Electron micrographs showed that dengue virions are characterized by a relatively smooth surface,... more Electron micrographs showed that dengue virions are characterized by a relatively smooth surface, with a diameter of approximately 500 Å , and an electron-dense are three structural proteins that occur in stoichiometric 1 Department of Biological Sciences amounts in the particle: core (C, 100 amino acids), mem-Purdue University brane (M, 75 amino acids), and envelope E, 495 amino West Lafayette, Indiana 47907 acids). The atomic structure for the homologous E pro-2 Division of Biology 156-29 tein of TBEV has an elongated shape consisting of a California Institute of Technology central domain (I) that connects an Ig-like domain (III) Pasadena, California 91125 to a dimerization domain (II) (Rey et al., 1995). Based on the shape of the molecule and the location of antibody epitopes, Rey et al. (1995) postulated that the E protein Summary would lie flat along the surface of the virus lipid bilayer.
Cluster-Based Cooperative Spectrum Sensing in Cognitive Radio Systems
In cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum se... more In cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more accurately. However, when the sensing observations are forwarded to a common receiver through fading channels, the sensing performance can be severely degraded. In this paper, we propose a cluster-based cooperative spectrum sensing method to improve the sensing performance. By separating all the secondary users into a few clusters and selecting the most favorable user in each cluster to report to the common receiver, the proposed method can exploit the user selection diversity so that the sensing performance can be enhanced. Furthermore, decision fusion and energy fusion are both studied and the analytical performance results are given. Numerical results show that the sensing performance is improved significantly as opposed to conventional spectrum sensing.
User cooperation for spectrum sensing in cognitive radios has been proposed in order to improve t... more User cooperation for spectrum sensing in cognitive radios has been proposed in order to improve the overall performance by mitigating multi-path fading and shadowing experienced by the users. However, user cooperation results in high energy consumption, extra time for results exchange, as well as delay and security risks. In this paper, we investigate the effects of cooperative spectrum sensing (CSS) on energy consumption and achievable performance. Our analysis is based on a limited time resources assumption. This implies that the time resources dedicated for CSS process are limited and shared between spectrum sensing and results reporting, which depend on the number of sensing users. Our results show that cooperation among large number of users not only causes high energy consumption, but it also degrades the performance. Motivated by these considerations, the number of sensing users is optimized for different setups: throughput maximization, energy consumption minimization, and energy efficiency maximization. The optimal number of the sensing users is computed in a closed-form for both throughput maximization and energy minimization setups, while a simple iterative algorithm is proposed for obtaining the optimal number of sensing users for maximizing energy efficiency. Moreover, a novel energy efficient approach is presented that is able to significantly improve energy efficiency without degrading achievable throughput.
| Cognitive radio is an exciting emerging technology that has the potential of dealing with the s... more | Cognitive radio is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum. Such revolutionary and transforming technology represents a paradigm shift in the design of wireless systems, as it will allow the agile and efficient utilization of the radio spectrum by offering distributed terminals or radio cells the ability of radio sensing, self-adaptation, and dynamic spectrum sharing. Cooperative communications and networking is another new communication technology paradigm that allows distributed terminals in a wireless network to collaborate through some distributed transmission or signal processing so as to realize a new form of space diversity to combat the detrimental effects of fading channels. In this paper, we consider the application of these technologies to spectrum sensing and spectrum sharing. One of the most important challenges for cognitive radio systems is to identify the presence of primary (licensed) users over a wide range of spectrum at a particular time and specific geographic location. We consider the use of cooperative spectrum sensing in cognitive radio systems to enhance the reliability of detecting primary users. We shall describe spectrum sensing for cognitive radios and propose robust cooperative spectrum sensing techniques for a practical framework employing cognitive radios. We also investigate cooperative communications for spectrum sharing in a cognitive wireless relay network. To exploit the maximum spectrum opportunities, we present a cognitive space-time-frequency coding technique that can opportunistically adjust its coding structure by adapting itself to the dynamic spectrum environment.
Feedback control systems wherein the control loops are closed through a real-time network are cal... more Feedback control systems wherein the control loops are closed through a real-time network are called networked control systems (NCSs). The insertion of the communication network in the feedback control loop makes the analysis and design of an NCS complex. Driving our research effort into NCSs is the point of view that the design of both the communication protocols and the interacting controlled system should not be treated as separate. In the co-design approach we propose, network issues such as bandwidth, quantization, survivability, reliability and message delay will be considered simultaneously with controlled system issues such as stability, performance, fault tolerance and adaptability. Thus, we study network scheduling when a set of NCSs are connected to the network and arbitrating for network bandwidth. We first define the basic concepts of network scheduling in NCSs. Then, we apply the rate monotonic scheduling algorithm to schedule a set of NCSs. We also formulate the optimal scheduling problem under both rate-monotonic-schedulability constraints and NCS-stability constraints, and give an example of how such optimization is carried out. Next, the assumptions of ideal transmission are relaxed: we study the above network scheduling problem with network-induced delay, packet dropouts, and multiple-packet transmissions taken into account.
