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- Coldrey, Mikael, 1972
(författare)
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Estimation and Performance Analysis of Wireless Multiple Antenna Communication Channels
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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 theproblem of parameter estimation of distributed sources. Due to, e.g., localscattering around the transmitter, the source (as seen from the receiver)appears spatially distributed. A characterization of the spatial channel, inparticular mean direction of arrival and spatial spread, is of interest for optimizationand performance prediction of future communication systems. Nonparametricbeamforming-based estimators are derived and analyzed for thelocalization of distributed sources, and it is found that they provide goodestimation performance. Parametric generalized beamformers are also presentedand analyzed. It is found that they also yield competitive performancecompared to existing algorithms.The second part of the thesis deals with Multiple-Input Multiple-Output(MIMO) and Single-Input Single-Output (SISO) channel estimation. A simpleand straightforward way of estimating the unknown channel is to transmitknown training/pilot sequences. In the recent past, a number of publicationshave suggested Superimposed Pilots (SIP) for channel estimation in communicationsystems. However, the performance gain achieved by SIP comparedto conventional (time-multiplexed) training is still questionable. To evaluatethe 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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| 2. |
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| 3. |
- Coldrey, Mikael, 1972, et al.
(författare)
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Training-Based MIMO Systems: Part I - Performance Comparison
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A simple and straightforward way of estimating the unknown communication channel is to transmit known training/pilot sequences. Conventionally, these non-information carrying pilots are time-multiplexed with the data and, therefore, consume valuable bandwidth. Hence in the recent past, a number of publications have instead suggested superimposing pilots to the data to perform channel estimation in, e.g., MIMO systems. However, the performance gain achieved by using superimposed pilots (SIP) compared to the more conventional time-multiplexedpilot scheme is not well studied and motivates further research. In this paper we attempt to make a fair comparison between the two schemes, their respective maximum information rate is computed and compared using lower bounds. The theory is applied to a block-wise flat-fading MIMO channel and it is found that in certain scenarios (such as many receive antennas and/or short channel coherence times), it is beneficial to use SIP. Finally, an abstract projection-based viewpoint of the training-based models using vector spaces is given.
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| 4. |
- Coldrey, Mikael, 1972, et al.
(författare)
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Training-Based MIMO Systems: Part II - Improvements using a Variable Coding Rate Scheme
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper the channel throughput performance is addressed for MIMO systems that employ transmission of known training sequences for channel estimation. In the companion paper, it was found that systems based on superimposed pilots (SIP) suffer from poor channel estimates, since there is interfering data power present during channel estimation. By allowing channel re-estimation, this data can be utilized as additional training power, which significantly improves the channel estimates. As the channel estimates improve, a higher coding rate can successfully be applied. These variable coding rate schemes can also be applied to conventional time-multiplexed pilot schemes. However, our numerical examples show a larger performance increase in channel throughput if applied to a SIP scheme.
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| 5. |
- Lioliou, Panagiota, 1982, et al.
(författare)
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Performance Analysis of Relay Channel Estimation
- 2009
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Ingår i: 43rd Asilomar Conference on Signals, Systems and Computers; Pacific Grove, CA; United States; 1 November 2009 through 4 November 2009. - 1058-6393. - 9781424458271 ; , s. 1533-1537
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Konferensbidrag (refereegranskat)abstract
- Amplify-and-Forward (AF) relays can be used to enhance the channel in Multiple-Input-Multiple-Output (MIMO) wireless communication systems. However, optimizing the channel requires Channel State Information (CSI). This paper is concerned with the performance of relay channel estimation. A Least Squares (LS) based algorithm for the estimation of all relevant channel parameters was recently proposed by the authors. It is based on creating different compound channels by varying the gain factors at the relays. From this, the individual links from source to relay and from relay to destination, are revealed using LS. To investigate the algorithm performance, the Cramér-Rao lower Bound (CRB) is computed and compared with the asymptotic covariance of the proposed estimator. Furthermore, we propose and analyze an improved algorithm that is efficient for high Signal-to-Noise Ratio (SNR). Computer simulations demonstrate the performance of the algorithm. The results indicate that the asymptotic expressions are in good agreement with the simulations.
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| 6. |
- Persson, Patrik, et al.
(författare)
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Design and evaluation of a 2 x 2 MIMO repeater
- 2009
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Ingår i: European Conference on Antennas and Propagation, EuCAP 2009, Proceedings. - 9783000245732 ; , s. 1509-1512
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Konferensbidrag (refereegranskat)abstract
- In this paper the design and measurement-based evaluation of an amplify-and-forward 2 x 2 MEMO repeater is presented. During the design phase, simulations were made to study different scenarios and repeater parameter settings. The evaluation of the repeater was made using field trials in Kista, Stockholm, Sweden. Three scenarios were considered; coverage, outdoor-to-indoor, and LOS MEMO rank enhancement. The overall results showed good improvement in received signal strength, ranging from only a few dB up to 25 dB depending on the particular measurement scenario. Moreover, the concept of repeater-aided rank enhancement in LOS also showed good results.
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| 7. |
- Wolfgang, Andreas, 1977, et al.
(författare)
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Advanced Repeaters in Cellular Communication Systems
- 2009
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Ingår i: 3rd European Conference on Antennas and Propagation, EuCAP 2009; Berlin; Germany; 23 March 2009 through 27 March 2009. - 9783000245732 ; , s. 1504-1508
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Konferensbidrag (refereegranskat)abstract
- A repeater can be used in a wireless link to improve the Signal-to-Noise Ratio (SNR) at the receiver. However, if the transmitter and the receiver use multiple antennas a repeater may serve additional purposes. In this paper we particularly investigate the effect of repeaters on the singular values of the Multiple-Input Multiple-Output (MIMO) channel matrix. Furthermore the effect of repeaters in a cellular system, the interdependence of antenna array design, and system aspects such as scheduling are highlighted.
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