In this paper, we propose a novel node architecture introducing directional antennas into full duplex wireless (FDW) technology. In the proposed architecture, each element of switched-beam antenna is connected to a software switch for directional antenna selection. A node needs only one set of digital and analog cancellation circuits, which is almost the same circuit scale and complexity of the conventional omnidirectional FDW node. In addition, we propose a MAC protocol for the proposed node architecture with FDW and directional antennas for avoiding collisions and obtaining the advantages of both techniques. We evaluate the performance of the proposed protocol via computer simulations, and show that the proposed protocol can improve end-to-end throughput performance up to 114 percent in a line-type multihop network. Moreover, we extend the proposed MAC protocol for mitigating the performance degradation in two-way traffic in line-type multihop networks, and confirm its effectiveness. To the best of our knowledge, this is the first work that attempts to use directional antennas in FDW networks.

Peer-to-peer (P2P) system is an overlay network of peer computers without centralized servers, and many applications have been developed for such networks such as file sharing systems. Because a set of peers dynamically changes, design and verification of efficient protocols is a challenging task. In this paper, we consider an object searching problem under a resource model such that there are some replicas in a system and the lower bound of the ratio /spl rho/=n'/n is known in advance, where n' is a lower bound of the number of peers that hold original or replica for any object type and n is the total number of peers. In addition, we consider object searching with probabilistic success, i.e., for each object search, object must be found with at least probability 0</spl sigma/<1. To solve such a problem efficiently, we propose a new communication structure, named probabilistic weak quorum systems (PWQS), which is an extension of coterie. Then, we propose a fault-tolerant protocol for searching for objects in a P2P system. In our method, each peer does not maintain global information such as the set of all peers and a logical topology with global consistency. In our protocol, each peer communicates only a small part of a peer set and, thus, our protocol is adaptive for huge scale P2P network.

The Gordon Bell Prize recognizes significant achievements in the application of supercomputers to scientific and engineering problems.In this special session the winners of the 1990 pm"ze will give presentations about i!heir winning entries in the competition.