| 1. |
- Bergman, Svante, 1979-, et al.
(författare)
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Adaptive spatial bit loading using imperfect channel state information
- 2005
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Ingår i: Proceedings of International Workshop on Optical and Electronic Device Technology for Access Networks, Aalborg, Denmark.
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Konferensbidrag (refereegranskat)abstract
- Using information about the channel at the transmitter can improve the performance of multi-input multi-output (MIMO) communication systems. When perfect channel state information (CSI) is available, data can be multiplexed and optimized over independent spatial channels. When the available channel information is imperfect or partial, crosstalk between the spatial channels is inevitable complicating the design since the performance of the spatial streams has to be considered jointly. In this paper an efficient algorithm for bit and power loading on the spatial channels is presented. Focus is on maximizing the data rate at fixed bit error rate and reasonable computational complexity.
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| 2. |
- Bergman, Svante, 1979-, et al.
(författare)
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Design of robust linear dispersion codes based on imperfect
- 2006
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Ingår i: Proceedings European Signal Processing Conference.
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the design of codes for multiple-input multiple-output communication systems. The transmission scheme utilizes imperfect channel state information (CSI) in the design, assuming that maximum-likelihood detection is employed at the receiver. It is argued that channel diagonalizing codes are not robust to imperfections in the CSI. A robust non-diagonalizing code with good minimum distance separation between received codewords is proposed. The design is very suitable for systems operating at high data rates since the complexity scales nicely with the number of antennas. Numerical results show that the proposed code outperforms a state-of-the-art diagonalizing precoder.
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| 3. |
- Bergman, Svante, 1979-, et al.
(författare)
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Joint Bit Allocation and Precoding for MIMO Systems With Decision Feedback Detection
- 2009
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Ingår i: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476. ; 57:11, s. 4509-4521
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system employing decision feedback (DF) detection at the receiver. Both the transmitter as well as the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, a diagonal transmission (i.e., orthogonalization of the channel matrix) is optimal for some criteria. Surprisingly, it was shown five years ago that for the family of Schur-convex functions an additional rotation of the symbols is necessary. However, if the bit loading is optimized jointly with the linear transceiver, then this rotation is unnecessary. Similarly, for DF MIMO optimized transceivers a rotation of the symbols is sometimes needed. The main result of this paper shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, the rotation of the symbols becomes unnecessary, and because of this, also the DF part of the receiver is not required. The proof is based on a relaxation of the available bit rates on the individual substreams to the set of positive real numbers. In practice, the signal constellations are discrete and the optimal relaxed bit loading has to be rounded. It is shown that the loss due to rounding is small, and an upper bound on the maximum loss is derived. Numerical results are presented that confirm the theoretical results and demonstrate that orthogonal transmission and the truly optimal DF design perform almost equally well.
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| 4. |
- Bergman, Svante, 1979-, et al.
(författare)
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Lattice based linear precoding for MIMO block codes
- 2007
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Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. - 1424407281 - 1424407273 ; , s. 329-332
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Konferensbidrag (refereegranskat)abstract
- Herein, the design of linear dispersion codes for block based multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice with large coding gain. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate that there is a potential gain of several dB by using the method compared to channel inversion with adaptive bit loading.
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| 5. |
- Bergman, Svante, 1979-, et al.
(författare)
-
Lattice-based linear precoding for MIMO channels with transmitter CSI
- 2008
-
Ingår i: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476. ; 56:7, s. 2902-2914
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the design of linear dispersion codes for multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice generator matrix with large minimum distance separation. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere-packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate significant gains by using the proposed method compared to channel diagonalization with adaptive bit loading.
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| 6. |
- Bergman, Svante, 1979-, et al.
