Rain Outage Research Articles

A method to estimate trends in distributions of 1 min rain rates from numerical weather prediction data

AbstractIt is known that the rain rate exceeded 0.01% of the time in the UK has experienced an increasing trend over the last 20 years. It is very likely that rain fade and outage experience a similar trend. This paper presents a globally applicable method to estimate these trends, based on the widely accepted Salonen‐Poiares Baptista model. The input data are parameters easily extracted from numerical weather prediction reanalysis data. The method is verified using rain gauge data from the UK, and the predicted trend slopes of 0.01% exceeded rain rate are presented on a global grid.

Effects of Climatic Change On Gsm Signal in Lagos Metropolitan Terrain

The nexus of this study is to examine thoroughly the dependence of climatological parameters on GSM signal, especially in a metropolitan terrain. To validate this work, field measurements were carried out in the ITU regions of Lagos metropolitan area. The measurement system consisted of live documented radio base stations (BS) data transmitting at 13GHz, 15GHz and 23GHz in seven sites that constituted a metropolitan environment. The seven sites were segmented into non-urban (rural), suburban, urban, Ex-urban, dense-urban, micro-urban and peri-urban propagation environment. The Rain outage of the annual unavailability of the region of metropolitan data was collected using a Lenovo Laptop with installed path loss software alongside a licensed key called DONGLE. Results of this effort reveal that climate change affects signal propagation.

Microwave Attenuation and Prediction of Rain Outage for Wireless Networks in Pakistan's Tropical Region

The microwave attenuation due to rainfall in tropical regions has not been very widely studied yet. In Pakistan's tropical environment, line-of-sight microwave communication links were set up and have been operated for several years to study the microwave attenuation characteristics due to tropical rainfall. In this paper the experimental results are presented, including the cumulative distributions of microwave attenuation and the relationship between specific attenuation and rainfall rate. In addition, a rain outage prediction model is proposed which not only predicts microwave radio link performance but will also be useful in calculating the link degradations due to interference issues. The main focus of this research work has been done keeping in mind the wireless networks of Pakistan. The results show that the rainfall rate, the microwave propagation characteristics, and outage predictions in Pakistan differ from the International Radio Consultative Committee predictions and ITU recommendation P530.7/8, respectively.

Cell-site diversity performance of millimeter-wave fixed cellular systems operating at frequencies above 20 GHz

The dominant propagation factor affecting the reliability of millimeter-wave fixed cellular systems operating at frequencies above 20 GHz is rain attenuation. Cell-site diversity is an available method to reduce the rain outage time for these systems. The paper presents an analytical procedure for the evaluation of the outage performance of a cell-site diversity system. Numerical results are compared with available experimental data taken from Canada and the UK. The agreement was found to be quite encouraging. The dependence of cell-site diversity gain on climatic conditions is also investigated and some useful conclusions are deduced.

Prediction of Triple-Site Diversity Performance in Earth-Space Communication

In heavy rain climatic regions (e.g., climatic zones F, H, K, L, M, N, P given by C.C.I.R.) attenuation caused by rain presents a great problem for satellite communications, at frequencies above 10 GHz. Double-site diversity is an available method to reduce the rain outage time for these systems. In some severe cases, double-site protection can be proved to be inadequate and consequently triple-site diversity becomes indispensable. In this paper, a first approach is presented for estimating the improvement in rain outage performance caused by triple-site diversity protection. The method is based on the lognormal assumption for the point rainfall rate distribution at the location under consideration. Experimental results taken from some parts of the United States such as New Jersey, Florida and Atlanta, Georgia are compared with the theoretical values and the agreement was found to be encouraging.

New rain rate analyses to assess rain attenuation on satellite ehf communications

AbstractThis paper provides estimates of the frequency of occurrence, duration and probability of satellite EHF communication outages due to attenuation by rain. These can be used to determine optimum frequencies, power levels and the need for space diversity of terminals or other alternatives to maintain reliable communications. Ten years of 1 min rain rates at each of 12 U.S. cities were used in conjunction with an attenuation model to quantify communication outages at locations representing a variety of climatic regimes. Analyses of the 1 min rain rates and outage estimates at 10, 30 and 45 GHz for elevation angles of 10°, 30°, 50° and 70° are presented.

