Adjacent satellite interference effects as applied to the outage performance of an earth- space system located in a heavy rain climatic region

Interference effects are of utmost importance to the reliable design of modern satellite communication systems operating at Ku and Ka bands. In these frequencies rain attenuation is the dominant fading mechanism particularly for Earth-space systems located in subtropical and tropical regions. On the other hand, the main propagation effect on interference between two adjacent satellite systems is considered to be the differential rain attenuation. The subject of the paper is the development of a procedure for the prediction of carrier-to-noise plus interference ratio (cnir) statistics, under the presence of rain fading conditions, applied to heavy rain climatic regions. The method is based on a model of convective raincells and the gamma distribution assumption for point rainfall rate statistics, which fits better than lognormal distribution in subtropical and tropical regions. A tropical raindrop size distribution is also adopted for the calculation of the power-law parameters of specific rain attenuation. The numerical results are concentrated on the analytical examination of various operational parameters upon the CNIR statistics and the subsequent outage performance of the system. Comparison of the proposed model with an already existing one is attempted and the necessity of the present procedure for application to locations belonging to subtropical/tropical zones becomes obvious.     

Adjacent Satellite Interference Effects on the Outage Performance of a Dual Polarized Triple Site Diversity Scheme

The design of reliable, modern satellite communication networks, in which both frequency and orbital congestion are increasing, requires modeling of interference effects. The dominant sources of aggravation of nominal interference due to propagation phenomena are assumed to be differential rain attenuation from an adjacent satellite communication network operating at the same frequency and cross polarization due to rain and ice-crystals. A physical methodology to predict the statistics of the carrier-to-noise-plus-total-interference (CNIDR), which has already been applied to single and double-site systems, is extended to include triple-site diversity reception schemes. This method is based on a model of convective raincells model and the lognormal assumption for both the point rainfall statistics and slant path rain attenuation. The statistical properties of spatial inhomogeneity of rain attenuation over six satellite slant paths is firstly here presented. A set of simple, approximate formulas are presented which follow from a regression analysis on the previous theoretical results. The results serve to examine the influence of various parameters upon the total availability performance.     

A comparison of copolar and cochannel satellite interference prediction models with experimental results at 11.6 and 20 GHz

One of the main propagation effects on interference between adjacent Earth–space paths is the differential rain attenuation. In the present paper, two existing copolar and cochannel satellite interference prediction models are compared with experimental data of this kind, derived from radar or attenuation measurements. The comparison shows a quite satisfactory agreement and this combined with the fact that the data refer to satellites quite displaced in the geostationary orbit leads to the following conclusion: the predictive models under consideration can be used not only for fixed satellite systems but also for mobile systems using general antennas with low gains. Copyright © 2000 John Wiley & Sons, Ltd.     

Ice crystals and raindrop canting angle effects applied to satellite interference prediction with respect to heavy rain climatic zones

For frequencies above 10GHz the performance of the operating satellite systems is mainly aggravated because of the potential existing severe rain attenuation. As a result of the above fading mechanism, the dominant interference sources encountered in this frequency band are the following: differential rain attenuation induced by an adjacent satellite system operating in the same frequency, and cross talk between orthogonally polarized signals. The latter source concerns of course satellite systems employing the dual polarization mode. In the present paper, an already existing method to predict interference statistics, due to above reasons, is properly modified to include ice crystals and raindrop canting angle effects. The assumption that the point rainfall rate statistics follows a gamma form, valid for heavy rain climatic regions such as J, M, N, P, Q zones, is also adopted. The sensitivity of various parameters affecting the interference performance, after introducing the novel assumptions, is finally investigated.     

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.     

Adaptive terminal to base station assignment in BFWA systems

In point-multipoint systems the signal to interference plus noise ratio highly depends on the assignment of terminal stations (TS) to base stations (BS). The Broadband Fixed Wireless Access (BFWA) systems operate at high carrier frequencies. In this frequency range wave propagation is highly influenced by precipitation. Applying site diversity can mitigate rain attenuation effects. Present contribution provides a special site diversity method adopting genetic algorithm to adaptively optimize TS-BS assignments from point of view of the interference in BFWA service area. Rain events are generated with a Markov modeled simulation of the rain cell translations.     

