Average Fade Research Articles

Characterization of indoor wireless channel at 5 GHz U-NII bands

The paper reports on the experiments undertaken at the University of Wollongong to characterise fading profiles and delay parameters of an indoor wireless channels at 5 GHz U-NII bands. The measurements were undertaken at different locations around the campus with results recorded for a post-processing to calculate the Rician K-factor, the level crossing rate and the average fade duration as well as mean excess delay, rms delay spread, and the coherence bandwidth of the channel. The presented measurement results can be useful in developing a Markov chain based model of the transport channel for IEEE802.11a or HYPRLAN-2 networks. The results also indicate scenarios where the coherence bandwidth of the channel is smaller than the width of the sub-carrier OFDM channels in either of the mentioned systems.

MIMO Channel Statistics in the Presence of Non-Uniform Angle Spread

We give analytical expressions for correlation, spectrum, level crossing rate, and average fade duration for the multiple-antenna fading channel in the presence of nonuniform power azimuth spectrum (PAS). Classical expressions for uniform PAS are a special case of these expressions. The expressions are valid for any antenna patterns and for any PAS.

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.

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

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.

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.

A Study of Fading Property Indoors Without Glass Frame from an Ozone Accelerated Test

We studied the fading behavior of bare, ink-jet printed samples hung indoors, from the point of view of gasfastness (ozone-fastness). Bare samples were hung in a home environment for 1 year. The samples showed an average fading tendency similar to that of a 15-ppm·h ozone accelerated test at 24°C 60% RH. Taking into account wide divergences in home environment and climate, we set 40 ppm·h as the one-year equivalent level of fading, and we studied the influence of temperature, relative humidity and ozone concentration on the ozone accelerated test.

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.

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.

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.

Average level crossing rate and average fade duration of selection diversity

The average level crossing rate and average fade duration of the output signal envelope of a selection diversity combiner, operating on independent, but nonidentical fading input branch signals are derived. The exact closed-form results are valid for arbitrary diversity order, and are obtained for Rayleigh, Ricean, and Nakagami fading input signals.

Spatial diversity analysis for digital TV systems

Spatial diversity for digital TV systems has been studied using the results of a measurement campaign of the radio channel complex frequency response for two different situations: an outdoor-indoor channel and an indoor-indoor channel. It is shown that the actual improvement of spatial diversity is not only the mean level increase, but the reduction of both the level crossing rate (LCR) and the average fade duration (AFD). The mean level gain is in the range 1.2-3 dB for the indoor-indoor channel and within 1.4-2.9 dB for the outdoor-indoor channel and the LCR/AFD improvement is between 9.5 and 15 dB for both environments. To explain the behavior of the diversity system, high resolution angle of arrival and delay information was obtained. It is concluded that it is the interference of the direct propagation path with the main reflections that causes the received field to follow a standing wave pattern and shapes the spatial diversity gain behavior.

Level crossing rate and average fade duration for pure selection and threshold selection diversity-combining systems

Exact and closed-form expressions for the level crossing rate and average fade duration are presented for the M-branch Pure Selection Combining and for the two-branch Threshold Selection Combining schemes, assuming independent branches in a Rayleigh environment. The analytical results are thoroughly validated by reducing the general case to some special cases, for which the solutions are known, and by means of simulation for the more general case. The plots presented here are also compared with those of the general solution recently published for the Equal Gain and Maximal Ratio Combining and an agreeable coherence is found. Copyright © 2001 John Wiley & Sons, Ltd.

Second-order statistics for diversity-combining techniques in Nakagami-fading channels

Exact and closed-form expressions for the level crossing rate and average fade duration are presented for the M branch pure selection combining (PSC), equal gain combining (EGC), and maximal ratio combining (MRC), techniques, assuming independent branches in a Nakagami (1960) environment. The analytical results are thoroughly validated by reducing the general case to some special cases, for which the solutions are known, and by means of simulation for the more general case. The model developed here is general and can be easily applied to other fading statistics (e.g., Rice).