By using spatial diversity, multiple-input-multiple-output （MIMO） radar can improve detection performance for fluctuating targets. In this paper, we propose a spatial fluctuation target model for MIMO radar, where t...By using spatial diversity, multiple-input-multiple-output （MIMO） radar can improve detection performance for fluctuating targets. In this paper, we propose a spatial fluctuation target model for MIMO radar, where targets are classified as non-fluctuating target, Rayleigh target and Rician target. Based on Stein＇s lemma, we use relative entropy to study detection performance of optimum detector for Rician target. It is found that in low signal noise ratio （SNR） region, the performance improvement of MIMO radar for detecting Rician target depends on array gain, which is related to the number of receivers. In high SNR region, the improvement of performance depends on diversity gain, which is related to the product of the number of receivers and the number of transmitters. The conclusions of this paper are important for designing MIMO radar system.展开更多
Accurately characterizing the wireless small-scale fading channel has been a challenging task in the wireless communication era due to the surrounding environment. Therefore, this paper introduces a new technique to e...Accurately characterizing the wireless small-scale fading channel has been a challenging task in the wireless communication era due to the surrounding environment. Therefore, this paper introduces a new technique to experimentally characterize the small-scale fading taking under consideration real environmental conditions. By conducting a two dimensional measurement while the mobile receiver is moving;a more accurate channel will be achieved. Two-dimensional measurement refers to collecting data from the receiver along the x and y direction. The two-dimensional measurement data contain far more information than a one-dimensional data collected. In order to represent the small-scale channel along with the real environmental conditions, new approaches are necessary to configure the two-dimensional system and to analyze the 2D data. The new approach this paper introduces for the characterization is that the measurements are conducted on a receiver while it is moving in a two dimensional manner, under different scenarios, Line-of-sight, Non-line-of-sight, and Two-wave-Diffuse Power. The experiment was conducted in a 7 meters long by 4 meters wide room, wherein the distance between the transmitter antenna and receiver is about 3 meters. Those scenarios represent different real-time conditions where obstacles differ from one scenario to another. For example, the line of sight scenario assumes there a clear line of sight between transmitter and receiver, Non line of sight assumes many obstacles between the transmitter and receiver, i.e. walls, cabinets, etc. and Two Wave Diffuse Power assumes a metallic reflector surrounding the receiver. The experiment showed more accurate results when compared to the one dimensional measurement that has been done in the past where receiver is moving in one direction and also receiver being fixed where a constructive and destructive interference is not captured. The two dimensional measurement technique, i.e. capturing data while receiver moving in both x and y directions, provided ess展开更多
GPS navigation signal includes vital information such as orbital parameters, clock error coefficients etc. This received signal which is extremely weak is affected by several errors during its propagation and is of th...GPS navigation signal includes vital information such as orbital parameters, clock error coefficients etc. This received signal which is extremely weak is affected by several errors during its propagation and is of the order of 10-16 W. The noise floor of this signal is 400 times higher than the transmitted signal. The situation becomes much worse particularly when the GPS receiver is located at urban areas where the multipath effect is predominant in the code and carrier phase measurements. GPS usage is not limited to the aircraft en-route navigation and missile guidance where the user receives the satellite signals from the open sky. At the present time, it has become an essential utility in the car navigation, mobile phones, surveying and aircraft landing application. The signal propagation characteristics particularly the short-term variations severely affect the quality, availability and continuity of the system. In this paper, short-term propagation characteristics of GPS signal are modeled and analyzed. Short-term variations are mainly due to multipath reflections and Doppler shift which degrades the quality of received signal particularly in urban environments. The variation of signal quality with respect to user velocity is observed using Rayleigh and Rician fading models.展开更多
