Adaptive channel and power allocation of downlink multi-user MC-CDMA systems

The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very attractive multiple access technique for high-rate data transmission in the future wireless communication systems. This paper is focused on the joint channel and power allocation in the downlink transmission of multi-user MC-CDMA systems and considers the throughput maximization problem as a mixed integer optimization problem. For simple analysis, the problem is divided into two less complex sub-problems: power allocation and channel allocation, which can be solved by a suboptimal Adaptive Power Allocation (APA) algorithm and an optimal Adaptive Channel Allocation (ACA) algorithm, respectively. By combining APA and ACA algorithms, an adaptive channel and power allocation scheme is proposed. The numerical results show that the proposed APA algorithm is more suitable for MC-CDMA systems than the conventional equal power allocation algorithm, and the proposed channel and power allocation scheme can significantly improve the system throughput performance.     

Utility function of TCP

Understanding the TCP congestion control mechanism from a global optimization point of view is not only important in its own right, but also crucial to the design of other transport layer traffic control protocols with provable properties. In this paper, we derive a global utility function and the corresponding optimal control law, known as TCP control law, which maximizes the global utility. The TCP control law captures the essential behaviors of TCP, including slow start, congestion avoidance, and the binary nature of congestion feedback in TCP. We find that the utility function of TCP is linear in the slow start phase and is proportional to the additive increase rate and approaches the well-known logarithm function as the data rate becomes large in the congestion avoidance phase. We also find that understanding the slow start phase with a fixed threshold is critical to the design of new transport layer control protocols to enable quality of service features. Finally, as an application, we design a Minimum Rate Guaranteed (MRG) traffic control law that shares the same utility function as the TCP control law. Our simulation study of the MRG control law indicates that it is indeed TCP friendly and can provide minimum rate guarantee as long as the percentage of network resource consumed by the MRG flows is moderately small.     

A new algorithm based on auxiliary virtual topology for sub-path protection in WDM optical networks

This paper proposes a new survivable algorithm named sub-path protection based on auxiliary virtual topology (SPAVT) to tolerate the single-link failure in WDM optical networks. First, according to the protection-switching time constraint, SPAVT searches multiple pairs of primary and backup paths for each node pair in the network by the off-line manner, and then map these paths to the virtual topology. When a connection request arrives, SPAVT only needs to run one time of the Dijkstra’s algorithm to search a virtual route in virtual topology, where the route may consist of multiple pairs of sub-paths, to meet the protection-switching time constraint. Then, according to the shared resources policy, SPAVT chooses an optimal pair of sub-paths. Simulation results show that SPAVT has smaller blocking probability and lower time complexity than conventional algorithms.     

Opportunistic channel selection approach under collision probability constraint in cognitive radio systems

In this work, we consider a cognitive radio system with multiple primary channels and one secondary user, and then we introduce a channel-usage pattern model and some basic concepts in this system. Based on this system model and the basic concepts, we propose two opportunistic channel selection algorithms to optimize the throughput of the secondary user: minimum collision rate channel selection algorithm and minimum handoff rate channel selection algorithm. According to the two algorithms, we, respectively, present the channel selection scheme based on minimum collision rate algorithm (CSS-MCRA) and the channel selection scheme based on minimum handoff rate algorithm (CSS-MHRA) under the constraint that the collision probability is bounded below collision tolerable level. Theoretical analysis and simulation results both show that, on one hand, both CSS-MCRA scheme and CSS-MHRA can follow the constraint of collision tolerable level; on the other hand, the performance of CSS-MCRA scheme is better than that of CSS-MHRA scheme if handoff latency is zero or very low, while the performance of CSS-MHRA scheme is better than that of CSS-MCRA scheme if handoff latency is long enough.     

A new certificateless aggregate signature scheme

Aggregate signatures are useful in special areas where the signatures on many different messages generated by many different users need to be compressed. In this paper, we study aggregate signatures in certificateless public key settings. We first present the notion and security model of certificateless aggregate signature schemes. Then we give an efficient certificateless aggregate signature scheme. Our scheme is existentially unforgeable under adaptive chosen-message attacks assuming the computational Diffie–Hellman problem is hard.     

