Now showing items 697-716 of 1107

    • Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells 

      Rice, W.D.; Kono, J.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Helm, M.; Ewers, B.; Chernikov, A.; Koch, M.; Chatterjee, S.; Khitrova, G.; Gibbs, H.M.; Schneebeli, L.; Breddermann, B.; Kira, M.; Koch, S.W. (2013)
      We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we ...
    • On a Class of Minimum Energy Controls Related to Spline Functions 

      Netravali, Arun N.; de Figueiredo, Rui J.P. (1975-07-20)
      The problem of determining a minimum energy control for a dynamically interconnected set of p single-input single-output finite-dimensional linear time-varying dynamical systems, for which the outputs are constrained to ...
    • On Beamforming with Finite Rate Feedback in Multiple Antenna Systems 

      Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2003-10-20)
      In this paper, we study a multiple antenna system where the transmitter is equipped with quantized information about instantaneous channel realizations. Assuming that the transmitter uses the quantized information for ...
    • On Capacity of Gaussian â Cheapâ Relay Channel 

      Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-12-01)
      In this paper, we derive the capacity of the Gaussian degraded â cheapâ relay channel, consisting of nodes using â cheapâ radios operating in TDD mode when transmitting and sending in the same frequency band. The TDD ...
    • On Channel State Information in Multiple Antenna Block Fading Channels 

      Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2000-11-20)
      Motivated by large capacity gains in multiple antenna systems when perfect channel state information is available at both receiver and transmitter, we examine the achievable rates of channel measurement based techniques. ...
    • On Design Criteria and Construction of Non-coherent Space-Time Constellations 

      Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam; Johnson, Don (2002-07-20)
      We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple antenna system, when both the transmitter and the receiver are unaware of the channel coefficients. Using Stein's lemma ...
    • On Design Criteria and Construction of Non-coherent Space-Time Constellations 

      Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-10-20)
      We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple-antenna system, when the channel state information is available neither at the transmitter nor at the receiver. It ...
    • On Diversity and Multiplexing Gain of Multiple Antenna Systems with Transmitter Channel Information 

      Khoshnevis, Ahmad; Sabharwal, Ashutosh (2004-10-01)
      We quantify the multiplexing-diversity tradeoff of a multiple-input multiple-output (MIMO) system, when the channel state information (CSI) is known perfectly at the receiver and partially at the transmitter. The partial ...
    • On Joint Distributions for Arbitrary Variables 

      Baraniuk, Richard G.; Cohen, Leon (1995-01-01)
      There has been considerable interest in the problem of joint representations for variables other than time and frequency. In this letter we compare the methods of Cohen and of Baraniuk and Jones and show their equivalence ...
    • On Limits of Antenna Packing in Low Power Systems 

      Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-09-01)
      We evaluate spectral efficiency limits of low power portable communication devices which are only constrained by fixed transceiver aperture G "subset&equal" real<sup>3</sup> for mounting antennas. A new notion of ...
    • On Multipath Channel Estimation for CDMA Systems Using Multiple Sensors 

      Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam (2001-03-20)
      This paper focuses on the design of a multiuser receiver structure for the reverse link of a code-division multiple-access communication system, in the presence of multipath effects and using an antenna array at the base ...
    • On Nearly Orthogonal Lattice Bases 

      Neelamani, Ramesh; Dash, Sanjeeb; Baraniuk, Richard G. (2005-07-01)
      We study "nearly orthogonal" lattice bases, or bases where the angle between any basis vector and the linear subspace spanned by the other basis vectors is greater than 60&deg;. We show that a nearly orthogonal lattice ...
    • On Outage and Capacity for Orthogonal Transmit Diversity 

      Muharemovic, Tarik; Aazhang, Behnaam (2001-09-20)
      Assuming that only the receiver has perfect channel state information, we analyze the orthogonal transmit diversity (OTD). First, we consider the case of fast fading or <i>ergodic</i> channels. We demonstrate that for a ...
    • On Power Control with Finite Rate Feedback for Cooperative Relay Networks 

      Ahmed, Nasir; Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-03-01)
      Power control strategies with finite rate feedback are studied for the cooperative channel. The main contribution of this paper is to show that quantized feedback information can lead to significant reduction in outage ...
    • On the Asymptotic Performance of Multiple Antenna Channels with Fast Channel Feedback 

      Khoshnevis, Ahmad; Sabharwal, Ashutosh (2005-10-01)
      In this paper, we analyze the asymptotic performance of multiple antenna channels where the transmitter has either perfect or finite bit channel state information. Using the diversitymultiplexing tradeoff to characterize ...
    • On the Capacity of `Cheap' Relay Networks 

      Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-04-20)
      We consider the communication problem in a multi-hop relay network where the intermediate relay nodes cannot transmit and receive at the same time. The motivation for this assumption comes from the fact that current radios ...
    • On the Complexity of Vector Searching 

      Hirschberg, D.S. (1978-06-20)
      The vector searching problem is, given k-vector A (a k-vector) is a vector that has k components, over the integers) and given a set B of n distinct k-vectors, to determine whether or not A is a member of set B. Comparisons ...
    • On the Correlation Structure of Multiplicity M Scaling Functions and Wavelets 

      Gopinath, Ramesh A.; Odegard, Jan E.; Burrus, C. Sidney (1992-05-20)
      None
    • On the Correlation Structure of Multiplicity M Scaling Functions and Wavelets 

      Gopinath, Ramesh A.; Odegard, Jan E.; Burrus, C. Sidney (1992-01-15)
      In this paper we study the auto-correlation and cross-correlation structure of the scaling and wavelet functions associated with compactly supported orthonormal wavelet basis. These correlation structures play an important ...
    • On the Design of LP IIR Filters with Arbitrary Frequency Response 

      Vargas, Ricardo; Burrus, C. Sidney (2001-05-01)
      This paper introduces an iterative algorithm for designing IIR digital filters that minimize a complex approximation error in an Lp sense. The algorithm combines ideas that have proven successful in the similar problem ...