Low Earth Orbit(LEO)satellite communications can provide global coverage in the sixth generation communication(6G)networks.To combat the strong Partial Band Interferences(PBIs)and multipath fading in LEO satellite com...Low Earth Orbit(LEO)satellite communications can provide global coverage in the sixth generation communication(6G)networks.To combat the strong Partial Band Interferences(PBIs)and multipath fading in LEO satellite communication systems,the Multicarrier Direct Sequence Code Division Multiple Access(MC-DS-CDMA)technique is a promising alternative to the traditional Single-carrier Direct Sequence Code Division Multiple Access(SC-DS-CDMA)system for its advantages of high bandwidth efficiency,superior interference rejection capability,and low complexity of parallel signal processing.However,limited studies have been conducted on the performance analysis of MC-DS-CDMA acquisition systems in the presence of a large Doppler shift,a unique characteristic of LEO satellite communications.To bridge this gap,we investigate the performance of MC-DS-CDMA systems with two-dimensional acquisition and noncoherent equal gain combining over Rician fading channel in the presence of the Doppler shift and PBIs.The performance metrics are detection probability and Mean Square Error(MSE)of the Doppler factor and delay.Specifically,we derive the closed-form expressions for the MSE and the Probability Density Function(PDF)of the acquisition decision variable and obtain the detection probability.We conduct extensive numerical experiments to verify the theoretical analysis and performance gain of MC-DSCDMA over the SC-DS-CDMA.The results show that MC-DS-CDMA with two-dimensional acquisition is more robust to multipath Rician fading than SC-DS-CDMA.Moreover,MC-DS-CDMA outperforms SC-DS-CDMA regarding the detection probability and MSE when combating the strong PBIs.展开更多
Medical image segmentation is a crucial process for computer-aided diagnosis and surgery.Medical image segmentation refers to portioning the images into small,disjointed parts for simplifying the processes of analysis...Medical image segmentation is a crucial process for computer-aided diagnosis and surgery.Medical image segmentation refers to portioning the images into small,disjointed parts for simplifying the processes of analysis and examination.Rician and speckle noise are different types of noise in magnetic resonance imaging(MRI)that affect the accuracy of the segmentation process negatively.Therefore,image enhancement has a significant role in MRI segmentation.This paper proposes a novel framework that uses 3D MRI images from Kaggle and applies different diverse models to remove Rician and speckle noise using the best possible noise-free image.The proposed techniques consider the values of Peak Signal to Noise Ratio(PSNR)and the level of noise as inputs to the attention-U-Net model for segmentation of the tumor.The framework has been divided into three stages:removing speckle and Rician noise,the segmentation stage,and the feature extraction stage.The framework presents solutions for each problem at a different stage of the segmentation.In the first stage,the framework uses Vibrational Mode Decomposition(VMD)along with Block-matching and 3D filtering(Bm3D)algorithms to remove the Rician.Afterwards,the most significant Rician noise-free images are passed to the three different methods:Deep Residual Network(DeRNet),Dilated Convolution Auto-encoder Denoising Network(Di-Conv-AE-Net),andDenoising Generative Adversarial Network(DGAN-Net)for removing the speckle noise.VMDand Bm3D have achieved PSNR values for levels of noise(0,0.25,0.5,0.75)for reducing the Rician noise by(35.243,32.135,28.214,24.124)and(36.11,31.212,26.215,24.123)respectively.The framework also achieved PSNR values for removing the speckle noise process for each level as follows:(34.146,30.313,28.125,24.001),(33.112,29.103,27.110,24.194),and(32.113,28.017,26.193,23.121)forDeRNet,Di-Conv-AE-Net,and DGAN-Net,respectively.The experiments that have been conducted have proved the efficiency of the proposed framework against classical filters such as Bilateral,Frost展开更多
To meet the high-performance requirements of fifth-generation(5G)and sixth-generation(6G)wireless networks,in particular,ultra-reliable and low-latency communication(URLLC)is considered to be one of the most important...To meet the high-performance requirements of fifth-generation(5G)and sixth-generation(6G)wireless networks,in particular,ultra-reliable and low-latency communication(URLLC)is considered to be one of the most important communication scenarios in a wireless network.In this paper,we consider the effects of the Rician fading channel on the performance of cooperative device-to-device(D2D)communication with URLLC.For better performance,we maximize and examine the system’s minimal rate of D2D communication.Due to the interference in D2D communication,the problem of maximizing the minimum rate becomes non-convex and difficult to solve.To solve this problem,a learning-to-optimize-based algorithm is proposed to find the optimal power allocation.The conventional branch and bound(BB)algorithm are used to learn the optimal pruning policy with supervised learning.Ensemble learning is used to train the multiple classifiers.To address the imbalanced problem,we used the supervised undersampling technique.Comparisons are made with the conventional BB algorithm and the heuristic algorithm.The outcome of the simulation demonstrates a notable performance improvement in power consumption.The proposed algorithm has significantly low computational complexity and runs faster as compared to the conventional BB algorithm and a heuristic algorithm.展开更多
