Multiterminal global routing: A deterministic approximation scheme

We consider the problem of routing multiterminal nets in a two-dimensional gate-array. Given a gate-array and a set of nets to be routed, we wish to find a routing that uses as little channel space as possible. We present a deterministic approximation algorithm that uses close to the minimum possible channel space. We cast the routing problem as a new form of zero-one multicommodity flow, an integer-programming problem. We solve this integer program approximately by first solving its linear-program relaxation and then rounding any fractions that appear in the solution to the linear program. The running time of the rounding algorithm is exponential in the number of terminals in a net but polynomial in the number of nets and the size of the array. The algorithm is thus best suited to cases where the number of terminals on each net is small.     

无线Mesh网络中一种分布式路由方案

在多射频多信道无线Mesh网络中,链路负载和节点位置的变化将导致网络性能的下降。针对此问题,在混合无线网状路由协议反应式路由基础上,设计了一种新的混合信道分配的分布式路由算法。该算法在路由建立的同时可实现以数据流为单位的最优信道分配,且能避免因单节点失效导致整个网络崩溃的危险。仿真结果表明,提出的RHCA算法较传统算法在网络吞吐量和端到端平均时延方面均有显著优势。另外,在节点移动场景下,所提出的分布式路由算法较其他方法能获得更高的吞吐量和更好的稳健性。     

A fast deterministic smallest enclosing disk approximation algorithm

We describe a simple and fast -time algorithm for finding a (1+?)-approximation of the smallest enclosing disk of a planar set of n points or disks. Experimental results of a readily available implementation are presented.     

Efficient approximation algorithms for the routing open shop problem

We consider the routing open shop problem being a generalization of two classical discrete optimization problems: the open shop scheduling problem and the metric traveling salesman problem. The jobs are located at nodes of some transportation network, and the machines travel on the network to execute the jobs in the open shop environment. The machines are initially located at the same node (depot) and must return to the depot after completing all the jobs. It is required to find a non-preemptive schedule with the minimum makespan. The problem is NP-hard even on the two-node network with two machines. We present new polynomial-time approximation algorithms with worst-case performance guarantees.     

On deterministic approximation of DNF

We develop several quasi-polynomial-time deterministic algorithms for approximating the fraction of truth assignments that satisfy a disjunctive normal form formula. The most efficient algorithm computes for a given DNF formulaF onn variables withm clauses and > 0 an estimateY such that ¦Pr[F] –Y¦ in time which is , for any constant. Although the algorithms themselves are deterministic, their analysis is probabilistic and uses the notion of limited independence between random variables.Research supported in part by National Science Foundation Operating Grant CCR-9016468, National Science Foundation Operating Grant CCR-9304722, United States-Israel Binational Science Foundation Grant No. 89-00312, United States-Israel Binational Science Foundation Grant No. 92-00226, and ESPRIT Basic Research Grant EC-US 030.Research partially done while visiting the International Computer Science Institute and while at Carnegie Mellon University.     

Improved deterministic approximation algorithms for Max TSP

We present an O(n³)-time approximation algorithm for the maximum traveling salesman problem whose approximation ratio is asymptotically , where n is the number of vertices in the input complete edge-weighted (undirected) graph. We also present an O(n³)-time approximation algorithm for the metric case of the problem whose approximation ratio is asymptotically . Both algorithms improve on the previous bests.     

A fault-tolerant routing scheme in dynamic networks

In dynamic networks,links and nodes will be deleted or added regularly.It is very essential for the routing scheme to have the ability of fault-tolerance.The method to achieve such a goal is to generate ore than one path for a given set of source and destination.In this paper,the idea of inderval routing is used to construct a new scheme(Multi-Node Label Interval Routing Scheme,or MNILIR scheme)to realizee fault-tolerance.Interval routing is a space-efficinet routing method for netwroks ,but the method is static and determinative,and it cannot realize faulttoloerance.In MNLIR scheme some nodes will have more than one label,thus some parirs of destination and source will have more than one path;the pairs of nodes, which have inheritance relation,will have the shortest path.Using this character,MNLIR scheme has better overall routing performance than the former interval routing scheme,which can be proven by simulations.The common problem concerning the insertion and deletion of nodes and links is considered in this paper.So if the networks have some changes in topology,MNLIR scheme may find alternative path for certain paris of nodes.In this way,fault-tolerance can be realized with only a little space added to store the multi-node labels.     

A 3.4713-approximation algorithm for the capacitated multicast tree routing problem

Given an underlying communication network represented as an edge-weighted graph G=(V,E), a source node sV, a set of destination nodes DV, and a capacity k which is a positive integer, the capacitated multicast tree routing problem asks for a minimum cost routing scheme for source s to send data to all destination nodes, under the constraint that in each routing tree at most k destination nodes are allowed to receive the data copies. The cost of the routing scheme is the sum of the costs of all individual routing trees therein. Improving on our previous approximation algorithm for the problem, we present a new algorithm which achieves a worst case performance ratio of , where ρ denotes the best known approximation ratio for the Steiner minimum tree problem. Since ρ is about 1.55 at the writing of the paper, the ratio achieved by our new algorithm is less than 3.4713. In comparison, the previously best ratio was .     

A deterministic tabu search algorithm for the capacitated arc routing problem

The capacitated arc routing problem (CARP) is a difficult optimisation problem in vehicle routing with applications where a service must be provided by a set of vehicles on specified roads. A heuristic algorithm based on tabu search is proposed and tested on various sets of benchmark instances. The computational results show that the proposed algorithm produces high quality results within a reasonable computing time. Some new best solutions are reported for a set of test problems used in the literature.     

A direction-based geographic routing scheme for intermittently connected mobile networks

In an intermittently connected mobile network, a complete routing path from a source to a destination cannot be guaranteed most of the time. Therefore, traditional routing methods for mobile ad hoc networks are not applicable in such a network. Current approaches for intermittently connected mobile networks are primarily based on redundant transmission and single-copy opportunistic routing. However, they incur either high overhead due to excessive transmissions, or long delay due to incorrect path choices during forwarding. In this paper, we propose a direction-based geographic (DIG) routing scheme for intermittently connected mobile networks. Relying on geographic location information, the packets are routed in a path approximately to the shortest path from the source node to the destination, which significantly reduces the overhead in redundant transmission and decreases the transmission delay in the single-copy opportunistic routing. Theoretical analysis and trace-driven experimental results show that DIG provides low transmission delay with low overhead in comparison with the schemes in the redundant transmission and single-copy opportunistic routing.