Sight Links Research Articles

AN ULTRA-WIDEBAND QUASI-PLANAR ANTENNA WITH ENHANCED GAIN

A new ultra-wideband antenna with enhanced and nearly constant gain is presented. This quasi-planar antenna is composed of a CPW-fed printed monopole and a short horn, both made out of a single substrate. The measurements demonstrate an almost ∞at peak gain of 5:5dBi § 0:7dB from 2.5GHz to 15GHz with the average gain difierence in XZ plane is roughly 2dB up to 8GHz, which further rise to 6dB at 10GHz. The antenna also has a nearly linear phase response in this band. Well tested performance both in frequency and time domains, along with broad azimuth pattern, results in minimal ringing of a radiated pulse. The new antenna is suitable for establishing good line of sight link for UWB transmission and other broadband applications.

Investigation of wind and rain effects in a foliated tropical region for fixed wireless access

This paper investigates the effects of trees on fixed wireless access operating at 5.8 GHz frequency of the Unlicensed National Information Infrastructure (UNII) band. Measurements are focused on the temporal scale of the received signal strength for a three different links (one line of sight (LOS) link and two non-line of sight (NLOS) link). The statistical characterisation of the combined effects of typical weather phenomena often experienced in a tropical region is presented. As expected, the LOS link is not affected even during heavy rain condition. However, the presence of trees in the vicinity of the transmission path can cause relevant signal deterioration in the case of NLOS link, where the fading of the received signal varies from 2 to 16 dB as the strength of wind and rain increases. Rician distribution can be used to characterise the temporal variation of these weather effects. The work reported in this paper enables the effects of wind, rain and humidity to be properly taken into consideration in the deployment of fixed wireless links in a foliated channel, allowing an optimisation of planning for the end users.

UHF Propagation Along a Cargo Hold on Board a Merchant Ship

The characterization of a Line of Sight (LOS) and a Non-Line of Sight (NLOS) link is performed over the military Ultra High Frequency (UHF) band (225 to 450 MHz). This is done using experimental results collected inside the cargo hold of a merchant ship. By analyzing the guiding effect associated with the cargo hold and its sub-structures, the channel characteristics of the environment can be determined. This important propagation mechanism is analyzed using the 3-D ray tracing simulator. Path loss for both topologies is studied and linear path loss models are proposed. Small-scale channel characteristics, such as the number of multipath components, decay factor of the multipath components and Root-Mean-Square (RMS) delay spread are studied and compared for the LOS and NLOS scenarios. Due to the guiding effect and multiple reflections along the cargo hold, both the LOS and NLOS scenarios are found to exhibit similar channel characteristics. A linear decay function is proposed to model the average Power Delay Profiles (PDPs). It is concluded that the linear model provides a good representation for the shape of the impulse responses for a cluttered environment with reflective substructures. This study is useful for the implementation of wireless sensor networks for status monitoring in maritime applications.

Evaluation of visible light communication channel delay profiles for automotive applications

Abstract In this article, we present channel delay profiles based on simulated data regarding the practical conditions for the use of visible light communication (VLC) in automotive applications such as Intelligent Transportation Systems (ITS). Practical vehicular LED headlamp and street lamp that consider the lighting regulation for transportation are used to design the ITS scenarios based on VLC. We modeled two usage scenarios, crossroad and metropolitan street, using the CATIA V5 tool. Measurements for the VLC channel delay profile evaluation were then gathered by using a ray-tracing scheme employing commercial LightTools software under the vehicle-to-vehicle and vehicle-to-infrastructure (V2I) communication links. From the obtained channel impulse responses from both scenarios, we derived the VLC channel delay profiles. From them, we found that the common property of the delay profile was composed of dominant multiple line of sight (LOS) links and a less number of non-LOS delay taps. However, the channel delay profile for the V2I link and metropolitan scenario show more dispersive channel characteristics due to the reflection and diffusion of the visible light.

