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Characterization of the interference patterns observed in B-mode images (i.e. , speckle statistics) is a valuable tool in tissue characterization. However, changes in echo amplitudes unrelated to speckle, including power loss due to attenuation and diffraction, can bias these metrics, undermining their utility. Tissue with high attenuation such as the uterine cervix are especially affected. The purpose of this study was to demonstrate and quantify the effects of attenuation and diffraction on speckle statistics and to propose methods of compensation. Analysis was performed on simulated diffuse scattering phantoms of varying attenuation with simulated transducers at 9 and 5 MHz center frequency. Application in the in vivo macaque cervix using a clinical scanner is also presented. Nakagami and homodyned K distribution parameters were calculated in parameter estimation regions (PERs) of varying size within simulations and experiments. Changes in speckle statistics parameters with respect to PER size and depth were compared with and without two different compensation schemes. It has been shown that compensation for attenuation and diffraction is necessary to produce speckle statistics estimates that do not depend on medium attenuation or PER size. Reducing the dependence on these factors connects speckle statistics estimates more closely with the microstructure of the probed medium. [ABSTRACT FROM AUTHOR]

One of the schemes which are likely to be adopted in the forthcoming wireless communication standards is the so-called spatial modulation (SM). However, the wireless channels pertaining to such standards will mostly be frequency selective because of the involved high data rates, and SM technique alone can not overcome the resulting signal distortion. In this context, orthogonal frequency division multiplexing (OFDM) has been used as an efficient solution to combat this impediment, and space-time block coding (STBC)-OFDM has followed as an innovative approach merging the viable features of OFDM and the reliability enhancement capabilities of STBC. Obviously, SM solutions in the presence of multiple users communicating in frequency selective channels should be targeted. To fulfill such a need, a new SM-based architecture incorporating STBC-OFDM and CDMA is proposed in this work and is shown to exhibit a performance which is superior to state-of-the-art alternatives. Furthermore, its sensitivity to the aforementioned adverse parameters is studied in Nagakami channel.

In recent years, end-to-end wireless communication has gained significant attention in the field of wireless communication. In this paper, we propose a new approach to achieving end-to-end wireless communication using convolutional neural networks (CNNs) in the presence of Nakagami fading, Additive white Gaussian noise (AWGN), and multiple-input multiple-output (MIMO) fading channels. Further, we have applied the bursty noise to the AWGN channel. We first develop a CNN-based transmitter architecture that can efficiently encode information bits into signals, followed by a CNN-based receiver architecture that can accurately decode the received signals. Our proposed method leverages the strengths of CNNs in learning and extracting features from raw data and applies them to wireless communication. We then evaluate the performance of our proposed method by extensive sets of simulations in different AWGN, Nakagami fading, and MIMO fading channel scenarios. The simulation results show that the method proposed shows superior performance compared to existing state-of-the-art techniques at low Signal to Noise ratio(SNR) in terms of bit error rate (BER) and Binary cross-entropy loss. Our proposed method can be a promising solution for achieving end-to-end wireless communication in various practical applications.

Abstract This paper considers non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the nearby users while it requires the help of a dedicated relay to communicate with the cell-edge users. We derive exact closed form expression for the outage probabilities experienced by the downlink users and the system outage probability of the considered CDRT network with full-duplex relaying (FDR) technique. Further, we derive approximate closed form expressions for the ergodic rates achieved by the users. The channel of all the links experience Nakagami fading distribution and the analysis takes into account the residual interference generated due to the imperfect successive interference cancelation (I-SIC) technique. We provide numerical and simulation results to identify the impact of key system parameters on the outage and ergodic rate performance of the users and the system outage performance. The outage and ergodic rate performance of users in the considered FDR-based NOMA-CDRT system has been observed to be significantly improved compared to a FDR-based OMA (orthogonal multiple access)-CDRT system. It is observed that random selection of NOMA power allocation coefficients at the BS leads to higher outage for the near users compared to the far users. We determine numerical results for the NOMA power allocation coefficient that leads to equal outage performance for both the users. Finally, we derive analytical expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability. Through extensive numerical and simulation studies, we establish that OPA can lead to significant reduction of system outage probability compared to random selection of power allocation coefficients at the BS.

