G. Kramer

University of California, Berkeley, Berkeley, MO, United States

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Publications (7)2.62 Total impact

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    M. Gastpar, G. Kramer
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    ABSTRACT: An upper bound is established on the usefulness of noisy feedback for the interference channel (IC). The bound is based on the Hekstra-Willems dependence-balance arguments for two-way channels. For Gaussian ICs, the results suggest that feedback loses its efficacy roughly when the noise variance on the feedback link is larger than on the forward link.
    Signals, Systems and Computers, 2006. ACSSC '06. Fortieth Asilomar Conference on; 12/2006
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    G. Kramer, M. Gastpar
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    ABSTRACT: Dependence balance bounds of Hekstra and Willems are generalized and refined. The new bounds are applied to the K-user multiaccess channel (MAC) with output feedback, and they are shown to establish the feedback sum-rate capacity for the Gaussian MAC when all users have the same per-symbol power constraints. The sum-rate capacity is achieved by Fourier modulated estimate correction. The feedback sum-rate capacity is shown to improve the no-feedback capacity by only log log K nats per use for large K. The new bounds also improve on cut-set bounds for asymmetric powers and rates.
    Information Theory Workshop, 2006. ITW '06 Punta del Este. IEEE; 04/2006
  • Source
    M. Gastpar, G. Kramer
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    ABSTRACT: An upper bound is established on the usefulness of noisy feedback for the two-user multiple-access channel (MAC). The bound generalizes a dependence-balance argument developed by Hekstra and Willems for the common-output two-way channel and the MAC with noiseless output feedback. Lower bounds based on block-coding and linear feedback strategies are also derived
    Communications, 2006 International Zurich Seminar on; 01/2006
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    G. Kramer, M. Gastpar, P. Gupta
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    ABSTRACT: Coding strategies that exploit node cooperation are developed for relay networks. Two basic schemes are studied: the relays decode-and-forward the source message to the destination, or they compress-and-forward their channel outputs to the destination. The decode-and-forward scheme is a variant of multihopping, but in addition to having the relays successively decode the message, the transmitters cooperate and each receiver uses several or all of its past channel output blocks to decode. For the compress-and-forward scheme, the relays take advantage of the statistical dependence between their channel outputs and the destination's channel output. The strategies are applied to wireless channels, and it is shown that decode-and-forward achieves the ergodic capacity with phase fading if phase information is available only locally, and if the relays are near the source node. The ergodic capacity coincides with the rate of a distributed antenna array with full cooperation even though the transmitting antennas are not colocated. The capacity results generalize broadly, including to multiantenna transmission with Rayleigh fading, single-bounce fading, certain quasi-static fading problems, cases where partial channel knowledge is available at the transmitters, and cases where local user cooperation is permitted. The results further extend to multisource and multidestination networks such as multiaccess and broadcast relay channels.
    IEEE Transactions on Information Theory 10/2005; · 2.62 Impact Factor
  • G. Kramer, M. Gastpar, P. Gupta
    IEEE Transactions on Information Theory - TIT. 01/2005;
  • Source
    G. Kramer, P. Gupta, M. Gastpar
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    ABSTRACT: Recent advances in multihopping are extended to relay networks having multiple antennas and multiple sources. As for the single-antenna and single-source case, one can achieve the ergodic capacity of wireless relay networks with phase fading if the relays are in a region near the source terminal, and if information is available only locally. The capacity results further generalize to Rayleigh fading, single-bounce fading, quasistatic fading problems, cases where partial channel knowledge is available at the transmitters, and cases where local user cooperation is permitted. The multisource networks considered are the multiaccess and broadcast relay channels.
    Communications, 2004 International Zurich Seminar on; 02/2004
  • M. Gastpar, G. Kramer, P. Gupta
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    ABSTRACT: Two coding strategies are developed for a multiple-relay channel having one source terminal and one destination terminal. The first strategy mimics multiple-antenna transmission, while the second strategy mimics multiple-antenna reception. Both approaches are based on the concept of "antenna-pooling" and extend prior art for the single-relay channel. The strategies achieve capacity when the terminals form two closely-spaced clusters.
    Information Theory, 2002. Proceedings. 2002 IEEE International Symposium on; 02/2002

Publication Stats

2k Citations
2.62 Total Impact Points

Institutions

  • 2006
    • University of California, Berkeley
      • Department of Electrical Engineering and Computer Sciences
      Berkeley, MO, United States
  • 2002
    • École Polytechnique Fédérale de Lausanne
      Lausanne, Vaud, Switzerland