UWB for multi-gigabit/s communications beyond 60 GHz

The recently allocated 71---76 GHz and 81---86 GHz bands provide an opportunity for realizing Line Of Sight (LOS) links for directional point-to-point "last mile" applications. An efficient use of this spectrum may allow wireless to finally "catch up" with wires, leading to systems such as "multi-Gigabit wireless Ethernet," and "wireless fiber." However, the transmission at such a frequency range is characterized by several additional challenges compared to lower frequency bands, from both technological and propagation point of view, which makes difficult to use them efficiently. In this scenario, IR (Impulse Radio) UWB (Ultra Wide Band) technology might offer some more degrees of freedom for the design of a highly integrated and low cost transceiver. This work has at its core the design and BER (Bit Error Rate) performance evaluation of an IR-UWB architecture based on an 85 GHz up-conversion stage of train of Gaussian pulses having duration lower than 1 ns. Finally, we compare performance of this architecture with the ones of a more traditional continuous wave communications system with FSK (Frequency Shift Keying) modulation. Simulation results show that BER performance, in presence of RF non-linearities, for an IR-UWB transceiver architecture operating at 85 GHz (with same data rate and bandwidth) are better than a coherent BFSK scheme working in a similar scenario. Finally, some conclusions are reported, pointing out the UWB antenna design and the future works related to the modeling of the channel at frequencies beyond 60 GHz and the implementation of the test bed.

Estimation of Path Length Reduction Factor by Using One Year Rain Attenuation Statistics over a Line of Sight Link Operating at 28.75 GHz in Amritsar (INDIA)

The effect of environmental factors in general and rain droplets in particular, on microwave propagation is a very well known fact now. If the rain droplets are present in an inhomogeneous way across the path length of the microwave communication system then, a new concept of path length reduction factor is introduced which accounts for the inhomogeneous nature of the rain droplets along the path length of the microwave signal. The present paper presents results of path length reduction factor using data on attenuation levels obtained on a LOS link operating at 28.75 GHz in Amritsar region and its comparison with Crane’s and ITU-R’s model.

Clear-Air Signal Level Measurement for Microwave Line-of-Sight Link Application in South Africa

This paper presents an analysis of the 19.5 GHz clear-air signal level measurement variations over a line of sight link set up between two campuses of University of KwaZulu-Natal in Durban, South Africa. The measurement over the link spans a period of eleven months. An analytical expression for fade depth exceedance is proposed for KwaZulu-Natal, in South Africa. The link outage probability is compared with the results obtained from two ITU-R models as per Recommendations P.530-8 and P.530-12, Morita's model for Japan, and the model of Vigants used in the United States. The Morita model over sea and coastal regions gives an outage probability of 0.060%, compared to 0.037% obtained from the measurements, with the two ITU-R models also giving close values of 0.027% and 0.024%, respectively. However, Vigants' model is found to be the least appropriate for outage estimation in South Africa.

CMOS Phased Array Transceiver Technology for 60 GHz Wireless Applications

Based on the indoor radio-wave propagation analysis, and the fundamental limits of CMOS technology it is shown that phased array technology is the ultimate solution for the radio and physical layer of the millimeter wave multi-Gb/s wireless networks. A low-cost, single-receiver array architecture with RF phase-shifting is proposed and design, analysis and measurements of its key components are presented. A high-gain, two-stage, low noise amplifier in 90 nm-CMOS technology with more than 20 dB gain over the 60 GHz spectrum is designed. Furthermore, a broadband analog phase shifter with a linear phase and low insertion loss variation is designed, and its measured characteristics are presented. Moreover, two novel beamforming techniques for millimeter wave phased array receivers are developed in this paper. The performance of these methods for line-of-sight and multipath signal propagation conditions is studied. It is shown that one of the proposed beamforming methods has an excess gain of up to 14 dB when the line of sight link is obstructed by a human.

