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15 results on '"Kim, Tùng T."'

1. Coded Modulation with Mismatched CSIT over Block-Fading Channels

Author

Kim, Tung T. and Fabregas, Albert Guillen i

Subjects
Computer Science - Information Theory
Abstract

Reliable communication over delay-constrained block-fading channels with discrete inputs and mismatched (imperfect) channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as Gaussian random variables, whose variances decay as a power of the signal-to-noise ratio (SNR). A special focus is placed on the large-SNR decay of the outage probability when power control with long-term power constraints is used. Without explicitly characterizing the corresponding power allocation algorithms, we derive the outage exponent as a function of the system parameters, including the CSIT noise variance exponent and the exponent of the peak power constraint. It is shown that CSIT, even if noisy, is always beneficial and leads to important gains in terms of exponents. It is also shown that when multidimensional rotations or precoders are used at the transmitter, further exponent gains can be attained, but at the expense of larger decoding complexity., Comment: submitted to the IEEE Transactions on Information Theory. To be presented (in part) at the 2009 IEEE International Symposium on Information Theory, Seoul, South Korea, June-July 2009

Published
2009

2. Combining Long-Term and Low-Rate Short-Term Channel State Information over Correlated MIMO Channels

Author

Kim, Tùng T., Bengtsson, Mats, Larsson, Erik G., and Skoglund, Mikael

Subjects
feedback communication, Teknik och teknologier, Engineering and Technology, adaptive systems, fading channels, information rates, MIMO systems
Abstract

A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme. ©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Tùng T. Kim, Mats Bengtsson, Erik G. Larsson and Mikael Skoglund, Combining Long-Term and Low-Rate Short-Term Channel State Information over Correlated MIMO Channels, 2008, IEEE Transactions on Wireless Communications, (7), 7, 2409-2414.http://dx.doi.org/10.1109/TWC.2008.060989

Published
2008

14. Scheduling Power Consumption With Price Uncertainty.

Author

Kim, Tùng T. and Poor, H. Vincent

Abstract

The problem of causally scheduling power consumption to minimize the expected cost at the consumer side is considered. The price of electricity is assumed to be time-varying. The scheduler has access to past and current prices, but only statistical knowledge about future prices, which it uses to make an optimal decision in each time period. The scheduling problem is naturally cast as a Markov decision process. Algorithms to find decision thresholds for both noninterruptible and interruptible loads under a deadline constraint are then developed. Numerical results suggest that incorporating the statistical knowledge into the scheduling policies can result in significant savings, especially for short tasks. It is demonstrated with real price data from Commonwealth Edison that scheduling with mismatched modeling and online parameter estimation can still provide significant economic advantages to consumers. [ABSTRACT FROM PUBLISHER]

Published
2011
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15. On Source Transmission Over MIMO Channels With Limited Feedback.

Author

Kim, Tùng T., Skoglund, Mikael, and Caire, Giuseppe

Subjects
*CODING theory, *DIGITAL signal processing, *DATA transmission systems, *DIGITAL communications, *MIMO systems
Abstract

The problem of source-channel coding over a multiple-antenna (MIMO) channel with quantized channel state information at the transmitter (CSIT) is considered. Upper bounds on the distortion exponents achieved with partial CSIT under a long-term power constraint are developed. It is shown that the distortion exponent with perfect CSIT grows unbounded as the ratio between the channel and source bandwidth increases, while the exponent achieved with any feedback link of fixed, finite resolution is bounded above by a polynomial of the product between the number of transmit and number of receive antennas. The resolution of the feedback link should grow with the bandwidth ratio to make the distortion exponent scale as fast as that in the perfect- CSIT case. We show that in order to achieve the optimal scaling the CSIT feedback resolution must grow logarithmically with the bandwidth ratio for MIMO channels, and faster than linear for the single-input single-output channel. The achievable distortion exponent of some hybrid schemes with heavily quantized feedback is also derived. The results demonstrate that dramatic performance improvement over the case of no CSIT can be achieved by combining simple schemes with a very coarse CSIT feedback. [ABSTRACT FROM AUTHOR]

Published
2009
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