Terje Tjelta

Semi-Markov multistate modeling of the land mobile propagation channel for geostationary satellites

This paper describes a new semi-Markov propagation channel model for land mobile satellite systems using geostationary satellites. The multistate model switches between propagation states representing line-of-sight, shadowing, or blockage of the signal. The duration of times spent in each state follow probability distributions recommended by the radiocommunication sector of the International Telecommunication Union (ITU-R). The actual parameters to be used with the ITU-R distributions were modified and fitted to observed data. The open-area state durations follow a power-law distribution, while the state durations for both the shadowed and the blocked states follow a lognormal distribution. Parameters for both two- and three-state models are extracted from an L-band measurement campaign performed by Inmarsat in the United Kingdom. Propagation channel models characterizing the fading within the open, shadowed, or blocked propagation states are described as well. The semi-Markov models represent an improvement over the more commonly used Markov models where the duration in each state follows an exponential distribution. The new model enables more accurate prediction and simulation of system performance and availability.

Worldwide techniques for predicting the multipath fading distribution on terrestrial LOS links: background and results of tests

In 1988, the International Telecommunication Union (ITU) adopted new methods for predicting the deep-fading distribution due to multipath propagation for the average worst month on ultra high-frequency (UHF)-super high frequency (SHF) terrestrial line-of-sight (LOS) links. Employing refractivity gradient statistics available from world maps, the methods were recommended for application in all regions of the world. One method for the deep-fading range did not utilize detailed path profile information and was designed for preliminary planning or licensing purposes. A second method, which did employ the path profile was intended for more detailed design purposes. A multipath fading data base comprising some 246 links (including 34 over water) in 23 countries of the world has now been assembled for testing and revising these methods. Revisions to the geoclimatic model used in both methods and an associated method for predicting the shallow-fading distribution have been adopted by Study Group 3 of the new radiocommunications sector of the ITU (ITU-R). This paper summarizes the basis of the original and revised versions of the deep-fading prediction methods and presents the results of the most extensive tests to date. Some discussion of potential future revisions is also provided.

Worldwide techniques for predicting the multipath fading distribution on terrestrial LOS links: comparison with regional techniques

A revised worldwide method has been recommended by the Radiocommunications Sector of the International Telecommunication Union (ITU-R) in Recommendation ITU-R 530-8 for predicting the deep-fading distribution due to multipath propagation in the average worst month on VHF-EHF terrestrial line-of-sight links. This paper presents detailed testing results for the revised method on a 239-link database from 22 countries around the world in comparison with results for the leading regional methods still frequently used by some link designers for worldwide applications (viz., the Barnett-Vigants (1972, 1970) method of the United States and the Morita (1970) method of Japan). An evaluation of the form of the prediction equation is given for the revised and previous ITU-R methods and several regional methods. The revised ITU-R method is shown to perform significantly better than the other methods for both overland and coastal/overwater links.

Systematic development of new multivariable techniques for predicting the distribution of multipath fading on terrestrial microwave links

Multipath fading data obtained from 47 terrestrial microwave line-of-sight links in France and the United Kingdom are analyzed to derive narrowband prediction equations for the deep fading range of the cumulative distribution for the average worst month. A large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed. The improvement is achieved by increasing the number of prediction variables, using the most statistically significant variables, introducing a zonally varying geoclimatic factor, and employing more accurate analysis techniques. A reasonable choice of variables for system design includes path length, radio frequency, path inclination, and the grazing angle of specular reflection from the average terrain profile. A physical interpretation of the results suggests that a large amount of multipath fading is caused by ground reflection in combination with fading of the direct wave through the atmosphere. >

Predicting Combined Rain and Wet Snow Attenuation on Terrestrial Links

Radio links are used in all parts of the world, and must operate reliably in local climatic conditions. Attenuation due to rain has been extensively studied, but the additional loss due to wet snow has received less attention. Until recently there has been no wet-snow prediction model in general use. This paper reviews a recently developed prediction method for the attenuation due to combined rain and wet snow, proposes an extension to account for path inclination, and gives practical evidence of the excess attenuation caused by wet snow. The proposed model is based on data compiled by the International Telecommunication Union (ITU), and is applicable anywhere in the world. The basis of the predication method has recently been adopted in an ITU recommendation.

