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With an objective of ubiquitous connectivity around the world with enhanced spectral efficiency, intelligent reflecting surfaces (IRS) integrated satellite-terrestrial communications is a topic of research interest specially in infrastructure-deficient terrains. In line with this vision, this paper entails the performance analysis of satellite-terrestrial networks leveraging both aerial and terrestrial IRS nodes, with the support of high altitude platforms (HAPS) over diverse fading channels including shadowed Rician, Rician, and Nakagami-m fading channels. The merits of IRS in enhancing spectral efficiency is analyzed through closed-form expressions of outage probability and ergodic rate. Further, the average symbol error rate analysis for the higher-order quadrature amplitude modulation (QAM) schemes such as hexagonal QAM, rectangular QAM, cross QAM, and square QAM is performed. Practical constraints like antenna gains, path loss, and link fading are considered to characterize the satellite terrestrial links. Finally, a comparison between the HAPs based IRS node and terrestrial IRS nodes is performed and various insights are drawn under various fading scenarios and path loss conditions. Our results demonstrate that aerial IRS nodes offer superior performance in terms of outage probability, ergodic rate, and symbol error rate for higher-order QAM schemes. Additionally, the study reveals that the ergodic rate in aerial IRS systems scales with the number of IRS elements, while terrestrial IRS systems rely on the diversity of the satellite-HAP link.

The capture effect is a frequently observed phenomenon in vehicular ad hoc networks (VANETs) communication. When conflicts arise during time slot access, failure to access does not necessarily occur; instead, successful access may still be achieved. The capture effect can enhance the likelihood of multiple access and improve communication efficiency. The security of VANETs communication is undoubtedly the primary concern. One crucial approach to enhance security involves the design of an efficient and reliable medium access control (MAC) protocol. Taking into account both aspects, we propose a novel framed slotted Aloha (FSA) MAC protocol model. Firstly, we derive the closed-form expression for the capture probability in the Rician fading channel in this paper. Subsequently, we analyze how the number of vehicles and time slots influence the success probability of vehicle access channels as well as examine the impact of the capture effect on this success probability. Then, under constraints regarding vehicle access channel success probability, we derive optimal values for slot numbers, access times, and transmission power while proposing a comprehensive implementation method to ensure high access channel success probabilities. We verify both theoretical derivations and proposed methods through simulation experiments. [ABSTRACT FROM AUTHOR]

The capture effect is a frequently observed phenomenon in vehicular ad hoc networks (VANETs) communication. When conflicts arise during time slot access, failure to access does not necessarily occur; instead, successful access may still be achieved. The capture effect can enhance the likelihood of multiple access and improve communication efficiency. The security of VANETs communication is undoubtedly the primary concern. One crucial approach to enhance security involves the design of an efficient and reliable medium access control (MAC) protocol. Taking into account both aspects, we propose a novel framed slotted Aloha (FSA) MAC protocol model. Firstly, we derive the closed-form expression for the capture probability in the Rician fading channel in this paper. Subsequently, we analyze how the number of vehicles and time slots influence the success probability of vehicle access channels as well as examine the impact of the capture effect on this success probability. Then, under constraints regarding vehicle access channel success probability, we derive optimal values for slot numbers, access times, and transmission power while proposing a comprehensive implementation method to ensure high access channel success probabilities. We verify both theoretical derivations and proposed methods through simulation experiments.

