Fade Duration Research Articles

Level Crossing Rate and Average Fade Duration of the Select-and-Hold Policy of Selection Diversity Combining in a Rayleigh Fading Channel

The select-and-hold policy (SAH) is a general form of selection diversity combining (SDC). In this letter, we provide closed-form expressions for average level crossing rate and average fade duration for Nth-order SAH-SDC. The diversity branches are assumed to be independent and identical Rayleigh fading channels. A useful guideline for choice of the holding time is also obtained.

Channel Capacity and Second-Order Statistics in Weibull Fading

The second-order statistics and the channel capacity of the Weibull fading channel are studied. Exact closed-form expressions are derived for the average level crossing rate, the average fade duration, as well as the average Shannon's channel capacity of the Weibull fading process. Numerical results are presented to illustrate the proposed mathematical analysis and to examine the effects of the fading severity on the concerned quantities.

Spatio–Temporal Rain Attenuation Model for Application to Fade Mitigation Techniques

We present a new stochastic-dynamic model useful for the planning and design of gigahertz satellite communications using fade mitigation techniques. It is a generalization of the Maseng-Bakken and targets dual-site dual-frequency rain attenuated satellite links. The outcome is a consistent and comprehensive model capable of yielding theoretical descriptions of: 1) long-term power spectral density of rain attenuation; 2) rain fade slope; 3) rain frequency scaling factor; 4) site diversity; and 5) fade duration statistics using a novel method based on Markov Chains. We also present a simple rain attenuation synthesizer matching the predictions of the theoretical model.

12-GHz Fade Durations and Intervals in the Tropics

Direct-to-home very small aperture terminals systems operating at frequencies above 10 GHz in tropical climates are subjected to many fade occurrences due to heavy rain. In addition to annual and worst month cumulative rainfall rate and rain fade exceedances, statistics of seasonal and diurnal variations, together with average event length and separation, are needed to give the detailed insights for system design. This paper presents seasonal fade duration statistics and fade interval characteristics for a wet, tropical location in Lae, Papua New Guinea (PNG), measured over four years using satellite beacon and collocated radiometer receivers.

A new multi‐state fading model for mobile satellite channels based upon AFD and LCR data

AbstractUsing measured data on average fade duration (AFD) and level crossing rate (LCR), we obtain new analytical expressions for the probability density function (pdf) of received signal envelope in a mobile satellite channel, via a new method. The measured data for an urban environment comes from Kanatas et al. Proceedings of the 1997 International Mobile Satellite Conference, Pasadena, CA, 16–18 June, 1997; 169–175, but the new method is general in nature and can be applied to other environments. The method is less direct than curve‐fitting to a histogram of the ‘raw’ measured fading amplitude data, but is comparable in complexity and yields good results. Our new model is a composite one, similar to other composite models given in the literature, e.g. the Loo and Lutz models, but in contrast to these, the new model affords a completely closed‐form expression for the pdf. As with these other composite models, the new model is amenable to the development of computer simulations of mobile satellite channel amplitude time series realizations, and can be combined with state transition models to provide a complete multi‐state fading model. Copyright © 2004 John Wiley & Sons, Ltd.

Measured pedestrian movement and bodyworn terminal effects for the indoor channel at 5.2 GHz

[Summary]: Human body effects such as antenna-body interaction and scattering caused by pedestrian movement are important indoor radio propagation phenomena at microwave frequencies. This paper reports measurements and statistical analysis of the indoor narrowband propagation channel at 5.2 GHz for two scenarios: a fixed line-of-sight (LOS) link perturbed by pedestrian movement and a mobile link incorporating a moving bodyworn terminal. Two indoor environments were considered for both types of measurements: an 18 m long corridor and a 42 m2 office. The fixed-link results show that the statistical distribution of the received envelope was dependent on the number of pedestrians present. However, fading was slower than expected, with an average fade duration of more than 100 ms for a Doppler frequency of 8.67 Hz. For the bodyworn terminal, mean received power values were dependent on whether or not the user's body obstructed the LOS. For example, in the corridor the average non-line-of-sight (NLOS) pathloss was 5.4 dB greater than with LOS