Recent technological advances have enabled distributed control systems to be implemented via netw... more Recent technological advances have enabled distributed control systems to be implemented via networks. This allows feedback control loops to be closed over a shared communication channel. Network-induced delays are inevitable, however, when transmitting digital data between control devices. This paper analyzes the stability of such networked control systems (NCS). We first review some previous work on this topic, offering some improvements. We analyze the influence of the sampling rate and network delay on system stability. We further study the stability of NCS using a hybrid system stability analysis technique
Electron micrographs showed that dengue virions are characterized by a relatively smooth surface,... more Electron micrographs showed that dengue virions are characterized by a relatively smooth surface, with a diameter of approximately 500 Å , and an electron-dense are three structural proteins that occur in stoichiometric 1 Department of Biological Sciences amounts in the particle: core (C, 100 amino acids), mem-Purdue University brane (M, 75 amino acids), and envelope E, 495 amino West Lafayette, Indiana 47907 acids). The atomic structure for the homologous E pro-2 Division of Biology 156-29 tein of TBEV has an elongated shape consisting of a California Institute of Technology central domain (I) that connects an Ig-like domain (III) Pasadena, California 91125 to a dimerization domain (II) (Rey et al., 1995). Based on the shape of the molecule and the location of antibody epitopes, Rey et al. (1995) postulated that the E protein Summary would lie flat along the surface of the virus lipid bilayer.
Cluster-Based Cooperative Spectrum Sensing in Cognitive Radio Systems
In cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum se... more In cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more accurately. However, when the sensing observations are forwarded to a common receiver through fading channels, the sensing performance can be severely degraded. In this paper, we propose a cluster-based cooperative spectrum sensing method to improve the sensing performance. By separating all the secondary users into a few clusters and selecting the most favorable user in each cluster to report to the common receiver, the proposed method can exploit the user selection diversity so that the sensing performance can be enhanced. Furthermore, decision fusion and energy fusion are both studied and the analytical performance results are given. Numerical results show that the sensing performance is improved significantly as opposed to conventional spectrum sensing.
User cooperation for spectrum sensing in cognitive radios has been proposed in order to improve t... more User cooperation for spectrum sensing in cognitive radios has been proposed in order to improve the overall performance by mitigating multi-path fading and shadowing experienced by the users. However, user cooperation results in high energy consumption, extra time for results exchange, as well as delay and security risks. In this paper, we investigate the effects of cooperative spectrum sensing (CSS) on energy consumption and achievable performance. Our analysis is based on a limited time resources assumption. This implies that the time resources dedicated for CSS process are limited and shared between spectrum sensing and results reporting, which depend on the number of sensing users. Our results show that cooperation among large number of users not only causes high energy consumption, but it also degrades the performance. Motivated by these considerations, the number of sensing users is optimized for different setups: throughput maximization, energy consumption minimization, and energy efficiency maximization. The optimal number of the sensing users is computed in a closed-form for both throughput maximization and energy minimization setups, while a simple iterative algorithm is proposed for obtaining the optimal number of sensing users for maximizing energy efficiency. Moreover, a novel energy efficient approach is presented that is able to significantly improve energy efficiency without degrading achievable throughput.
| Cognitive radio is an exciting emerging technology that has the potential of dealing with the s... more | Cognitive radio is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum. Such revolutionary and transforming technology represents a paradigm shift in the design of wireless systems, as it will allow the agile and efficient utilization of the radio spectrum by offering distributed terminals or radio cells the ability of radio sensing, self-adaptation, and dynamic spectrum sharing. Cooperative communications and networking is another new communication technology paradigm that allows distributed terminals in a wireless network to collaborate through some distributed transmission or signal processing so as to realize a new form of space diversity to combat the detrimental effects of fading channels. In this paper, we consider the application of these technologies to spectrum sensing and spectrum sharing. One of the most important challenges for cognitive radio systems is to identify the presence of primary (licensed) users over a wide range of spectrum at a particular time and specific geographic location. We consider the use of cooperative spectrum sensing in cognitive radio systems to enhance the reliability of detecting primary users. We shall describe spectrum sensing for cognitive radios and propose robust cooperative spectrum sensing techniques for a practical framework employing cognitive radios. We also investigate cooperative communications for spectrum sharing in a cognitive wireless relay network. To exploit the maximum spectrum opportunities, we present a cognitive space-time-frequency coding technique that can opportunistically adjust its coding structure by adapting itself to the dynamic spectrum environment.
Feedback control systems wherein the control loops are closed through a real-time network are cal... more Feedback control systems wherein the control loops are closed through a real-time network are called networked control systems (NCSs). The insertion of the communication network in the feedback control loop makes the analysis and design of an NCS complex. Driving our research effort into NCSs is the point of view that the design of both the communication protocols and the interacting controlled system should not be treated as separate. In the co-design approach we propose, network issues such as bandwidth, quantization, survivability, reliability and message delay will be considered simultaneously with controlled system issues such as stability, performance, fault tolerance and adaptability. Thus, we study network scheduling when a set of NCSs are connected to the network and arbitrating for network bandwidth. We first define the basic concepts of network scheduling in NCSs. Then, we apply the rate monotonic scheduling algorithm to schedule a set of NCSs. We also formulate the optimal scheduling problem under both rate-monotonic-schedulability constraints and NCS-stability constraints, and give an example of how such optimization is carried out. Next, the assumptions of ideal transmission are relaxed: we study the above network scheduling problem with network-induced delay, packet dropouts, and multiple-packet transmissions taken into account.
Recent technological advances have enabled distributed control systems to be implemented via netw... more Recent technological advances have enabled distributed control systems to be implemented via networks. This allows feedback control loops to be closed over a shared communication channel. Network-induced delays are inevitable, however, when transmitting digital data between control devices. This paper analyzes the stability of such networked control systems (NCS). We first review some previous work on this topic, offering some improvements. We analyze the influence of the sampling rate and network delay on system stability. We further study the stability of NCS using a hybrid system stability analysis technique
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