Summary: Communication through satellite is of great task and importance especially in the world of telecommunication infrastructure. It plays a leading role for future communication systems. However, the performance of the satellite communication system is dominated by the channel conditions overwhelmed by multipath fading and ionospheric scintillation effects. Maximum ratio combining (MRC) previously used to tackle this problem is characterized with hardware complexity resulted in long processing time, while threshold combining (TC) with simple hardware display poor performance. Thus, evaluation of hybrid TC‐MRC, with closed‐form expression over composite Rayleigh and Rician fading channel is necessary. In this paper, TC and MRC are combined to improve the signal quality and performance. The data are modulated using M‐ary quadrature amplitude modulation and transmitted over the combined effects. The received signals at varying paths are scanned to select the best paths. A mathematical expression using the probability density function of composite Rayleigh and Rician fading channel for mean integrated square error (MISE) is derived. The model is efficiently simulated and the performance is estimated. The results show that the hybrid TC‐MRC model achieves lower MISE and processing time compared to threshold combiner and even maximum ratio combiner, and thereby enhance the performance of the satellite communication system. [ABSTRACT FROM AUTHOR]

Employing low resolution analog-to-digital converters in massive multiple-input multiple-output (MIMO) has many advantages in terms of total power consumption, cost and feasibility. However, such advantages come together with significant challenges in channel estimation and data detection due to the severe quantization noise present. In this study, we first derive linear minimum mean-square-error channel estimator for cyclic-prefix (CP) free single carrier MIMO (SC-MIMO) under frequency-selective channel. Then, we propose a novel iterative receiver for quantized CP-free uplink wideband SC-MIMO for uncorrelated or correlated Rayleigh and Rician fading channels. This detector utilizes an efficient message passing algorithm based on Bussgang decomposition, reduced state sequence estimation and Ungerboeck factorization. Therefore, it achieves remarkable complexity reduction and exhibits significant performance advantages compared to the existing quantized SC-MIMO receivers from the literature. [ABSTRACT FROM AUTHOR]

In smart grid (SG) communications, the home area network (HAN) plays a vital role in managing data transmission among communicating devices through a smart meter (SM). Rician fading distribution closely replicates an indoor communication channel in SG HAN system. Thus, channel link is modeled as a Rician fading channel in this paper and Multi‐user selection scheme is employed in SM. Further, a closed‐form expression for average bit error probability (ABEP) performance of indoor dynamic HANs with communicating devices using phase‐shift keying (PSK) modulation is derived and analyzed the effect of traffic intensity, the total number of devices and Rician factor for the considered system. The expression for average channel capacity (ACC) of the SG HAN system is also derived and analyzed by varying the parameters of interest. [ABSTRACT FROM AUTHOR]

We study the uplink and downlink achievable rate of full-duplex large-scale multi-input multioutput (MIMO) systems with a base station (BS) and users over Rician fading channels, based on maximum ratio combining/maximum ratio transmission and zero-forcing reception/zero-forcing transmission processing. Contrary to previous related works over Rayleigh fading channels, this paper assumes that the fast fading MIMO channel matrix follows the Rice distribution which will be more common in future 5G wireless communication systems. We derive approximate expressions of the uplink and downlink achievable rate for perfect channel state information when the number of BS antennas grows large. Based on the theoretical analysis, it is found that when the antennas of the BS are large enough and the power scaling law is applied properly, the impact of multi-user interference, loop interference, inter-user interference, and noise can be suppressed. In addition, the simulation results show that the uplink and downlink achievable rates increase with the number of BS antennas and they will converge to fixed values with the increasing Rician K-factor.

We develop a comprehensive framework to characterize and optimize the performance of a unmanned aerial vehicle (UAV)-assisted D2D network, where D2D transmissions underlay cellular transmissions. Different from conventional non-line-of-sight (NLoS) terrestrial transmissions, aerial transmissions are highly likely to experience line-of-sight (LoS). As such, characterizing the performance of mixed aerial-terrestrial networks with accurate fading models is critical to precise network performance characterization and resource optimization. We first characterize closed-form expressions for a variety of performance metrics such as frame decoding error probability (referred to as reliability), outage probability, and ergodic capacity of users. The terrestrial and aerial transmissions may experience either LoS Rician fading or NLoS Nakagami-m fading with a certain probability. Based on the derived expressions, we formulate a hierarchical bi-objective mixed-integer-nonlinear-programming (MINLP) problem to minimize the total transmit power of all users and maximize the aggregate throughput of D2D users subject to quality-of-service (QoS) measures (i.e., reliability and ergodic capacity) of cellular users. We model the proposed problem as a bi-partite one-to-many matching game. To solve this problem, we first obtain the optimal closed-form power allocations for each D2D and cellular user on any possible subchannel, and then incorporate them to devise efficient subchannel and power allocation algorithms. Complexity analysis of the proposed algorithms is presented. Numerical results verify the accuracy of our derived expressions and reveal the significance of aerial relays compared to ground relays in increasing the throughput of D2D pairs especially for distant D2D pairs. [ABSTRACT FROM AUTHOR]

