Showing papers on "Fading distribution published in 2008"

The industrial indoor channel: large-scale and temporal fading at 900, 2400, and 5200 MHz

Abstract: In this paper, large-scale fading and temporal fading characteristics of the industrial radio channel at 900, 2400, and 5200 MHz are determined. In contrast to measurements performed in houses and in office buildings, few attempts have been made until now to model propagation in industrial environments. In this paper, the industrial environment is categorized into different topographies. Industrial topographies are defined separately for large-scale and temporal fading, and their definition is based upon the specific physical characteristics of the local surroundings affecting both types of fading. Large-scale fading is well expressed by a one-slope path-loss model and excellent agreement with a lognormal distribution is obtained. Temporal fading is found to be Ricean and Ricean K-factors have been determined. Ricean K-factors are found to follow a lognormal distribution.

Capacity of MRC on Correlated Rician Fading Channels

Abstract: A new exact explicit expression is derived for the ergodic capacity of maximal ratio combining (MRC) schemes over arbitrarily correlated Rician fading channels. This is used to study the effects of channel correlation on the ergodic capacity. Numerical results reveal that both the phase and the magnitude of correlation have an impact on the ergodic capacity of Rician fading channels. This is in contrast to correlated Rayleigh fading, where the phase of the correlation has no effect on the ergodic capacity. It is also observed that negatively correlated branches in Rician fading may lead to an increase in ergodic capacity beyond that obtained by uncorrelated branches.

Spectral Efficiency of Distributed MIMO Cellular Systems in a Composite Fading Channel

Abstract: In this paper, accurate approximations of the spectral efficiency are presented for co-located multiple-input multiple-output (C-MIMO) and distributed MIMO (D-MIMO) cellular systems in the composite channel model, which includes path loss, shadow fading, and multipath fading. Firstly, conditioned on the desired user position, the analytical approximations of the mean and variance of the mutual information are derived for C-MIMO and D-MIMO at high SNR. Because the exact distribution of the mutual information in a composite Rayleigh- lognormal environment is difficult to analyze, we apply Gaussian approximation to the distribution of the mutual information. Then, the growth in ergodic capacity and outage capacity of a D-MIMO channel with the number of antennas as well as the variance of the shadow fading is well understood. Assuming that the users are randomly distributed in the cell, the closed-form expressions for the mean spectral efficiency and mean outage spectral efficiency are derived. Finally, the numerical results are presented which validate the analytical results.

Outage Analysis of Decode-and-Forward Relaying Over Nakagami- $m$ Fading Channels

Abstract: In this letter, closed-form outage probability expressions are presented for an -relays dual-hop plus a direct link network, in which the decode-and-forward relaying protocol is employed. Our analysis significantly extends previous results on Rayleigh fading, considering a Nakagami- fading environment with either equal or distinct second hops fading parameters to average power ratios. Various numerical examples illustrate the proposed analysis.

Closed-form error analysis of the non-identical Nakagami-m relay fading channel

Abstract: We present closed-form expressions for the average bit error probability (ABEP) of BPSK, QPSK and M-QAM of an amplify-and-forward average power scaling dual-hop relay transmission, over non-identical Nakagami-m fading channels, with integer values of m. Additionally, we evaluate in closed-form the ABEP under sufficiently large signal-to-noise ratio for the source-relay link, valid for arbitrary rn. Numerical and simulation results show the validity of the proposed mathematical analysis and point out the effect of the two hops unbalanced fading conditions on the error performance.

Capacity of the Multiple Spot Beam Satellite Channel With Rician Fading

Abstract: In this correspondence, the uplink of a multibeam satellite system with Rician fading is analyzed under the framework of Wyner's Gaussian cellular multiple access channel. In this framework the received signal at a given multibeam antenna is the sum of signals transmitted by users within that beam's cell area plus a factor 0 les alpha les 1 times the sum of the signals transmitted by users from adjacent cells plus ambient Gaussian noise. Both one-dimensional (1-D) linear, and 2-D hexagonal cellular arrangements are considered. In addition, we consider a modified version of the 1-D linear arrangement whereby users from cells further than adjacent cells contribute to intercell interference. It is assumed that the distance between the antenna elements is small compared to the distance between a user and the satellite. Thus when fading is present, a particular user's fading coefficient is the same at each multibeam antenna. This is the fundamental difference between the multibeam satellite fading channel and the terrestrial cellular fading channel, in which each user experiences independent fading at each base station. Using a Haar measure approximation we derive closed form approximations for the capacity of the satellite fading channel for the scenarios when optimal joint decoding and linear minimum mean square error filtering is employed at the ground station. These approximations are shown to be in close agreement to Monte Carlo simulation results for large dimensional systems. It is shown that fading causes a loss in capacity compared to the nonfading channel. Furthermore, at high signal-to-noise ratio (SNR) this loss is independent of the intercell interference and topology of the system, but is dependent on the distribution of the fading coefficients and the number of users per beam.

