Now showing items 1121-1140 of 1783

  • 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, ...
  • 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 (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 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 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 EFFICIENT DIGITAL FILTERING 

    CHU, SHUNI (1981)
    Part I: Multistage Multirate Digital Filtering. A theorem is introduced which is useful in deriving equivalent multirate filter structures. Frequency responses of multistage multirate filters are derived and defined in ...
  • 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 REALIZATION OF DIGITAL FILTERS 

    AGARWAL, RAMESH CHANDRA (1974)
  • On the application of graphics processor to wireless receiver design 

    Wu, Michael (2010)
    In many wireless systems, a Turbo decoder is often combined with a soft-output multiple-input and multiple-output (MIMO) detector at the receiver to maximize performance in many 4G and beyond wireless standards. Although ...
  • 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 capacity of infinite population random multiple access collision channels 

    Paris, Bernd-Peter (1991)
    The task of controlling the access to a shared communication medium is addressed. More specifically, the problem of finding the control strategy which maximizes the throughput is considered for the infinite population ...