| 11. |
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| 12. |
- Hyberg, Per, et al.
(författare)
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Array Mapping : Optimal Transformation Matrix Design
- 2002
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 2905-2908
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Konferensbidrag (refereegranskat)abstract
- Mapping of the data output vector from an existing antenna array onto the data vector of an imaginary array of more suitable configuration is well known in array signal processing. By mapping onto an array manifold of lower dimension or uniform structure for example., processing speed can be improved. Conditions for the retaining of DOA error variance under such mapping have been formulated by several authors but the equally important systematic mapping errors, the bias, has been less treated to date. This paper uses a geometrical interpretation of a Taylor expansion of the DOA estimator cost function to derive an alternative design of the mapping matrix that almost completely removes the bias. The key feature of the proposed design is that it takes the orthogonality between the manifold mapping errors and certain gradients of the estimator cost function into account.
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| 13. |
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| 14. |
- Jaldén, Joakim, 1976-, et al.
(författare)
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An Exponential Lower Bound on the Expected Complexity of Sphere Decoding
- 2004
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. ; , s. 393-396
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Konferensbidrag (refereegranskat)abstract
- The sphere decoding algorithm is an efficient algorithm used to solve the maximum likelihood detection problem in several digital communication systems. The sphere decoding algorithm has previously been claimed to have polynomial expected complexity. While it is true that the algorithm has an expected complexity comparable to that of other polynomial time algorithms for problems of moderate size it is a misconception that the expected number of operations asymptotically grow as a polynomial function of the problem size. In order to illustrate this point we derive an exponential lower bound on the expected complexity of the sphere decoder.
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| 15. |
- Jaldén, Joakim, 1976-, et al.
(författare)
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Semidefinite Programming for Detection in Linear Systems – Optimality Conditions and Space-Time Decoding
- 2003
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Ingår i: IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 9-12
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Konferensbidrag (refereegranskat)abstract
- Optimal maximum likelihood detection of finite alphabet symbols in general requires time consuming exhaustive search methods. The computational complexity of such techniques is exponential in the size of the problem and for large problems sub-optimal algorithms are required. In this paper, to find a solution in polynomial time, a semidefinite programming approach is taken to estimate binary symbols in a general linear system. A condition under which the proposed method provides optimal solutions is derived. As an application, the proposed algorithm is used as a decoder for a linear space-time block coding system and the results are illustrated with numerical examples.
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| 16. |
- Jansson, Magnus, et al.
(författare)
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Structured Covariance Matrix Estimation : A Parametric Approach
- 2000
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 3172-3175
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Konferensbidrag (refereegranskat)abstract
- The problem of estimating a positive semi-definite Toeplitz covariance matrix consisting of a low rank matrix plus a scaled identity from noisy data arises in many applications. We propose a computationally attractive (noniterative) covariance matrix estimator with certain optimality properties. For example, under suitable assumptions the proposed estimator achieves the Cramer-Rao lower bound on the covariance matrix parameters. The resulting covariance matrix estimate is also guaranteed to possess all of the structural properties of the true covariance matrix. Previous approaches to this problem have either resulted in computationally unattractive iterative solutions or have provided estimates that only satisfy some of the structural relations
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| 17. |
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| 18. |
- Jöngren, George, et al.
(författare)
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Structured Spatial Interference Rejection Combining
- 2000
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Ingår i: Proceedings European Signal Processing Conference.
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Konferensbidrag (refereegranskat)abstract
- Modern communication systems are often interferencelimited. By modeling the co-channel interference asspatially colored, temporally white Gaussian noise, itis straightforward to incorporate interference rejectionin the metric of a sequence estimator. In general, estimates of both the channels and the spatial color of theco-channel interference and the noise are needed. In thiswork, a structured model for the spatial noise covariancematrix is proposed and maximum likelihood estimates ofthe parameters are derived. The choice of model orderis also addressed. Simulation results show large gains due to the use of these structured estimates compared with the conventional, unstructured, approach.
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| 19. |
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| 20. |
- Klang, Göran, et al.
(författare)
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Interference Rejection in Systems Employing Transmit Diversity
- 2002
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Ingår i: European Signal Processing Conference. - : EUSIPCO. - 2219-5491.
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Tidskriftsartikel (refereegranskat)abstract
- Space diversity methods provide excellent means for increasing the robustness against interference and noise in communication systems. This is well known for systems using multiple receive antennas and it holdsforsystems applying transmit diversity as well. In fact, the use of transmit diversity provide two independent means for reducing the impact of interference. Via the diversity gain and via the code rate, both related to the underlying space-time code. In this paper, we are considering the use of space diversity methods in conjunction with interference rejection combining (IRC) to mitigate the impact of interference and noise for interference limited scenarios. Transmit diversity schemes based on space-time block codes (STBC) are assumed. We elucidate the importance of taking into account the spatio-temporal correlation induced by cochannel users employing transmit diversity. A novel space-time IRC (STIRC) scheme is proposed to handle the problem. The STIRC scheme combines the simplicity of conventional IRC while taking the structure of interfering users into account. Simulation examples demonstrate significant gains compared to the use of conventional IRC.
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