A novel method for predicting site dependent specific rain attenuation of millimeter radio waves

There is a need for validation and improvement of propagation prediction methods for the safe design and operation of millimeter radio communication systems. At this frequency range, propagation related degradation is primarily caused by rainfall. Our goal is an improved method for predicting specific attenuation due to rainfall. A general method for establishing the relationship between rainfall rate and specific attenuation is developed. Drop size distributions (DSDs) measured by a Joss distrometer are analyzed, and three climate classification parameters, rain rate, DSD median, and DSD mode, are used in the development of the new methods. These parameters are investigated as candidate classes to categorize drop size distributions. Categories of the classes are then established to improve the long-term DSD estimate. The typical long-term DSD is used to derive new prediction methods that are compared with observed attenuation. The influence of wind on the rainfall measurements is studied, and a corresponding correction is suggested, reducing the prediction error significantly. Testing of the three new methods using measurements at 40 and 60 GHz shows noticeable improvement over the method recommended by the International Telecommunication Union (ITU) using measurements at 60 GHz at deep attenuation.

Climate trends and variability of rain rate derived from long‐term measurements in Norway

Radio systems are affected by rainfall, and the attenuation increases significantly with rain rate and frequency. Above about 10 GHz rainfall must generally be considered for estimating expected link availability with sufficient attenuation margin included. Rain rate is a key factor, and depending on climate, it will dictate the possible path length and other factors such as antenna size, for the planned performance of a system that operates at higher frequencies than about 10 GHz. This paper presents results from an analysis of Norwegian tipping bucket rain gauge data from 1967 to 2013. It is found that the rain rate currently used by the Radiocommunication Sector of the International Telecommunication Union recommendation for attenuation prediction, R0.01—the rate exceeded for 0.01% of an average year—has actually increased in all parts of the country from where long-term data exist. Moreover, the year to year variability is significant. The increase may well be seen as a consequence of climate change. Such a change may cause higher attenuation effects than expected when radio links are designed following “normal” dimensioning procedures.

An Evaluation of Future Mobile Networks Backhaul Options

Mobile networks and services have grown dramatically since digital networks were introduced in the early nineties. Now operators want to provide broadband services over the Internet to mobile and wireless users. The pressure on the transport network will increase dramatically, and more cost effective solutions for the backhaul are urgently needed. This includes both physical layer and higher protocol levels of the network. This paper addresses backhaul transport layer issues from an operators view. It addresses the most promising solutions, looks at emerging technology aspects, and provides cost estimates. The work has been performed within the Telenor Group’s COmmoN TEchnology and STrategy (CONTEST) program.

Measured and modeled spatial rain rate correlation to improve the prediction method for satellite site diversity

Rainfall rate varies both temporarily and spatially. Radio systems, where rain attenuation causes outages, may take advantage of this effect to increase the radio link or satellite link availability using diversity techniques. In the Oslo region with Norwegian Meteorological Institute located at Blindern, there are 24 tipping bucket rain gauges within 50 km radius of the institute where each station has 5 years or more of simultaneous data periods with the station at the institute. The simultaneous data have been used to calculate spatial rain rate correlation and derive a prediction method based on separation distance and orientation with respect to dominating weather direction. Part of joint rain rate distribution was fitted to lognormal to find the measured correlation coefficients. In addition, an analysis of independent radiosonde data suggests that prevailing wind at 700 hPa or 850 hPa altitude (approximately 3000 m or 1500 m above sea level), conditioned thunderstorm index in the range of 15 to 20, may be used to identify the actual rainfall movement or dominant weather direction. Compared with current recommended method by the Radiocommunication Sector of International Telecommunication Union, the new method gives an improved site diversity prediction judged by site selection of minimum 20 GHz attenuation data measured in 2012 from Earth stations located at Nittedal and Kjeller separated by 23 km.

Space - time dynamic channel model for broadband fixed wireless access

Broadband fixed wireless access is a point-to-multipoint technology for providing broadband services. These systems need a space-time channel model which accounts for the spatial and temporal variation of rain attenuation for simulating fading mitigation techniques such as adaptive coding and modulation, and other capacity enhancing techniques. In this paper we study the space-time correlation of rain attenuation, and propose a simulation model for generating correlated rain attenuation time series base on the generalised Maseng-Bakken model. In addition, the parameter beta controlling rain attenuation dynamics in the Maseng-Bakken model have been extracted from measurements and shows variations with location within a single rain event.