A hybrid-duplex aeronautical communication system (HBD-ACS) consisting of a full-duplex-enabled ground station (GS) and two half-duplex (HD) air stations (ASs) is proposed as a direct solution to the spectrum crunch faced by the aviation industry. The closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions in aeronautical communications over Rician fading channels are derived for a successive interference cancellation (SIC) detector. Similar expressions are also presented for an interference ignorant (II) detector and the HD-equivalent modes at GS and ASs. Through the outage and finite SNR diversity gain analysis conducted at the nodes, and system level, residual self-interference (SI) and inter-AS interference are found to be the primary limiting factors in the proposed HBD-ACS. Further investigations revealed that the II and SIC detectors in the proposed HBD-ACS are suitable for the weak and strong interference scenarios, respectively. When compared with the HD-ACS, the proposed HBD-ACS achieves a lower outage probability and higher diversity gains at higher multiplexing gains when operating at low SNRs. The finite SNR analysis also showed the possibility of the proposed HBD-ACS being able to attain interference-free diversity gains through proper management of the residual SI. Hence, the proposed HBD-ACS is more reliable and can provide a better throughput compared with the existing HD-ACS at low-to-moderate SNRs. [ABSTRACT FROM AUTHOR]

Many technological advances have aided in the evolution of society and in the improvement of many services. Where many of the existing methodologies present large consumption of computational memory as well as slowness in sending data. With this focus, the present study aims to develop DES (Discrete Event Simulation) based model. This model is called CBEDE (Coding of Bits for Entities by means of Discrete Events) and aims to improve the transmission of content in wireless telecommunication systems. The present study implemented a model CBEDE applied to a system, and advanced modulation format DBPSK in a simulation environment, the Simulink simulation environment of the MATLAB software, improving the transmission of data, through a pre-coding process of bits applying discrete events in the signal before of the modulation process. The signal transmission on the channel occurs in the discrete domain with the implementation of discrete entities in the process of bit generation applied at a low level of abstraction in a wireless telecommunication system. The simulation considered the advanced Differential Binary Phase Shift Keying (DBPSK) as the modulation format for signal transmission in an AWGN channel. The results show improvements of 79.89% in memory utilization, related to information compression, in the context of the research. [ABSTRACT FROM AUTHOR]

In this paper, the advantages of joint detection (JD) in a hybrid-duplex unmanned aerial vehicle (UAV) communication system (HBD-UCS) are investigated as a step toward addressing spectrum scarcity in UAV communications. Through extensive outage probability and finite signal-to-noise-ratio diversity gain analysis, we showed that the performance of JD is independent of the strength and the data rate of the inter-UAV interference signal. On the contrary, the successive interference cancellation (SIC) detector requires the data rate of the interfering UAV to be less than the ground station before meaningful performance can be seen. At the system level, it is observed that the half-duplex UAV communication system outperforms the HBD-UCS with JD at moderate and high SNR regimes, as the latter is constrained by self-interference at the full-duplex ground station. Finally, we investigated the multiplexing gain region and showed that the joint detector offers higher diversity gain over a wide range of multiplexing gains over the interference ignorant and the SIC detector. [ABSTRACT FROM AUTHOR]