Extra-high frequency line-of-sight propagation for future urban communications

Spectrum congestion at conventional microwave frequencies has forced communication system designers to explore and investigate higher and higher frequencies, well into the millimetric band. This part of the radio spectrum is currently underutilized and offers a very wide bandwidth and permits higher data rates as well as more channels. This paper presents measurements, analysis and modeling of propagation losses for a 97-GHz line-of-sight terrestrial link. The link was established in an urban environment over a path length of 6.5 km and operated over a period of more than a year. An overview of path geometry, experimental equipment and data acquisition, and data processing is first given. The annual distribution of the measured rain attenuation at 97 GHz is discussed in connection with that of the rainfall rate at the receiving point, and compared with the current ITU-R rain attenuation prediction model. Extensive experimental results on rain fade durations, long-term fade statistics and amplitude scintillations carried out using data recorded from this link are also presented. The experimental results concerning rain attenuation modeling indicate that the agreement between the measured rain attenuation values and those computed on the basis of the ITU-R rain attenuation prediction model is not entirely satisfactory. However, the results presented in this paper are only based on data collected over a period of one year, thus the difference between reported and modeled rain attenuation distributions may be attributed to expected year-to-year variations in rain fall rate and its associated attenuation distributions. Therefore, the experimental results appear to indicate that further research is necessary to fully validate the ITU-R rain attenuation model at higher millimeter wave frequency band over longer period of time. Nevertheless, the experimental results have established a considerable degree of confidence in the feasibility of millimeter wave link systems with short distance and low power requirements.

Measurements and analysis of the indoor wideband millimeter wave wireless radio channel and frequency diversity characterization

The paper presents results of frequency domain measurements conducted to evaluate the effectiveness of frequency diversity in mitigating the effects of multipath fading in indoor microcellular channels employing an omnidirectional receive antenna in the band 63.4-65.4 GHz. The performance of frequency diversity for 155 MHz and other channel bandwidths to accommodate modulated signals with data rates up to 155 Mb/s is presented. Results are obtained using maximum selection combining and presented as functions of frequency separation between the diversity branch signals. Improvements in the level crossing rate and average fade duration are given together with improvement in the k-Rician factor. The root mean square (rms) delay spread (/spl tau//sub rms/) and coherence bandwidth (/spl beta//sub c/) of the channel are also presented as functions of distance between terminals. Values of /spl beta//sub c/ for correlation levels of 0.9, 0.7, and 0.5 are given together with the cumulative distribution functions of /spl tau//sub rms/. The levels below which the coherence bandwidth stays for 90% of receiver positions are estimated. Measurements were repeated under identical test conditions but with the receive omnidirectional antenna replaced by a directional horn in order to characterize the effect of the receive antenna radiation pattern on the indoor radio channel characteristics.

On the rain attenuation dynamics: spatial‐temporal analysis of rainfall rate and fade duration statistics

AbstractKnowledge about the dynamic characteristics of rain attenuation is of utmost importance for many applications in terrestrial and satellite communication systems operating at frequencies above 10 GHz. Long‐term rain rate statistics and rain rate duration statistics are usually available from meteorological data. In this paper, a spatial–temporal analysis is employed in order to evaluate the rain attenuation power spectrum of a terrestrial/satellite path. The predicted power spectrum is compared with experimental data. Based on the spectral analysis of rainfall rate a method for converting rain rate duration statistics to link fade duration statistics is also proposed. Fade duration statistics are presented for terrestrial and satellite links and compared with available experimental data. The agreement between the predicted results and the experimental data has been found to be quite encouraging. Finally, numerical results are presented for various climatic zones, elevation angles and frequencies. Some very useful conclusions concerning the dynamic properties of rain attenuation for a microwave path are deduced. Copyright © 2003 John Wiley & Sons, Ltd.

