Fade Duration Research Articles

On Access Attempt Delay with Channel-Adaptive Random Access

In this letter, the pdf of access attempt delay of channel-adaptive random access is derived from that of fade duration of a frequency-flat fading channel. The mean and the variance of access attempt delay are also computed using the moments of fade duration.

Modelling and simulation of a generalised vehicle‐to‐vehicle fading channel

This study presents statistical properties of the vehicle-to-vehicle Nakagami–Hoyt channel model with diffused line of sight (LOS) under isotropic condition. The envelope and phase probability density functions, spatial-time autocorrelation function, the power spectral density, level crossing rate, the average duration of fade, squared time autocorrelation function and mean-square error of time autocorrelation function of the Nakagami–Hoyt channel have been derived under the assumption that both the transmitter and receiver are mobile having omnidirectional antennas and a diffused LOS component is present. The model has been validated using the inverse fast Fourier transform-based simulator. The simulator and analytical results corroborate.

A Study of the Influence of Path Loss and Short Term Fading on the Performance of Mobile Radio System

The mobile radio channel places strong limitations on the performance of wireless communication systems because the transmission principle in wireless communication is more complex than those of the wired networks. In this paper we discuss the radio propagation with an objective to provide an overview of various characteristics of radio channel and an understanding of the process and factors that influences these characteristics. Section I describe a typical outdoor scenario for terrestrial mobile radio channel and principle causes of information loss (multipath fading). Section II presents the various radio channel characteristics like path loss which is used to denote the local average received signal power relative to the transmit power and helps in providing the information on coverage area. Other higher order statistical characteristics such as level crossing rate (lcr) and average duration of fade (adf), which relates the time rate of change of the received signal to the signal level and velocity of the mobile, are also considered to study the influence of short term fading on the performance of the wireless system. Section III contains the observed path loss and its comparison with the simulated path loss propagation models. Lcr and adf are obtained from the received signal envelop in section IV to study the system performance. The simulated results obtained in section III and section IV provide valuable information on coverage area, and choice of suitable data rate, word length, modulation, and coding schemes as stated in table1.

Fade duration statistics for Ku-band satellite links

Fade duration database was built to enhance the study of propagation characterises in the Equatorial region. The data was measured via a beacon receiver Ku-band whereby the antenna was directed to a SUPERBIRD-C2 satellite at 12.255GHz. The performance of the measured data has been compared with ITU-R model, Kormanyos et al. and Paulson–Gibbins. The results show that the Paulson–Gibbins fits well with measured data with a low RMS error of 0.2dB. The number of statistics available for the equatorial is small and the periods of measurement are short compared to those for temperate regions.

Average level crossing rate and fading duration of multiuser single relay cooperation wireless uplinks

We investigate the average Level Crossing Rate (LCR) and Average Fading Duration (AFD) of multiuser single relay cooperation wireless uplinks over independent and non-identically distributed (i.ni.d) Ray-leigh fading channels. We first present the statistical analyses of the first-hop equivalent envelope. Then, we investigate the LCR and AFD of an equivalent end-to-end envelope, and present the closed-form solutions to LCR and AFD, which are given with integral forms. Finally, we derive the Laplace approximations of LCR and AFD as well as the upper and lower bounds. The numerical results of LCR show that the upper bound is tight. For multiuser systems with different number of mobile users, the analyses indicate that the LCRs are approximately the same at the low level of the envelope. However, at the high level of the envelope there are reasonable differences among the curves of LCRs. Due to that fact that AFD is the inverse function of LCR, the results for AFD are the opposite.

Second-order statistics of dual-hop transmission with an amplify-and-forward relay over Rician and Weibull fading channels

The level-crossing rate (LCR) and average fade duration (AFD) are the second-order statistics that are useful for the design of adaptive transmission and coding systems over wireless fading channels. These second-order statistics are analyzed for dual-hop transmissions with a fixed-gain amplify-and-forward relay, where the Rician and Weibull fading channels are considered. To evaluate the LCR and AFD, we also derived the lower and upper bounds on the LCR and AFD which are useful when the exact closed-forms of the LCR and AFD are difficult to obtain. To illustrate the performance of the dual-hop relay channel, numerical results of the outage probability, the LCR and AFD are presented.

