A Model for the Detailed Analysis of Radio Links Involving Tree Canopies

Detailed analysis of tree canopy interaction with incident radiowaves has mainly been limited to remote sensing for the purpose of forest classification among many other applications. This represents a monostatic configuration, unlike the case of communication links, which are bistatic. In general, link analyses have been limited to the application of simple, empirical formulas based on the use of specific attenuation values in dB/m and the traversed vegetated mass as, e.g., the model in Recommendation ITU-R P.833-8 [1]. In remote sensing, two main techniques are used: Multiple Scattering Theory (MST) [2][5] and Radiative Transfer Theory (RT), [5] and [6]. We have paid attention in the past to MST [7][10]. It was shown that a full application of MST leads to very long computation times which are unacceptable in the case where we have to analyze a scenario with several trees. Extensive work using MST has been also presented by others in [11][16] showing the interest in this technique. We have proposed a simplified model for scattering from tree canopies based on a hybridization of MST and a modified physical optics (PO) approach [16]. We assume that propagation through a canopy is accounted for by using the complex valued propagation constant obtained by MST. Unlike the case when the full MST is applied, the proposed approach offers significant benefits including a direct software implementation and acceptable computation times even for high frequencies and electrically large canopies. The proposed model thus replaces the coherent component in MST, significant in the forward direction, but keeps the incoherent or diffuse scattering component present in all directions. The incoherent component can be calculated within reasonable times. Here, we present tests of the proposed model against MST using an artificial single-tree scenario at 2 GHz and 10 GHz

Radio-wave propagation prediction model tuning of land cover effects

The effect of land cover is incorporated in the radio propagation prediction algorithm of Q-Rap. It is implemented by optimizing both the effective height of the land cover, hence affecting obstruction-loss calculations, and by adding terms to the basic transmission loss algorithm. A complete set of separate coefficients to these terms is determined for each land cover type. The optimization method improves the standard deviation of the error from 9.6 to 6.3 dB for measurements and predictions done at 390 MHz. This is an improvement of 3.3 dB over the original model that comprises the free-space loss equation with obstruction loss calculations for multiple knife edges. At this frequency, the correlation coefficient between the measured and predicted values improved from 79.5% to 85.6%. At 2145 MHz, the optimization method improves the standard deviation of the error from 16.2 to 8.6 dB, as well as the correlation coefficient between the measurements and predicted values from 56.2% to 70.5%. The use of the correlation coefficient between the measured and predicted signal values, in addition to the standard deviation of the error and mean error as criteria to be used when evaluating propagation prediction models, is also proposed in this paper. A basis for best practices in tuning propagation prediction algorithms in radio planning tools using semi-empirical models is presented.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=25hj201

Wireless Channel Path-Loss Modelling for Agricultural and Vegetation Environments: A Survey

This work undertakes an extensive survey of the channel modelling methods and path-loss characterization carried out in agricultural fields and vegetation environments in an attempt to study the state-of-the-art in this field, which, though vastly explored, still presents extremely diverse opportunities and challenges. The interface for communication between nodes in a typical agricultural field is the wireless channel or air interface, making it imperative to address the impairments that are exclusive to such a communication scenario by studying the characteristics of the medium. The performance of the channel is a direct indicator of the quality of communication. It is required to have a lucid understanding of the channel to ensure quality in transmission of the required information, while simultaneously ensuring maximum capacity by employing limited resources. The impairments that are the very nature of a typical wireless channel are treated in an explicit manner covering the theoretical and mathematical models, analytical aspects and empirical models. Although there are several propagation models characterized for generic indoor and outdoor environments, these cannot be applied to agricultural, vegetation, forest and foliage scenarios due to the various additional factors that are specific to these environments. Owing to the wide variety, size, properties and span of the foliage, it also becomes extremely challenging to develop a generic predictive model for all kinds of crops or vegetation. The survey is categorized into fields containing specific crops, greenhouse environment and forest/foliage scenarios and the key findings are presented

30 GHz Path Loss Modeling and Performance Evaluation for Noncoherent M-ary Frequency Shift Keying in the 30 GHz Band

A candidate millimeter-wave (mmWave) frequency band and modulation scheme that could fit to many present and future applications has been presented in this work. As is being explored by industry, we also suggest the 30 GHz band as a candidate carrier frequency and non-coherent frequency shift keying (NC-FSK) as a potential modulation scheme for future communication applications. The primary applications are aimed at 5th generation (5G) cellular type systems. Propagation measurements were conducted for outdoor and indoor environments using directional horn antennas for both co-polarized and cross-polarized antenna configurations to model the path loss for our candidate band. The measurements were conducted in typical line-of-sight (LOS) and non-LOS (NLOS) environments in a large building on the University of South Carolina campus, specifically at Swearingen Engineering Center. Several propagation path loss (PL) models are presented based upon this collected data. We can use these PL models in link budgets for estimating transmit power, antenna gains, receiver characteristics (e.g., noise figure), and link distances. The measurements also contribute to the body of knowledge on wireless channel propagation path loss for bands near 30 GHz. Another measurement campaign was also conducted at the USC campus to measure a unique and complicated vegetation attenuation that may be considered a large challenge to mmWave systems. Radio wave attenuation and depolarization effects through several broadleaf evergreen shrubs at 31 GHz are reported, based upon measurements. To obtain a comparative reference for this mmWave attenuation, another measurement was also conducted at 5 GHz. From these measurements, we analyzed the proportional relationships between the attenuation and the shrub density (related to species), depth, and measurement geometry. Three different shrub species with different densities and depths, and for different measurement geometries, were employed. Results are in terms of measured specific attenuations at 31 GHz—the attenuation in dB/m. These will also be useful for link budget design, and outdoor and outdoor-indoor models for future mmWave communication. For our 5G modulation scheme candidate, we evaluate its performance at 31 GHz via an empirical 3-D mmWave channel simulator: the NYUSIM channel model. As with all digital communication systems, performance is measured in terms of error ratios, and we evaluate the bit error rate (BER) performance of NC-FSK for different symbol rates over a variety of wireless mmWave channels. The NC-FSK scheme is known to be energy efficient for large alphabet size, and this is one of its virtues. Another is that since it is a form of FM, nonlinear amplification (far less costly than linear amplification) can be used. The performance evaluations enable us to present enhancements and trade-offs that can be done to improve the system performance by adjustment of the design parameters, i.e., modulation alphabet size and symbol rate, which together determine bandwidth (BW)