This Letter studies performance of a dual-hop decode-and-forward relaying network employing a wireless-powered relay antenna with transmit antenna selection for the first hop and maximal ratio combining for the second hop. Compact expressions for outage probability and upper-bound on channel capacity are derived. Monte Carlo simulation results are given to verify theoretical analyses. [ABSTRACT FROM AUTHOR]

Routing protocol and congestion control in Transmission Control Protocol (TCP) have important roles in wireless mobile network performance. In wireless communication, the stability of the path and successful data transmission will be influenced by the channel condition. This channel condition constraints come from path loss and the multipath channel fading. With these constraints, the algorithm in the routing protocol and congestion control is confronted with the uncertainty of connection quality and probability of successful packet transmission, respectively. It is important to investigate the reliability and robustness of routing protocol and congestion control algorithms in dealing with such situation. In this paper, we develop a detailed approach and analytical throughput performance with a cross layer scheme (CLS) between routing and congestion control mechanism based on signal to noise ratio (SNR) in Rician and Rayleigh as multipath fading channel. We proposed joint routing and congestion control TCP with a cross layer scheme model based on SNR (RTCP-SNR). We compare the performance of RTCP-SNR with conventional routing-TCP and routing-TCP that used CLS with routing aware (RTCP-RA) model. The analyses and the simulation results showed that RTCP-SNR in a multipath channel outperforms conventional routing-TCP and RTCP-RA. [ABSTRACT FROM AUTHOR]

Considering both non-line-of-sight (NLoS) and line-of-sight (LoS) transmissions, the transitional behaviors from noise-limited regime to dense interference-limited regime have been investigated for the fifth generation (5G) small cell networks (SCNs). Besides, we identify four performance regimes based on base station (BS) density, i.e., 1) the noise-limited regime, 2) the signal-dominated regime, 3) the interference-dominated regime, and 4) the interference-limited regime. To characterize the performance regime, we propose a unified framework analyzing the future 5G wireless networks over generalized shadowing/fading channels, in which the user association schemes based on the strongest instantaneous received power and the strongest average received power can be studied, while NLoS/LoS transmissions and multislop path loss model are considered. Simulation results indicate that different factors, i.e., noise, desired signal, and interference, successively and separately dominate the network performance with the increase of BS density. Hence, our results shed new light on the design and management of SCNs in urban and rural areas with different BS deployment densities. [ABSTRACT FROM PUBLISHER]

We here introduce an extension and natural generalization of both the $\kappa$-$\mu$ shadowed and the classical Beckmann fading models: the Fluctuating Beckmann (FB) fading model. This new model considers the clustering of multipath waves on which the line-of-sight (LoS) components randomly fluctuate, together with the effect of in-phase/quadrature power imbalance in the LoS and non-LoS components. Thus, it unifies a variety of important fading distributions as the one-sided Gaussian, Rayleigh, Nakagami- $m$, Rician, $\kappa$ -$\mu$, $\eta$- $\mu$, $\eta$ -$\kappa$, Beckmann, Rician shadowed, and the $\kappa$- $\mu$ shadowed distribution. The chief probability functions of the FB fading model, namely probability density function, cumulative distribution function, and moment generating function are derived. The second-order statistics such as the level crossing rate and the average fade duration are also analyzed. These results can be used to derive some performance metrics of interest of wireless communication systems operating over FB fading channels [ABSTRACT FROM PUBLISHER]

Framed slotted aloha (FSA) is a multiple access protocol widely used in wireless communication for its simplicity and effectivity. The theoretical maximum channel utilization of FSA is approximately equal to 0.37 irrespective of the capture effect. In fact, the capture effect is a common phenomenon in wireless communication, which can increase the channel utilization. In this paper, we derive the closed-form expressions of capture probabilities under Rayleigh, Rician and Nakagami-m fading channels, respectively, and further give the optimal frame length which maximizes the channel utilization in the FSA-based networks. The numerical results are given for indicating the capture probabilities under different fading channels and their impacts on the optimal frame length and the maximum channel utilization. [ABSTRACT FROM AUTHOR]