Abstract In this paper, estimators of the Nakagami-lognormal (NL) distribution based on the method of log-moments have been derived and thoroughly analyzed. Unlike maximum likelihood (ML) estimators, the log-moment estimators of the NL distribution are obtained using straightforward equations with a unique solution. Also, their performance has been evaluated using the sample mean, confidence regions and normalized mean square error (NMSE). The NL distribution has been extensively used to model composite small-scale fading and shadowing in wireless communication channels. This distribution is of interest in scenarios where the small-scale fading and the shadowing processes cannot be easily separated such as the vehicular environment.

In this paper, we obtain a low-complexity closed-form formula for the outage probability of the energy-harvested decode-and-forward (DF) relay-aided underlay Device-to-device (D2D) communications in Nakagami fading channel. By proposing a new idea which finds the power splitting factor in simultaneous wireless information and power transfer (SWIPT) energy-harvesting system such that the transmit power of the relay node in the second time slot is fixed in a pre-defined value, the obtained closed-form expression is valid for both energy-harvested and non-energy-harvested scenarios. This formula is based on n-point generalized Gauss-Laguerre and m-point Gauss-Legendre solutions. It is shown that n is more effective than m for reducing the formula complexity. In addition to a good agreement between the simulation results and numerical analysis based on normalized mean square error (NMSE), it is indicated that (n, m)=(1, 4) and (n, m)=(1, 2) are the appropriate choices, respectively for 0.5≤ µ

ABSTRAK Kanal transmisi radio berkontribusi pada terjadinya efek fading yang dapat berpengaruh pada terjadinya penurunan kualitas sinyal pada penerima. Salah satu solusi yang digunakan untuk menekan efek fading adalah penggunaan Spatial Diversity di sisi penerima. Pada penelitian ini digunakan suatu teknik Dynamic Spatial Diversity Combining yang memadukan Selection Combining, Equal Gain Combining, dan Maximal Ratio Combining untuk mendapatkan kinerja combiner yang lebih efektif dan efisien. Simulasi dilakukan dengan menggunakan modulasi BPSK pada beberapa jenis kanal yaitu Rayleigh, Rician, Nakagami-m, Weibull, dan Suzuki. Hasil simulasi MATLAB menunjukkan bahwa secara umum kanal yang mendapatkan perbaikan kinerja penerimaan, dimana nilai terendah sebesar 2 dB terjadi pada kanal Suzuki dan tertinggi sebesar 4 dB pada kanal Weibull. Kata kunci: fading, spatial diversity, rayleigh, rician, weibull, nakagami, suzuki. ABSTRACT Radio transmission channels contribute to the occurrence of fading effects that can affect the decrease in signal quality at the receiver. One solution that is used to suppress fading effects is the use of Spatial Diversity on the receiving side. In this research, a Dynamic Spatial Diversity Combining technique is used which combines Selection Combining, Equal Gain Combining, and Maximal Ratio Combining to get a more effective and efficient combiner performance. Simulation is done using BPSK modulation on several types of canals, namely Rayleigh, Rician, Nakagamim, Weibull, and Suzuki. The MATLAB simulation results show that in general canals that get improved performance, where the lowest value of 2 dB occurs on the Suzuki channel and the highest is 4 dB on the Weibull canal. Keywords: fading, spatial diversity, rayleigh, rician, weibull, nakagami, suzuki.

This paper considers non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the nearby users while it requires the help of a dedicated relay to communicate with the cell-edge users. We derive exact closed form expression for the outage probabilities experienced by the downlink users and the system outage probability of the considered CDRT network with full-duplex relaying (FDR) technique. Further, we derive approximate closed form expressions for the ergodic rates achieved by the users. The channel of all the links experience Nakagami fading distribution and the analysis takes into account the residual interference generated due to the imperfect successive interference cancelation (I-SIC) technique. We provide numerical and simulation results to identify the impact of key system parameters on the outage and ergodic rate performance of the users and the system outage performance. The outage and ergodic rate performance of users in the considered FDR-based NOMA-CDRT system has been observed to be significantly improved compared to a FDR-based OMA (orthogonal multiple access)-CDRT system. It is observed that random selection of NOMA power allocation coefficients at the BS leads to higher outage for the near users compared to the far users. We determine numerical results for the NOMA power allocation coefficient that leads to equal outage performance for both the users. Finally, we derive analytical expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability. Through extensive numerical and simulation studies, we establish that OPA can lead to significant reduction of system outage probability compared to random selection of power allocation coefficients at the BS. [ABSTRACT FROM AUTHOR]

