Journal of Computer and Robotics
Volume:4 Issue: 1, Summer and Autumn 2011

Mobile computing systems are made up of different components among which Mobile Support Stations (MSSs) play a key role. This paper proposes an efficient MSS-based non-blocking coordinated checkpointing scheme for mobile computing environment. In the scheme suggested nearly all aspects of checkpointing and their related overheads are forwarded to the MSSs and as a result the workload of Mobile Hosts (MHs) will reduce substantially. Moreover, the total amount of exchanging checkpoint requests will be decreased in order to have a batch transmission of such requests. The scheme is also enhanced using a simple data structure to have fewer propagating checkpoint requests and avoid the avalanche effect in the system. Simulation results show that compared to other existing algorithms, in the proposed scheme the average number of propagating requests and checkpoints, the average elapsed time for each checkpointing process, and the size of system messages are significantly lower and smaller, respectively. Thus considering its distinguishing features, the proposed approach would be efficient and suitable for mobile computing environment.

Quorum based asynchronous protocols -which guarantee overlap between two asynchronous neighbor nodes at least in a time interval for data transmission- have serious problems in broadcasting packets because nodes have no information about their neighbors’ schedules. Synchronous protocols need to synchronize the whole network that leads to less delay but more energy consumption. In contrast, asynchronous protocols need no clock synchronization and save more energy but impose high delays. This article proposes a hybrid mechanism for broadcasting packets which uses the advantages of both synchronous and asynchronous protocols to solve the broadcasting problem in the quorum systems. The mechanism is cluster-based, that is, it uses an asynchronous protocol for communication between cluster-heads and a synchronous protocol for connecting a cluster-head to its members in a cluster. Simulation results indicate that compared with other methods, the mechanism suggested in this paper improves the rate of power saving and end to end delay.

Coverage quality of targets is one of the most significant criteria for some applications such as surveillance and environmental monitoring. Cost is also an important factor for the coverage problem in visual sensor networks. Therefore, the present study aims to investigate a novel coverage problem by considering both cost and coverage quality. To accomplish this purpose, firstly a criterion for the coverage quality of visual sensors is defined with regard to the attributes of lens of their camera. Then, considering cost and quality objective functions, MaxQuality Min-Cost Selection problem (MQMCS) is addressed and formulated as a bi-objective programming. Finally, two centralized and distributed algorithms that with a high probability can find a cover set with the maximum coverage quality and the minimum number of sensors are proposed.

The purpose of this study was to design a logic-based switching H2/H∞ state-feedback controller for continuous-time LTI singular perturbation systems. To this end, a hybrid control scheme based on a Genetic Algorithm (GA)-based supervisor is proposed which manages the combination of two controllers. A convex LMI-Based formulation of both fast and slow subsystem controllers leads to a structure which ensures a good performance in both transient and steady state phases. The stability analysis uses Lyapunov techniques, inspired from switching system theory, to prove that a system with the proposed controller remains globally stable despite the configuration (controller) changing.

In the near future, embedded processors need to support more network applications, computation-intensive packet-processing tasks will become heavier, and new performance bottlenecks will be introduced in the embedded system designs. Since memory access delay and also the number of processor registers significantly affect processor performance, cache and register file are two major parts in designing embedded processor architectures. Increasing the sizes of cache and register file leads to the performance improvement in packetprocessing tasks in high traffic networks with too many packets, but the increased area, power consumption, and memory access delay are the overheads of these techniques. Therefore, implementing these components in the optimum size is of great interest in the design of embedded processors. In this regard, this paper explores the effect of cache and register file size on the performance of processors while considering power consumption in calculating the optimum size of these components for embedded applications. The results show that although having bigger caches and register files helps with the performance improvement in embedded processors, increasing the size of these parameters beyond the threshold level makes the performance improvement saturated and finally decreased. Furthermore, a major part of the power of embedded processors is consumed in the memory.

This paper introduces a novel gesture recognition method. In the method, hand trajectory is represented by the sequence of symbols and each symbol has a specific membership degree obtained from the genetic algorithm training. In order to determine the membership degree of input observations sequence in a class, the system uses the linear combination of membership degrees of observations in sequence. Because of using negative and positive samples for training gesture classes in the proposed method, the recognition system has a good performance in distinguishing very similar gestures. Experiments show that the method developed in this study outperforms HMM and SOMM methods in different gesture datasets.

Since most of visual data is stored in the compressed form, investigating semantic retrieval techniques with the description capability of image semantics in the image compression domain is highly desirable. Regardless of the fact that content based image retrieval (CBIR) based on the Vector Quantization (VQ) compression method is more accurate than the other methods, it is expected that semantic retrieval can also be effective. Thus, the goal of this study is to develop a novel automatic image annotation method in the compressed domain. To this end, firstly the images are compressed using the VQ compression method and then are segmented into equal rectangular regions. Each region in the labelled image will be assigned a visual weight that will be calculated. In the annotation process, the relevance model which is a joint probability distribution of the word annotations and the image regional and global features vector is computed through the training set. Therefore, the unlabelled images are annotated. Finally, the image is retrieved on the basis of its semantic concepts. The experiments over 5k Corel images have shown that the retrieval performance of the method suggested here is higher than that of other methods in the uncompressed domain.

Compactness and lightness make high-speed axial-flux machines eligible for distributed generation application with microturbine. In a high-speed generator driven by micro-turbines, the rotor speed is normally above 30,000 rpm and may even exceed 100,000 rpm. The frequency for flux variation is more than 1 kHz. Therefore, designing such a highspeed generator is quite different, in mechanical and electromagnetic respects, from designing conventional generators with low speed and low frequency. Important considerations in designing high-speed axial-flux generators (HSAFG) for microturbine are discussed in this paper. Results of the efficiency sensitivity versus air gap of the machine are also presented.