In general, MIMO upgrades the radio communication with improved capacity and reliability. As there is a presence of multiple antennas at transmitter and receiver side, the proper Transmit Antenna Selection (TAS) for attaining effective performance is still a challenging point. This paper intends to introduce a TAS algorithm in LTE system using Self-Adaptive Grey Wolf Optimization (SAGWO) for improving the system performance. It introduces self-adaptiveness in the Grey Wolf Optimization (GWO) by determining the capacity improvement accomplished by each candidate solution for the TAS problem followed by updating the candidate solution based on the improvement. The simulation model considers both Rayleigh channel and Rician channel, for four antenna configurations like 2 × 2, 3 × 2, 4 × 2 and 4 × 4. To the next of the simulation, it compares the performance of SAGWO-TAS with EDB-TAS, ECB-TAS, ABC-TAS, GA-TAS, FF-TAS, PSO-TAS and GWO-TAS, i.e., traditional TAS models using Artificial Bee Colony (ABC), Ergodic Capacity (ECB), Euclidean Distance (EDB), Firefly (FF), Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and GWO, respectively. It observes the BER (bit error ratio) and mean BER at varied SNR (signal-to-noise ratio) in the analysis section. The analysis proves that the BER is highly reduced for proposed optimal TAS model. [ABSTRACT FROM AUTHOR]

It is well-known that data from diffusion weighted imaging (DWI) follow the Rician distribution. The Rician distribution is also relevant for functional magnetic resonance imaging (fMRI) data obtained at high temporal or spatial resolution. We propose a general regression model for non-central χ (NC-χ) distributed data, with the heteroscedastic Rician regression model as a prominent special case. The model allows both parameters in the Rician distribution to be linked to explanatory variables, with the relevant variables chosen by Bayesian variable selection. A highly efficient Markov chain Monte Carlo (MCMC) algorithm is proposed to capture full model uncertainty by simulating from the joint posterior distribution of all model parameters and the binary variable selection indicators. Simulated regression data is used to demonstrate that the Ricianmodel is able to detect the signal much more accurately than the traditionally used Gaussian model at low signal-to-noise ratios. Using a diffusion dataset from the Human Connectome Project, it is also shown that the commonly used approximate Gaussian noise model underestimates the mean diffusivity (MD) and the fractional anisotropy (FA) in the single-diffusion tensor model compared to the Rician model. [ABSTRACT FROM AUTHOR]

Many statistical distributions including Rayleigh, Rician, Nakagami-m, Hoyt, η-µ and κ-µ are proposed in literature to model fading in wireless Communication systems. This paper presents the study of MIMO system in a recently proposed Two Wave with Diffuse Power (TWDP) fading model, having two specular multipath components in the presence of diffusely propagating waves. It has been verified that the TWDP fading model is better suited to represent real world frequency selective fading on the basis of data collected from wireless sensor networks. This paper studies the performance of MIMO system in TWDP fading scenario. Upper and lower bounds of the capacity for MIMO system have been derived in TWDP fading scenario. [ABSTRACT FROM AUTHOR]

Low density parity check (LDPC) codes are one of the best error correcting codes in today’s coding world and are known to approach the Shannon limit. As with all other channel coding schemes, LDPC codes add redundancy to the uncoded input data to make it more immune to channel impairments. In this paper, the impact of low-Density Parity-Check code (LDPC) on the performance of system under Binary Phase Shift keying (BPSK) over an Additive White Gaussian Noise (AWGN) and other fading (Raleigh and Rician) channels is investigated. Obtained results show that LDPC can improve transceiver system for various channel types. At Bit Error Rate (BER) of 10-4 such code with code rate of ½ reduces the Signal to Noise Ratio (SNR) by range of 6.5 to 9 dB for fading channels in contrast to uncoded system. By studying modern research it has been found that turbo code can achieved same manner but LDPC decoder faster than turbo decoder and can be implemented in parallel.