Channel Capacity Limits of Cognitive Radio in Asymmetric Fading Environments

Abstract: Cognitive radio technology is an innovative radio design concept which aims to increase spectrum utilization by exploiting unused spectrum in dynamically changing environments. By extending previous results, we investigate the capacity gains achievable with this dynamic spectrum approach in asymmetric fading channels. More specifically, we allow the secondary-to- primary and secondary-to-secondary user channels to undergo Rayleigh or Rician fading, with arbitrary link power. In order to compute the capacity, we derive the distributions of ratios of Rayleigh and Rician variables. Compared to the symmetric fading scenario, our results indicate several interesting features of the capacity behaviour under both average and peak received power constraints. Finally, the impact of multiple primary users on the capacity under asymmetric fading has also been studied.

Performance analysis of system with selection combining over correlated Rician fading channels in the presence of cochannel interference

Abstract: Dual-diversity receiver employing selection combining (SC) is often used in wireless communication systems due to its simplicity. Ability of the Rician model to describe fading in wireless communications is the reason to derive infinity-series representations for both the probability density function (PDF) and the cumulative distribution function (CDF) of output signal-to-interference ratio (SIR) at the dual SC receiver over correlated Rician fading channels in the presence of correlated Rayleigh distributed cochannel interference (CCI). These expressions are used to study wireless system performance criteria, such as outage probability and average bit error probability (ABEP).

Outage Capacity of MIMO Poisson Fading Channels

Abstract: The information outage probability of a shot-noise limited direct detection multiple-input-multiple-output (MIMO) optical channel subject to block fading is considered. Information is transmitted over this channel by modulating the intensity of a number of optical signals, one corresponding to each transmit aperture, and individual photon arrivals are observed at multiple receive photodetector apertures. The transmitted signals undergo multiplicative fading. The fading occurs in coherence intervals of fixed duration in each of which the channel fade matrix remains constant, and changes across successive such intervals in an independent and identically distributed fashion. The transmitter and the receiver are assumed to be provided with perfect channel state information (CSI). An optimization formulation for the outage probability problem is outlined and an exact characterization of the optimal average conditional duty cycles is provided.

Analysis of microdiversity and dual channel macrodiversity in shadowed fading channels using a compound fading model

Abstract: Wireless channels are affected by short-term fading and long-term fading (shadowing). A compound fading model was proposed for the modeling of shadowed fading channels which resulted in a closed form solution for the probability density function (pdf) of the signal-to-noise ratio (SNR). This model is applied to a case where both micro- and macro-diversity schemes are implemented to mitigate short-term fading and shadowing, respectively. Using the compound fading model, it is shown that the pdf of the signal-to-noise ratio after the implementation of maximal ratio combining (MRC) at the micro level and selection combining (SC) at the macro level can be expressed in analytical form. Even when branch correlation exists, the pdf still can be expressed in analytical form. Thus, the compound pdf model offers significant improvement over approaches which use lognormal pdf for shadowing. The performance of a coherent binary phase shift keying (BPSK) modem is evaluated using this approach. The results demonstrate the simplicity and usefulness of the compound pdf in the performance analyses of shadowed fading channels even when branch correlation exists at the base station or correlation exists between base stations.

Diversity-Multiplexing Tradeoff for the Slow Fading Interference Channel

Abstract: We establish the high SNR diversity-multiplexing tradeoff of the fading interference channel, for a general interference level and under the assumption that transmitters and receivers are equipped with a single antenna each.