Experimental characterisation of ultra‐wideband off‐body radio channels considering antenna effects

Experimental investigation to characterise the ultra-wideband (UWB) off-body radio propagation channel for body-centric wireless communication is presented. The measurements were performed in an indoor environment using active UWB wireless tags. Two different kinds of receiver antennas have been used; namely a small form factor (SFF) antenna and miniaturised co-planar waveguide-fed tapered slot antenna to investigate their effects on the radio channel behaviour. Statistical analysis is performed on the radio channel data and the results demonstrated that the lognormal distribution provides the best fit for off-body propagation channel path-loss models. Comparison of results shows that a reduction of 29% path-loss exponent is noticed for the SFF antenna. In addition to this, second-order channel parameters such as fade probability, level-crossing rate and average fade duration are also investigated and compared for the two antennas.

Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations - including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor - as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.

Dynamic Channel Modeling for Multi-Sensor Body Area Networks

A channel model for time-variant multi-link wireless body area networks (WBANs) is proposed in this paper, based on an extensive measurement campaign using a multi-port channel sounder. A total of 12 nodes were placed on the body to measure the multi-link channel within the created WBAN. The resulting empirical model takes into account the received power, the link fading statistics, and the link auto- and cross-correlations. The distance dependence of the received power is investigated, and the link fading is modeled by a log-normal distribution. The link autocorrelation function is divided into a decaying component and a sinusoidal component to account for the periodical movement of the limbs caused by walking. The cross-correlation between different links is also shown to be high for a number of specific on-body links. Finally, the model is validated by considering several extraction-independent validation metrics: multi-hop link capacity, level crossing rate (LCR) and average fade duration (AFD). The capacity aims at validating the path-loss and fading model, while the LCR and AFD aim at validating the temporal behavior. For all validation metrics, the model is shown to satisfactorily reproduce the measurements, whereas its limits are pointed out.

Channel Characterization of Walking Passerby's Effects on 2.48-GHz Wireless Body Area Network

A statistical analysis of walking passerby's effects on narrowband wireless body area network (WBAN) in outdoor and indoor environments at 2.48 GHz is presented. Experiments were conducted to measure the dynamic channel responses of various on-body links with four sets of pre-defined passerby movements while the user remains stationary in a standing posture. On-body links that experienced fades greater than 20 dB from the static path gain were identified. The effects of passerby movement types, in both outdoor and indoor environments, were analyzed and compared to the effects of user's motions such as walking and running. Parameters for the Ricean distribution, which was found to be a good fit for channel gain variation, are presented to model the channel up to the second-order statistics, such as level crossing rate and average fade duration. The parameters allow the use of fading channel simulators to reproduce the passerby's effects in the on-body channels.

Second‐order statistics of multiuser relay cooperation systems over Nakagami‐m fading channels

SUMMARYTo attain overall recognition of the effect of Nakagami‐m channel parameters on the second‐order statistics and to present a guide to the design and configuration of systems, we investigate the average level crossing rate (LCR) and average fading duration (AFD) of multiuser single relay cooperation wireless communications, in which the multiple mobile users communicate with base station under the help of single relay. On the basis of the statistical channel state information (CSI) between mobile users and relay, a single user is selected to communicate with base station. For the multiuser relay cooperation communications, we first present the integral expressions to the LCR and AFD of equivalent end‐to‐end envelope by using strict mathematical proof. Then with appropriate approximation, we obtain the closed‐form solutions to the upper and lower bounds of average LCR and AFD as well as the ones of Laplace approximation. Finally, on the basis of the derivations, we validate the approximations to LCR and AFD, and investigate the effect of the system parameters on LCR and AFD. The comparison results show that the derivations match well the simulations, and the exact values can be bounded by the obtained upper and lower bounds. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Measurements and Analysis of Propagation Channels in High-Speed Railway Viaducts

This paper reports (i) a set of measurements of the wireless propagation channel at 930 MHz, conducted along the "Zhengzhou-Xian" high-speed railway of China in various railway viaduct scenarios, and (ii) an analysis and modeling of the small-scale and large-scale channel parameters based on those measurements. The environment can be categorized into four cases, covering viaducts with different heights and in different suburban environments. Small values of fade depth, level crossing rates, and average fade duration are observed. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale amplitude fading. An analysis of the envelope autocovariance function shows that the coherence distance is less than 10 cm. The Ricean K-factor is modeled as a piecewise-linear function of distance. Moreover, a breakpoint path loss model is developed and shadow fading is investigated using the same break point as for the distance-dependent K-factor model. The Suzuki distribution is found to offer a good fit for the composite multipath/shadowing channels. We find that the viaduct height H, together with the number of surrounding scatterers, significantly affects the small- and large-scale channel parameters. These results are applicable to both normal-speed and high-speed railways, and will be useful in the modeling of railway viaduct channels and the design of railway wireless communication systems.