Framed slotted aloha (FSA) is a multiple access protocol widely used in wireless communication for its simplicity and effectivity. The theoretical maximum channel utilization of FSA is approximately equal to 0.37 irrespective of the capture effect. In fact, the capture effect is a common phenomenon in wireless communication, which can increase the channel utilization. In this paper, we derive the closed-form expressions of capture probabilities under Rayleigh, Rician and Nakagami-m fading channels, respectively, and further give the optimal frame length which maximizes the channel utilization in the FSA-based networks. The numerical results are given for indicating the capture probabilities under different fading channels and their impacts on the optimal frame length and the maximum channel utilization.

Purpose To estimate the spatially varying noise map using a redundant series of magnitude MR images. Methods We exploit redundancy in non-Gaussian distributed multidirectional diffusion MRI data by identifying its noise-only principal components, based on the theory of noisy covariance matrices. The bulk of principal component analysis eigenvalues, arising due to noise, is described by the universal Marchenko-Pastur distribution, parameterized by the noise level. This allows us to estimate noise level in a local neighborhood based on the singular value decomposition of a matrix combining neighborhood voxels and diffusion directions. Results We present a model-independent local noise mapping method capable of estimating the noise level down to about 1% error. In contrast to current state-of-the-art techniques, the resultant noise maps do not show artifactual anatomical features that often reflect physiological noise, the presence of sharp edges, or a lack of adequate a priori knowledge of the expected form of MR signal. Conclusions Simulations and experiments show that typical diffusion MRI data exhibit sufficient redundancy that enables accurate, precise, and robust estimation of the local noise level by interpreting the principal component analysis eigenspectrum in terms of the Marchenko-Pastur distribution. Magn Reson Med 76:1582-1593, 2016. © 2015 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Purpose Diffusional kurtosis imaging (DKI) is sensitive to the effects of signal noise due to strong diffusion weightings and higher order modeling of the diffusion weighted signal. A simple noise correction scheme is proposed to remove the majority of the noise bias in the estimated diffusional kurtosis. Methods Weighted linear least squares (WLLS) fitting together with a voxel-wise, subtraction-based noise correction from multiple, independent acquisitions are employed to reduce noise bias in DKI data. The method is validated in phantom experiments and demonstrated for in vivo human brain for DKI-derived parameter estimates. Results As long as the signal-to-noise ratio (SNR) for the most heavily diffusion weighted images is greater than 2.1, errors in phantom diffusional kurtosis estimates are found to be less than 5 percent with noise correction, but as high as 44 percent for uncorrected estimates. In human brain, noise correction is also shown to improve diffusional kurtosis estimates derived from measurements made with low SNR. Conclusion The proposed correction technique removes the majority of noise bias from diffusional kurtosis estimates in noisy phantom data and is applicable to DKI of human brain. Features of the method include computational simplicity and ease of integration into standard WLLS DKI post-processing algorithms. [ABSTRACT FROM AUTHOR]

• An improved deep persistent meomory network is proposed for enhancing MRI images. • The proposed network introduces nonlinearity via quantum-ReLU activation function. • The proposed model utilizes a combined loss function with MMSE and SSIM losses. • Experiments validate that the proposed method outperforms SoA methods. • Our model has a better performance on stationary and non-stationary Rician distributed MR images. Magnetic Resonance Imaging (MRI) is extensively employed in medical, scientific and investigative contexts today. Noise on the other hand, restricts the diagnostic utility of MR images by deteriorating their quality during acquisition. The noise in single coil magnitude MRI has stationary Rician distribution and images reconstructed with parallel MR-imaging techniques have non-stationary noise levels. Recently, deep learning models are finding ubiquitous employment in image restoration tasks, owing to their powerful capabilities in learning and solving inverse-problems. Nonetheless, only a few such techniques have been reported to suppress noise in MRI. In this paper, we propose a robust MR image denoising approach based on the concept of memory persistence. Accordingly, we improvised and optimized the deep model of memory networks by introducing a data sensitive activation function and a robust cost function, resulting in a compact design with improved noise filtering, feature preservation and enhanced performance. Experiments on real and synthetic data reveal that the proposed method outperformed state-of-the-art (SoTA) methods. [ABSTRACT FROM AUTHOR]