We characterize the accuracy of analyzing the performance of a non-orthogonal multiple access (NOMA) system where users are ranked according to their distances instead of instantaneous channel gains, i.e., product of their distance-based path-loss and fading channel gains. Distance-based ranking of users is analytically tractable and can lead to important insights. However, it may not be appropriate in a multipath fading environment where a near user suffers from severe fading while a far user experiences weak fading. Since the ranking of users (and in turn interferers) in an NOMA system has a direct impact on coverage probability analysis, the impact of the traditional distance-based ranking, as opposed to instantaneous signal power-based ranking, needs to be understood. This will enable us to identify scenarios where distance-based ranking, which is easier to implement compared with instantaneous signal power-based ranking, is acceptable for the system performance analysis. To this end, in this paper, we derive the probability of the event when distance-based ranking yields the same results as instantaneous signal power-based ranking, which is referred to as the accuracy probability. We characterize the probability of accuracy considering Nakagami- $m$ fading channels and three different spatial distribution models of user locations in NOMA, namely, the Poisson point process (PPP), the Matern cluster process (MCP), and the Thomas cluster process (TCP). For all these models of users’ locations, we assume that the spatial locations of the base stations (BSs) follow a homogeneous PPP. We show that the accuracy probability decreases with the increasing number of users and increases with the path-loss exponent. In addition, through examples, we illustrate the impact of accuracy probability on uplink and downlink coverage probabilities. Closed-form expressions are presented for the Rayleigh fading environment. The effects of fading severity and users’ pairing on the accuracy probability are also investigated. [ABSTRACT FROM AUTHOR]

In this paper, a low-complexity closed-form formula for the outage probability of the energy-harvested direct and decode-and-forward (DF) relay-aided underlay device-to-device (D2D) communications in Nakagami fading channel is derived. By proposing a new procedure, the power splitting factor in simultaneous wireless information and power transfer (SWIPT) energy-harvesting system is easily found such that the transmit power of the transmitter node in the direct and the relay node in a relay-aided D2D communications is fixed in a pre-defined value. Using the proposed procedure, the obtained closed-form expression is valid for both energy-harvested and non-energyharvested scenarios. This formula is based on n-point generalized Gauss-Laguerre and m-point Gauss-Legendre solutions. It is shown that n is more effective than m for reducing the formula complexity. In addition to a good agreement between the simulation results and numerical analysis based on normalized mean square error (NMSE), it is indicated that (n, m)=(1, 4) and (n, m)=(1, 2) are the appropriate choices, respectively for 0.5≤ μ <0.7 and μ ≥0.7, where μ is the fading shape factor. As shown in this investigation, increasing the average distance between the D2D pair and cellular user introduces lower interference, which is the reason for decreasing the outage probability. Furthermore, it is clear that increasing the Nakagami fading shape factor is the reason for decreasing the depth of fading, its fluctuations and the outage probability. [ABSTRACT FROM AUTHOR]

We derive exact closed-form expressions for Long Range (LoRa) bit error probability and diversity order for channels subject to Nakagami-m, Rayleigh and Rician fading. Analytical expressions are compared with numerical results, showing the accuracy of our proposed exact expressions. In the limiting case of the Nakagami and Rice parameters, our bit error probability expressions specialize into the non-fading case.

The feasibility of using ultrasonic Nakagami imaging to evaluate thermal lesions induced by microwave ablation (MWA) in ex vivo porcine liver was explored. Dynamic changes in echo amplitudes and Nakagami parameters in the region of the MWA-induced thermal lesion, as well as the contrast-to-noise ratio (CNR) between the MWA-induced thermal lesion and the surrounding normal tissue, were calculated simultaneously during the MWA procedure. After MWA exposure, a bright hyper-echoic region appeared in ultrasonic B-mode and Nakagami parameter images as an indicator of the thermal lesion. Mean values of the Nakagami parameter in the thermal lesion region increased to 0.58, 0.71 and 0.91 after 1, 3 and 5 min of MVA. There were no significant differences in envelope amplitudes in the thermal lesion region among ultrasonic B-mode images obtained after different durations of MWA. Unlike ultrasonic B-mode images, Nakagami images were less affected by the shadow effect in monitoring of MWA exposure, and a fairly complete hyper-echoic region was observed in the Nakagami image. The mean value of the Nakagami parameter increased from approximately 0.47 to 0.82 during MWA exposure. At the end of the postablation stage, the mean value of the Nakagami parameter decreased to 0.55 and was higher than that before MWA exposure. CNR values calculated for Nakagami parameter images increased from 0.13 to approximately 0.61 during MWA and then decreased to 0.26 at the end of the post-ablation stage. The corresponding CNR values calculated for ultrasonic B-mode images were 0.24, 0.42 and 0.17. This preliminary study on ex vivo porcine liver suggested that Nakagami imaging have potential use in evaluating the formation of MWA-induced thermal lesions. Further in vivo studies are needed to evaluate the potential application. [ABSTRACT FROM AUTHOR]