Image denoising is a classical problem in image processing. Its essential goal is to preserve the image features and to reduce noise effiectively. The nonlocal means(NL-means) filter is a successful approach proposed ...Image denoising is a classical problem in image processing. Its essential goal is to preserve the image features and to reduce noise effiectively. The nonlocal means(NL-means) filter is a successful approach proposed in recent years due to its patch similarity comparison. However, the accuracy of similarities in this algorithm degrades when it suffiers from heavy noise. In this paper, we introduce feature similarities based on a multichannel filter into NL-means filter. The multi-bank based feature vectors of each pixel in the image are computed by convolving from various orientations and scales to Leung-Malik set(edge, bar and spot filters), and then the similarities based on this information are computed instead of pixel intensity. Experiments are carried out with Rician noise. The results demonstrate the superior performance of the proposed method. The wavelet-based method and traditional NL-means in term of both mean square error(MSE) and perceptual quality are compared with the proposed method, and structural similarity(SSIM) and quality index based on local variance(QILV) are given.展开更多
The performance of transmit diversity （TD） assisted amplify-and-forward （AF） relay system with partial relay selection, which experiences mixed Rayleigh and Rician fading channels, is investigated. We first invest...The performance of transmit diversity （TD） assisted amplify-and-forward （AF） relay system with partial relay selection, which experiences mixed Rayleigh and Rician fading channels, is investigated. We first investigate the closed-form expression of the cumulative distribution function for the end-to-end equivalent signal-to-noise ratio （SNR）, and then the exact expressions of outage probability and average symbol error probability （SEP） are derived. The theoretical observations are verified by the Monte Carlo simulation results.展开更多
In most of the previous researches on the multiple-input multiple-output (MIMO) channel estimation, the fading model has been assumed to be Rayleigh distributed. However, the Rician fading model is suitable for microc...In most of the previous researches on the multiple-input multiple-output (MIMO) channel estimation, the fading model has been assumed to be Rayleigh distributed. However, the Rician fading model is suitable for microcellular mobile systems or line of sight mode of WiMAX. In this paper, the training based channel es-timation (TBCE) scheme in the spatially correlated Rician flat fading MIMO channels is investigated. First, the least squares (LS) channel estimator is probed. Simulation results show that the Rice factor has no effect on the performance of this estimator. Then, a new linear minimum mean square error (LMMSE) technique, appropriate for Rician fading channels, is proposed. The optimal choice of training sequences with mean square error (MSE) criteria is investigated for these estimators. Analytical and numerical results show that the performance of proposed estimator in the Rician channel model compared with Rayleigh one is much better. It is illustrated that when the channel Rice factor and/or the correlation coefficient increase, the per-formance of the proposed estimator significantly improves.展开更多
This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenario...This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.展开更多
The pilotless frame synchronization approach and implementations of LDPC code are the crucial issue of LDPC decoder. The Maximum-A-Posteriori probability( MAP) decoder has a perfect frame synchronization error rate( F...The pilotless frame synchronization approach and implementations of LDPC code are the crucial issue of LDPC decoder. The Maximum-A-Posteriori probability( MAP) decoder has a perfect frame synchronization error rate( FSER) performance. In this paper,a theoretical derivation of the FSER performance of pilotless frame synchronization for LDPC code is presented. The FSER performance by theoretical analysis coincides well with that by simulation in additive white Gaussian channel and Rician fading channel. So it is estimated the FSER performance of an LDPC code by theoretical analysis can be used instead of the simulations which are much more time-consuming.展开更多
With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fad...With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fading waveforms.Compared with the existing stochastic models,the proposed simulator needs only one trial to obtain the desired statistical properties even if the number of samples is not large enough.Moreover,the proposed simulation model can directly generate multiple uncorrelated waveforms for different fading scenarios,such as single-input single-output frequency selective channels and multiple-input multiple-output channels.The performance evaluation and comparison show that the proposed simulator is efficient and accurate.展开更多