Measurement of Rain Induced Attenuation over a Line of Sight Link Operating at 28.75 GHz at Amritsar (INDIA)

The need of higher bandwidth systems has led the system designer to shift into higher frequency region. But working at these high frequency regions is not that easy. The paper presents results of the measurements of rain induced attenuation of a LOS link operating at 28.75 GHz at Amritsar (31°36′ N 74° 52′ E) for a single event that occurred on the 15th Nov., 2004. The results have been compared with those of ITU-R Model. It is observed that there is a significant difference between the attenuation levels measured and those predicted by using ITU-R model.

All-Optical 500-Mb/s UWB Transceiver:An Experimental Demonstration

We propose and demonstrate experimentally, for the first time, a prototype for all-optical ultra-wideband (UWB) transceiver at 500 Mb/s. We report 1) UWB pulse optimization that takes into account the transmitter RF front end and the U.S. federal communications commission (FCC) spectral mask, 2) a new approximate match filter receiver using optical signal processing, and 3) modulation at 500 Mb/s. Our previous optimization of UWB pulse shapes was based only on the FCC spectral mask, without taking into account the frequency response of the RF components (amplifier and antenna) in the UWB transmitter. Here, we modify our pulse optimization technique to ensure that the equivalent isotropic radiated power (EIRP) from the transmitter meets FCC specifications. For the RF hardware used, we achieve 63.6% efficiency over the FCC mask, which yields an 11.6- and a 5.9-dB improvement over Gaussian monocycle and doublet pulses, respectively. We also introduce simple optical signal processing at the receiver that allows the incoming RF signal to be matched against a square pulse whose duration is adapted to the channel. The exact matched filter would require a new optimized pulse that would include not only hardware frequency response but channel effects that vary with antenna placement as well. The proposed approximation allows a simple variation of the pulse duration: an increase to account for pulse expansion in the channel but an upper limit to combat multipath effects. Finally, we demonstrate the optimized pulse and approximate match filter receiver at 500 M/s. We attain a 10-6bit error rate at a 65-cm separation line of sight (LOS) link with simple on-off keying and no forward error correction.

A method for predicting rain attenuation in terrestrial point-to-point line of sight links at 97 GHz

Rain attenuation caused by electromagnetic scattering and absorption is a major design parameter for setting up satellite communication systems operating at frequencies above 10 GHz. In this paper, a method for predicting rain attenuation in terrestrial point-to-point line of sight links at 97 GHz is proposed using previously available experimental data obtained in the south of UK over a period of more than a year. Rainfall rate and percentage of time are used as input data in the proposed prediction method. Results show that our prediction method based on artificial neural networks reveals very good agreement with the experimental data.

Differential evolution based prediction of rain attenuation over a LOS terrestrial link situated in the southern United Kingdom

The principal objective of a rain attenuation prediction method is to achieve acceptable estimates of the attenuation incurred on the signal due to rain. In this paper, a differential evolution (DE) based model for predicting rain attenuation in a terrestrial point‐to‐point line of sight (LOS) link at 97 GHz is proposed using previously available experimental data obtained in the southern United Kingdom. Rainfall rate and percentage of time are used as input data in the proposed prediction model. Excellent agreement between the experimental data and the model output indicates that the presented DE based method may efficiently be used for accurate prediction of the rain attenuation levels.

Prony technique for prediction of ray parameters in LOS links due to tropospheric multipath

A Prony algorithm is utilised in the process of predicting relative amplitudes and angles of arrival of rays in line of sight (LOS) links using phase and amplitude data. The technique showed much better performance compared with the use of Fourier transform.