Simulation models with correct statistical properties for rayleigh fading channels

In this paper, new sum-of-sinusoids statistical simulation models are proposed for Rayleigh fading channels. These new models employ random path gain, random initial phase, and conditional random Doppler frequency for all individual sinusoids. It is shown that the autocorrelations and cross correlations of the quadrature components, and the autocorrelation of the complex envelope of the new simulators match the desired ones exactly, even if the number of sinusoids is as small as a single-digit integer. Moreover, the probability density functions of the envelope and phase, the level crossing rate, the average fade duration, and the autocorrelation of the squared fading envelope which contains fourth-order statistics of the new simulators, asymptotically approach the correct ones as the number of sinusoids approaches infinity, while good convergence is achieved even when the number of sinusoids is as small as eight. The new simulators can be directly used to generate multiple uncorrelated fading waveforms for frequency selective fading channels, multiple-input multiple-output channels, and diversity combining scenarios. Statistical properties of one of the new simulators are evaluated by numerical results, finding good agreements.

MIMO capacity, level crossing rates and fades: The impact of spatial/temporal channel correlation

It is well known that Multiple Input Multiple Output (MIMO) systems offer the promise of achieving very high spectrum efficiencies (many tens of bit/s/Hz) in a mobile environment. The gains in MIMO capacity are sensitive to the presence of spatial and temporal correlation introduced by the radio environment. In this paper, we examine how MIMO capacity is influenced by a number of factors e.g., a) temporal correlation b) various combinations of low/high spatial correlations at either end, c) combined spatial and temporal correlations. In all cases, we compare the channel capacity that would be achievable under independent fading. We investigate the behaviour of “capacity fades,” examine how often the capacity experiences the fades, develop a method to determine level crossing rates and average fade durations and relate these to antenna numbers. We also evaluate the influence of channel correlation on the capacity autocorrelation and assess the fit of a Gaussian random process to the temporal capacity sequence. Finally we note that the particular spatial correlation structure of the MIMO channel is influenced by a large number of factors. For simplicity, it is desirable to use a single overall correlation measure which parameterizes the effect of correlation on capacity. We verify this single parameter concept by simulating a large number of different spatially correlated channels.

Level crossing rate and average fade duration of MRC and EGC diversity in ricean fading

The average level crossing rate and average fade duration of the output signal of a maximal ratio combiner (MRC) and equal gain combiner (EGC), operating on independent Ricean fading input branch signals, are derived. Exact, closed-form results are obtained for MRC diversity, while precise expressions for EGC diversity are presented with an infinite series method. The results are valid for an arbitrary number of independent, identically distributed diversity branches, isotropic scattering, and a specular component perpendicular to the line of motion of the mobile.

Impact of fade duration and elevation angle on time correlation of the mobile satellite channel

Satellite systems are expected to assume a very important role in the implementation of the Global Information Infrastructure due to their flexibility and capability for providing global coverage a...

Approximate urban area call drop‐out probability estimation in mobile multi‐satellite systems

AbstractLand mobile satellite (LMS) systems require constellations of multiple satellites to compensate for the large blockage probabilities suffered in urban areas. An approximate methodology based on the street masking function (MKF) or mask concept is presented for the evaluation of system availability. MKFs are graphical representations of the angles (azimuths and elevations) for which a satellite is visible from the terminal's location in the street. MKFs can also be used in the evaluation of second order statistics such as durations of fades or connections. In this paper, the applicability of the mask concept is demonstrated by performing a study of the probability of successful call completion in a LEO‐based satellite telephony service. Copyright © 2003 John Wiley & Sons, Ltd.