MIMO system can provide higher capacity in independent conditions. When the spatial-temporal fading correlation exists, the capacity may decrease. In this paper, the geometrical MIMO channel model is presented with Ri...MIMO system can provide higher capacity in independent conditions. When the spatial-temporal fading correlation exists, the capacity may decrease. In this paper, the geometrical MIMO channel model is presented with Rician factor. Based on the MIMO ergodic capacity, the capacity bounds are derived with arbitrary finite number of antennas. The bounds are derived in the exact expressions in doubly correlated MIMO R/clan channel. Then a simple expression for the capacity bounds is attained for the high SNR. Finally, the tightness of derived bounds is verified by Monte Carlo simulation.展开更多
As an alternative to satellite communications,multi-hop relay networks can be deployed for maritime long-distance communications.Distinct from terrestrial environment,marine radio signals are affected by many factors,...As an alternative to satellite communications,multi-hop relay networks can be deployed for maritime long-distance communications.Distinct from terrestrial environment,marine radio signals are affected by many factors,e.g.,weather conditions,evaporation ducting,and ship rocking caused by waves.To ensure the data transmission reliability,the block Markov superposition transmission(BMST)codes,which are easily configurable and have predictable performance,are applied in this study.Meanwhile,the physical-layer network coding(PNC)scheme with spatial modulation(SM)is adopted to improve the spectrum utilization.For the BMST-SMPNC system,we propose an iterative algorithm,which utilizes the channel observations and the a priori information from BMST decoder,to compute the soft information corresponding to the XORed bits constructed by the relay node.The results indicate that the proposed scheme outperforms the convolutional coded SM-PNC over fast-fading Rician channels.Especially,the performance can be easily improved in high spatial correlation maritime channel by increasing the memory m.展开更多
HAPs(High-Altitude Platforms)are one of the most promising alternative infrastructures for providing wireless communications to overcome the shortcomings of terrestrial-tower-based and satellite systems.This paper inv...HAPs(High-Altitude Platforms)are one of the most promising alternative infrastructures for providing wireless communications to overcome the shortcomings of terrestrial-tower-based and satellite systems.This paper investigates a multipair two-way MM-AF(Massive MIMO Amplify-and-Forward)relay system over HAPs,where multiple user pairs exchange information within a pair through a relay with a very large number of antennas,and a HAP channel is modeled to follow a Rician fading distribution because of the presence of a line-of-sight path.First,the effect of hardware impairments on a multipair two-way MM-AF system is taken into consideration and is modeled using transmit and receive distortion noises.Then,ZFR/ZFT(Zero-Forcing Reception/Zero-Forcing Transmission)processing matrices of HDR(Half-Duplex Relaying)and FDR(Full-Duplex Relaying)with imperfect channel state information are presented.Finally,the asymptotic expressions of an end-to-end SINR are derived.Theoretical analyses and simulation results show that when the number of relay antennas grows very large,the SE(Spectral Efficiency)of an MM-AF relay system is limited by hardware impairments at the users instead of those at the relay,or by other types of interference.Thus,the quality of the hardware at a relay can be decreased without significantly degrading performance.展开更多
With the deployment of small cells and device to device communications in future heterogeneous networks,in many situations we would encounter mobile radio channels with partly blocked line of sight component,which are...With the deployment of small cells and device to device communications in future heterogeneous networks,in many situations we would encounter mobile radio channels with partly blocked line of sight component,which are well modeled by the Rician shadowed(RS) fading channel.In this paper,by the usage of Kummer transformation,a simplified representation of the RS fading channel with integral fading parameter is given.It is a finite series representation involving only exponential function and low order polynomials.This allows engineers not only the closed-form expressions for exact performance analysis over RS fading channel,but also the insights on the system design tactics.展开更多
基金Supported in part by the National Natural Science Foundation of China (Grant No. 60602048)in part by aviation science funds of China(Grant No. 20060112118)in part by the National Ministry Foundation of China (Grant No. 20094010040)
文摘By using spatial diversity, multiple-input-multiple-output （MIMO） radar can improve detection performance for fluctuating targets. In this paper, we propose a spatial fluctuation target model for MIMO radar, where targets are classified as non-fluctuating target, Rayleigh target and Rician target. Based on Stein＇s lemma, we use relative entropy to study detection performance of optimum detector for Rician target. It is found that in low signal noise ratio （SNR） region, the performance improvement of MIMO radar for detecting Rician target depends on array gain, which is related to the number of receivers. In high SNR region, the improvement of performance depends on diversity gain, which is related to the product of the number of receivers and the number of transmitters. The conclusions of this paper are important for designing MIMO radar system.
