Gene Eu Jan

Optimal Path Planning for Mobile Robot Navigation

Some optimal path planning algorithms for navigating mobile rectangular robot among obstacles and weighted regions are presented. The approach is based on a higher geometry maze routing algorithm. Starting from a top view of a workspace with obstacles, the so-called free workspace is first obtained by virtually expanding the obstacles in the image. After that, an 8-geomerty maze routing algorithm is applied to obtain an optimal collision-free path with linear time and space complexities. The proposed methods cannot only search an optimal path among various terrains but also find an optimal path for the 2-D piano movers problem with 3 DOF. Furthermore, the algorithm can be easily extended to the dynamic collision avoidance problem among multiple autonomous robots or path planning in the 3-D space.

A Lossless Data Compression and Decompression Algorithm and Its Hardware Architecture

In this paper, we propose a new two-stage hardware architecture that combines the features of both parallel dictionary LZW (PDLZW) and an approximated adaptive Huffman (AH) algorithms. In this architecture, an ordered list instead of the tree-based structure is used in the AH algorithm for speeding up the compression data rate. The resulting architecture shows that it not only outperforms the AH algorithm at the cost of only one-fourth the hardware resource but it is also competitive to the performance of LZW algorithm (compress). In addition, both compression and decompression rates of the proposed architecture are greater than those of the AH algorithm even in the case realized by software

A fault-tolerant object service on CORBA

Abstract The Common Object Request Broker Architecture (CORBA), is a major industrial standard for distributed object-based applications. Todays large-scale CORBA applications have to deal with object crashes, node failures, networks partitioning and unpredictable communication delays. Existing efforts to enhance the CORBA reliability can be roughly categorized into three approaches: integration approach, interception approach and service approach. Each approach has its own merits and prices. In this paper, we propose a service approach solution called Object Fault–tolerance Service (OFS). Solutions that adopt the service approach usually specify their service in terms of CORBA IDL interfaces. The implementations of such solutions in general do not modify the ORB infrastructure or IDL language mappings, and thus applications developed with those systems appear to be more portable. OFS differs from other service approach solutions in that OFS does not assume underlying support of reliable group communication. Applications with advance registration can rely on OFS for detection of object and node crashes, and for customized recovery. In this paper, we first present the service specification of OFS. We then give the system architecture of an OFS implementation. This OFS implementation is developed on the Solaris 2.5 platform and with IONAs Orbix 2.0. The performance evaluation of the OFS implementation is also presented. The preliminary experiments indicate that OFS overhead is minimal and client objects experience little response delay when a service object is under OFS surveillance.

A method for searching optimal routes with collision avoidance on raster charts

Collision avoidance is an intensive discussion issue for navigation safety. This article introduces a new routing algorithm for finding optimal routes with collision detection and avoidance on raster charts or planes. After the required data structure of the raster chart is initialized, the maze routing algorithm is applied to obtain the particular route of each ship. Those ships that have potential to collide will be detected by simulating the particular routes with ship domains. The collision avoidance scheme can be achieved by using the collision-area-marking method with collision avoidance rules at sea. The algorithm has linear time and space complexities, and is sufficiently fast to perform real-time routing on the raster charts.

A 4-geometry maze router and its application on multiterminal nets

The maze routing problem is to find an optimal path between a given pair of cells on a grid plane. Lees algorithm and its variants, probably the most widely used maze routing method, fails to work in the 4-geometry of the grid plane. Our algorithm solves this problem by using a suitable data structure for uniform wave propagation in the 4-geometry, 8-geometry, etc. The algorithm guarantees finding an optimal path if it exists and has linear time and space complexities. Next, to solve the obstacle-avoiding rectilinear and 4-geometry Steiner tree problems, a heuristic algorithm is presented. The algorithm utilizes a cost accumulation scheme based on the maze router to determine the Torricelli vertices (points) for improving the quality of multiterminal nets. Our experimental results show that the algorithm works well in practice. Furthermore, using the 4-geometry router, path lengths can be significantly reduced up to 12&percent; compared to those in the rectilinear router.