• Rayleigh and Nakagami-m fading distributions are considered. • Truncation is a consequence of energy criterion applied. • Fading channel performance is assessed. • Applications to 5G systems are provided. In this paper, Rayleigh and Nakagami-m fading channels are considered that are positively correlated. The received signal statistics specifically mean and variance of sum of fading and noise variables in cases where fading distributions are considered ranging from zero to infinity compared to cases where the fading and noise distributions are truncated due to applying the energy criterion to each distribution are considered. Average number of required bits are derived by calculating Shannon entropy for each case investigated. The number of measurements required for distribution reconstruction based on CS reduced complexity method for each case are also computed. Furthermore, the Bit-Error-Rate (BER) curves for all respective cases are derived and directly compared. The results impose the effect of truncation on the quantification of variances as well as average number of bits as measures of uncertainty and number of measurements for reconstruction. The BER curves produced account for the Gaussian statistical assumption adopted. Applications to 5G communications are provided and future directions are highlighted. [ABSTRACT FROM AUTHOR]

Perangkat mobile seperti notebook, handphone, tablet dan lain lain mulai berkembang adanya teknologi nirkabel (wireless) saat ini yang menjadi indikator kemajuan peradaban manusia memungkinkan perangkat komunikasi dapat berkomunikasi secara langsung dengan perangkat lainnya dalam posisi bergerak dan tanpa adanya jaringan infrastruktur yang tetap dan bersifat sementara, jaringan semacam ini disebut sebagai MANET (Mobile Ad Hoc Network). Dalam MANET, setiap node bergerak secara bebas, sehingga jaringan dapat mengalami perubahan topologi dengan cepat. Karena node dalam MANET memiliki jarak transmisi yang terbatas, beberapa node tidak bisa berkomunikasi secara langsung dengan node lainnya. Maka dari itu, pada studi perbandingan ini yang diteliti adalah skema MANET yang dihasilkan oleh file node-movement dan traffic-pattern yang telah ada pada distribusi network simulator. Penelitian ini menggunakan NS-2 sebagai network simulator dengan protokol proaktif MANET jenis OLSR (Optimized Link State Protocol) sebagai protokol routing yang digunakan serta menggunakan model transmisi TwoRayGround dan Nakagami sebagai pembanding yang ada pada NS-2. Hasil dari pengujian adalah suatu perbandingan performa dari model transmisi TwoRayGround dan Nakagami pada protokol routing OLSR di lingkungan MANET dengan menggunakan NS-2.

Narrowband Power Line Communications (NB-PLCs) are investigated as an alternative option for transferring low rate smart grid (SG) data via Medium Voltage (MV) power lines. In this framework, two variants of orthogonal frequency division multiplexing are examined, namely Filtered-OFDM (F-OFDM) and Wavelet-OFDM (W-OFDM), in an attempt to determine which of them is capable of transmitting low rate SG data to greater distances over non-branched MV power lines. The reach of NB-PLC signals via MV power lines is estimated, taking into account the transfer function of the relevant PLC channels and noise mechanisms as well as the specific features of the two modulation options under consideration. Simulations show that NB-PLC transmission constitutes a technically feasible and economically affordable option for exchanging low rate data with remote SG nodes dispersed over the MV grid. Moreover, simulations show that F-OFDM allows low rate data transmission to considerably greater distances compared to W-OFDM. [ABSTRACT FROM AUTHOR]