文摘Accurately characterizing the wireless small-scale fading channel has been a challenging task in the wireless communication era due to the surrounding environment. Therefore, this paper introduces a new technique to experimentally characterize the small-scale fading taking under consideration real environmental conditions. By conducting a two dimensional measurement while the mobile receiver is moving;a more accurate channel will be achieved. Two-dimensional measurement refers to collecting data from the receiver along the x and y direction. The two-dimensional measurement data contain far more information than a one-dimensional data collected. In order to represent the small-scale channel along with the real environmental conditions, new approaches are necessary to configure the two-dimensional system and to analyze the 2D data. The new approach this paper introduces for the characterization is that the measurements are conducted on a receiver while it is moving in a two dimensional manner, under different scenarios, Line-of-sight, Non-line-of-sight, and Two-wave-Diffuse Power. The experiment was conducted in a 7 meters long by 4 meters wide room, wherein the distance between the transmitter antenna and receiver is about 3 meters. Those scenarios represent different real-time conditions where obstacles differ from one scenario to another. For example, the line of sight scenario assumes there a clear line of sight between transmitter and receiver, Non line of sight assumes many obstacles between the transmitter and receiver, i.e. walls, cabinets, etc. and Two Wave Diffuse Power assumes a metallic reflector surrounding the receiver. The experiment showed more accurate results when compared to the one dimensional measurement that has been done in the past where receiver is moving in one direction and also receiver being fixed where a constructive and destructive interference is not captured. The two dimensional measurement technique, i.e. capturing data while receiver moving in both x and y directions, provided ess
文摘GPS navigation signal includes vital information such as orbital parameters, clock error coefficients etc. This received signal which is extremely weak is affected by several errors during its propagation and is of the order of 10-16 W. The noise floor of this signal is 400 times higher than the transmitted signal. The situation becomes much worse particularly when the GPS receiver is located at urban areas where the multipath effect is predominant in the code and carrier phase measurements. GPS usage is not limited to the aircraft en-route navigation and missile guidance where the user receives the satellite signals from the open sky. At the present time, it has become an essential utility in the car navigation, mobile phones, surveying and aircraft landing application. The signal propagation characteristics particularly the short-term variations severely affect the quality, availability and continuity of the system. In this paper, short-term propagation characteristics of GPS signal are modeled and analyzed. Short-term variations are mainly due to multipath reflections and Doppler shift which degrades the quality of received signal particularly in urban environments. The variation of signal quality with respect to user velocity is observed using Rayleigh and Rician fading models.
基金supported by the State Key Program of NSFC(No.U1836201)and NSFC(No.92038302).
