Slant Path Links Research Articles

Experimental Assessment of Cloud Attenuation in a Q-Band Slant-Path Link

Experimental Assessment of Cloud Attenuation in a Q-Band Slant-Path Link

Excess Loss by Urban Building Shadowing and Empirical Slant Path Model

Excess loss due to building shadowing is regarded as an obstacle effect by buildings existing on the radio propagation path in relation to the service coverage performance of the next-generation mobile communication. In order to overcome the limitations of a geometric or deterministic modeling of existing obstacle loss models (ITU-R, W-I, and W-B model) and increase the accuracy of prediction of excess loss below 10 GHz in real urban environments, the improved empirical model is proposed by adding new variable and optimized fitting parameter values to the existing ITU-R model's formula. New variable and optimized parameter values reflect complex building structure and building height and their propagation impact through measurement. For validation of the proposed model, the self-verification and cross-verification were performed using the measured data from Korea and Japan. The measured data as well as the proposed model were presented as root-mean-square error that can be compared with other existing models in accuracy. The new proposed empirical model showed good agreement with the measured data compared to the existing geometric and deterministic models. In conclusion, the proposed model can be applied to the slant path link below 10 GHz frequency.

Slant-path coherent free space optical communications over the maritime and terrestrial atmospheres with the use of adaptive optics for beam wavefront correction.

As a continuation of our previous work [Appl. Opt.54, 1453 (2015)APOPAI0003-693510.1364/AO.54.001453] in which we have studied the performance of coherent free space optical (FSO) communication systems operating over a horizontal path, in this paper we study the coherent FSO system operating over a general slant path. We evaluated system bit-error-rate (BER) in the case when the quadrature phase-shift keying (QPSK) modulation format is applied and when an adaptive optics (AO) system is employed to mitigate the air turbulence effects for both maritime and terrestrial air transmission scenarios. We adopted a multiple-layer scheme to efficiently model the FSO slant-path links. The atmospheric channel fading was characterized by the wavefront phase distortions and the log-amplitude fluctuations. We derived analytical expressions to characterize log-amplitude fluctuations of air turbulence by asserting the aperture averaging within the frame of the multiple-layer model. The obtained results showed that use of AO enabled improvement of system performance for both uplinks and downlinks, and also revealed that it is more beneficial for the FSO downlinks. Also, AO employment brought larger enhancements in BER performance for the maritime slant-path FSO links than for the terrestrial ones, with an additional striking increase in performance when the AO correction is combined with the aperture averaging.

Derivation of Z-γ (Reflectivity-Specific Attenuation) Relation for Satellite Link in Tropical Region

The investigation of deriving the Z-γ (reflectivity-specific attenuation) relation is critical in the development of a novel rain attenuation prediction for a satellite link using radar information. Comparison between S-band radar derived reflectivity data and measured received power signals of X-band RazakSAT’s Malaysian remote satellite link is presented. RazakSAT’s satellite link received power during clear sky and rainy conditions are compared to extract the rain attenuation values. The specific attenuation of the link can be derived from the rain attenuation values. The S-band radar with horizontal polarization reflectivity information was used to compare the likely rain attenuation along the same RazakSAT satellite propagation paths. Both reflectivity information and specific attenuation data are tabulated during the RazakSAT operation in 2009 to derive the relationship. Later, the radar reflectivity values, Z are converted into specific attenuation, γ using the derived relationship of the Z-γ to calculate the rain attenuation and fade margin for a slant path link. The current rain attenuation prediction is using point rainfall but in this technique the reflectivity values is being explored. The relationship is derived using similar path length, elevation angle, time and date from the RazakSAT link and the radar information for both stratiform and convective events. Therefore, the relationship can be a good landmark for the future engineers and researchers to estimate the rain attenuation using radar information.

New physical‐mathematical model for predicting slant‐path rain attenuation statistics based on inverse Gaussian distribution

A new physical-mathematical model for predicting first-order rain attenuation statistics for slant-path links is presented in this study. It is assumed that point rain rate and slant-path rain attenuation follow the inverse Gaussian (IG) distribution. The statistical parameters of the IG distribution of the induced rain attenuation on a slant path are calculated in terms of the rain rate statistical parameters by adopting a spatial inhomogeneity model for specific rain attenuation. The method is validated using experimental data taken from Database of Study Group 3 (radiowave propagation) of International Telecommunication Union-Radio (ITU-R), hereafter named DBSG3 and with simulated rain attenuation data using the Synthetic Storm Technique on recent rain rate measurements in Athens, Greece. Its performance is also compared to the ITU-R P. 618-10 model. The proposed model shows better performance comparing to the ITU-R model and the results are very encouraging.

An Analysis of Conditional Site Diversity: A Study at Ka-Band

The use of EHF and SHF frequencies above 20 GHz is becoming increasingly important for high-capacity communication systems. Whether these systems are slant-path links, terrestrial fixed links, or deep-space links, the high bandwidths available and the relatively low spectral congestion are very attractive. One of the main disadvantages of these frequency bands is that the attenuation caused by meteorological effects can become significant, and the attenuation caused by clouds, rain, and atmospheric gases becomes very large. The largest attenuation events are caused by rain and clouds with a high liquid water content. In order to provide high-availability links, it is possible to use site diversity, by providing two spatially independent terminals. The spatial separation of the terminals reduces the probability of both terminals being faded. In this paper, we present an analysis of two spatially unique measurements of a satellite-based 20.7-GHz beacon. The results show that even at modest separations there is still the opportunity for significant availability improvements using site diversity. The probability density functions (pdfs) conditioned on the single-site attenuation level are presented. These demonstrate a characteristic shape and could form the basis of future modeling approaches.

Letter: Evaluation of total radiowave attenuation statistics for slant path links from phenomenon‐based attenuation distributions

AbstractThis contribution suggests a method how to combine effect‐specific cumulative distributions of attenuation to a total‐attenuation distribution as required e.g. in long‐term frequency scaling applications. The method is believed to be applicable for frequencies up to about 40 GHz. It has been tested with 20 GHz radiometric data collected near Moscow and the agreement found between our measurements and the results of this procedure is remarkably good.