Ka-band Earth-space propagation research in Japan

Earth-space propagation studies in Japan were originally concerned with measuring atmospheric absorption and rain attenuation by means of a suntracker and a radiometer, following which a number of long-term experiments were performed using various experimental and commercial satellites. The first experiments involving Ka-band Earth-space propagation measurements in Japan were carried out in 1977 using the Engineering Test Satellite Type II, and since 1978, these experiments have been conducted using Japan's domestic communication satellite. Based on these studies to date, the understanding of Earth-space propagation characteristics at higher frequency bands, modeling of propagation channels, and development of countermeasure technologies have shown dramatic progress. In Japan at present, advanced propagation studies are under way in wideband digital-transmission satellite systems for the forthcoming multimedia era. This paper summarizes recent study activities concerning wave propagation in Ka-band Earth-space paths and related topics, such as radiometeorology in Japan. Last, future plans for conducting Ka-band and millimeter-wave propagation experiments by using the Japanese experimental satellite “COMETS” and rain observations in tropical regions by “TRMM” are introduced briefly     

Wave attenuation characteristics of the 11.5 GHz Earth-space path in Warsaw region

In Poland wave attenuation measurements in the Earth-space path, operating at 11.5 GHz, have been carried on simultaneously with the rain rate measurements, accomplished under the propagation path in five spaced out sites. Moreover the accuracy of prediction models, used for prediction of attenuation due to rain, was evaluated. The obtained results are presented in the paper.     

Noise Temperature Increase Effect on Total Outage Analysis of an Interfered Satellite Link

The ever increasing demand for bandwidth and multimedia services has led to the employment of Ka and V band in modern satellite communication networks. In these frequency bands, rain attenuation is the most dominant fading mechanism deteriorating the performance of the Earth-space links. Moreover, interference due to propagation phenomena increases the outage time of the satellite links and should be taken into account for the reliable design of a satellite communication network. In this paper, a physical propagation model for the prediction of carrier-to-noise plus interference ratio statistics of a broadband satellite link incorporating the receiver noise temperature increase due to rain, is presented The obtained numerical results highlight the significance of the latter effect and investigate the impact of various operational, geometrical and climatic parameters in the total outage analysis. Some simple mathematical formulas for the prediction of the carrier-to-noise plus interference ratio, based on the above theoretical results, are also presented.     

A Terrestrial Rain Depolarization Compensation Experiment at 11.7 GHz

Depolarization caused by rain at 11.7 GHz is due to both differential phase shift and attenuation. In dual polarized communications systems it gives rise to interference which may be severe enough to cause an outage even though the allotted fade margin has not been exceeded. Described is a depolarization compensation experiment over a 10 km path with near circular polarization at 11.7 GHz. It made use of a turnstile junction feed system under computer control. Data presented demonstrate the stable performance of the method used during several rain events. At fades below about 15 dB significant isolation improvements were achieved, compared to a fixed cross-polarization channel. Finally, a method using the turnstile is suggested to receive two nonorthogonal signals without interference.     

The role of rain in satellite communications

The most fundamental obstacle encountered in design of satellite communication systems at frequencies above 10 GHz is attenuation by rain. The microwave power radiated toward an earth station, being limited by factors such as available primary power and size of antenna on the satellite, is insufficient, with present technology, to overcome the large attenuation produced by intense rain cells on the earth-space path. The resultant loss of signal makes for unreliable transmission. In what follows, methods of measurement of this attenuation at various frequencies and a technique called path diversity that substantially improves the reliability are presented. Other degradations produced by rain, such as depolarization, interference, increase in earth-station noise, and deterioration of earth-station antenna performance, are also discussed.     