Design and implementation of an agent-based collaborative product design system

The evolution of computer science and technology has brought new opportunities for multidisciplinary designers and engineers to collaborate with each other in a concurrent and coordinated manner. The development of computational agents with unified data structures and software protocols contributes to the establishment of a new way of working in collaborative design, which is increasingly becoming an international practice. In this paper, based on the analysis of the dynamic nature of collaborative design process, a new framework for collaborative design is described. This framework adopts an agent-based approach and relocates designers, managers, systems, and the supporting agents in a unified knowledge representation scheme for product design. In order to model the constantly evolving design process and the rationales resulted from design collaboration, a Collaborative Product Data Model (CPDM) and a constraint-based Collaborative Design Process Model (CDPM) are proposed to facilitate the management and coordination of the collaborative design process as well as design knowledge management. A prototype system of the proposed framework is implemented and its feasibility is evaluated using a real design scenario whose objective is designing a set of dining table and chairs.     

Estimating the Laplace-Beltrami Operator by Restricting 3D Functions

We present a novel approach for computing and solving the Poisson equation over the surface of a mesh. As in previous approaches, we define the Laplace-Beltrami operator by considering the derivatives of functions defined on the mesh. However, in this work, we explore a choice of functions that is decoupled from the tessellation. Specifically, we use basis functions (second-order tensor-product B-splines) defined over 3D space, and then restrict them to the surface. We show that in addition to being invariant to mesh topology, this definition of the Laplace-Beltrami operator allows a natural multiresolution structure on the function space that is independent of the mesh structure, enabling the use of a simple multigrid implementation for solving the Poisson equation.     

Impacts of geographical knowledge, spatial ability and environmental cognition on image searches supported by GIS software

Google Earth search function was used to study the impacts of small-scale spatial ability, large-scale environmental cognition, and geographical knowledge on new technology usage. The participants were 153 junior high students from central Taiwan. Geography grades served as indicators of prior knowledge, mental rotation and abstract reasoning skills as indicators of spatial ability, and sketch maps of school neighborhoods as indicators of environmental cognition (including landmark representation, intersection representation, and frame of reference). Lastly, the authors announced the landmarks searching worksheet and asked the participants to accomplish 16 familiar and unfamiliar landmark searching tasks using Google Earth with keyword search function disabled. The result showed the strongest predictor of landmark searching performance is ‘frame of reference’ in environmental cognition, followed by ‘mental rotation’ of spatial ability, ‘landmark representation’ of environmental cognition, and geographical knowledge. Google Earth landmark searches require complex cognitive processing; therefore, our conclusion is that GIS-supported image search activities give students good practice of active knowledge construction.     

Applying a novel decision rule to the sphere-structured support vector machines algorithm

The traditional sphere-structured support vector machines algorithm is one of the learning methods. It can partition the training samples space by means of constructing the spheres with the minimum volume covering all training samples of each pattern class in high-dimensional feature space. However, the decision rule of the traditional sphere-structured support vector machines cannot assign ambiguous sample points such as some encircled by more than two spheres to valid class labels. Therefore, the traditional sphere-structured support vector machines is insufficient for obtaining the better classification performance. In this article, we propose a novel decision rule applied to the traditional sphere-structured support vector machines. This new decision rule significantly improves the performance of labeling ambiguous points. Experimental results of seven real datasets show the traditional sphere-structured support vector machines based on this new decision rule can not only acquire the better classification accuracies than the traditional sphere-structured support vector machines but also achieve the comparable performance to the classical support vector machines. An erratum to this article can be found at     

A methodology for quantitative evaluation of local electrical conductivity: from micron to submicron

The local electrical conductivity of aluminum thin film with dimensions from micron to submicron was quantitatively measured by a four-point atomic force microscope (AFM) technique. The technique is a combination of the principles of four-point probe method and standard AFM. A silicon nitride based AFM probe with a V-shaped two-dimensional sliced structure tip was patterned by using conventional photolithography method. The probe was then etched to four parallel electrodes isolated from each other, for the purpose of performing current input and electrical potential drop measurement. The spacing between electrodes is smaller than 1.0 μm, which facilitates the quantitative electrical conductivity measurement of ultrathin film. The four-point AFM probe technique is capable of measuring surface topography together with local conductivity simultaneously. The technique was applied to a series of 99.999% aluminum thin films with thicknesses from micron to submicron. The repeatable measurements demonstrate the capability of this technique and its possible extension to be used for fast in situ electrical properties characterization of submicron interconnects that widely applied in nanosensors and nanodevices.