Analysis of the rain outage performance of route diversity systems

Route diversity systems as available means to improve the rain outage performance are examined by comparison to tandem systems. A general and somewhat rigorous analysis for the evaluation of the joint probability on a pair of opposite hops has been performed, which is valid for any frequency. The total rain outage performance has been shown explicitly to be given approximately by the summation of joint probabilities on pair hops of the diversity system. Finally, a general and compact algorithm for the evaluation of the path length enlargement effect has been constructed which is valid for any frequency, above 10 GHz and single hop‐length of the corresponding tandem system.

Advanced Communications Satellite Systems

Demand for in-orbit capacity through the use of satellite systems will continue throughout the next two decades. The potential of the 30/20 GHz frequency band for fixed satellite services will be exploited. However, many technology questions must be answered if the band is to be used commercially because of the high rain fades that can occur at these high frequencies. NASA has conducted a technology development program in high gain antenna and on-board switching and processing systems which can be combined such that cost competitive services are possible at acceptable rain outage percentages. Other supporting technologies have also been pursued including transmitters, both tube type and solid state, and low noise receivers. The critical technologies have been combined into an experimental satellite payload; an experimental flight is planned to verify these technologies and enable development of operational systems. Implementation of such systems would be by commercial carriers and could occur in the early 1990's, depending on the demand for additional or bit capacity. The high capacity systems that can be made possible through the use of the 30/20 GHz band and the employment of frequency reuse technology will contribute to the continued downward trend in circuit costs and may allow new and innovative satellite services.

Route Diversity Effect on 20 GHz Band Radio Relay Links

Rain outage performance on route diversity systems, necessary for the circuit design of millimeter communication systems, is examined by comparing it to that of a tandem system. The analysis is mainly based on the attenuation data measured over about two and a half years at the 20 GHz band on 13 tandem links near Tokyo. It is shown that the joint probability of rain attenuation on two paths can be expressed as a function of the path correlation coefficient on the two paths under consideration, and the evaluation of the rain outage performance can be approximated by the joint probability on pair hops of a diversity route. An estimation method using the path length enlargement effect is proposed for the estimation of the route diversity improvement.

The Use of Resource Sharing and Coding to Increase the Capacity of Digital Satellites

Resource sharing is a technique which can improve the circuit availability of digital satellites operating at frequencies above 10 GHz, without requiring large fade margins. In this paper, the resource sharing concept is generalized by fully exploiting the available clear-air carrier-to-noise ratio of the satellite link to achieve very high transmission capacity while maintaining low rain outage. During clear-air conditions, convolutional codes with a large channel signaling alphabet are employed to permit a high rate of information transfer. When the fade depth exceeds the built-in fade margin, the signaling alphabet is reduced and enough time slots are borrowed from a resource sharing reserved pool to maintain the data rate at the fade site. It is shown that this approach greatly diminishes the impact of rain attenuation on satellite communications. Effective utilized capacities exceeding 85 percent of that possible if it never rains are feasible, and the increase in capacity compared to a system not using resourcesharing protection is typically a factor of 3-10.

Rain attenuation characteristics on 20 GHz band multirelay links

The performance of rain outage time on multirelay links that are necessary for circuit design of millimeter communication systems is examined. The analysis is based on about four years of rain attenuation data at 20 GHz band on 13 tandem links near Tokyo. Using these data, the path separation dependency of the joint probability and the path correlation coefficient due to rain are made clear. Also, the outage time probability and the thermal noise accumulation due to rain on multirelay links are evaluated on the basis of observed data. These results are applicable to the design of a millimeter wave multirelay transmission system.