An approximation of the symbol error probability (SEP) of the cross QAM (XQAM) signal in a single-input multiple-output system over dual correlated Rayleigh, Nakagami-m, Nakagami-n (Rice) and Nakagami-q (Hoyt) fading channels is derived. The maximal-ratio combining is considered as the diversity technique, and the average SEP is obtained by using the moment generating function (MGF). Arbitrarily tight approximations for the Gaussian Q-function and the generalized Gaussian Q-function are obtained from the numerical analysis technique; the trapezoidal rule. The resulting expressions consist of a finite sum of MGF's which are easily evaluated and accurate enough. In addition, a transformation technique is used to derive independent channels from the correlated channels which are then used in the analysis. The simulation results show excellent agreement with the derived approximation expressions. [ABSTRACT FROM AUTHOR]

In this paper, an FrFT appended OFDM system has been proposed. In the proposed system, the FrFT block has been appended at the output of OFDM transmitter to combat the effect of multipath fading. The performance of the proposed system in terms of BER has been evaluated in different channel environments like AWGN, Rayleigh, Rician and Nakagami for a 1024-PSK and 1024-QAM modulation technique. From the simulation results, it has been found that the proposed system provides a gain of 5.5 dB in SNR to achieving BER of 10 −2.1 for 1024-PSK modulation technique in Rayleigh fading channel as compared to the traditional OFDM system. For 1024-QAM modulation technique, the proposed system provides an improvement of 4.6 dB to achieve 10 −2.4 BER in Rayleigh fading channel. [ABSTRACT FROM AUTHOR]

Narrowband Power Line Communications (NB-PLCs) are investigated as an alternative option for transferring low rate smart grid (SG) data via Medium Voltage (MV) power lines. In this framework, two variants of orthogonal frequency division multiplexing are examined, namely Filtered-OFDM (F-OFDM) and Wavelet-OFDM (W-OFDM), in an attempt to determine which of them is capable of transmitting low rate SG data to greater distances over non-branched MV power lines. The reach of NB-PLC signals via MV power lines is estimated, taking into account the transfer function of the relevant PLC channels and noise mechanisms as well as the specific features of the two modulation options under consideration. Simulations show that NB-PLC transmission constitutes a technically feasible and economically affordable option for exchanging low rate data with remote SG nodes dispersed over the MV grid. Moreover, simulations show that F-OFDM allows low rate data transmission to considerably greater distances compared to W-OFDM.

In this paper, we derive the error probability of multi-hop networks employing code-division multiple access transmission in a multiuser environment. The standard Gaussian approximation is used to model the multiple access interference in the network. We consider multi-hop networks employing serial, parallel, and selection relaying using the decode-and-forward technique. For the selection relaying, we consider two schemes; namely, the threshold-based relay selection and the maximum relay selection. In addition, we investigate the effect of different system parameters on the error performance of the system, such as the spreading gain, the number of interfering users, and the path loss exponent. Results show that as the number of users increases, the improvement coming from the relaying decreases. [ABSTRACT FROM AUTHOR]

We investigate the performance of the best-worse relay selection strategy in a two way cooperative non-regenerative relay network, where the relay is selected to maximize the worst Signal to Noise Ratio (SNR) of two links. In contrast to existing work, we aim to provide a theoretical performance analysis for this scheme under the more practical Nakagami channel. Closed-form expression of the probability density function for the SNRs of both two links is derived, based on which the outage probability of the best-worse relay selection is obtained. It is shown that the best-worse relay selection scheme achieves full diversity gain. Furthermore, the asymptotic packet error ratio with SNR increasing is also analyzed through rigorous derivations. The accuracy of our derivation is validated by computer simulations. [ABSTRACT FROM AUTHOR]

Abstract: The derivation of statistically optimal similarity measures for intensity-based registration is possible by modeling the underlying image noise distribution. The parameters of these distributions are, however, commonly set heuristically across all images. In this article, we show that the estimation of the parameters on the present images largely improves the registration, which is a consequence of the more accurate characterization of the image noise. More precisely, instead of having constant parameters over the entire image domain, we estimate them on patches, leading to a local adaptation of the similarity measure. While this basic idea of creating locally adaptive metrics is interesting for various fields of application, we present the derivation for ultrasound imaging. The domain of ultrasound is particularly appealing for this approach, due to the inherent contamination with speckle noise. Furthermore, there exist detailed analyses of suitable noise distributions in the literature. We present experiments for applying a bivariate Nakagami distribution that facilitates modeling of several scattering scenarios prominent in medical ultrasound. Depending on the number of scatterers per resolution cell and the presence of coherent structures, different Nakagami parameters are required to obtain a valid approximation of the intensity statistics and to account for distributional locality. Our registration results on radio-frequency ultrasound data confirm the theoretical necessity for a spatial adaptation of similarity metrics. [Copyright &y& Elsevier]

