将MC CDMA和空时分组编码相结合,构建出一种新的MC CDMA系统下行链路方案(ST MC CD MA)。该方案利用MC CDMA中固有的频率分集和空时分组码的空间分集来抵抗多径,提高系统性能。详细分析了该方案的信号变换形式和处理过程,从理论上给出...将MC CDMA和空时分组编码相结合,构建出一种新的MC CDMA系统下行链路方案(ST MC CD MA)。该方案利用MC CDMA中固有的频率分集和空时分组码的空间分集来抵抗多径,提高系统性能。详细分析了该方案的信号变换形式和处理过程,从理论上给出了系统采用最大比合并时的误码率性能。仿真结果表明,在瑞利衰落信道和较多用户条件下,该系统较传统MC CDMA具有明显的性能改善。展开更多
Ningbo and its surrounding area is the forefront in the rapid economic development in the Yangtse delta, and the main production area for food supplies, cotton, edible oil and hemp; and at the same time, is the main a...Ningbo and its surrounding area is the forefront in the rapid economic development in the Yangtse delta, and the main production area for food supplies, cotton, edible oil and hemp; and at the same time, is the main area for wetland protection in Zhejiang Province. Our objectives were to quantify land cover change in Ningbo and its surrounding area from 1987 to 2000 and to analyze the causative factors of the change. Using 30-m resolution Landsat TM/ETM+ data and maximum likelihood classifica- tion method, we classified the study area into six land cover types: forest, agriculture, urban, freshwater, seawater and bottomland. The research results showed that significant changes in land cover occurred in the study area, and that agriculture and urban land cover change dominated most of the land cover change and were main causes for the changes of other types with human activities, such as urbanization, industrialization, etc. being the main factor while it was not very obvious whether climatic conditions have any role in the land cover changes. Agriculture, bottomland and other nature dominated land cover types are undergoing signifi- cant changes due to industrialization and urbanization, which threaten the stabilization of the environment. The study conclusion called for finding reasonable ways to solve the problems between land cover change and land use.展开更多
About one third of the water needed for agriculture in the world is generated by melting snow. Snow cover, surface and ground water recharge are considered as sustainable and renewable resources. It is therefore neces...About one third of the water needed for agriculture in the world is generated by melting snow. Snow cover, surface and ground water recharge are considered as sustainable and renewable resources. It is therefore necessary to identify and study these criteria. The aim of this study is to determine the spatial and temporal distribution of snow cover in the district of the Sheshpir basin in Fars province (in south of Iran). Ground-based observation of snow covers, especially in mountainous areas, is associated with many problems due to the insufficient accuracy of optical observation, as opposed to digital observation. Therefore, GIS and remote sensing technology can be partially effective in solving this problem. Images of Landsat 5<sup>TM</sup> and Landsat 7<sup>TM</sup> satellites were used to derive snow cover maps. The images in ENVI 4.8 software were classified by using the maximum likelihood algorithm. Other spatial analyses were performed in ARC-GIS 9.3 software. The maximum likelihood method was accuracy assessed by operation points of testing. The least and the average of overall accuracy of produced maps were found to be 91% and 98%, respectively. This demonstrates that the maximum likelihood method has high performance in the classification of images. Overall snow cover and the review of terrain through the years 2008-2009 and 2009-2010 showed that snow cover begins to accumulate in November and reaches its highest magnitude in February. Finally, no trace of snow can be observed on the surface of the basin in the month of May. By average, 34% of the basin is covered in snow from November through to May.展开更多
In this paper, a Complex Wavelet Packet （CWP-MC-CDMA） system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized...In this paper, a Complex Wavelet Packet （CWP-MC-CDMA） system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re- ceiver antennas in the uplink, we employ the Space Diversity Combining （SDC） technique to improve the sys- tem pertbrmance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh lading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial lading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate （BER） performance over the Discrete Fourier Transform （DFT） and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.展开更多
A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to ...A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.展开更多
The minimum vertex cover problem(MVCP)is a well-known combinatorial optimization problem of graph theory.The MVCP is an NP(nondeterministic polynomial)complete problem and it has an exponential growing complexity with...The minimum vertex cover problem(MVCP)is a well-known combinatorial optimization problem of graph theory.The MVCP is an NP(nondeterministic polynomial)complete problem and it has an exponential growing complexity with respect to the size of a graph.No algorithm exits till date that can exactly solve the problem in a deterministic polynomial time scale.However,several algorithms are proposed that solve the problem approximately in a short polynomial time scale.Such algorithms are useful for large size graphs,for which exact solution of MVCP is impossible with current computational resources.The MVCP has a wide range of applications in the fields like bioinformatics,biochemistry,circuit design,electrical engineering,data aggregation,networking,internet traffic monitoring,pattern recognition,marketing and franchising etc.This work aims to solve the MVCP approximately by a novel graph decomposition approach.The decomposition of the graph yields a subgraph that contains edges shared by triangular edge structures.A subgraph is covered to yield a subgraph that forms one or more Hamiltonian cycles or paths.In order to reduce complexity of the algorithm a new strategy is also proposed.The reduction strategy can be used for any algorithm solving MVCP.Based on the graph decomposition and the reduction strategy,two algorithms are formulated to approximately solve the MVCP.These algorithms are tested using well known standard benchmark graphs.The key feature of the results is a good approximate error ratio and improvement in optimum vertex cover values for few graphs.展开更多