Performance analysis of QAM in a two-wave with diffuse power fading environment

Abstract: This letter investigates the average bit error rate (BER) performance of quadrature amplitude modulation in a two-wave with diffuse power (TWDP) fading environment. In TWDP fading, the received signal is composed of two specular components in addition to the diffuse component. The cumulative distribution function of TWDP fading is used to derive the BER expression in closed-form. Numerical and simulation results are presented to show the impact of different TWDP fading scenarios on the error performance.

Gaussian fading interference channels: Power control

Abstract: In this paper we consider power allocation policies for 2-user Gaussian interference channels (IFC) with ergodic fading, perfectly known at all terminals. Based on recently found outer bounds on the capacity region of unfaded IFCs, we determine the power allocation that maximizes a sum-rate outer bound. With this power allocation both users are simultaneously active when the power of the interfering signals is small relative to the power of the intended signals. Otherwise, only the user with the largest fading gain is active, similar to multi-access and broadcast channels. By considering a simplified version of the Han-Kobayashi region, we derive the power allocation that maximizes a sum-rate inner bound. Numerical results for iid Rayleigh fading show that the inner and our bounds are very close to one another. The structure of the determined power allocation policies suggests that practical power allocations can be designed based on only a bit of channel state information.

Bivariate nakagami-m distribution with arbitrary correlation and fading parameters

Abstract: New, exact expressions concerning the bivariate Nakagami-m processes with arbitrary correlation and fading parameters are derived. More specifically, the following are obtained in the present work: joint moment generating function; joint probability density function; joint cumulative distribution function; power correlation coefficient; and several statistics related to the signal-to-noise ratio at the output of the selection combiner, namely, outage probability, probability density function, and mean SNR. The expressions make use of the well known generalized Laguerre polynomials. They are mathematically tractable and flexible enough to accommodate a myriad of correlation scenarios, useful in the analysis of a more general fading environment. We maintain, however, that a relation among the correlation coefficients of the corresponding Gaussian components must be kept so that convergence is attained.

An Improved Deterministic SoS Channel Simulator for Multiple Uncorrelated Rayleigh Fading Channels

Abstract: The generation of multiple uncorrelated Rayleigh fading waveforms is often demanded for simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels. In this letter, an improved deterministic sum-of-sinusoids (SoS) channel simulator with a new parameter computation method is proposed to simulate a large number of uncorrelated Rayleigh fading processes. Compared with the existing SoS channel simulators, the proposed deterministic SoS model yields a much better simulation efficiency while still preserving satisfactory approximations to the desired statistical properties of the reference model.

The $\kappa-\mu$ Distribution Applied to the Analysis of Fading in Body to Body Communication Channels for Fire and Rescue Personnel

Abstract: In this letter, we perform a novel characterization of the fading experienced in body to body communications channels for fire and rescue personnel using the recently proposed kappa - mu distribution. A transmitter positioned on the lead fire person and four strategically placed, time-synchronized 2.45-GHz receivers situated on the protective helmet and shoulders of another team member allowed small-scale signal variation to be recorded while a rescue team of four persons performed a building sweep and search type operation. A general kappa - mu model with parameters kappa=2.31 and mu=1.19 was obtained using maximum likelihood estimation and shown to provide a good fit to measured data. Level crossing rates for these channels are also presented.

Impact of Channel Errors on Decentralized Detection Performance of Wireless Sensor Networks: A Study of Binary Modulations, Rayleigh-Fading and Nonfading Channels, and Fusion-Combiners

Abstract: We provide new results on the performance of wireless sensor networks in which a number of identical sensor nodes transmit their binary decisions, regarding a binary hypothesis, to a fusion center (FC) by means of a modulation scheme. Each link between a sensor and the fusion center is modeled independent and identically distibuted (i.i.d.) either as slow Rayleigh-fading or as nonfading. The FC employs a counting rule (CR) or another combining scheme to make a final decision. Main results obtained are the following: 1) in slow fading, a) the correctness of using an average bit error rate of a link, averaged with respect to the fading distribution, for assessing the performance of a CR and b) with proper choice of threshold, on/off keying (OOK), in addition to energy saving, exhibits asymptotic (large number of sensors) performance comparable to that of FSK; and 2) for a large number of sensors, a) for slow fading and a counting rule, given a minimum sensor-to-fusion link SNR, we determine a minimum sensor decision quality, in order to achieve zero asymptotic errors and b) for Rayleigh-fading and nonfading channels and PSK (FSK) modulation, using a large deviation theory, we derive asymptotic error exponents of counting rule, maximal ratio (square law), and equal gain combiners.