文摘Low Earth Orbit(LEO)satellite communications can provide global coverage in the sixth generation communication(6G)networks.To combat the strong Partial Band Interferences(PBIs)and multipath fading in LEO satellite communication systems,the Multicarrier Direct Sequence Code Division Multiple Access(MC-DS-CDMA)technique is a promising alternative to the traditional Single-carrier Direct Sequence Code Division Multiple Access(SC-DS-CDMA)system for its advantages of high bandwidth efficiency,superior interference rejection capability,and low complexity of parallel signal processing.However,limited studies have been conducted on the performance analysis of MC-DS-CDMA acquisition systems in the presence of a large Doppler shift,a unique characteristic of LEO satellite communications.To bridge this gap,we investigate the performance of MC-DS-CDMA systems with two-dimensional acquisition and noncoherent equal gain combining over Rician fading channel in the presence of the Doppler shift and PBIs.The performance metrics are detection probability and Mean Square Error(MSE)of the Doppler factor and delay.Specifically,we derive the closed-form expressions for the MSE and the Probability Density Function(PDF)of the acquisition decision variable and obtain the detection probability.We conduct extensive numerical experiments to verify the theoretical analysis and performance gain of MC-DSCDMA over the SC-DS-CDMA.The results show that MC-DS-CDMA with two-dimensional acquisition is more robust to multipath Rician fading than SC-DS-CDMA.Moreover,MC-DS-CDMA outperforms SC-DS-CDMA regarding the detection probability and MSE when combating the strong PBIs.
文摘Medical image segmentation is a crucial process for computer-aided diagnosis and surgery.Medical image segmentation refers to portioning the images into small,disjointed parts for simplifying the processes of analysis and examination.Rician and speckle noise are different types of noise in magnetic resonance imaging(MRI)that affect the accuracy of the segmentation process negatively.Therefore,image enhancement has a significant role in MRI segmentation.This paper proposes a novel framework that uses 3D MRI images from Kaggle and applies different diverse models to remove Rician and speckle noise using the best possible noise-free image.The proposed techniques consider the values of Peak Signal to Noise Ratio(PSNR)and the level of noise as inputs to the attention-U-Net model for segmentation of the tumor.The framework has been divided into three stages:removing speckle and Rician noise,the segmentation stage,and the feature extraction stage.The framework presents solutions for each problem at a different stage of the segmentation.In the first stage,the framework uses Vibrational Mode Decomposition(VMD)along with Block-matching and 3D filtering(Bm3D)algorithms to remove the Rician.Afterwards,the most significant Rician noise-free images are passed to the three different methods:Deep Residual Network(DeRNet),Dilated Convolution Auto-encoder Denoising Network(Di-Conv-AE-Net),andDenoising Generative Adversarial Network(DGAN-Net)for removing the speckle noise.VMDand Bm3D have achieved PSNR values for levels of noise(0,0.25,0.5,0.75)for reducing the Rician noise by(35.243,32.135,28.214,24.124)and(36.11,31.212,26.215,24.123)respectively.The framework also achieved PSNR values for removing the speckle noise process for each level as follows:(34.146,30.313,28.125,24.001),(33.112,29.103,27.110,24.194),and(32.113,28.017,26.193,23.121)forDeRNet,Di-Conv-AE-Net,and DGAN-Net,respectively.The experiments that have been conducted have proved the efficiency of the proposed framework against classical filters such as Bilateral,Frost
基金supported in part by the National Natural Science Foundation of China under Grant 61771410in part by the Sichuan Science and Technology Program 2023NSFSC1373in part by Postgraduate Innovation Fund Project of SWUST 23zx7101.
文摘To meet the high-performance requirements of fifth-generation(5G)and sixth-generation(6G)wireless networks,in particular,ultra-reliable and low-latency communication(URLLC)is considered to be one of the most important communication scenarios in a wireless network.In this paper,we consider the effects of the Rician fading channel on the performance of cooperative device-to-device(D2D)communication with URLLC.For better performance,we maximize and examine the system’s minimal rate of D2D communication.Due to the interference in D2D communication,the problem of maximizing the minimum rate becomes non-convex and difficult to solve.To solve this problem,a learning-to-optimize-based algorithm is proposed to find the optimal power allocation.The conventional branch and bound(BB)algorithm are used to learn the optimal pruning policy with supervised learning.Ensemble learning is used to train the multiple classifiers.To address the imbalanced problem,we used the supervised undersampling technique.Comparisons are made with the conventional BB algorithm and the heuristic algorithm.The outcome of the simulation demonstrates a notable performance improvement in power consumption.The proposed algorithm has significantly low computational complexity and runs faster as compared to the conventional BB algorithm and a heuristic algorithm.