A frequency-modulated continuous wave (FMCW) radar is used to sounding wireless channel. An intermediate frequency signal of the FMCW radar can be treated simultaneously as a frequency-domain signal as well as a time-domain signal when the modulation time is sufficiently long. This distinctive compatibility enables the FMCW radar system to measure the normalized impulse response for the power delay profile and Rician K-factor by using an oscilloscope. This theory is fully demonstrated and experiments are performed in the reverberation chamber for the small-scale fading environments of Rayleigh and Rician conditions, and all measurements are verified by using the oscilloscope. [ABSTRACT FROM AUTHOR]

Highlights: [•] A framework transforms magnitude multi-echo MRI signals to Gaussian distributed. [•] Accurate T 2-distribution estimation is achieved using the transformed signals. [•] Spurious cerebrospinal fluid peak in the T 2 distribution is eliminated. [•] The blurring of two nearby distinct T 2 components is corrected. [•] The quantitative estimation of T 2-related parameters is more precise. [ABSTRACT FROM AUTHOR]

In this paper, the performance of beamforming (BF) for a dual-hop amplify-and-forward (AF) relay network, where the source and destination are each equipped with multiple antennas, is investigated. It is assumed that the source-relay and relay-destination channels experience mixed fading distributions, namely, correlated Nakagami-m/Rician and correlated Rician/Nakagami-m, respectively. By considering fixed-gain relaying, analytical expressions for outage probability (OP) and average symbol error rate (ASER) are derived in closed-form. Numerical results are presented to demonstrate the efficacy of our performance analysis, also illustrate the impact of channel correlation, fading severity, Rician factor and antenna configuration on the performance of the system. It is shown that the correlated Nakagami-m/Rician fading channel can achieve better performance than the correlated Rician/Nakagami-m fading channel with the increase of fading severity parameter, and the correlated Rician/Nakagami-m fading channel may outperform the correlated Nakagami-m/Rician fading channel by enlarging the Rician factor. [ABSTRACT FROM AUTHOR]

Spectrum sensing is a key technical challenge for cognitive radio (CR). It is well known that multi-cycle cyclostationarity (MC) detector is a powerful method for spectrum sensing. However, conventional MC detector is difficult to implement due to its high computational complexity. This paper pays attention to the fact that the computation complexity can be reduced by simplifying the test statistic of conventional MC detector. Based on this simplification process, an improved MC detector is proposed. Compared with the conventional one, the proposed detector has the low-computational complexity and sufficient-accuracy on sensing performance. Subsequently, the sensing performances are further investigated for the cases of Rayleigh, Nakagami-m, Rician, composite Rayleigh fading-lognormal shadowing and composite Nakagami fading-lognormal shadowing channels, respectively. Furthermore, the square-law combining (SLC) is introduced to improve the detection capability over fading-shadowing channels. The corresponding closedform expressions of average detection probability are derived for each case by the moment generation function (MGF) approach. Finally, illustrative and analytical results show that the efficiency and reliability of proposed detector and the improvement on sensing performance by SLC over composite fading-shadowing channels. [ABSTRACT FROM AUTHOR]

