M.O. Al-Nuaimi

A discrete RET model for millimeter-wave propagation in isolated tree formations

In this paper, a method based on the Radiative Energy Transfer theory (RET) to estimate the scattered radio signals from isolated groups of trees is presented. The proposed method consists of measuring the re-radiation function of each tree in the group, parameterising the function and subsequently using these in a discrete algorithm to estimate the overall attenuation at any location within the forest scenario. The discrete algorithm (dRET) presented here has some major improvements over previously published ones, offering substantially enhanced applicability. These improvements allow the use of larger vegetation cells, the enhancement of angular resolution of predicted results and the consideration of the receiving antenna radiation pattern. The estimated received signals using the re-radiation function, on the one hand, and its parameterised counterpart, on the other hand, are compared with measurements performed inside an anechoic chamber on Ficus Benjamina indoor plants at 20 and 62.4 GHz. The overall model performance was assessed in terms of RMS error between measured and predicted results.

A generic narrowband model for radiowave propagation through vegetation

This paper aims to describe the results of a 15 months consortium project to study the effects of microwave and millimetre wave propagation radio signals through vegetation. The aim of the project was to provide a generic model for the determination of propagation loss through vegetation, and was to be achieved by a combination of an extensive campaign of measurements and deterministic modelling. The proposed model is ideally suited to micro- and picocellular radio service planning, and with the aid of a forest database giving dimensions, locations and tree types, the model may be used for macrocellular radio system planning.

A Wideband Frequency-Domain Channel-Sounding System and Delay-Spread Measurements at the License-Free 57- to 64-GHz Band

A channel-sounding impulse-response identification system using the swept-frequency method is presented for the 57- to 64-GHz band. The swept-frequency channel sounder offers high time and frequency resolution of 1 ns and 625 kHz, respectively. The high dynamic range (70 dB) and the constant power output enable the nonlinearities of the channel-sounding system to be overcome within the coverage range, which is on the order of a picocell. This paper also reports the measurements and the analysis of wideband propagation data for various indoor radio channels at the 57- to 64-GHz band. The propagation characteristics are assessed for six different propagation environments. The results of the measurements for four environments are compared when horn antennas are employed at both terminal stations, and also when a horn and an omnidirectional antenna are used at the Tx and Rx terminals, respectively. Examining the statistical distributions of the multipath dispersion, the 90th percentile is about the same for both antenna configurations. For all environments under investigation, it was observed that the static delay spread values at the 90th percentile were below 62 ns.

Multipath delay spread and signal level measurements for indoor wireless radio channels at 62.4 GHz

This paper reports the 62.4 GHz fixed wideband propagation measurements undertaken in six different LOS indoor environments (corridors and rooms) inside three buildings. Measurement analyses are presented in respect of static RMS delay spreads and received signal level. Uniformity of delay spread was observed for all the cases investigated. A correlation is observed with the static delay spread increasing monotonically with increasing base-portable receiver antennas separation. For low values of the received signal level the delay spread values are relatively high and vice-versa. It has been observed that important indoor radio channel characteristics are determined by the principal structure of the environments and do not depend significantly on minor details like furniture and room fixtures.

Time-Variant Radio Channel Characterization and Modelling of Vegetation Media at Millimeter-Wave Frequency

Results of an extensive measurement campaign to characterize and model dynamic effects on the radio channel in vegetation media at 40 GHz, are presented. Using two small trees in an anechoic chamber, narrowband fast-fading measurements, utilizing co-polarized signals, were conducted to obtain radio channel characterization. This was performed as a function of the bi-static scattering angle, wind speed, wind incidence, and tree species. Furthermore, a modelling methodology is investigated and assessed as to its feasibility as a means to model vegetation dynamics effects on propagation. A radio channel model based on a simplified set of Markovian parameters, is proposed. The model is representative of the radio signal in the three main identified propagation regions around a vegetation volume as a mean to satisfactorily model highly time-variant radio signals. The propagation regions considered are receiver angular sections (in the azimuth plane) around the tree, where the received signal behaves distinctly for each region. Model validation results are presented using one of the tree species.