Rain Attenuation Ratios on Short Microwave and Millimeter Wave Bands Earth-Space Paths

The knowledge of the ratio of rain attenuation at one frequency to that at another on slant paths is useful for the design of satellite-to-Earth communication links and up-link power control systems. It is well known that the rain attenuation is influenced by parameters of precipitation along the slant path such as DSD (raindrop size distribution), raindrop temperature, rainfall rate, and so on. In this paper, based on several DSDs applied to various climate zones, at short microwave and long millimeter wave bands, the attenuation ratios are estimated on Earth-space paths. A comparison of the prediction results with the experiment data in Boston and Kashima areas is carried out. It is shown that the M-P and Weibull DSD applied to rain attenuation ratios estimation are better DSD at higher latitude regions. The Guangzhou DSD applied to rain attenuation ratios prediction is better in tropical and subtropical areas in China. The lognormal DSD may be a appropriate DSD applied to predict rain attenuation ratios in tropical areas at A_down>1dB or R>15mm/h. However, the attenuation ratios predicted by the Guangzhou DSD disagree with by the lognormal DSD, it requires that the DSD applied to predict rain attenuation ratios are further studied in tropical areas.     

Characteristics of fading on low-elevation angle Earth-space pathswith concurrent rain attenuation and scintillation

Signal-level variations on Ku-band low-elevation Earth-space paths, where large signal fades due to rain and tropospheric scintillations sometimes occur simultaneously, are examined. The difference in the amplitude variation rate for rain attenuation and scintillation fading is used to extract the effects of the two phenomena individually from raw data with the aid of a filtering technique. Characteristics of signal fading during rain are discussed on the basis of the analysis. It is shown that the decrease of signal level due to scintillation is much smaller than that due to rain attenuation, particularly for time percentages below 0.1%. However, for time percentages above about 1%, the effect of scintillation becomes dominant and no longer negligible, particularly for low-margin systems operating at low elevation angles     

Total CNIDR degradation during rain fade conditions of a dual polarized satellite link suffering from double adjacent satellite interference

Atmospheric impairments have a significant influence on the performance of modern satellite communication networks, working at Ku, Ka and potentially Q/V frequency bands. Both differential rain attenuation from an adjacent satellite system, operating at the same frequency range, and cross‐polarization phenomena on dual polarized satellite systems due to rain and ice crystals, induce a further aggravation on the already limited signal‐to‐noise‐plus‐total‐interference ratio (CNIDR), due to the frequency and orbital congestion of today's global communication satellite constellation. In the present paper, a new statistical methodology, towards the modelling of CNIDR under rain fade conditions, is proposed to include interference effects by two adjacent satellites, incorporating the impact of correlated fading channels (spatial rainfall inhomogeneity) of multiple slant paths. The method is based on a convective raincell model and the lognormal assumption for both the point rain‐rate statistics and the slant‐path rain attenuation. The obtained numerical results indicate the significant impact of the second interfering satellite on the aggravation of total interference effects. Some simple mathematical formulas for the prediction of the CNIDR, based on the derived theoretical results, and demonstrating the influence of various link parameters on the total link availability statistics, are also presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of ANFIS Power Control for Downlink CDMA‐Based LMDS Systems

Rain attenuation and intercell interference are two crucial factors in the performance of broadband wireless access networks such as local multipoint distribution systems (LMDS) operating at frequencies above 20 GHz. Power control can enhance the performance of downlink CDMA‐based LMDS systems by reducing intercell interference under clear sky conditions; however, it may damage system performance under rainy conditions. To ensure robust operation under both clear sky and rainy conditions, we propose a novel power‐control scheme which applies an adaptive neuro‐fuzzy inference system (ANFIS) for downlink CDMA‐based LMDS systems. In the proposed system, the rain rate and the number of users are two inputs of the fuzzy inference system, and output is defined as channel quality, which is applied in the power control scheme to adjust the power control region. Moreover, ITU‐R P.530 is employed to estimate the rain attenuation. The influence of the rain rate and the number of users on the distance‐based power control (DBPC) scheme is included in the simulation model as the training database. Simulation results indicate that the proposed scheme improves the throughput of the DBPC scheme.     

