In this work, we investigate a three-user cognitive communication network where a primary two-user multiple access channel suffers interference from a secondary point-to-point channel, sharing the same medium. While the point-to-point channel transmitter—transmitter 3—causes an interference at the primary multiple access channel receiver, we assume that the primary channel transmitters—transmit...

The capacity region of the multiple antenna (transmit and receive) broadcast channel is considered. We propose an outer bound to the capacity region by converting this nondegraded broadcast channel into a degraded one with users privy to the signals of users ordered below them. We extend our proof techniques in the characterization of the sum capacity of the multiple antenna broadcast channel t...

How can a group of distributed secondary users make rendezvous on one among a set of available channels, whose exact content is a priori unknown to the participants? Let us assume that secondary users scan the set of channels, attempting to make rendezvous with each other. Each user has several radios that are concurrently used to achieve rendezvous. We propose two rendezvous algorithms for use...

This paper considers the problem of power allocation between the two senders in the multiple access channel. Two power allocation criteria are developed. In particular, in the first criterion, the total available power is allocated between the two users such that the two users have the same achievable rate. In addition, the second criterion allocates the total available power such that the sum ...

We consider a scenario where N users try to access a common base station. Associated with each user is its channel state and a finite queue which varies with time. Each user chooses his power and the admission control variable in a dynamic manner so as to maximize his expected throughput. The throughput of each user is a function of the actions and states of all users. The scenario considers th...

This paper looks into various ways of extending a Geometrically Based Single Bounce Channel Model into a Multiple Bounce one, the main motivation being to overcome some of the limitations of the former models. Three different strategies to implement the way rays are bounced are described and compared, a comparison between diffuse scattering and specular reflection being also investigated; as ex...

1 This work was supported in part by NASA grant NAG5-12025 and by the National Science Foundation. The views expressed here are those of the authors and do not necessarily represent those of NASA or the National Science Foundation. ABSTRACT Content-based image retrieval (CBIR) uses features that can be extracted from the images themselves. In previous work we have shown that using more than one...

Wireless networks have been widely deployed in the past few years. With rapidly increasing number of users, it is important to maximize utilization of given resources to achieve high performance. Among many approaches, the aim of this dissertation is in utilizing available frequency spectrum, which may be divided into multiple non-overlapping channels. Particularly, we focus on the case where w...