Attenuation of a WiMax signal by vegetation . A research paper as Assignment

Abstract: During this research, the vegetation as a continuous medium and a collection of scatterers is considered. Dielectric properties of vegetative material are discussed. The relation between electromagnetic and biometric parameters of vegetation is established. Methods of measurements of attenuation and electromagnetic signal strength are reviewed. Available experimental data of attenuation are discussed, analyzed and the directions of future research must be stated.

1. Overview of WiMax and attenuation:

WiMAX(Worldwide Interoperability for Microwave Access) is a wireless communications standard designed to provide 30 to 40 megabit-per-second data rates, [Carl Weinschenk, "Speeding Up WiMax". IT Business Edge, April 16, 2010.]with the 2011 update providing up to 1 Gbit/s for fixed stations. The name "WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to promote conformity and interoperability of the standard.

WiMAX is described as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL". Mobile WiMAX communication system uses  microwave carrier of 2.5GHz  frequency band and modulation system is mainly OFDM for transmission of signals. [Yasumitsu Miyazaki et al.,Attenuation and Scattering Characteristics of Microwaves over Forests for WiMAX Wireless Communications.]

Attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance,  sunlight  is attenuated by dark glasses,  X-rays  are attenuated by lead, and  light and sound  are attenuated by water. In many cases, attenuation is an exponential function of the path length through the medium. When it comes to electromagnetic wave propagation, attenuation decreases the intensity of electromagnetic radiation due to  absorption  or scattering of photons. Attenuation does not include the decrease in intensity due to inverse-square law geometric spreading. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the path.

Talking about Radio communication, attenuation is an important consideration in the modern world of wireless telecommunication since it limits the range of radio signals; attenuation is obviously affected by the materials a signal must travel through (e.g., air, wood, concrete, rain), it must therefore be carefully studied and analyzed when a telecommunication system is being designed.

2. The impact of vegetation on remote sensing of the land surface

There are two types of interest arising in the area of remote sensing. The first one consists in revealing the screening effect of vegetative cover on the remote sensing of a land surface itself and developing technologies by taking this effect into consideration when assessing the land surface condition. The second one consists of developing technologies of remote sensing application for assessing the properties of vegetative cover. In both cases the attenuation of EM waves and its relation to biometrical features of vegetation is of a great importance.

3. The role and significance of attenuation by vegetation in remote sensing'

Remote sensing of environment is based on retrieving algorithms that relate the environmental parameters (such as soil moisture, vegetation biomass, forest stem volume, and others) to the remotely sensed radiation characteristics (brightness temperature Tb, backscattering coefficient s0, and others). There are three general types of the retrieving algorithms. The first one uses the experimentally obtained regression relations between geophysical and radiation parameters. A disadvantage of this approach is a limited application (often, the regression relation can be used only within the test site or the region it was obtained). The second technique is based on the neural network approach and is being successfully developed for last years [Reference to be inserted].

4. General approach for EM waves propagation in vegetation.

The investigation of EM wave’s propagation, attenuation, emission, and scattering in vegetation canopies meets some difficulties. From a theoretical point of view vegetation canopies are principally random media with inhomogeneities of varying forms and dimensions. In the frequency band of interest the dimensions of leaves and stalks, brunches and trunks are comparable with the wavelength making it extremely difficult to model propagation in such a medium due to the required application of diffraction theory to examine the scattering by a single inhomogeneity.            Figure 1: Microwave propagation in Mobile WiMax wireless communication [A.A. Chukhlantsev, “Microwave emission and scattering from vegetation canopies,” Journal of Electromagnetic Waves and Applications, Vol. 6, No. 8, pp. 1043 – 1068, 1992]            