(författare)
-
Optimal Bit Loading for MIMO Systems with Decision Feedback Detection
- 2009
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Ingår i: 2009 IEEE Vehicular Technology Conference. - : IEEE. - 9781424425167 ; , s. 831-835
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Konferensbidrag (refereegranskat)abstract
- This paper considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system employing decision feedback (DF) detection at the receiver. Both the transmitter as well as the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, a diagonal transmission (i.e., orthogonalization of the matrix channel) is optimal for some criteria. Surprisingly, it was shown five years ago that for the family of Schur-convex functions an additional rotation of the symbols is necessary. However, if the bit loading is optimized jointly with the linear transceiver, then the rotation is unnecessary. Similarly, for DF MIMO transceivers, a rotation of the symbols is sometimes needed. The main result of this paper shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, the rotation of the symbols becomes unnecessary and, consequently, also the DF part of the receiver is not required.
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| 7. |
- Bergman, Svante, 1979-, et al.
(författare)
-
Spatial multiplexing over Rician fading channels : Linear precoding transmission strategies
- 2005
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Ingår i: Nordic Conference on Radio Science and Communications (RVK).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Using information about the channel at the transmittercan improve the performance of multi-input multi-output(MIMO) communication systems. When perfect channelstate information (CSI) is available, data can be multiplexed and optimized over independent spatial channels.However, when the available channel information is imperfect or partial, crosstalk between the spatial channels isinevitable complicating the design of the transmitted data.This paper extends our earlier work on practical bit andpower loading algorithmsthat enable the use of partial CSIfor spatial multiplexing, to the case of correlated Ricianfading CSI models. Furthermore, the bit and power loading algorithm is updated for improved BER performanceas well as lower computational complexity.
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| 8. |
- Jaldén, Niklas, 1978-, et al.
(författare)
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Cross layer implementation of a multi-user MIMO test-bed
- 2010
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Konferensbidrag (refereegranskat)abstract
- This paper describes an implementation of a realtime multi-user multiple-input multiple-output (MU-MIMO) communication system, with cross-layer channel-aware scheduling. The system is implemented using software reconfigurable nodes that may be configured as either user terminals, or as base stations, communicating in the GSM 1800 uplink band. Three different commonly used scheduling algorithms (based on channel state information fed back by the receiver nodes) are studied and compared experimentally for three different signal to noise ratios in an indoor non line of sight environment. It is shown that channel-aware scheduling increases not only the system throughput, but also the fairness. Further, using the possibility of changing antenna polarization through software controlled switches, the multiuser gains may be increased even further, both in total throughput as well as fairness.
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| 9. |
- Järmyr, Simon, 1982-, et al.
(författare)
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Long-term adaptive precoding for decision feedback equalization
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - : IEEE. - 9781424414833 ; , s. 2897-2900
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Konferensbidrag (refereegranskat)abstract
- We consider the communication of digital signals over a multiple-input multiple-output wireless channel, using a linear precoder at the transmitter and a non-linear decision feedback equalizer at the receiver. This receiver structure can exploit the signal constellation properties by using successive quantization and interference cancellation. Recently, optimal precoder designs have been found for a wide range of performance measures assuming that perfect channel-state information (CSI) is available. Herein, we propose a design taking CSI uncertainty into account by utilizing the first and second order statistics of the channel. The resulting precoder exhibits improved performance compared to similar methods based on long-term statistics.
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| 10. |
- Martin, Cristoff, et al.
(författare)
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Spatial loading based on channel covariance feedback and channel estimates
- 2004
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Ingår i: Proceedings European Signal Processing Conference.
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Konferensbidrag (refereegranskat)abstract
- Techniques for communication over flat multi-input, multi-output (MIMO) channels are well established when either perfect channel state information or no channel state information is available at the transmitter. However, communication over channels where the transmitter has access to partial or imperfect information has received less attention. If explored, such information could improve system performance and reduce the demand on feedback channels or the quality of channel estimates. In this paper, a simple design scheme is introduced, that approximately maximizes the data rates of MIMO communication systems where the transmiter have access to partial channel state information in the form of covariance feedback or erroneous channel estimates. The presented algorithm is computationally attractive and gains compared with systems not exploring this information are demonstrated.
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