Transmit antenna selection with receive maximal-ratio combining (TAS/MRC) and transmit antenna selection with receive selection combining (TAS/SC) are two attractive multiple-input–multiple-output (MIMO) protocols. In this paper, we present a framework for the comparative analysis of TAS/MRC and TAS/SC in a two-hop amplify-and-forward relay network. In doing so, we derive exact and asymptotic expressions for the symbol error rate (SER) in Nakagami-m fading. Using the asymptotic expressions, the SNR gap between the two protocols is quantified. Given that the two protocols maintain the same diversity order, we show that the SNR gap is entirely dependent on the array gain. Motivated by this, we derive the SNR gap as a simple ratio of the respective array gains of the two protocols. This ratio explicitly takes into account the impact of the number of antennas and the fading severity parameter m. In addition, we address the fundamental question of “How to allocate the total transmit power between the source and the relay in such a way that the SER is minimized?” Our answer is given in the form of new compact expressions for the power allocation factor, which is a practical design tool that optimally distributes the total transmit power in the network. [ABSTRACT FROM PUBLISHER]

A unified analysis of statistical models for describing fading, shadowing, and shadowed fading channels is presented from a pedagogical viewpoint. The different probability density functions such the Rayleigh, Nakagami, gamma, generalized gamma, Weibull, lognormal, Nakagami-lognormal, K distribution, generalized K distribution, and Nakagami inverse Gaussian distribution are presented and the relationships among them are detailed. These density functions are compared in terms of two quantitative measures, namely the amount of fading and outage probability. A general approach to fading and shadowed fading channels using a cluster based approach is also presented to link several of the distributions. It is expected that this overview will be very helpful to students and educators who are engaged in the study of wireless systems and the adverse impact of fading and shadowing in wireless data transmission. [ABSTRACT FROM AUTHOR]

We derive new unified probability density function (pdf) formulas based on the generalized Laguerre polynomial series expansion that cover a wide range of small-scale fading distributions in wireless communications. The unified envelope pdf covers many known Laguerre polynomial-series-based pdf's and small-scale fading distributions, which include the multiple-waves-plus-diffuse-power (MWDP) fading, κ-μ, Nakagami-m, Rician (Nakagami-n), Nakagami-q (Hoyt), Rayleigh, Weibull, and α-μ (Stacy) distributions as special cases. We highlight that the unified pdf formulas are general and applicable to characterize the distribution of any random variable defined on the positive range. We then propose two truncated forms of the pdf and prove that the original pdf and both truncated forms satisfy the properties of a valid pdf. A new cumulative distribution function and a moment-generating function of this pdf are derived. We also analyze the truncation error for the case when only a finite number of terms are kept in the series expansion. [ABSTRACT FROM AUTHOR]

The switching rates of dual selection combining diversity and dual switch-and-stay combining diversity in Rayleigh, Rician and Nakagami-m (n-i half-integer or integer) fading are derived. Closed-form or single integral expressions are obtained for both the cases of balanced channels and unbalanced channels. [ABSTRACT FROM AUTHOR]

The Nakagami-m distribution is an important fading model in wireless communications. Generation of independent and bivariate Nakagami-m samples is required when studying some practical applications. However, methods for simulating Nakagami-m fading channels available in the literature are complex. This paper proposes simple efficient methods for generating independent Nakagami-m fading envelope samples for arbitrary values of in and correlated bivariate Nakagami-m fading envelope samples having a common value of m, for arbitrary values of m ⩾ 0.8. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasonic tissue characterization through composite probability distributions such as Nakagami-lognormal, Nakagami-gamma, Nakagami-inverse Gaussian has been found to be useful. Such a probabilistic description also depicts heavy tails which arise from multiple scattering in tissue besides local and global variations in scattering cross-sections. A new composite probability distribution, viz. Nakagami-generalized inverse Gaussian distribution (NGIGD) with four parameters is proposed which under different limiting conditions results in approximating the known distributions. A salient aspect of the new distribution is that the probability density function (pdf) of NGIGD variate is available in closed form and is analytically tractable. [Copyright &y& Elsevier]