基金the Postgraduate Innovation Ability Cultivating Foundation of China(No.Z-SY-009)
文摘Image denoising is a classical problem in image processing. Its essential goal is to preserve the image features and to reduce noise effiectively. The nonlocal means(NL-means) filter is a successful approach proposed in recent years due to its patch similarity comparison. However, the accuracy of similarities in this algorithm degrades when it suffiers from heavy noise. In this paper, we introduce feature similarities based on a multichannel filter into NL-means filter. The multi-bank based feature vectors of each pixel in the image are computed by convolving from various orientations and scales to Leung-Malik set(edge, bar and spot filters), and then the similarities based on this information are computed instead of pixel intensity. Experiments are carried out with Rician noise. The results demonstrate the superior performance of the proposed method. The wavelet-based method and traditional NL-means in term of both mean square error(MSE) and perceptual quality are compared with the proposed method, and structural similarity(SSIM) and quality index based on local variance(QILV) are given.
基金supported by China Important National Science and Technology Specific Projects (2009ZX03007-003-01)Sino-Finland International Cooperation Program of MOST (2010DFB10410)
文摘The performance of transmit diversity （TD） assisted amplify-and-forward （AF） relay system with partial relay selection, which experiences mixed Rayleigh and Rician fading channels, is investigated. We first investigate the closed-form expression of the cumulative distribution function for the end-to-end equivalent signal-to-noise ratio （SNR）, and then the exact expressions of outage probability and average symbol error probability （SEP） are derived. The theoretical observations are verified by the Monte Carlo simulation results.
文摘In most of the previous researches on the multiple-input multiple-output (MIMO) channel estimation, the fading model has been assumed to be Rayleigh distributed. However, the Rician fading model is suitable for microcellular mobile systems or line of sight mode of WiMAX. In this paper, the training based channel es-timation (TBCE) scheme in the spatially correlated Rician flat fading MIMO channels is investigated. First, the least squares (LS) channel estimator is probed. Simulation results show that the Rice factor has no effect on the performance of this estimator. Then, a new linear minimum mean square error (LMMSE) technique, appropriate for Rician fading channels, is proposed. The optimal choice of training sequences with mean square error (MSE) criteria is investigated for these estimators. Analytical and numerical results show that the performance of proposed estimator in the Rician channel model compared with Rayleigh one is much better. It is illustrated that when the channel Rice factor and/or the correlation coefficient increase, the per-formance of the proposed estimator significantly improves.
文摘This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.
基金Supported by the National Natural Science Foundation of China(No.61271230,61472190)the Open Research Fund of National Mobile Communications Research Laboratory,Southeast University(No.2013D02)the Open Research Fund of National Key Laboratory of Electromagnetic Environment,China Research Institute of Radiowave Propagation(No.201500013)
文摘The pilotless frame synchronization approach and implementations of LDPC code are the crucial issue of LDPC decoder. The Maximum-A-Posteriori probability( MAP) decoder has a perfect frame synchronization error rate( FSER) performance. In this paper,a theoretical derivation of the FSER performance of pilotless frame synchronization for LDPC code is presented. The FSER performance by theoretical analysis coincides well with that by simulation in additive white Gaussian channel and Rician fading channel. So it is estimated the FSER performance of an LDPC code by theoretical analysis can be used instead of the simulations which are much more time-consuming.
基金Supported by the Science and Technology Innovation Foundation of Tianjin (No.10FDZDGX00400)
文摘With an improved Rayleigh fading model and a zero-mean stochastic sinusoid as the scattering and specular components respectively,a stochastic simulation model is proposed for the generation of Rayleigh and Rician fading waveforms.Compared with the existing stochastic models,the proposed simulator needs only one trial to obtain the desired statistical properties even if the number of samples is not large enough.Moreover,the proposed simulation model can directly generate multiple uncorrelated waveforms for different fading scenarios,such as single-input single-output frequency selective channels and multiple-input multiple-output channels.The performance evaluation and comparison show that the proposed simulator is efficient and accurate.