Wideband propagation measurements for indoor Rician fading radio channels at 62.4 GHz

Distributions of 62.4 GHz wideband propagation measurements undertaken in two different indoor radio channels to measure space-frequency correlation functions are presented. The values of 90th percentile of the coherence bandwidth at 0.9 correlation level for all locations stays below 72 MHz. Minimum and maximum B/sub 0.9/ coherence bandwidths obtained in a long narrow corridor with a directional horn transmit and an omnidirectional receive antenna are 1.10 MHz and 105.33 MHz respectively. It has been observed that the coherence bandwidth is highly variable with the location of the receiver with respect to the base station.

Characterisation of depolarisation of radio signals by single trees at 20 GHz

Measurements investigating how vegetation depolarises a propagating signal have been performed and presented for a number of different trees. From the measurements it can be seen that significant depolarisation takes place at the rotation angles which coincide with the measured nulls of the 360/spl deg/ attenuation patterns especially for the conifer trees. In some cases, it has been seen that the transmitted vertical linearly polarised wave has been depolarised to a near horizontally polarised wave by the vegetation material. The depolarisation occurs as a result of the various components of the tree having currents induced in them. The various tree components are then re-transmitting the waves at different polarisations resulting in an overall depolarisation of the originally transmitted wave. With the metal tree it can be seen that the amount of depolarisation increases as more and more branches are added to the structure. This shows that the various components of the tree are responsible for the depolarisation of the incident signal.

Performance Analysis of Reflection Paths for Millimeter Wavelength Systems

The work presented here aims at providing deeper knowledge on the behavior of non-line-of-sight (NLOS) links that particularly benefit from a specular reflection for fixed wired access systems (FWA) operating in the 40 GHz bands. For comparison purposes, the performance of the proposed NLOS link has been assessed in contrast with that of an unobstructed line-of sight (LOS) link. Both of the measured links were carried out in urban environments in order to explore the statistical propagation effects in such areas. Both links attain a dominant signal and hence are modeled using a Rician envelope distribution. Comparisons considered in terms of signal variations, cumulative curves and Rician K-factor have indicated the potential usefulness of the received reflected signals.

Restoration of the RET Phase Function Using Deconvolution

The influence of vegetation has become an important aspect of the design of wireless communication links. In recent years theory of Radiative Energy Transfer (RET) has been adapted as a reliable tool to predict the radiowave propagation through and near vegetation. The developed RET prediction model requires 4 input independent parameters, which so far had to be established from one measurement only, thus limiting their accuracy. An independent measurement which is termed the phase function can readily yield 2 of the 4 input parameters independently, which significantly increases the accuracy of these parameters. However one major factor influencing the phase function measurement is the radiation pattern of the receiving antenna. The measured curve will be the result of the convolution of the antenna radiation pattern and the phase function of the vegetation medium. The measurement curve therefore needs to undergo a deconvolution process before any RET input parameters can be derived from it. This paper presents the deconvolution method developed using optimal compensation deconvolution methods. Deconvolution is demonstrated using both simulation signal shapes and those measured in vegetation set up in the anechoic chamber. This paper discusses different cases of optimal compensation filtering with the relative curves shown.

Radiative Energy Transfer Based Model for Radiowave Propagation in Inhomogeneous Forests

This paper presents a radiowave propagation model for inhomogeneous forests based on the radiative energy transfer theory (RET). This model, which is a discretised version of the RET, is able to simulate the behaviour of radiowaves inside a forest which contains various kinds of vegetation and free space gaps. To do this, the forest is divided into non-overlapping square cells, each one with different propagation characteristics. The propagation properties of each cell rely on specific propagation parameters, which are extracted from the vegetation using an appropriate practical method which is also described in this paper. The model performance is assessed through comparison with directional spectrum measurements carried out in an isolated inhomogeneous forest at 11.2 and 40 GHz.