A new maze routing approach for path planning of a mobile robot

A new path planning approach for a mobile robot among obstacles of arbitrary shape is presented. This approach is based on a higher geometry maze routing algorithm. Starting from a top view of a workspace with obstacles, the so-called free workspace is first obtained by virtually expanding the obstacles in the image. After that, the 8-geometry maze routing algorithm is applied to obtain a shortest collision-free path. The proposed method is not only able to search a shortest path with rotation scheme but also capable to rotate the robot configuration to pass a narrow passage intelligently. The time complexity of the algorithm is O(N), where N is the number of pixels in the free workspace. Furthermore, for many researchers who work on dynamic collision avoidance for multiple autonomous robots and optimal path searching among various terrains (weighted regions), the concept of this algorithm can be applied to solve these problems.

An Efficient Algorithm for Perfect Load Balancing on Hypercube Multiprocessors

This paper proposes a simple yet efficient algorithm to distribute loads evenly on multiprocessor computers with hypercube interconnection networks. This algorithm was developed based upon the well-known dimension exchange method. However, the error accumulation suffered by other algorithms based on the dimension exchange method is avoided by exploiting the notion of regular distributions, which are commonly deployed for data distributions in parallel programming. This algorithm achieves a perfect load balance over P processors with an error of 1 and the worst-case time complexity of O(M log2P), where M is the maximum number of tasks initially assigned to each processor. Furthermore, perfect load balance is achieved over subcubes as well—once a hypercube is balanced, if the cube is decomposed into two subcubes by the lowest bit of node addresses, then the difference between the numbers of the total tasks of these subcubes is at most 1.

Effective load balancing on highly parallel multicomputers based on superconcentrators

Tree and mesh architectures have been considered as two of the most highly scalable parallel multicomputers due to their scalabilities which are superior to those of hypercubes. However, the load balancing on these two multicomputer systems are not as well as we expected. The worst case of tree architecture requires O(M/spl times/p/spl times/logp) routing time for redistributing the workload over the system and it requires O(M/spl times//spl radic/p) for mesh architecture while pipelined packet routing scheme is used. In this paper, we propose an approach based on superconcentrators to reduce the above bounds to O(Mlogp) for both cases with only additional O(p) cost. Furthermore, by using this scheme, the underlying systems can leave the load balancing problem entirely to the superconcentrator so that there does not arise any additional workload of the systems. In addition, this scheme also adds extra communicating paths to the processors so that it not only increases the communication capacity among the processors but also could tolerate edge faults of the systems.

Concentration, load balancing, partial permutation routing, and superconcentration on cube-connected cycles parallel computers

The cube-connected cycles (CCC) was proposed by Preparata and Vuillemin as an efficient general-purpose parallel system for its fixed-degree, and compact and regular layout. In this paper, a few of the basic algorithms on CCC(n,2^n) interconnection networks are addressed and then applied to concentration, superconcentration, partial permutation routing, and load-balancing problems. The results show that both concentration and superconcentration problems can be solved in O(n) time and the on-line partial permutation routing problem in O(n^2) time with O(1) buffers for each node, where n is the dimension of CCC(n,2^n) interconnection networks. The load-balancing problem based on superconcentration can be solved in O(Mn) time, where M is the maximum number of tasks in each node.

Optimal Interceptions on Two-Dimensional Grids with Obstacles

(Email: b0170@mail.ntou.edu.tw)This article presents efficient and practical methods for path planning of optimal intercep-tions on two-dimensional grids with obstacles, such as raster charts or non-distorted digitalmaps. The proposed methods search for optimal paths from sources to multiple moving-targets by a novel higher geometry wave propagation scheme in the grids, instead of thetraditional vector scheme in the graphs. Byintroducing a time-matching scheme, the optimalinterception paths from sources to all the moving-targets are obtained among the combi-nations with linear time and space complexities. Two optimal path planning methods formultiple one-to-one interceptions, the MIN-MAX and MIN-AVG, are applied to emulatethe real routing.KEY WORDS