Relay Stations (RSs) can be deployed in a wireless network to extend its coverage and improve its capacity. Smart (directional) antennas can enhance the functionalities of RSs by forming the beam only towards intended receiving Subscriber Stations (SSs). In this paper, we study a joint problem of selecting a beam width and direction for the smart antenna at each RS and determining the RS assignment for SSs in each scheduling period. The objective is to maximize a utility function that can lead to a stable and high-throughput system. We define this as the Beam Scheduling and Relay Assignment Problem (BS-RAP). We show that BS-RAP is NP-hard, present a Mixed Integer Linear Programming (MILP) formulation to provide optimal solutions and present two polynomial-time greedy algorithms, one of which is shown to have a constant factor approximation ratio.

Advanced collaborative computing environments are one of the most important tools for integrating high-performance computers and computations and for interacting with colleagues around the world. However, heterogeneous characteristics such as network transfer rates, computational abilities, and hierarchical systems make the seamless integration of distributed resources a challenge. In this paper, we argue that advanced collaborative computing environments need an infrastructure of network services to support distributed and quality guaranteed multimedia applications. Accordingly, we propose the design of network services for high-performance collaborative computing. We present a collaborative environment network service infrastructure (CENSI) to embed network services into various systems intelligently and elastically. We also discuss three management modules: a three-party matching module (resources, requests, and network services), a module for performance monitoring and evaluation of group communications, and a module for distribution topology analysis

Distributed computing middleware needs to support a wide range of resources, such as diverse software components, various hardware devices, and heterogeneous operating systems and architectures. Current technologies are unable to implement a maintenance-free platform to be compatible with such different computing environments. This situation is presenting an increasing challenge as Grid computing becomes more widespread. The infrastructure of network services (CENSA and CENSI) has been proposed to address this challenge. A seamless Grid computing environment, supported by network services, is composed of various streams such as data, video, audio, and text. We define a mathematical model of capability matching for three-party agreements: requests from users, resources, and network services. Based on the mathematical model, we provide a general approach for capability matching. We also present a new language schema for capability description. As an example, we embed the general matchmaker in the architecture of the access Grid. Several tests of accuracy and performance are discussed.

Efficient execution of applications requires insight into how the system features impact the performance of the application. For distributed systems, the task of gaining this insight is complicated by the complexity of the system features. This insight generally results from significant experimental analysis and possibly the development of performance models. This paper presents the Prophesy project, an infrastructure that aids in gaining this needed insight based upon experience. The core component of Prophesy is a relational database that allows for the recording of performance data, system features and application details.

With the growing presence of multimedia-enabled systems, we will see an integration of collaborative computing concepts into future scientific and technical workplaces. Desktop teleconferencing is common today, while more complex teleconferencing technology that relies on the availability of multipoint-enabled tools is starting to become available on PCs. A critical problem when using these collaborative tools is archiving multistream, multipoint meetings and making the content available to others. Ideally, one would like the ability to capture, record, play back, index, annotate, and distribute multimedia stream data as easily as we currently handle text or still-image data. The Argonne Voyager project is exploring and developing media server technology needed to provide such a flexible, virtual multipoint recording/playback capability. In this article we describe the motivating requirements, architecture, implementation, operation, performance, and related work.