基金Acknowledgements This work was supported by National 13asie Research Program of China （2009CB320401）, National Natural Science Foundation of China （60972075, 61072055）, Key Scientific and Technologi- cal Project of China 2010ZX03003-003-01, and Fundamental Research Funds for the Central Universities （2009RC0116）.
文摘MIMO system can provide higher capacity in independent conditions. When the spatial-temporal fading correlation exists, the capacity may decrease. In this paper, the geometrical MIMO channel model is presented with Rician factor. Based on the MIMO ergodic capacity, the capacity bounds are derived with arbitrary finite number of antennas. The bounds are derived in the exact expressions in doubly correlated MIMO R/clan channel. Then a simple expression for the capacity bounds is attained for the high SNR. Finally, the tightness of derived bounds is verified by Monte Carlo simulation.
基金the National Key Research and Development Program of China(No.2017YFE0112600)the National Science Foundation of China[No.61971454,No.91438101&No.61771499]the National Science Foundation of Guangdong,China[No.2016A030308008].
文摘As an alternative to satellite communications,multi-hop relay networks can be deployed for maritime long-distance communications.Distinct from terrestrial environment,marine radio signals are affected by many factors,e.g.,weather conditions,evaporation ducting,and ship rocking caused by waves.To ensure the data transmission reliability,the block Markov superposition transmission(BMST)codes,which are easily configurable and have predictable performance,are applied in this study.Meanwhile,the physical-layer network coding(PNC)scheme with spatial modulation(SM)is adopted to improve the spectrum utilization.For the BMST-SMPNC system,we propose an iterative algorithm,which utilizes the channel observations and the a priori information from BMST decoder,to compute the soft information corresponding to the XORed bits constructed by the relay node.The results indicate that the proposed scheme outperforms the convolutional coded SM-PNC over fast-fading Rician channels.Especially,the performance can be easily improved in high spatial correlation maritime channel by increasing the memory m.
基金supported by the Major Research Plan of the National Natural Science Foundation of China(No.91438115)the National Natural Science Foundation of China(Nos.61371123,61301165,61671472)+4 种基金Jiangsu Province Natural Science Foundation(No.BK20160079)Special Financial Grant of The China Postdoctoral Science Foundation(No.2015T81079)China Postdoctoral Science Foundation(No.2014M552612)Jiangsu Postdoctoral Science Foundation(No.1401178C)the Preresearch Project Foundation(No.9140C020306130C02007).
文摘HAPs(High-Altitude Platforms)are one of the most promising alternative infrastructures for providing wireless communications to overcome the shortcomings of terrestrial-tower-based and satellite systems.This paper investigates a multipair two-way MM-AF(Massive MIMO Amplify-and-Forward)relay system over HAPs,where multiple user pairs exchange information within a pair through a relay with a very large number of antennas,and a HAP channel is modeled to follow a Rician fading distribution because of the presence of a line-of-sight path.First,the effect of hardware impairments on a multipair two-way MM-AF system is taken into consideration and is modeled using transmit and receive distortion noises.Then,ZFR/ZFT(Zero-Forcing Reception/Zero-Forcing Transmission)processing matrices of HDR(Half-Duplex Relaying)and FDR(Full-Duplex Relaying)with imperfect channel state information are presented.Finally,the asymptotic expressions of an end-to-end SINR are derived.Theoretical analyses and simulation results show that when the number of relay antennas grows very large,the SE(Spectral Efficiency)of an MM-AF relay system is limited by hardware impairments at the users instead of those at the relay,or by other types of interference.Thus,the quality of the hardware at a relay can be decreased without significantly degrading performance.
基金sponsored by the National Natural Science Foundation of China under grant No.61171089the Training Program of the Major Research Plan of the National Natural Science Foundation of China under grant No.91438104
文摘With the deployment of small cells and device to device communications in future heterogeneous networks,in many situations we would encounter mobile radio channels with partly blocked line of sight component,which are well modeled by the Rician shadowed(RS) fading channel.In this paper,by the usage of Kummer transformation,a simplified representation of the RS fading channel with integral fading parameter is given.It is a finite series representation involving only exponential function and low order polynomials.This allows engineers not only the closed-form expressions for exact performance analysis over RS fading channel,but also the insights on the system design tactics.