Theoretical relationship between rain depolarisation and attenuation

An approximate theoretical relationship between rain depolarisation and attenuation, valid for Earth-space paths at microwave and millimetre wavelengths, is presented. The relationship is sufficiently general that it allows the prediction of rain-depolarisation statistics from attenuation statistics available for other frequencies, polarisations and elevation angles.     

Site diversity against rain fading in LMDS systems

Local Multipoint Distribution Services (LMDS) system is a fixed cellular radio based point-to-multipoint technology in the microwave band providing broadband services. These systems need very accurate network planning method because of the variable carrier-to-interference ratio (C/I) in the whole service area and high sensitivity for meteorological phenomena especially for precipitation. The effects of a moving rain cell over an LMDS system was analyzed and site diversity as one possible countermeasure technique is demonstrated. The location dependent C/I in the LMDS service area under rainy conditions with and without site diversity technique was calculated applying a rain shower profile.     

Site diversity for satellite earth terminals and measurements at 28GHz

This work reviews site diversity concepts and models and presents the results of a site diversity experiment, in which radiometers were used to measure attenuation on Earth-space paths, performed at Columbus, Ohio, for a period of one year. Attenuation statistics are presented first in the form of the joint probability density function of attenuation at the two sites. From these are derived the cumulative two-dimensional distribution of attenuation at both sites, the cumulative distribution of attenuation at each site, the effective cumulative distribution of attenuation for a diversity system that always switches to the better of two signals, and the effective cumulative distribution of attenuation for a system with maximal-ratio signal combining. The switched-system diversity gain is compared with D.B. Hodge's (1982) predictive model, and the diversity improvement is compared with L. Boithias' (Radiowave Propagation, McGraw-Hill, 1987) model. Fade-duration and interfade-interval statistics are presented for each site and for systems that use switching and maximal-ratio combining. Rain-rate and interrainfall interval statistics are included     

Rain fades on low elevation angle Earth-satellite paths:comparative assessment of the Austin, Texas, 11.2 GHz experiment

Only a few years of rain attenuation data for Earth-space paths are available for low elevation angle paths, and these show a consistent tendency by the CCIR fade prediction model to underpredict rain fades. The authors contribute to the database four years of 11.2 GHz measurements, taken on a 5.8° elevation path in Austin, Texas, USA and assess higher than predicted fade results with respect to earlier measurements and the CCIR model. At the fiducial 0.01 percent of time, the rain fall rate was 73 mm/h and the attenuation exceeded the 25 dB measurement fade margin. It is found that the monthly variability of rain fall rates and decibel fades follows a normal distribution. Durations of rainfall and fades are classified into events, episodes, interevent gaps (longer than 4.2 h), and interepisode gaps (shorter than 4.2 h). Rainfall interevent gaps and event durations, as well as fade event, episode, and gap durations are log-normally distributed     

Orbital and site diversity systems in rain environment: Radar-derived results

During the summers of 1981 and 1982, an experiment was carried out in the Po River Valley with the scope of evaluating the statistical performance of diversity systems for earth to satellite links experiencing rain attenuation. The data were collected by anS-band meteorological radar scanning a32deginclined plane having the SIRIO path as its highest radial. Attenuation values directly measured through the satellite beacon at 11.6 GHz were used to "calibrate" the radar on event basis, in order to properly convert reflectivity into specific attenuation. In a previous paper the performance of site diversity (SD) systems was presented for earth terminals spaced from 1 to 20 km. In this paper, the same set of data is processed to simulate orbital diversity (OD) systems, which employ two satellites angularly spaced and one earth terminal. Aperture anglesthetaup to95deghave been considered. The results show that this diversity scheme already has a significant gain withtheta = 30degwhere at 10 dB single link attentuation the gain (as defined by Hodge) is 2.5 dB and it increases steadily asthetaincreases. The comparison between orbital diversity and site diversity performances shows that the site separation is linearly related to the orbital diversity aperture angle for any single link attenuation of the site diversity configuration.