Two‐layer LMDS system architecture: DAVIC‐based approach and analysis

AbstractDespite the growing interest for LMDS systems there have been only a few commercial implementations until now especially outside of the U.S.A. The use of hierarchical structure through two‐layer networking has been even rarer. In many cases LMDS systems have strong advantages against their competitors to cover the last mile. In this article, we review and analyze the standards currently available and describe the European two‐layer trial system developed in 1996–2000. We show why further development towards IP based LMDS is useful in the future. Most of our recommendations are based on results derived from the European Union supported research project CABSINET. It had the aim of demonstrating the viability of a 40 GHz cellular digital television system with a return channel to offer interactive services. Two systems were tested: a line of sight link using QPSK, and a non‐line of sight with COFDM modulation scheme. In the RF‐subsystems, the greatest difficulty of any viable LMDS system is to obtain a moderately low price for the user receiver, while fulfilling the hard OFDM requirements in terms of phase noise, stability and spectrum restrictions. Several options have been studied in order to design the subsystems with the smallest cost. This paper will present the architectures of the transmitters, nomadic terminals, and the design of the IF/RF subsystems for both types of modulations. The discussion is focused on system engineering and selections required in order to build a full two‐layer LMDS system. Copyright © 2002 John Wiley & Sons, Ltd.

Measurement of Equivalent Dielectric Parameters of Sandstorms from the Microwave Attenuation

The theory is presented for one method of determining the equivalent dielectric parameters of sand storms from microwave propagation measurement over a line of sight link. The method required the transmission of linear polarized or circle-polarized signal and attenuation measurement. The equivalent dielectric parameters of sandstorms determined at frequencies of 33.5 GHz and 93 GHz over a terrestrial link.

Analysis and modelling of rain fade durations at 97 GHz in 6.5 km urban link

The authors present a statistical analysis and discuss modelling of the duration of rain fades derived from data collected at 97 GHz using an experimental terrestrial line of sight link of 6.5 km which has been in operation since August 1998 across the city of Portsmouth. The presented results provide an insight into what can be expected at these frequencies if they are to be used for future urban terrestrial EHF communication systems. The possible implications for optimum data throughput are outlined.

Point rainfall rate cumulative distribution function valid at various locations

Designing line of sight (LOS) or satellite link systems, needs yearly point rain rate statistics for several percentages of time, in the locations of interest. This is necessary to estimate within an average year, the time percentage during which attenuation due to rain is significant, and consequently the future link performance and availability. The Letter describes a new procedure which is a probability law for predicting point rainfall rate cumulative distribution. Comparisons between theoretical predictions and experimental data collected in several temperate and tropical localities show good agreement.

Holographic prediction of ray parameters in line-of sight links due to tropospheric multipath

Ducting in LOS radio links is investigated. A technique is proposed to estimate the number of refracted rays that could reach the receiver due to the presence of a duct, their angle of arrival and their relative amplitude in comparison to the direct ray.

Experimental observation of horizontal refractivity gradients during periods of multipath propagation

The Propagation en Air Clair et Météorologie 3 (PACEM 3) experiment was intended to provide a better understanding of the physical situations and mechanisms that cause multipath propagation on line of sight links. In this experiment we investigated both the horizontal and the vertical gradients of the refractive index. In this paper, after a description of the experiment, we present some results from the aircraft data analysis. During two nights when radio data demonstrated the existence of multipath propagation, the meteorological situations were different, but both involved important horizontal refractivity gradients. The first night showed the combined effect of the wind circulation and relief. We locally found a 15‐unit increase in the N value over 10 km. During the second night we observed the arrival and the passage of a moist air mass inducing at the transition a difference of 15–20 N units over about 5 km. A ray‐tracing computation taking into account horizontal gradients of refractivity gives evidence of the influence of these horizontal variations upon the area of interfering rays.

Effect of meteorological conditions on scintillation fading in the oxygen absorption region

The effect of the absorption mechanism on the amplitude of the scintillations on a 4-km line of sight link at 54.5 GHz in different meteorological conditions is examined. When atmospheric temperature turbulence is dominant, the absorption mechanism causes the amplitude of the scintillations to be significantly increased for the large outer scale of turbulence sizes. When water vapor pressure fluctuations begin to dominate, the enhancement of the scintillations is suppressed, and the effect of the absorption mechanism on the amplitude scintillations is minimal.