Many supervised classification algorithms have been proposed, however, they are rarely evaluated for specific application. This research examines the performance of machine learning classifiers support vector machine ...Many supervised classification algorithms have been proposed, however, they are rarely evaluated for specific application. This research examines the performance of machine learning classifiers support vector machine (SVM), neural network (NN), Random Forest (RF) against maximum classifier (MLC) (traditional supervised classifier) in forest resources and land cover categorization, based on combination of Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) and Landsat Thematic Mapper (TM) data, in Northern Tanzania. Various data categories based on Landsat TM surface reflectance, ALOS PALSAR backscattering and their derivatives were generated for various classification scenarios. Then a separate and joint processing of Landsat and ALOS PALSAR data were executed using SVM, NN, RF and ML classifiers. The overall classification accuracy (OA), kappa coefficient (KC) and F1 score index values were computed. The result proves the robustness of SVM and RF in classification of forest resource and land cover using mere Landsat data and integration of Landsat and PALSAR (average OA = 92% and F1 = 0.7 to 1). A two sample t-statistics was utilized to evaluate the performance of the classifiers using different data categories. SVM and RF indicate there is no significance difference at 5% significance level. SVM and RF show a significant difference when compared to NN and ML. Generally, the study suggests that parametric classifiers indicate better performance compared to parametric classifier.展开更多
Most countries’ land use and land cover (LULC) are changing dramatically today. Most of these changes are related to the way humans and the environment interact. Various methodologies and data sources have been used ...Most countries’ land use and land cover (LULC) are changing dramatically today. Most of these changes are related to the way humans and the environment interact. Various methodologies and data sources have been used in conjunction with remote sensing (RS) to categorize and map changes in LULC. This study used RS and Geographic Information System (GIS) tools to analyze LULC change and transitions from 1984 to 2022 in a tropical forested landscape in southwest Mauritania. Using a suitable and high-quality collection of Landsat satellite images. For the classification and creation of LULC maps for the selected periods, the supervised technique using a maximum likelihood classifier was used. The results indicated that there was a remarkable change in all classes of LULC, with an increase in all classes, except barren land, which had a tremendous decrease of −68.58% for the total study area. Therefore, for the total study area, an increase in agricultural land (221%), water bodies (118.46%), vegetation (57.50%), and built-up areas (14.65%) was observed. We believe that by informing policymakers, environmental managers, and the general public about the current changes, our study will help the region to establish appropriate land use rules that may lead to policy document development.展开更多
文摘将MC CDMA和空时分组编码相结合,构建出一种新的MC CDMA系统下行链路方案(ST MC CD MA)。该方案利用MC CDMA中固有的频率分集和空时分组码的空间分集来抵抗多径,提高系统性能。详细分析了该方案的信号变换形式和处理过程,从理论上给出了系统采用最大比合并时的误码率性能。仿真结果表明,在瑞利衰落信道和较多用户条件下,该系统较传统MC CDMA具有明显的性能改善。
基金Project (No. 40072096) supported by the National Natural Science Foundation of China
文摘Ningbo and its surrounding area is the forefront in the rapid economic development in the Yangtse delta, and the main production area for food supplies, cotton, edible oil and hemp; and at the same time, is the main area for wetland protection in Zhejiang Province. Our objectives were to quantify land cover change in Ningbo and its surrounding area from 1987 to 2000 and to analyze the causative factors of the change. Using 30-m resolution Landsat TM/ETM+ data and maximum likelihood classifica- tion method, we classified the study area into six land cover types: forest, agriculture, urban, freshwater, seawater and bottomland. The research results showed that significant changes in land cover occurred in the study area, and that agriculture and urban land cover change dominated most of the land cover change and were main causes for the changes of other types with human activities, such as urbanization, industrialization, etc. being the main factor while it was not very obvious whether climatic conditions have any role in the land cover changes. Agriculture, bottomland and other nature dominated land cover types are undergoing signifi- cant changes due to industrialization and urbanization, which threaten the stabilization of the environment. The study conclusion called for finding reasonable ways to solve the problems between land cover change and land use.
