing omni-directional receive antenna in the band 63.4-65.4 GHz. The performance of frequency diversity for 155 MHz and other channel handwidths to accommodate modulated signals with data rates up to 155 Mb/s is presented. Results are obtained using maximum selection combining and presented as functions of frequency separation between the diversity branch signals. Improvement in the level crossing rate and average fade duration is given together with improvement in the k-Rician factor. The root mean square (rms) delay spread ([[tau].sub.rms]) and coherence bandwidth ([[beta].sub.c]) of the channel are also presented as functions of distance between terminals. Values of Dc for correlation levels of 0.9, 0.7, and 0.5 are given together with the cumulative distribution functions of [[tau].sub.rms]. The levels below which the coherence bandwidth stays for 90% of receiver positions are estimated. Measurements were repeated under identical test conditions but with the receive omni-directional antenna replaced by a directional horn in order to characterize the effect of the receive antenna radiation pattern on the indoor radio channel characteristics. Index Terms--Coherence bandwidth, diversity, indoor channel, millimeter wave, radio-wave propagation, RMS delay spread, wireless LAN.

The results of an extensive study on analog PAL signals interfered with by digital DVB-T signals are presented in this paper. The study covers a theoretical evaluation of the interference problems, field and laboratory measurements, and even a national survey among TV installation companies. The field measurements are reported in part I of the paper. These measurements explain the origin of co-channel and some of the adjacent channel interference problems. However, some customers reported interference in areas where the field measurements showed that the protection ratios for PAL signals interfered with by DVB-T adjacent channel signals were met. As these customers lived in flats in multistory buildings with Master Antenna TV (MATV) installations the study was extended to analyze the role of these installations in the interference problems. As will be seen, it has been found that part of the interference problems are due to the amplifiers of the MATV installations in buildings. These amplifiers, designed to operate in an analog scenario, are not prepared to cope with adjacent channel DVB-T signals. The nonlinear effects of the amplifiers give rise to intermodulation problems. The ITU-R recommendations [1] recognize that the presence of non linear amplifiers at the receiver could be a source of problems and that higher protection ratios may be needed. However, no value of the required increase of the protection ratios is given in the recommendations. As result of the laboratory tests of commercial amplifiers conducted in the study presented in this report, it has been found that an increase of the protection ratios between 12 to 16 dB would be needed to avoid a significant degradation of the PAL TV signal in these amplifiers. It has also been found that most of the interference situations are not due just to the fact of the interfering signal being a DVB-T format but that the signal amplitude of any significant signal in the passband of the filter will cause interference. Therefore, MATV system distribution needs planning factors associated with the distribution of any signals near the main signal. To be able to generalize the conclusions and to evaluate the importance of the interference problems a survey among companies who install communal telecommunication infrastructure in Spain was conducted. The results of this poll are present in Section HI. Index Terms--Adjacent-channel, co-channel, digital television, DVB-T, interference, measurement.

The results of an extensive study on analog PAL signals interfered with by digital DVB-T signals are presented in this paper. The research work covers field measurements, laboratory measurements, a theoretical evaluation of the interference problems, and even a national survey among TV installation companies. The main objective is the identification and explanation of the interference problems reported at several towns since the start of DVB-T broadcasting. This paper is organized in two parts. Part I includes the description of the field measurements, whereas the laboratory measurements and the poll results are described in Part II. It has been found that the frequency plan is part of the source of the interference problems, particularly in the case of co-channel interference. Another source for the problems is that different radiation elements are used, at the same site, for broadcasting DVB-T and analog TV signals. As it is stated in ETSI documents [1], the use of a different antenna dedicated to DVB-T may require ERP restrictions to protect existing analog services. The power ratios between digital and analog TV signals at the broadcasting station should be adjusted in order to meet the protection ratios at every point within the coverage area. The required power ratio would depend on the specific shape of the radiation pattern of each antenna. Finally, it has been found that an important part of the interference problems are due to the amplifiers of the Master Antenna Television (MATV) systems in buildings. The results of the laboratory tests and the theoretical analysis conducted to determine the increment of the protection ratio required by the presence of these amplifiers are presented in Part H of the paper. Index Terms--Adjacent-channel, co-channel, digital television, DVB-T, field measurement, interference.

Byline: Inigo Cuinas (1), Manuel Garcia Sanchez (1) Keywords: reflection coefficient; transmission coefficient; dielectric coefficient; electromagnetic properties; building materials Abstract: The results of various experiments performed to characterize electromagnetic properties of typical building materials at BRAN (Broadband Radio Access Networks) and MVDS (Multipoint Video Distribution System) bands are presented and compared. Transmission and reflection coefficients were measured as functions of the angle of incidence, using a wideband sounder based on the swept frequency technique. A high precision angular positioning system was built and used in co-ordination with the measurement equipment.The dielectric constants ([epsilon].sub.r) were estimated by comparing values predicted with a multiple successive internal reflection model and measured transmission and reflection coefficients. It has been found that the variation of the dielectric constant value with the frequency does not necessarily follow the same trend for different materials. For example, the measured [epsilon].sub.r for plasterboard presents an increment withfrequency (2.02 at 5.8 GHz, 2.5 at 41.5 GHz -- measured by theauthors --, 2.58 at 59.5 GHz, and 2.81 at 60.2 GHz -- given byliterature --), while the values for glass follow a wanderingpattern (6.06 at 5.8 GHz, 5--10 at 10 GHz, 3.41 at 41.5 GHz, 7.51at 57.6 GHz, and 5.29 at 60.2 GHz). Moreover, the measured[epsilon].sub.r for a brick wall at 5.8 GHz (3.58) shows differenceswith values reported at 2 GHz (4.44). Author Affiliation: (1) Departamento de Teoria do Sinal e Comunicacions, Universidade de Vigo, Campus Universitario S/N, 36200, Vigo, Spain Article History: Registration Date: 13/10/2004