A Model for Correlated Rician Fading Channels Based on a Finite Queue

Abstract: We study the problem of approximating the family of hard-decision frequency-shift keying demodulated correlated flat Rician fading channels via a recently introduced queue-based channel (QBC) model for binary communication channels with memory For a given ldquodiscretizedrdquo fading channel, we construct a QBC whose noise process is statistically ldquocloserdquo in the Kullback-Leibler sense to the error or noise process that is generated by the fading channel, and the modeling accuracy is evaluated in terms of noise autocorrelation function (ACF) and channel capacity Numerical results indicate that the QBC provides a good approximation of the fading channels for a wide range of channel conditions Furthermore, it estimates the noise ACF more accurately than the finite-state Markov models that have been recently studied by Pimentel , while, at the same time, remaining mathematically tractable

Performance Analysis of Free-Space Optical Systems in Gamma-Gamma Fading

Abstract: Atmospheric turbulence induced fading is one of the main impairments affecting free-space optics (FSO). Gamma-gamma fading has become the dominant fading model for FSO links because of its excellent agreement with measurement data for a wide range of turbulence conditions. In this paper, we express the bit error rate of intensity modulated FSO with direct detection in single-input single-output and multiple-input multiple-output gamma-gamma fading channels as generalized infinite power series with respect to the signal-to- noise ratio. For fast numerical evaluation these power series are truncated to a finite number of terms and an upper bound for the associated approximation error is provided. Another contribution of this paper is the extension of the well-known RF concepts of diversity and combining gain to FSO and gamma-gamma fading.

Ergodic two-user interference channels: Is separability optimal?

Abstract: The optimality of separable encoding and decoding over parallel channels (fading states) for ergodic fading two-user interference channels (IFCs) is studied using a one-sided IFC as a model For an ergodic fading one-sided IFC with non-fading direct links and a fading cross-channel link, it is shown that separability can be strictly suboptimal except for the cases where all the parallel channels are of the same type, ie, all of them are either strong but not very strong or very strong channels A recent result on the sum-capacities of classes of ergodic strong and very strong IFCs is used to show that encoding and decoding jointly over all parallel channels is optimal when either the strong or very strong interference conditions hold on average over all channels

On the Secrecy Capacity of Fading Cognitive Wireless Networks

Abstract: In this paper, we compute the primary exclusive region (PER) and the secrecy capacity at a primary receiver in a fading cognitive radio network. We consider Rayleigh fading and log-normal shadowing. We also study the effect of secrecy capacity on the PER. We show that log-normal shadowing and Rayleigh fading can degrade the PER by about 40% and the secrecy capacity by about 70%.

Cooperative Fading Regions for Decode and Forward Relaying

Abstract: Cooperative transmission protocols over fading channels are based on a number of relaying nodes to form virtual multi-antenna transmissions. Diversity provided by these techniques has been widely analyzed for the Rayleigh fading case. However, short range or fixed wireless communications often experience propagation environments where the fading envelope distribution is meaningfully different from Rayleigh. The main focus in this paper is to investigate the impact of fading distribution on performances of collaborative communication. Cooperative protocols are compared to co-located multi-antenna systems by introducing the concept of cooperative fading region. This is the collection of fading distributions for which relayed transmission can be regarded as a competitive option (in terms of performances) compared to multi-antenna direct (noncooperative) transmission. The analysis is dealt with by adopting the information theoretic outage probability as the performance metric. Cooperative link performances at high SNR are conveniently expressed here in terms of diversity and coding gain as outage parameters that are provided by the fading statistics of the channels involved in collaborative transmission. Advantages of cooperative transmission compared to multi-antenna are related to the propagation environment so that the analysis can be used in network design.