Level crossing rate in terms of the characteristic function: a new approach for calculating the fading rate in diversity systems

The level crossing rate (LCR) of a random process conveys useful information about the underlying process, and is of interest in diverse engineering fields. In wireless communications, it is related to the system characteristics such as handoff, outage probability, fading rate, average duration of fades, velocity (or maximum Doppler shift) of the mobile, and the effect of diversity on fading. The LCR formula was originally derived by Rice in terms of the joint probability density function (pdf) of the underlying process and its time derivative. In this letter, we express the LCR in terms of the joint characteristic function (cf). This new formula is useful for many cases where the joint cf is simpler to derive than the associated joint pdf. As an application and for a direct-sequence code-division multiple-access system, the fading rate at the output of a RAKE receiver with either maximal ratio combiner or postdetection equal gain combiner, operating over a frequency-selective fading channel with different path statistics, is easily calculated using the new cf-based LCR formula.

Analytical level crossing rates and average fade durations for diversity techniques in Nakagami fading channels

The level crossing rates (LCRs) and average fade durations (AFDs) of a fading channel find diverse applications in the evaluation and design of wireless communication systems. Analytical expressions for these quantities are available in the literature for certain diversity reception techniques, but are generally limited to the Rayleigh fading channel, with few exceptions. Moreover, the methods employed are usually specific to a certain channel/diversity pair, and thus cannot be applied to all cases of interest. Using a unified methodology, we derive analytical expressions for the LCRs and AFDs for three diversity reception techniques and a general Nakagami (1960) fading channel. We provide novel analytical expressions for selection combining (SC) and equal-gain combining (EGC), and rederive in a more general manner the case of maximal-ratio combining (MRC). It is shown that our general results reduce to some specific cases previously published. These results are used to examine the effects of the diversity technique, the number of receiving branches and severity of the fading on the concerned quantities. It is observed that as the Nakagami m-parameter and the diversity order increase, the behavior of the combined received envelope for EGC follows closely the one for MRC, and distances itself from SC.

Average level crossing rate and average fade duration of low-order maximal ratio diversity with unbalanced channels

The average level crossing rate and average fade duration of a maximal ratio diversity combiner, operating on independent, unequal power Rayleigh fading branches in isotropic scattering, are derived in closed-form for dual-branch diversity, and as definite integrals for threefold and fourfold diversity.

Spatial and Temporal Variations of the Indoor Wireless EHF Channel

This paper reports line-of-sight propagation measurements performed at 37.2 GHz between two terminals in an empty room in order to investigate the spatial and temporal fadings in terms of antenna directivity and human motion, respectively. The empirical data base consists of recordings of CW envelope fading waveforms with a fixed transmitter and either moving or stationary receiver. The reported results include amplitude fading distributions, propagation loss gradients, level crossing rates and fade durations statistics. These results can be used in the modeling, design reliable operation of local multi-point communication systems.

Simple closed-form solutions for level crossing rate and average fade duration in Nakagami-m equal gain combining

Simple closed-form approximations for level crossing rate and average fade duration in an M-branch Nakagami-m (1960) equal gain combining scheme are presented. The proposed closed-form formulas yield results that are almost indistinguishable from the exact solution to which intricate expressions involving M-fold integration are required.

Radio Transmission and Experimental Channel Characterisation Usingan MBS Platform Operating in the 40 GHz Band

This paper focuses on results obtained in the ACTS SAMBA project. The project's main objective was the implementation of a Trial Platform providing a full duplex radio link of 34 Mbit/s to prove the technical feasibility with today's technology and to evaluate the main MBS functionality for the public cellular MBS segment. Thus, extensive field trials were carried out in the city of Aveiro, Portugal, in different environments and using the 40 GHz band. The paper starts with an introductory analysis of the radio channel impairments and discusses the various appropriate mitigation techniques. A brief description of the SAMBA Trial Platform used in the measurements campaign is presented concentrating on the description of the main technical solutions related with the physical layer. Then, representative measurements results collected in an urban and in an indoor environment are analysed so as to evaluate the system performance, focusing on the cell coverage area and transmission quality. This study is made analysing parameters such as: received power level, bit error rate, fitted Rice distribution parameters to model the small-scale fading, power level cumulative distribution functions, level crossing rate and average fade duration of the signals received in the two diversity antennas and the resulted signal after combination. The achieved results constitute a significant forward step for the MBS development.