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We study two distinct, but overlapping networks which operate at the same time, space and frequency. The first network consists of n randomly distributed primary users which form either an ad hoc network, or an infrastructure-supported ad hoc network in which l additional base stations support the primary users. The second network consists of m randomly(More)
— We consider beamforming in a cognitive network with multiple primary users and secondary users sharing the same spectrum. In particular, we assume that each secondary transmitter has Nt antennas and transmits data to its single-antenna receiver using beamforming. The beamformer is designed to maximize the cognitive user's signal-to-interference ratio(More)
—We study a cognitive network consisting of a single primary transmitter and multiple secondary, or cognitive, users. The primary transmitter, located at the center of the network, communicates with primary receivers within a disc called the primary exclusive region (PER). Inside the PER, no cognitive users may transmit, in order to guarantee an outage(More)
This paper analyzes the impact and benefits of infrastructure support in improving the throughput scaling in networks of n randomly located wireless nodes. The infrastructure uses multi-antenna base stations (BSs), in which the number of BSs and the number of antennas at each BS can scale at arbitrary rates relative to n. Two schemes are introduced in this(More)
—We consider a cognitive network consisting of n cognitive users uniformly distributed with constant density among primary users. Each user has a single transmitter and a single receiver, and the primary and cognitive users transmit concurrently. The cognitive users use single-hop transmission in two scenarios: (i) with constant transmit power, and (ii)(More)
— We study the problem of relay selection in a wireless cooperative network. Assuming a single source, a single destination, and N uniformly distributed candidate relays, we seek to select a set of cooperating relays to minimize the total transmission time of a fixed amount of data. We propose two selection methods: Best expectation, which adaptively(More)
—We study a cognitive network consisting of multiple cognitive users communicating in the presence of a single primary user. The primary user is located at the center of the network, and the cognitive users are uniformly distributed within a circle around the primary user. Assuming a constant cognitive user density, the radius of this circle will increase(More)
—In this paper, we present a new cooperative communication scheme consisting of two users in half-duplex mode communicating with one destination over a discrete memoryless channel. The users encode messages in independent blocks and divide the transmission of each block into 3 time slots with variable durations. Cooperation is performed by partial(More)
—In this paper, we consider the single-user MIMO channel with per-antenna power constraint. We formulate the capacity optimization problem with per-antenna constraint in the SDP framework and analyze its optimality conditions. We establish in closed-form the optimal input covariance matrix as a function of the dual variable. We then propose a simple(More)