Spatial diversity for digital TV systems has been studied using the results of a measurement campaign of the radio channel complex frequency response for two different situations: an outdoor-indoor channel and an indoor-indoor channel. It is shown that the actual improvement of spatial diversity is not only the mean level increase, but the reduction of both the level crossing rate (LCR) and the average fade duration (AFD). The mean level gain is in the range [1.2-3] dB for the indoor-indoor channel and within [1.4-2.9] dB for the outdoor-indoor channel and the LCR/AFD improvement is between 9.5 and 15 dB for both environments. To explain the behavior of the diversity system, high resolution angle of arrival and delay information was obtained. It is concluded that it is the interference of the direct propagation path with the main reflections that causes the received field to follow a standing wave pattern and shapes the spatial diversity gain behavior. Index Terms--Average fade duration (AFD), digital terrestrial television, level crossing rate (LCR), mean level gain, spatial diversity.

A study of time dispersion in different indoor line-of-sight radio channels in the 492-862 MHz band is presented in-this paper. A combined method to filter the noise in the measured impulse response is described. The effect of frequency windowing on the impulse responses and the root mean square (rms) delay spread is also investigated. It has been found that, in general, the use of windows with lower side-lobe levels yields larger values of the rms delay spread. The relation between the mean delay and the rms delay spread has also been studied for copolar and crosspolar channels. The dependence of the coherence bandwidth on the rms delay spread has been considered, and an inverse relation has been tested for both components. Index Terms--Communication channels, communication systems, parameter estimation, UHF measurements, UHF radio propagation.

Wide-band indoor radio channel characterization for broadband radio access networks and Unlicensed National Information Infrastructure has been performed at 5.8 GHz, and results are given in this paper. Delay spreads of 8.8 and 17.2 ns and coherence bandwidths of 9.6 and 4 MHz have been found for line-of-sight (LOS) and obstructed line-of-sight (OLoS) situations, respectively. Results have been compared with predictions made using a ray-tracing tool. To get accurate predictions, a good description of the electromagnetic properties of the obstacles present in the environment is needed. Several experiments were made in order to characterize the electromagnetic parameters of six typical building materials. Transmission and reflection coefficients were measured using the free-space technique. A multiple successive internal reflection model was used to estimate the permittivity and conductivity by comparing the measured and predicted values of the coefficients. Several samples of each material were measured, and the results vary from sample to sample. This variation has been characterized by the calculation of confidence bands for the parameters. The influence of both the dielectric parameters and the order of reflections considered in the ray-tracing tool has been analyzed. The effect is reduced on narrow-band predictions but is more important on wide-band parameters as the delay spread. It is shown that the measured delay spread cumulative distribution function falls within the band predicted using the measured maximum and minimum values of permittivity. Index Terms--Indoor radio communication, materials testing, radio propagation, ray tracing.

The reduction of signal fading by using polarization diversity at a digital terrestrial TV receiver is evaluated. Two different diversity techniques, one operating at carrier (TV channel) level and the other at subcarrier level, are compared. A measurement campaign has been carried out in three different indoor environments using two antennas with orthogonal linear polarizations at the receiver. The polarization diversity gain has been calculated when maximum selection technique is used. As expected, the level crossing rate and the average fade duration are considerably reduced by the diversity system. Index Terms--AFD, digital terrestrial television, DVB-T, LCR, polarization diversity, short term fading.

In this letter, an improvement of the well-known internal multireflection model of transmission coefficients is proposed in order to obtain better agreement with complex measured data. The reason for the introduced changes is explained. To obtain the data, measurements were performed at 5.8 GHz using a vector network analyzer, which provided information on the amplitude and phase of the transmission coefficient. By comparing the model and measurements, both the real and imaginary parts of the material complex permittivity were estimated for four different building materials. Index Terms--Dielectric materials, electromagnetic scattering, permittivity measurement, urban propagation.

A wide band measurement campaign has been carried out in the DVB-T frequency band. The coherence bandwidth has been measured and its variation with the antennas separation is studied. Also, the relation between the coherence bandwidth and the rms delay spread is investigated. Index Terms--DVB-T, indoor propagation, coherence bandwidth, rms delay, frequency diversity.

Results of experiments made at 62.4 GHz in an urban mobile radio environment to characterize the coherence bandwidth are presented. The correlation coefficients between signal envelopes separated in frequency are measured and expressed as functions of distance from the base station. Due to the high variation of this coefficient with distance and in order to provide accurate estimates of the coherence bandwidth in the microcell, the correlation coefficient has to be measured over large sections. Two methods to calculate the coherence bandwidth are presented and compared. It is shown that estimating this parameter from the frequency correlation function obtained at each position may yield incorrect results. The coherence bandwidths for correlation levels of 0.5, 0.7, and 0.9 are given. A ray-tracing tool has been used to assist in interpreting experimental results. Index Terms--Coherence bandwidth, microcell, millimeter wave, radio-wave propagation.