| 1. |
- 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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| 2. |
- Brännmark, Lars-Johan, et al.
(författare)
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Robust loudspeaker equalization based on position-independent excess phase modeling
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING, VOLS 1-12. - 9781424414833 ; , s. 385-388
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Konferensbidrag (refereegranskat)abstract
- A well known problem in loudspeaker equalization is that mixed phase design of the inverse filter causes residual "pre-ringings" in the equalized system, due to the spatial variability of loudspeakerroom transfer functions. A common strategy for robust and perceptually acceptable equalization is therefore to use minimum phase filters only. In this paper, a method for cautious mixed phase equalization is proposed. By analysis of a set of room transfer functions, it is concluded that some non-minimum phase zeros are insensitive to receiver position, and can therefore be robustly inverted. The method improves upon a minimum phase equalization by extending the minimum phase model with a robustly invertible all pass link. Validation measurements show that the time-domain aspect of equalization is improved throughout the spatial region of interest, while preringings are kept at a very low and prespecified level.
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| 3. |
- Eilert, Johan, 1980-, et al.
(författare)
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Implementation of a Programmable Linear MMSE Detector for MIMO-OFDM
- 2008
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Ingår i: IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP,2008. - : IEEE. - 9781424414833 ; , s. 5396-5399
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Konferensbidrag (refereegranskat)abstract
- This paper presents a linear minimum mean square error (LMMSE) symbol detector for MIMO-OFDM enabled mobile terminals. The detector is implemented using a programmable baseband processor aimed for software-defined radio (SDR). Owing to the dynamic range supplied by the floating-point SIMD datapath, special algorithms can be adopted to reduce the computational latency of detection. The programmable solution not only supports different transmit/receive antenna configurations, but also allows hardware multiplexing to obtain silicon and power efficiency. Compared to several existing fixed-functional solutions, the one proposed in this paper is smaller, more flexible and faster.
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| 4. |
- Gudmundson, Erik, et al.
(författare)
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On Denoising via Penalized Least-Squares Rules
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - Piscataway, NJ : IEEE. - 9781424414833 ; , s. 3705-3708
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Konferensbidrag (refereegranskat)abstract
- Penalized least-squares (PELS) rules for signal denoising can be obtained via the use of various information criteria (AIC, BIC, etc.) or various minmax LS approaches. Let S denote the set of "significant" parameters in the denoising problem (which is to be determined), let n(S) be the dimension of S, and let n(S)rho denote the penalty term of a PELS criterion. We show that, depending on the expression for rho, the following cases can occur: type-1) If rho does not depend on S, then denoising via the corresponding PELS rule is equivalent to simple thresholding; and type-2) If rho depends on n(S) only, then the equivalence to thresholding no longer holds but the PELS rule can still be implemented quite efficiently. We also show that the use of BIC leads to an existing PELS rule of type-1 when the noise variance in the denoising problem is known, and to a novel PELS rule of type-2 when the noise variance is unknown.
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| 5. |
- Gudmundson, Erik, et al.
(författare)
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On the Reconstruction of Gapped Sinusoidal Data
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - Piscataway, NJ : IEEE. - 9781424414833 ; , s. 3513-3516
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Konferensbidrag (refereegranskat)abstract
- The problem of estimating a spectral representation of damped sinusoidal signals from a gapped data set is of considerable interest in several applications. In this paper, we propose a filterbank approach to provide such an estimate, by first reconstructing the missing data samples assuming that the spectral content of the missing data is similar to that of the available samples, and then forming a spectral representation of the reconstruced data set as a function of frequency and damping. Numerical examples illustrate the benefits of the proposed estimator as compared to currently available methods.
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| 6. |
- Hendeby, Gustaf, 1978-, et al.
(författare)
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On Nonlinear Transformations of Stochastic Variables and its Application to Nonlinear Filtering
- 2008
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Ingår i: Proceedings of the '08 IEEE International Conference on Acoustics, Speech and Signal Processing. - 9781424414840 - 9781424414833 ; , s. 3617-3620
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Konferensbidrag (refereegranskat)abstract
- A class of nonlinear transformation-based filters (NLTF) for state estimation is proposed. The nonlinear transformations that can be used include first (TT1) and second (TT2) order Taylor expansions, the unscented transformation (UT), and the Monte Carlo transformation (MCT) approximation. The unscented Kalman filter (UKF) is by construction a special case, but also nonstandard implementations of the Kalman filter (KF) and the extended Kalman filter (EKF) are included, where there are no explicit Riccati equations. The theoretical properties of these mappings are important for the performance of the NLTF. TT 2 does by definition take care of the bias and covariance of the second order term that is neglected in the TT 1 based EKF. The UT computes this bias term accurately, but the covariance is correct only for scalar state vectors. This result is demonstrated with a simple example and a general theorem, which explicitly shows the difference between TT 1, TT 2, UT, and MCT.
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| 7. |
- Huang, Jinliang, et al.
(författare)
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Discrete rate spectral efficiency for adaptive MIMO systems
- 2008
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 9781424414833 ; , s. 3089-3092
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Konferensbidrag (refereegranskat)abstract
- Adaptive modulation scheme has been widely used in multiple-input multiple-output (MIMO) systems to enhance spectral efficiency while maintaining bit-error rate (BER) under a target level. We consider two MIMO schemes, orthogonal space-time block codes (OSTBC) and spatial multiplexing with zero-forcing receiver (SM-ZF), that apply adaptive modulation and derive closed-form expressions of the average spectral efficiency. Based on the closed-form expression of the average spectral efficiency, a low complexity switching method is utilized to gain significant improvement in spectral efficiency over an adaptive modulation system using a single MIMO scheme.
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| 8. |
- Jorswieck, Eduard A., 1975-, et al.
(författare)
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The MISO interference channel from a game-theoretic perspective : A combination of selfishness and altruism achieves Pareto optimality
- 2008
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Ingår i: 2008 IEEE International Conference On Acoustics, Speech And Signal Processing. - : IEEE. - 9781424414833 ; , s. 5364-5367
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Konferensbidrag (refereegranskat)abstract
- We study the MISO interference channel from a game-theoretic perspective. Recently, it was shown that the rates at the non-cooperative Nash equilibrium (NE) strategy are poor especially in the medium and high SNR regimes. A reasonable outcome of the cooperative approach, close to the Pareto boundary of the achievable rate region, was shown to be the zero-forcing (ZF) strategy. In this work, we prove that any point on the Pareto boundary can be achieved by a certain linear combination of the NE and ZF strategies. A scalar weight per user chooses between "selfish" (NE) and altruistic (ZF) behavior. Thereby, the difficult beamforming optimization is reduced to a simple weight optimization. Different optimal operating points, e.g. maximum weighted sum-rate, the Nash-bargaining solution, or the Egalitarian solution, can be obtained by a computationally efficient iterative algorithm. The results are characterized by instantaneous achievable rate regions and the corresponding operating points.
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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. |
- Karlsson, Johannes, et al.
(författare)
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Joint source-channel mappings for the relay channel
- 2008
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Ingår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - 9781424414833 ; , s. 2953-2956
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Konferensbidrag (refereegranskat)abstract
- The three-node relay channel with a Gaussian source is studied for transmission subject to a low-delay constraint. A joint source-channel coding design algorithm is proposed and numerically evaluated. The designed system is compared to a reference system, based on modular source and channel coding, and the distortion-rate function for the Gaussian source, using known achievable rates on the relay channel. The structure of the source encoder and the relay mapping is visualized and discussed in order to gain understanding of how the system works. The relay mapping gets a structure that resembles a Wyner-Ziv code.
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