Rain Margin Improvement Using Resource Sharing in 12-GHz Satellite Downlinks

In this paper we consider the effectiveness of sharing a small pool of reserved time slots of a Time Division-Multiple-Access (TDMA) frame among a large number of ground stations to overcome rain fading. With this approach, a system dynamically assigns time slots from the reserved pool to ground stations experiencing fade depths above the built-in margin. Powerful error correcting codes can be introduced to occupy the extra time slots, providing 10 dB or more of extra fade margin. Because a large number of ground stations are competing for the limited reserved pool, blockage can occur if the number of simultaneous fades exceeds the maximum number that can be accommodated. Some factors that influence the effectiveness of resource sharing are the mutual fade statistics at the various sites, the traffic distribution within the network, the number of earth stations, the size of the reserved pool, and the rain outage objective. Since the mutual fade and traffic statistics are unavailable, we develop models that can be used to find a conservative bound on the required size of the reserved pool. The rain model accounts for diurnal, seasonal, and geographical correlation among attenuation events. Results for a maximum resource-sharing gain of 10 dB show that reserving six percent of the time slots ensures a realized fade gain in excess of 9 dB for a down-link outage objective of 0.005 percent if there are more than 50 ground stations in the network, each with two percent or less of the traffic.

The transmission capacity of multibeam communication satellites

The transmission capacity which can be provided by a geosynchronous multiple-beam satellite employing frequency reuse is studied. Like all communication channels, satellite capacity is limited by available power, transmission bandwidth, and noise. In addition, factors peculiar to satellite links include cochannel interference among neighboring beams, channel nonlinearity, nonuniformly distributed traffic, and for satellites operating at frequencies above 10-GHz, rain attenuation. The effects of these factors upon the capacity of a satellite system are examined in detail. Results for a 12/14-GHz system with assumed satellite parameters compatible with a space shuttle launch and small 5 m earth station antennas show that a capacity of about 30 Gbit/s can be provided if the unavailability due to rain outage is no greater than 0.1 percent, and that about 10 Gbit/s can be provided for an unavailability no greater than 0.01 percent. Efficient utilization of the geosynchronous arc is also explored, and current trends in communication satellites are discussed.

11-GHz Radio: Application of Rain Attenuation Data to 11-GHz Radio Path Engineering

This paper describes the procedures adopted at Bell Laboratories for using rain attenuation data to engineer 11-GHzz microwave radio hops and routes. Rain outage time charts, which show the rain outage time as a function of rain attenuation and hop length, are the basic tools in engineering the hops. The charts, their formulation, and the procedures for using the charts are described and illustrated with several examples. The procedures are used to demonstrate and quantify the sensitivity of allowable hop lengths to the available rain attenuation margin, the effects of a limited rain attenuation margin, and the effects of the variation in the outage in a single year from the 20-year average outage. Guidelines for judging if a hop or route is performing as engineered are developed.

Rain outage performance of tandem and route diversity systems at 11 GHz1

Long distance radio systems at 11 GHz are considered with respect to rain outage. Conventional tandem systems and simple route diversity systems are analyzed and compared on the basis of rain attenuation statistics obtained from radar observations. The comparisons appear to be very favorable to diversity systems in terms of the number of repeaters. Unfortunately, the available descriptions of joint probabilities of attenuation for pairs of radio paths allow only conservative analysis of very simple diversity systems, so that effective designs are not yet possible. Therefore, the need for further investigations on intense precipitation patterns still exists.

Rain Outage Performance of Tandem and Path Diversity 18-GHz Short Hop Radio Systems

The performance with respect to rain outage time of dual path diversity and non-path diversity (tandem) arrangements for 18-GHz short hop radio systems is computed and compared. The analysis is based on two extrapolations of R. A. Semplak's <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> three-year average of the measured probability distributions for rain attenuation at 18.5 GHz on a 6.4-km hop in New Jersey. The effects of merge hops and joint fading between hops in the diversity system, dependence of the rain attenuation distribution on hop length, and uncertainty in the tail of the distribution are included. The results show that (i) the performance of tandem systems relative to diversity systems increases as the system length increases, (ii) the difference in the number of repeaters per unit length required for short and long tandem systems is small, (iii) the performance of the diversity system is strongly dependent on the amount of joint fading between parallel paths, and (iv) the performance of the tandem system is strongly dependent on the tail of the attenuation distribution. Neither of the latter two factors is known from rain attenuation measurements, but if the joint attenuation probabilities are sufficiently high, then diversity shows no advantage over tandem for either of the assumed extrapolations. The uncertainty in the tail of the attenuation distribution and the sensitivity of the tandem system performance to it emphasize the need for reliable attenuation measurements out to a probability of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> .