Block fading is a popular channel model that approximates the behavior of different wireless communication systems. Automatic-repeat request (ARQ) protocols are used to provide reliable communication in wireless networks. In this paper the throughput of the basic selective-repeat (SR) ARQ in block fading environments is derived. Single-antenna ARQ systems employing both coherent BPSK and QPSK and noncoherent orthogonal BFSK are analyzed over block fading channels characterized by Rician and Nakagami fading distributions. Moreover, the performance of multi-input multi-output (MIMO) ARQ systems employing space-time block codes (STBCs) is derived. The effect of antenna correlation in MIMO ARQ systems is investigated analytically. Results show that longer block lengths improve the performance of basic ARQ protocols. Furthermore, the throughput gain obtained by increasing the block length is a decreasing function of the block length. As the fading severity of the channel increases, the performance improvement resulting from increasing the block length increases. [ABSTRACT FROM AUTHOR]

Abstract: A new probability density function (pdf) to describe the envelope of the backscattered echoes from tissues is proposed. The combined effect of multiple scattering and randomness arising from local and global variations in scattering cross-section is captured through Nakagami-inverse Gaussian distribution (NIGD). The proposed distribution has the advantage that it has a closed form unlike the realistic Nakagami-lognormal distribution (NLD). The degree of closeness, as measured in terms of Kullback-Leibler (KL) distance between two probability distributions is computed. It is shown that NIGD much more closely approximates NLD compared to Nakagami-gamma distribution (NGD) used to model such problems. (E-mail: karmeshu@mail.jnu.ac.in) [Copyright &y& Elsevier]

The bit-interleaved coded modulation (BICM) method is efficient in mitigating multipath fading by providing time diversity. In this paper, union bounds on the bit and packet error probabilities of the 81CM are derived. In the derivation, the authors assume the uniform interleaving of coded bits prior to mapping them onto the signal constellation. This results in a random distribution of the error bits in a codeword over the transmitted symbols. This distribution is evaluated, and the corresponding pairwise error probability is derived. Union bounds are functions of the distance spectrum of the channel code and the signal constellation used in the BICM system. The authors consider BICM systems operating over additive white Gaussian noise (AWGN), Rayleigh, Rician, and Nakagami fading channels. Results show that the new bounds are tight to simulation curves for different channel models. The proposed bounds are general for any coding scheme with a known distance spectrum. [ABSTRACT FROM AUTHOR]

Abstract: The theoretical SER of star constellations (-QAM) is calculated in frequency non-selective slowly fading channels, characterized by either Rician or Nakagami- statistics and corrupted by AWGN. Closed form expressions for the average SERs for Star -QAM are derived and analyzed, having the form of a single finite integral composed of elementary functions. Because of their simplicity, these expressions readily allow numerical evaluations in practical cases. [Copyright &y& Elsevier]

Block-fading is a popular channel model that approximates the behavior of different wireless communication systems. In this paper, a union bound on the error probability of binary- coded systems over block-fading channels is proposed. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. The distribution of error bits over the fading blocks is computed. For a specific distribution pattern, the pairwise error probability is derived. Block-fading channels modeled as Rician and Nakagami distributions are studied. We consider coherent receivers with perfect and imperfect channel side information (SI) as well as noncoherent receivers employing square-law combining. Throughout the paper, imperfect SI is obtained using pilot-aided estimation. A lower bound on the performance of iterative receivers that perform joint decoding and channel estimation is obtained assuming the receiver knows the correct data and uses them as pilots. From this, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Furthermore, the optimal energy allocation for pilot signals is found for different channel memory lengths. [ABSTRACT FROM AUTHOR]

Wireless transmission channels experience substantial signal degradation due to irregularities in the propagation path that impact synchronization between two communicating ends. Consequently, differential and noncoherent techniques that require no such synchronization have gained wide popularity. However, the transmitted data are still highly prone to transmission errors and appropriate error-control mechanisms have to be employed. Knowledge of the error statistics becomes crucial when designing these systems. A block-error rate (BLER) characteristic defines the error distribution within data blocks and in this paper, we propose a finite-state Markov chain-based method to evaluate BLERs in slow frequency-nonselective Rayleigh-fading channels for differential phase-shift keying. The methodology is then extended to the cases of faster Rayleigh and sub-Rayleigh fading. The model is verified by means of numerical simulation. The proposed model possesses many advantages of the well-developed Markov theory and may be easily extended to other modulation schemes such as noncoherent frequency shift keying. [ABSTRACT FROM AUTHOR]