This paper investigates a natural generalization of the \kappa - \mu fading channel in which the line-of-sight (LOS) component is subject to shadowing. This fading distribution has a clear physical interpretation and good analytical properties and unifies the one-side Gaussian, Rayleigh, Nakagami-m, Rician, \kappa - \mu, and Rician shadow fading distributions. The three basic statistical characterizations, i.e., probability density function (pdf), cumulative distribution function (cdf), and moment-generating function (mgf), of the \kappa - \mu shadowed distribution are obtained in closed form. Then, it is also shown that the sum and maximum distributions of independent but arbitrarily distributed \kappa - \mu shadowed variates can be expressed in closed form. This set of new statistical results is finally applied to modeling and analysis of several wireless communication systems, e.g., the proposed distribution has applications to land mobile satellite (LMS) communications and underwater acoustic communications (UAC). [ABSTRACT FROM PUBLISHER]

Purpose To examine the effects of the reconstruction algorithm of magnitude images from multichannel diffusion MRI on fiber orientation estimation. Theory and Methods It is well established that the method used to combine signals from different coil elements in multichannel MRI can have an impact on the properties of the reconstructed magnitude image. Using a root-sum-of-squares approach results in a magnitude signal that follows an effective noncentral-χ distribution. As a result, the noise floor, the minimum measurable in the absence of any true signal, is elevated. This is particularly relevant for diffusion-weighted MRI, where the signal attenuation is of interest. Results In this study, we illustrate problems that such image reconstruction characteristics may cause in the estimation of fiber orientations, both for model-based and model-free approaches, when modern 32-channel coils are used. We further propose an alternative image reconstruction method that is based on sensitivity encoding ( SENSE) and preserves the Rician nature of the single-channel, magnitude MR signal. We show that for the same k-space data, root-sum-of-squares can cause excessive overfitting and reduced precision in orientation estimation compared with the SENSE-based approach. Conclusion These results highlight the importance of choosing the appropriate image reconstruction method for tractography studies that use multichannel receiver coils for diffusion MRI acquisition. Magn Reson Med 70:1682-1689, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Features of the diffusion-time dependence of the diffusion-weighted magnetic resonance imaging (MRI) signal provide a new contrast that could be altered by numerous biological processes and pathologies in tissue at microscopic length scales. An anomalous diffusion model, based on the theory of Brownian motion in fractal and disordered media, is used to characterize the temporal scaling (TS) characteristics of diffusion-related quantities, such as moments of the displacement and zero-displacement probabilities, in excised rat hippocampus specimens. To reduce the effect of noise in magnitude-valued MRI data, a novel numerical procedure was employed to yield accurate estimation of these quantities even when the signal falls below the noise floor. The power-law dependencies characterize the TS behavior in all regions of the rat hippocampus, providing unique information about its microscopic architecture. The relationship between the TS characteristics and diffusion anisotropy is investigated by examining the anisotropy of TS, and conversely, the TS of anisotropy. The findings suggest the robustness of the technique as well as the reproducibility of estimates. TS characteristics of the diffusion-weighted signals could be used as a new and useful marker of tissue microstructure. [Copyright &y& Elsevier]

Simple series expressions for bit error rate (BER) of π/4 shifted differential quaternary phase-shift keying (π/4-DQPSK) over some common fading environments (Rayleigh, Rician and Nakagami-m) are derived. Both single- and multi-channel reception scenarios are considered. In case of multi-antenna reception, it is assumed that the fading is independent and identically distributed (IID), and the receiver follows optimum maximal ratio combining (MRC). The derived expressions, computed through probability density function (PDF)-based approach, give an exact match with moment-generating function (MGF)-based solutions but get rid of numerical integrations involved in MGF approach. Further, the analytical results presented in this article consist of finite or rapidly converging infinite series and thus a trade-off between precision and complexity can be easily realised by choosing a specific number of terms. Bounds on the error resulting from truncation of the infinite series are also derived. Moreover, it was shown that the series solutions, when reasonably truncated, still provide better approximations than the previous attempts. [ABSTRACT FROM PUBLISHER]