Achievable Rates with Imperfect Transmitter Side Information Using a Broadcast Transmission Strategy

Abstract: rdquoWe investigate the performance of the broadcast approach for various fading distributions, which correspond to different models of partial transmit channel state information (CSI). The first model considered is the quantized limited feedback. In this model, the receiver can send as feedback only a finite number of bits describing the fading gain. We derive the optimal power allocation for the broadcast approach for the quantized feedback model. For a Rayleigh fading channel, numerical results here show that if the feedback word can be longer than one bit, the broadcasting gain becomes negligible, due to diminished channel uncertainty. The second partial transmit CSI model is a stochastic Gaussian model with mean and variance information, which is commonly used for modeling the channel estimation error. In a single-input single-output (SISO) channel, this model also corresponds to the Ricean fading distribution, for which we derive maximal achievable broadcasting rates. We further consider a multiple-input single-output (MISO) channel, and derive the optimal power allocation strategy in a broadcast approach. Numerical results here show that uniform power allocation is preferable over beamforming power allocation in the region where broadcasting gain over single level coding is non-negligible.

Performance of Multiple-Access DCSK Communication over a Multipath Fading Channel with Delay Spread

Abstract: The bit error rate (BER) performances of variant delay multiple-access differential chaos-shift keying (VDMA-DCSK) communication systems over a multipath fading channel with delay spread are investigated. The BER formula of the VDMA-DCSK over the fading channel is evaluated. A two-ray Rayleigh fading channel model is used to simulate the VDMA-DCSK system. The theoretical and simulation results are presented and they match each other, which supports the theoretical analysis. The multipath performance of the VDMA-DCSK is compared with that of a benchmark coherent MA-CSK system and with that of an invariant delay MA-DCSK system. The results show that in the multipath fading channel with delay spread environment the VDMA-DCSK system performance decreases least.

Modulation Recognition in Multipath Fading Channels Using Cyclic Spectral Analysis

Abstract: In this paper, we propose a novel signal classification method using cyclic spectral analysis and neural networks for multipath fading channels. The proposed system provides excellent classification performance in realistic multipath fading channels at low SNR, while assuming no a priori knowledge of the signal statistics, including carrier frequency, phase offset, or symbol rate. Due to its insensitivity to these statistics and its robustness to multipath fading channels, the spectral coherence function (SOF) is employed in the proposed system to produce a highly reliable classifier. Additionally, by employing a multiple-antenna based system, even greater advantages are achieved by exploiting spatial diversity. Numerical results demonstrate the classifier performance under a variety of channel conditions.

An accurate closed-form approximation of the average probability of error over a log-normal fading channel

Abstract: The log-normal probability distribution is commonly used in wireless communications to model the shadowing and more recently the small scale fading for indoor ultra wideband communications. In this paper, an accurate closed-form approximation of the average probability of error over a log-normal fading channel is derived for various constellation types and sizes. This expression can be used to evaluate and compare easily the symbol-error performance of communication systems over a log-normal fading channel.

Performance of wireless multihop communications systems with cooperative diversity over fading channels

Abstract: We present closed-form bounds for the performance of wireless multihop communications systems with cooperative diversity over Nakagami-m fading channels. The end-to-end signal-to-noise ratio is formulated and upper bounded by using the inequality between harmonic and geometric means of positive random variables. Closed-form expression is derived for the moment-generating function and is used to obtain lower bounds for the average error probability. Numerical results are compared with computer simulations showing the tightness of the proposed bounds. Copyright © 2007 John Wiley & Sons, Ltd.

Performance of generalized selection combining receivers in K fading channels

Abstract: In this letter, we present a moment generating function (MGF) based performance analysis of generalized selection combining (GSC) receivers operating over independent and identically distributed (i.i.d.) K fading channels. Analytical expressions for the marginal MGF of the signal-to-noise ratio of a single diversity branch for integer plus one-half values of the fading parameter are obtained and used to efficiently evaluate the average error probability of GSC receivers.

Outage Probability of Opportunistic Amplify-and-Forward Relaying in Nakagami-m Fading Channels

Abstract: We address the outage performance for the opportunistic amplify-and-forward relaying strategies under Nakagami-m fading channels. A closed-form expression for the outage probability is derived. Simulation results verify our theoretical solutions.

Chaos-Coded Modulations Over Rician and Rayleigh Flat Fading Channels

Abstract: In this brief, we analyze a kind of chaos-coded modulations over both Rician and Rayleigh frequency non-selective uncorrelated fading in the presence of additive white Gaussian noise. We provide bounds both for the case when perfect channel-state information (CSI) is available at the decoder and when there is no CSI. We show that the bounds proposed can be tight enough to give reason of the behavior of these systems in a flat fading channel. We compare the results with a related trellis-coded modulation and show that the degradation in performance can be at least as low as with conventional coded modulation systems.