| 11. |
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| 12. |
- 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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| 13. |
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| 14. |
- Coldrey, Mikael, 1972, et al.
(författare)
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Higher order MIMO outdoor-to-indoor measurements using repeaters
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425198
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present results from a outdoor- to-indoor MIMO measurement campaign where we study the effect of repeaters on singular values, spatial richness, capacity, and delay spread distributions. We present results from different repeater scenarios such as, e.g. different outdoor/indoor repeater deployments with single/dual polarized antennas. The measurements show that repeaters significantly enhance the received SNR while they increase the delay spread and decrease the spatial richness of the MIMO channel. However, the main conclusion is that a significant increase in channel capacity is attained when deploying repeaters mostly thanks to their ability to provide spatial multiplexing over the high-quality eigenmodes they may provide. The number of such eigenmodes is limited by the number of repeaters, deployment, and their antennas. © 2010 IEEE.
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| 15. |
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| 16. |
- 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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| 17. |
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| 18. |
- 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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| 19. |
- 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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| 20. |
- Ding, Liqin, 1988, et al.
(författare)
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Shannon Capacity of LOS MIMO Channels with Uniform Circular Arrays
- 2022
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Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. ; 2022-September
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Konferensbidrag (refereegranskat)abstract
- The Shannon capacity for the line-of-sight (LOS) multiple-input multiple-output (MIMO) channel between two perfectly aligned uniform circular arrays (UCAs) is derived from the first principles in a tutorial fashion. It is well known that harmonically related complex exponentials (also known in the literature as orbital angular momentum (OAM) modes) are eigenmodes for the spatially continuous channel. We show that the corresponding eigenvalues can be expressed as Bessel functions of the first kind. We also show that the spatially discrete channel between two UCAs with the same finite number of Hertzian dipole antennas on both sides has eigenmodes that are spatially sampled continuous OAM modes, and discrete eigenvalues that are aliased versions of the continuous eigenvalues. Through numerical solution of Maxwell's equations, we verify that the discrete eigenvalues for UCAs with realistic dipole antennas are the same as with the Hertzian dipoles for the studied geometries (1~km hop distance, UCA radius 1 and 2 m, carrier frequency 70 GHz) as long as antenna spacing is not very dense.
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