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Träfflista för sökning "LAR1:cth ;spr:eng;pers:(Coldrey Mikael 1972)"

Sökning: LAR1:cth > Engelska > Coldrey Mikael 1972

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  • Coldrey, Mikael, 1972- (författare)
  • Channel Estimation in Wireless Communication Systems Employing Multiple Antennas
  • 2004
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • Antennas that are able to adaptively direct the transmitted (and received) energy are of great interest in future wireless communication systems. The directivity implies reduced transmit power and interference, and also a potential for increased capacity. The focus of this thesis is on channel estimation in wireless communication systems that employ multiple antennas. The thesis is divided into two parts, whereof the first part addresses the problem of parameter estimation of a distributed source. Due to, e.g., local scattering around the transmitter, the source, as seen from the receiver, appears spatially distributed. A characterization of the spatial channel, in particular mean direction of arrival and spatial spread, is of interest for system optimization and performance prediction. Low-complexity beamforming-based estimators are introduced for the estimation of direction and spatial spread of the distributed source. Despite not exploiting the model, the proposed non-parametric estimators are found to show very competitive performance compared to more complex parametric methods. Also provided is a statistical analysis of their performance. The second part of the thesis deals with Multiple-Input Multiple-Output (MIMO) channel estimation. A simple and straightforward way of estimating the unknown channel is to transmit known training/pilot sequences. In the recent past, a number of publications have suggested Superimposed Pilots (SIP) for channel estimation in MIMO systems. However, the performance gain achieved by SIP compared to conventional (time-multiplexed) training is still questionable. To evaluate the performance of the various training-based schemes, a lower bound on the ergodic channel capacity of a general training-based scheme applied to a block-wise flat-fading MIMO channel is derived and evaluated. It is found that in certain scenarios (many receive antennas and short channel coherence times), it is beneficial to also transmit data during the training mode (i.e. use SIP). The main conclusion though, is that the general SIP-scheme quite often reduces to the conventional time-multiplexed scheme, and, hence, renders the same capacity.
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  • Coldrey, Mikael, 1972- (författare)
  • Estimation and Performance Analysis of Wireless Multiple Antenna Communication Channels
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The focus of this thesis is on channel estimation in wireless communication systems that employ multiple antennas.<p/> The thesis is divided into two parts, whereof the first part addresses the problem of parameter estimation of distributed sources. Due to, e.g., local scattering around the transmitter, the source (as seen from the receiver) appears spatially distributed. A characterization of the spatial channel, in particular mean direction of arrival and spatial spread, is of interest for optimization and performance prediction of future communication systems. Nonparametric beamforming-based estimators are derived and analyzed for the localization of distributed sources, and it is found that they provide good estimation performance. Parametric generalized beamformers are also presented and analyzed. It is found that they also yield competitive performance compared to existing algorithms.<p/> The second part of the thesis deals with Multiple-Input Multiple-Output (MIMO) and Single-Input Single-Output (SISO) channel estimation. A simple and straightforward way of estimating the unknown channel is to transmit known training/pilot sequences. In the recent past, a number of publications have suggested Superimposed Pilots (SIP) for channel estimation in communication systems. However, the performance gain achieved by SIP compared to conventional (time-multiplexed) training is still questionable. To evaluate the performance of the various training-based schemes, a lower bound on the mutual information of a general training-based scheme applied to block-wise fading MIMO and SISO channels is derived and maximized. It is found that in certain scenarios it is beneficial to also transmit data during the training mode (i.e., use SIP). The main conclusion though, is that the general SIP-scheme quite often reduces to the conventional time-multiplexed scheme, and, hence, renders the same performance. The theory is also extended to the case when detected data symbols are used as additional training symbols, which significantly improves the channel estimation performance. An improved channel estimate leads to an improvement in the effective Signa-lto-Noise Ratio (SNR), and, thus, a higher coding rate may successfully be applied. The extended scheme shows a performance close to the fundamental capacity of the noncoherent MIMO channel.
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  • Resultat 1-10 av 23
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