文摘About one third of the water needed for agriculture in the world is generated by melting snow. Snow cover, surface and ground water recharge are considered as sustainable and renewable resources. It is therefore necessary to identify and study these criteria. The aim of this study is to determine the spatial and temporal distribution of snow cover in the district of the Sheshpir basin in Fars province (in south of Iran). Ground-based observation of snow covers, especially in mountainous areas, is associated with many problems due to the insufficient accuracy of optical observation, as opposed to digital observation. Therefore, GIS and remote sensing technology can be partially effective in solving this problem. Images of Landsat 5<sup>TM</sup> and Landsat 7<sup>TM</sup> satellites were used to derive snow cover maps. The images in ENVI 4.8 software were classified by using the maximum likelihood algorithm. Other spatial analyses were performed in ARC-GIS 9.3 software. The maximum likelihood method was accuracy assessed by operation points of testing. The least and the average of overall accuracy of produced maps were found to be 91% and 98%, respectively. This demonstrates that the maximum likelihood method has high performance in the classification of images. Overall snow cover and the review of terrain through the years 2008-2009 and 2009-2010 showed that snow cover begins to accumulate in November and reaches its highest magnitude in February. Finally, no trace of snow can be observed on the surface of the basin in the month of May. By average, 34% of the basin is covered in snow from November through to May.
基金Supported by China Postdoctoral Science Foundation, and Science Foundation of Jiangsu Province (BK2003089).
文摘In this paper, a Complex Wavelet Packet （CWP-MC-CDMA） system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re- ceiver antennas in the uplink, we employ the Space Diversity Combining （SDC） technique to improve the sys- tem pertbrmance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh lading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial lading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate （BER） performance over the Discrete Fourier Transform （DFT） and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.
文摘A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.
文摘The minimum vertex cover problem(MVCP)is a well-known combinatorial optimization problem of graph theory.The MVCP is an NP(nondeterministic polynomial)complete problem and it has an exponential growing complexity with respect to the size of a graph.No algorithm exits till date that can exactly solve the problem in a deterministic polynomial time scale.However,several algorithms are proposed that solve the problem approximately in a short polynomial time scale.Such algorithms are useful for large size graphs,for which exact solution of MVCP is impossible with current computational resources.The MVCP has a wide range of applications in the fields like bioinformatics,biochemistry,circuit design,electrical engineering,data aggregation,networking,internet traffic monitoring,pattern recognition,marketing and franchising etc.This work aims to solve the MVCP approximately by a novel graph decomposition approach.The decomposition of the graph yields a subgraph that contains edges shared by triangular edge structures.A subgraph is covered to yield a subgraph that forms one or more Hamiltonian cycles or paths.In order to reduce complexity of the algorithm a new strategy is also proposed.The reduction strategy can be used for any algorithm solving MVCP.Based on the graph decomposition and the reduction strategy,two algorithms are formulated to approximately solve the MVCP.These algorithms are tested using well known standard benchmark graphs.The key feature of the results is a good approximate error ratio and improvement in optimum vertex cover values for few graphs.
文摘Many supervised classification algorithms have been proposed, however, they are rarely evaluated for specific application. This research examines the performance of machine learning classifiers support vector machine (SVM), neural network (NN), Random Forest (RF) against maximum classifier (MLC) (traditional supervised classifier) in forest resources and land cover categorization, based on combination of Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) and Landsat Thematic Mapper (TM) data, in Northern Tanzania. Various data categories based on Landsat TM surface reflectance, ALOS PALSAR backscattering and their derivatives were generated for various classification scenarios. Then a separate and joint processing of Landsat and ALOS PALSAR data were executed using SVM, NN, RF and ML classifiers. The overall classification accuracy (OA), kappa coefficient (KC) and F1 score index values were computed. The result proves the robustness of SVM and RF in classification of forest resource and land cover using mere Landsat data and integration of Landsat and PALSAR (average OA = 92% and F1 = 0.7 to 1). A two sample t-statistics was utilized to evaluate the performance of the classifiers using different data categories. SVM and RF indicate there is no significance difference at 5% significance level. SVM and RF show a significant difference when compared to NN and ML. Generally, the study suggests that parametric classifiers indicate better performance compared to parametric classifier.
文摘Most countries’ land use and land cover (LULC) are changing dramatically today. Most of these changes are related to the way humans and the environment interact. Various methodologies and data sources have been used in conjunction with remote sensing (RS) to categorize and map changes in LULC. This study used RS and Geographic Information System (GIS) tools to analyze LULC change and transitions from 1984 to 2022 in a tropical forested landscape in southwest Mauritania. Using a suitable and high-quality collection of Landsat satellite images. For the classification and creation of LULC maps for the selected periods, the supervised technique using a maximum likelihood classifier was used. The results indicated that there was a remarkable change in all classes of LULC, with an increase in all classes, except barren land, which had a tremendous decrease of −68.58% for the total study area. Therefore, for the total study area, an increase in agricultural land (221%), water bodies (118.46%), vegetation (57.50%), and built-up areas (14.65%) was observed. We believe that by informing policymakers, environmental managers, and the general public about the current changes, our study will help the region to establish appropriate land use rules that may lead to policy document development.
