| 1. |
- Mowlér, Marc, et al.
(författare)
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Joint estimation of mutual coupling, element factor, and phase center in antenna arrays
- 2007
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; 2007:1, s. 030684-
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Tidskriftsartikel (refereegranskat)abstract
- A novel method is proposed for estimation of the mutual coupling matrix of an antenna array. The method extends previous work by incorporating an unknown phase center and the element factor (antenna radiation pattern) in the model, and treating them as nuisance parameters during the estimation of coupling. To facilitate this, a parametrization of the element factor based on a truncated Fourier series is proposed. The performance of the proposed estimator is illustrated and compared to other methods using data from simulations and measurements, respectively. The Cramer-Rao bound (CRB) for the estimation problem is derived and used to analyze how the required amount of measurement data increases when introducing additional degrees of freedom in the element factor model. We find that the penalty in SNR is 2.5 dB when introducing a model with two degrees of freedom relative to having zero degrees of freedom. Finally, the tradeoff between the number of degrees of freedom and the accuracy of the estimate is studied. A linear array is treated in more detail and the analysis provides a specific design tradeoff.
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| 2. |
- Mowlér, Marc, et al.
(författare)
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Methods and bounds for antenna array coupling matrix estimation
- 2007
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Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. - 1424407273 - 1424407281 ; , s. 881-884
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Konferensbidrag (refereegranskat)abstract
- A novel method is proposed for estimation of the mutual coupling matrix of an antenna array. The method extends previous work by incorporating an unknown phase center and the element factor (antenna radiation pattern) in the model, and treating these as nuisance parameters during the estimation of coupling. To facilitate this, a parametrization of the element factor based on a truncated Fourier series is proposed. The Cramer-Rao bound (CRB) for the estimation problem is derived and used to analyze how the required amount of measurement data increases when introducing a more and more flexible model for the element factor. Finally, the performance of the proposed estimator is illustrated using data from measurements on an 8-element antenna array.
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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
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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. |
- Björnson, Emil, 1983-, et al.
(författare)
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Beamforming utilizing channel norm feedback in multiuser MIMO systems
- 2007
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Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications. - : IEEE. - 9781424409556 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information.
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| 7. |
- Björnson, Emil, 1983-, et al.
(författare)
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Exploiting long-term statistics in spatially correlated multi-user MIMO systems with quantized channel norm feedback
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - : IEEE. - 9781424414833 ; , s. 3117-3120
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Konferensbidrag (refereegranskat)abstract
- In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization.
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| 8. |
- Björnson, Emil, 1983-, et al.
(författare)
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Exploiting Quantized Channel Norm Feedback Through Conditional Statistics in Arbitrarily Correlated MIMO Systems
- 2009
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Ingår i: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476. ; 57:10, s. 4027-4041
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Tidskriftsartikel (refereegranskat)abstract
- In the design of narrowband multi-antenna systems, a limiting factor is the amount of channel state information (CSI) available at the transmitter. This is especially evident in multi-user systems, where the spatial user separability determines the multi-plexing gain, but it is also important for transmission-rate adaptation in single-user systems. To limit the feedback load, the unknown and multi-dimensional channel needs to be represented by a limited number of bits. When combined with long-term channel statistics, the norm of the channel matrix has been shown to provide substantial CSI that permits efficient user selection, linear precoder design, and rate adaptation. Herein, we consider quantized feedback of the squared Frobenius norm in a Rayleigh fading environment with arbitrary spatial correlation. The conditional channel statistics are characterized and their moments are derived for both identical, distinct, and sets of repeated eigenvalues. These results are applied for minimum mean square error (MMSE) estimation of signal and interference powers in single- and multi-user systems, for the purpose of reliable rate adaptation and resource allocation. The problem of efficient feedback quantization is discussed and an entropy-maximizing framework is developed where the post-user-selection distribution can be taken into account in the design of the quantization levels. The analytic results of this paper are directly applicable in many widely used communication techniques, such as space-time block codes, linear precoding, space division multiple access (SDMA), and scheduling.
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| 9. |
- Björnson, Emil, 1983-, et al.
(författare)
-
Feedback design in multiuser MIMO systems using quantization splitting and hybrid instantaneous/statistical channel information
- 2008
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Ingår i: ICT-MobileSummit 2008 Conference Proceedings. - : IIMC International Information Management Corporation. - 9781905824083
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Konferensbidrag (refereegranskat)abstract
- In the design of next generation multiuser communication systems, multiple antenna transmission is an essential part providing spatial multiplexing gain and allowing efficient use of resources. A major limiting factor in the resource allocation is the amount of channel state information (CSI) available at the transmitter, particularly in multiuser systems where the feedback from each user terminal must be limited. To this effect we propose two independent approaches for an efficient representation of the channel in multiuser MIMO systems. In the first approach, channel quantization is considered where the total number of feedback bits is limited. A resource allocation scheme is proposed where the available rate is split between the scheduling phase, where all users feed back a coarse CSI quantization, and the precoding phase where the selected receivers refine their CSI. The optimum splitting of the available feedback rate provides a large increase in performance and even simple heuristic splitting gives a noticeable advantage. In the second approach, we exploit a combination of instantaneous and statistical channel information. For spatially correlated Rayleigh and Ricean channels, it is shown that the CSI to large extent can be represented by the channel norm when the long-term channel statistics are known. Within a minimum mean square error (MMSE) estimation framework, feedback of a few bits of the quantized channel norm is sufficient to perform efficient resource allocation and achieve performance close to that of full CSI.
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| 10. |
- Grotz, Joel, et al.
(författare)
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Applicability Of Interference Processing To DTH Reception
- 2006
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Ingår i: Ninth International Workshop on Signal Processing for Space Communications, September 2006.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Today fixed satellite broadcast reception has to compete efficiently with other means of broadcast content delivery to end-users. The ease of reception is essential to maintain a high penetration rate under more competitive conditions. The introduction of DVB-S2 increases efficiency and allows for a higher throughput or a reduction of the reception equipment requirements. This means that a robust broadcast reception is conceivable with a reduced direct-to-home (DTH) antenna size. The current interference situation at common geostationary broadcast positions dictates the spatial discrimination requirements of common direct-to-home (DTH) reception antennas. A more robust coding rate or a relaxation of the frequency coordination constraints would obviously relax the requirements on the reception front-end but only at the expense of a reduced aggregate efficiency. The use of known interference processing schemes for DTH reception has been investigated under dual reception path scenarios, see [1]. The present work extends the concept by introducing linear pre-processing (LPP) to combine coherent reception paths. These mechanisms will only be practical if the transmitted broadcast signals are compliant with established standards (ie. DVB-S [5] or DVB-S2 [4]). The maximization of the efficiency is a main objective under given reception environments. We show how multi-user detection techniques can increase efficiency and allow reduced antenna size under realistic conditions.
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