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- Bohlin, Patrik, 1974, et al.
(författare)
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Performance Evaluation of MIMO Communication Systems based Superimposed Pilots
- 2004
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Ingår i: IEEE International Conference on Acoustics, Speech, and Signal Processing; Montreal, Que; Canada; 17 May 2004 through 21 May 2004. - 1520-6149. ; 4, s. IV-425-IV-428-
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Konferensbidrag (refereegranskat)abstract
- 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. In this paper we introduce a framework for modeling a general SIP scheme, of which the conventional scheme is a special case. Utilizing this framework, we derive a lower bound on the channel capacity to compare the performance between the two systems. It is found that in certain scenarios (high SNR, many receive antennas and short coherence times), it is beneficial to also transmit data during the training mode (i.e., use SIP). The main conclusion though, is that for most cases where these kind of schemes would be realistic, i.e. for systems with coherence lengths of more than a few symbols, the general SIP-scheme reduces to the conventional scheme. Hence, rendering the same capacity.
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- Coldrey, Mikael, 1972
(författare)
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Channel Estimation in Wireless Communication Systems Employing Multiple Antennas
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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)
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On the use of beamforming for estimation of spatially distributed signals
- 2003
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Ingår i: IEEE International Conference on Acoustics Speech and Signal Processing, ICASSP '03, Hong Kong, China, APR 06-10. ; 5, s. 369-372
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Konferensbidrag (refereegranskat)abstract
- In wireless communications, spatially distributed signals originate from local scattering around the transmitter. Spatially distributed signals cause conventional high-resolution methods to show degradation in performance, since the underlying data model is of full rank theoretically. In this paper, a relationship between the distribution of the spatial spread and the Power Azimuth Spectrum is derived. Using this relationship, two simple and robust estimators based on the conventional beamformer and Capon's beamformer for estimation of the nominal direction and spatial spread are found. The proposed estimators show very good performance in numerical examples.
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