José Miguel García-Rubia

Propagation in the Ka Band: Experimental Characterization for Satellite Applications

The use of the Ka band (30/20 GHz) in satellite-communication systems is expected to grow in the next few years, with the launches and planned launches of more than 10 satellites in 2010 and 2011 that include some Ka-band capacity. New technical standards, such as DVB-S2 and OVB-RCS, can be used in this band. A better knowledge of the channel characteristics is required, as well as experimental time series of attenuation. A propagation experiment is being carried out in Madrid, Spain, with the objective of characterizing the propagation channel in the downlink subband. Propagation results are related to meteorological data obtained from co-located instruments. Results obtained after two years of the experiment are presented in this paper. Rain attenuation is the main propagation impairment in this band. That is why rain-propagation effects are analyzed in more detail, although other propagation effects are also considered, as well as their relative importance.

Attenuation Measurements and Propagation Modeling in the W-Band

The frequency range that extends from 70 to 115 GHz presents low gaseous attenuation and offers the possibility of implementing radio links with capabilities of transporting more than 1 Gb/s over distances up to a few kilometers. A better knowledge of the propagation characteristics of the atmosphere at these frequencies can benefit future technological advances, providing better performance in terms of the use of radio resources. Unfortunately, the number of propagation results communicated for this band is very small. In this paper, propagation in this frequency range is analyzed on the basis of two-year experimental measurements carried out in Madrid, Spain, on a commercial link working at 75 and 85 GHz. Rain attenuation is the most relevant propagation effect in the W-band. Attenuation measurements are processed to remove wet antenna effects, leaving only the path attenuation time series. Statistics obtained from these time series are compared with a number of model predictions that use rain information of various types as input data, assessing in this way their precision and usefulness.

Estimation of Rain Attenuation From Experimental Drop Size Distributions

Detailed measurements of the rain phenomena can be obtained from modern equipment that provides experimental drop size distributions (DSDs), which can be used to analyze the effects of past rain events or to predict their influence on colocated radio links. In this letter, the use of experimental DSDs to predict rain effects on millimeter-wave propagation is discussed from a practical point of view, taking advantage of the availability of measurements from various instruments. The derived results show that predictions can be calculated with reasonable accuracy, provided that some practical considerations are taken into account.

Joint results of long-term earth-space propagation experiments at 20-GHz in Canada and Europe

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Joint Statistics of Rain Attenuation at 20 GHz in Madrid and Aveiro

Rain attenuation is the most severe propagation impairment affecting radiowave signals in the Ka-band. The use of these frequencies for satellite communication systems is facilitated by the implementation of fade mitigation techniques (FMTs). Spatial correlation of rain rate and rain attenuation for distances of several hundred kilometers has been rarely characterized in experiments, however it is relevant for site diversity studies, with distances in this range, and for the design and operation of multibeam satellite systems with shared on-board radio resources. In this letter, experimental results regarding joint statistics of rain and rain attenuation are presented for Madrid, Spain, and Aveiro, Portugal, located 420 km apart. These results have been achieved from two years of simultaneous measurements of the Eutelsat HB-6 Ka-band beacon at 19.7 GHz. It is shown that high-attenuation events are independent, whereas there is some correlation for low-attenuation levels.

Five-year results of a slant-path propagation experiment at 20 GHz in Madrid

Satellite operators are starting to use the Ka-band (30/20 GHz) for communications systems requiring higher traffic capacity. The use of this band is expected to experience a significant growth in the next few years, as several operators have reported plans to launch new satellites with Ka-band capacity. It is worth mentioning the Ka-Sat satellite in Europe, launched in 2010, and ViaSat-1, of 2011, with coverage of USA1. Some other examples can be found in other parts of the World. Recent satellite communications standards, such as DVB-S22 or DVB-RCS3, which provide means to mitigate propagation impairments, have been developed with the objective of improving the use of the Ka-band, in comparison with previous technical standards. In the next years, the ALPHASAT satellite will bring about new opportunities4 for carrying out propagation and telecommunication experiments in the Ka- and Q/V-bands. Commercial uses are focused on the provision of high speed data communications, for Internet access and other applications. In the near future, it is expected that higher and higher data rates will also be needed to broadcast richer multimedia contents, including HD-TV, interactive content or 3D-TV. All of these services may be provided in the future by satellites of the current generation, whose life span can extend up to 2025 in some cases. Depending on local regulations, the available bandwidth for the satellite fixed and broadcasting services in the Ka-band is in excess of several hundred MHz, bidirectional, comprising more than 1 GHz for each sub-band in some cases. In this paper, the results of a propagation experiment that is being carried out at Universidad Politecnica de Madrid (UPM), Spain, are presented5. The objective of the experiment is twofold: gathering experimental time series of attenuation and analyzing them in order to characterize the propagation channel at these frequencies6. The experiment and statistical results correspond to five complete years of measurements. The experiment is described in more detail in Section II. Yearly characteristics of rain attenuation are presented in Section III, whereas Section IV is dedicated to the monthly, seasonal, and hourly characteristics. Section V covers the dynamic characteristics of this propagation effect, just before the conclusions are described in Section VI.