On the second order statistics of non-isotropic Nakagami Hoyt mobile to mobile fading channel

This paper presents second order statistical properties of the mobile to mobile Nakagami Hoyt channel model under non-isotropic condition. The spatial-time correlation function, the power spectral density (PSD), level crossing rate (LCR) and the average duration of fade (ADF) of the Nakagami Hoyt channel have been derived under the assumption that both the transmitter and receiver are non-stationary having non-omnidirectional antennas. Design of simulator using the Inverse Fast Fourier Transform (IFFT) based computation method has been applied for this model. The simulator and analytical results have been corroborated.

Measurement Attenuation by Estimate Fade Duration and Number of Fade in Tropical Climate

Attenuation due to rain is a fundamental cause of communication impairment on satellite-earth paths, specifically above 10GHz. Rainfall is a serious source of attenuation at such a frequency. This paper presents the rain fade duration statistics that can be obtained from measured data. These data were interpreted in several groups of attenuation exceeds the threshold, then to analyze the data and get rain fade duration statistics for a period of one year. Eventually, from these measured data, the number of events per year can be estimated; also with these data in per year can be estimated that Monsoon season has a higher number of fade events and longer the fade durations.

Joint results of long-term earth-space propagation experiments at 20-GHz in Canada and Europe

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Millimetre‐wave path‐loss variability between two body‐mounted monopole antennas

Variation of on-body millimetre-wave propagation channels with body movements has been studied experimentally. A statistical description of the propagation channel is presented, including path-loss probability distributions, level-crossing rates and average fade durations. The median path losses for the considered practical links with omnidirectional monopole antennas lied within the range of 55–88 dB. The signal variation was found to consist of two superimposed variations, in general: the long-term and short-term fadings, but was dominated by the much stronger long-term fading. The use of a simple two-state Markov process model to describe on-body communication links is also proposed and its limitations are discussed.

Average Fade Duration of Dual Selection Diversity over Correlated Unbalanced Nakagami-m Fading Channels in the Presence of Cochannel Interference

Average Fade Duration of Dual Selection Diversity over Correlated Unbalanced Nakagami-m Fading Channels in the Presence of Cochannel Interference

Low latitude ionospheric scintillation and zonal irregularity drifts observed with GPS-SCINDA system and closely spaced VHF receivers in Kenya

In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip −24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March–April than in September–October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30–160m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east–west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives the eastward electric fields.

Second order statistics of selection combining receiver over κ‐μfading channels subject to co‐channel interferences

Radio propagation performances in interference‐limited faded environment are studied in this paper. Selection combining (SC) based on signal‐to‐interference ratio (SIR) overκ‐μfading channels is performed. Probability density function (PDF) and cumulative distribution function (CDF) of the received SIR are determined. Based on the results obtained for PDF and CDF, infinite‐series expressions are derived for the output level crossing rate (LCR) and average fade duration (AFD). These second order statistical measures are regarded as necessary for supporting technical documentation in every radio communication link design. Influences of various system parameters such as fading severity and the number of co‐channel interferences affecting these measures are graphically presented and discussed.

Characterization of Wireless On-Body Channel Under Specific Action Scenarios at Sub-GHz Bands

Body area network is an emerging area of wireless communication for medical healthcare applications. This paper characterizes the narrowband wireless on-body channels under specific action scenarios by measurement at the three different sub-GHz frequencies of 444.5, 611, and 953 MHz, which are the candidate frequency bands of narrowband body area network systems with low data rates in IEEE 802.15.6 standard. The channel responses at ten different antenna positions were measured in an office room environment for the two dynamic action scenarios of “walking on the spot” (Action I) and “standing up/sitting down” (Action II). This paper provides generalized on-body channel models of Nakagami- $m$ and Weibull distributions for Actions I and II, respectively. Notably, this paper shows that the shadowing effect due to body movement is dominant over the multipath fading. The results were obtained by the statistical analyses of channel fading properties at three different frequencies including level crossing rate, average fade duration and channel dwelling time.