| 1. |
- Zhang, Xi, et al.
(författare)
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Power Allocation and Bit Loading for Spatial Multiplexing in MIMO Systems
- 2003
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - NEW YORK : IEEE. ; , s. 53-56, s. 53-56
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Konferensbidrag (refereegranskat)abstract
- The power assignment problem is important for Multiple-Input-Multiple-Output (MIMO) systems to achieve high capacity. Although this problem is solved by well-known water filling algorithms, this does not provide an optimal solution if the system is constrained to a fixed raw bit error rate threshold and to discrete modulation orders. In this work an approximate approach, called QoS based WF, is proposed to solve the power assignment problem with such constrains. It is shown to outperform quantization of the conventional water filling solution and a well known bit loading algorithm (Chow’s algorithm) used in the Digital Subscriber Lines (DSL).
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| 2. |
- Martin, Cristoff, et al.
(författare)
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Approximate Transmit Covariance Optimization of MIMO Systems with Covariance Feedback
- 2003
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Ingår i: Proceedings Asilomar Conference on Signals, Systems & Computers. - : IEEE. ; , s. 1047-1051
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Konferensbidrag (refereegranskat)abstract
- The data rate of a multiple input, multiple output (MIMO) communication link can be improved if knowledge about the channel statistics is exploited at the transmitter. However, many realistic system scenarios require computationally prohibitive Monte Carlo methods in order to optimize the transmit covariance for maximization of the exact mutual information. This paper instead considers an approximative approach to maximize the performance of a communication link where covariance feedback is available at the transmitter. The algorithm presented is based on an asymptotic expression of the mutual information that allows for correlation at both the transmit and the receive side of the system. From simulations we demonstrate significant gain over beamforming and pure divversity schemes in many realistic system scenarios.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Bengtsson, Mats, 1967-, et al.
(författare)
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Recent Advances on MIMO Processing in the SATURN Project
- 2002
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Ingår i: Proc. IST Mobile Communications Summit.
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Konferensbidrag (refereegranskat)abstract
- We highlight some recent results on the theory and algorithmsfor MIMO systems, obtained at the Royal Instituteof Technology (KTH) within the SATURN project.The paper includes a a new approximate expression forthe ergodic channel capacity of a MIMO system with correlatedfading, algorithms for MIMO beamforming underEIRP (equivalent isotropic radiated power) constraintsand a low-complexity algorithm for MIMO channel estimationin OFDM systems. Also, we show how transmitand beamformers can be determined in a decentralizedfashion without explicitly estimating the channel response.
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| 6. |
- Jöngren, George, et al.
(författare)
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Utilizing Partial Channel Information in the Design of Space-Time Block Codes
- 2002
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Ingår i: Proceedings of the 5th International Symposium on Wireless Personal Multimedia Communications (WPMC ’2002). - NEW YORK : IEEE. ; , s. 681-685
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Konferensbidrag (refereegranskat)abstract
- The assumption of no channel knowledge at the transmitter is inherent in the design of classical space-time codes for wireless communication. This work, on the other hand, assumes that non-perfect quantized channel information obtained from a feedback link is available at the transmitter and investigates how such channel knowledge can be incorporated into the design of space-time block codes. Efficient codes are found by means of a gradient search over a continuous alphabet. Simulation results for a Rayleigh fading scenario a system using two transmit antennas and one receive antenna show that significant gains are possible.
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| 7. |
- Klang, Göran, et al.
(författare)
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Space-time interference rejection cancellation in transmit diversity systems
- 2002
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Ingår i: International Symposium on Wireless Personal Multimedia Communications. - NEW YORK : IEEE. ; , s. 706-710
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Konferensbidrag (refereegranskat)abstract
- We consider the use of space diversity methods in conjunction withinterference rejection combining (IRC) to mitigate the impact of interferenceand noise for interference limited scenarios. The use of transmit diversityschemes in a system generally limits the interference rejection capabilities of IRC techniques. We introduce a novel space-time IRC (STIRC) scheme that exploits the spatio-temporal correlation induced by cochannel users employingtransmit diversity in the form of space-time block codes (STBC). Thus, thesystem can draw upon the benefits of interference rejection methods althoughtransmit diversity is being employed. Simulation examples are presented to illustrate the discussion and to highlight the importance of taking both the spatial and temporal structure of the interference into account.
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| 8. |
- Martin, Cristoff, et al.
(författare)
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Analytic Approximations of Eigenvalue Moments and Mean Channel Capacity for MIMO Channels
- 2002
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Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 2389-2392
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Konferensbidrag (refereegranskat)abstract
- Approximate second order moments of the squared singular values of the channel matrix of a multiple input multiple output (MIMO) system are derived. Correlation at both the receiver and the transmitter antenna arrays is allowed. The approximation converges to the true moments as either the number of transmit or receive antennas increases. Simulations indicate that the derived moments may provide a good approximation of the true moments even for realistic array sizes. As an application, an expression for the mean channel capacity is derived. The expression is simple enough to provide insight while offering promising performance when compared with simulated channel capacities.
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| 9. |
- Zhang, Xi, et al.
(författare)
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Joint Space-Frequency Optimization in Multi User MIMO System
- 2003
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Ingår i: IEEE International Symposium on Signal Processing and Information Technology. - NEW YORK : IEEE. ; , s. 170-173
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Konferensbidrag (refereegranskat)abstract
- Herein, joint space-time multiplexing in a multi carrier multiple input multiple output (MIMO) system is considered. Previous results concerning the spatial multiplexing optimization are used to address the joint problem of carrier assignment and choice of beamforming weights in a multi user MIMO system. For practical reasons, the joint optimization is divided into two parts: subcarrier assignment based on beamformer characteristics to adjust the carrier load, followed by beamforming optimization with subcarrier reassignment. The goal is to minimize total downlink transmit power while keeping the fixed user data rates. The proposed multiplexing scheme is evaluated on a number of numerical examples.
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| 10. |
- Bengtsson, Mats, 1967-, et al.
(författare)
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A generalization of weighted subspace fitting to full-rank models
- 2001
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 49:5, s. 1002-1012
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Tidskriftsartikel (refereegranskat)abstract
- The idea of subspace fitting provides a popular framework for different applications of parameter estimation and system identification. Previously, some algorithms have been suggested based on similar ideas, for a sensor array processing problem where the underlying data model is not low rank. We show that two of these algorithms (DSPE and DISPARE) fail to give consistent estimates and introduce a general class of subspace fitting-like algorithms for consistent estimation of parameters from a possibly full-rank data model. The asymptotic performance is analyzed, and an optimally weighted algorithm is derived. The result gives a lower bound on the estimation performance for any estimator based on a low-rank approximation of the linear space spanned by the sample data. We show that in general, for full-rank data models, no subspace-based method can reach the Cramer-Rao lower bound (CRB)
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