| 1. |
- 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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| 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. |
- Viberg, Mats, 1961, et al.
(författare)
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Maximum Likelihood Array Processing in Spatially Correlated Noise Fields Using Parameterized Signals
- 1997
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1941-0476 .- 1053-587X. ; 45, s. 996-1004
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the problem of estimating signal parameters using an array of sensors. This problem is of interest in a variety of applications, such as radar and sonar source localization. A vast number of estimation techniques have been proposed in the literature during the past two decades. Most of these can deliver consistent estimates only if the covariance matrix of the background noise is known. In many applications, the aforementioned assumption is unrealistic. Recently, a number of contributions have addressed the problem of signal parameter estimation in unknown noise environments based on various assumptions on the noise. Herein, a different approach is taken. We assume instead that the signals are partially known. The received signals are modeled as linear combinations of certain known basis functions. The exact maximum likelihood (ML) estimator for the problem at hand is derived, as well as a computationally more attractive approximation. The Cramer Rao lower bound (CRB) on the estimation error variance is also derived and found to coincide with the CRB, assuming an arbitrary deterministic model and known noise covariance.
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| 4. |
- You, Lei, et al.
(författare)
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Learning-Assisted Optimization for Energy-Efficient Scheduling in Deadline-Aware NOMA Systems
- 2019
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Ingår i: IEEE Transactions on Green Communications and Networking. - : Institute of Electrical and Electronics Engineers (IEEE). - 2473-2400. ; 3:3, s. 615-627
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study a class of minimum-energy scheduling problems in non-orthogonal multiple access (NOMA) systems. NOMA is adopted to enable efficient channel utilization and interference mitigation, such that base stations can consume minimal energy to empty their queued data in presence of transmission deadlines, and each user can obtain all the requested data timely. Due to the high computational complexity in resource scheduling and the stringent execution-time constraints in practical systems, providing a time-efficient and high-quality solution to 5G real-time systems is challenging. The conventional iterative optimization approaches may exhibit their limitations in supporting online optimization. We herein explore a viable alternative and develop a learning-assisted optimization framework to improve the computational efficiency while retaining competitive energy-saving performance. The idea is to use deep-learning-based predictions to accelerate the optimization process in conventional optimization methods for tackling the NOMA resource scheduling problems. In numerical studies, the proposed optimization framework demonstrates high computational efficiency. Its computational time is insensitive to the input size. The framework is able to provide optimal solutions as long as the learning-based predictions satisfy a derived optimality condition. For the general cases with imperfect predictions, the algorithmic solution is error-tolerable and performance scaleable, leading the energy-saving performance close to the global optimum.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- von Wrycza, Peter, 1981-, et al.
(författare)
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Spectrum Allocation from a Game Theoretic Perspective : Properties of Nash Equilibria
- 2008
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Ingår i: 2008 42ND ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, VOLS 1-4. - New York : IEEE. - 9781424429400 ; , s. 1542-1546
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Konferensbidrag (refereegranskat)abstract
- We consider a scenario consisting of two transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum. Applying a game theoretic framework, each pair is regarded as a player whose payoff function is the individual link rate and power is allocated using the iterative water-filling algorithm. We study the dynamics of such a game and find properties of the resulting Nash equilibria. For high interference scenarios, operating points admitting complete, partial or no overlap are possible and we present conditions under which the different Nash equilibria are achievable. Based on this analysis, a modified water-filling algorithm is designed to increase the sum-rate of the communication links. Its performance is compared to that of the iterative water-filling algorithm by numerical simulations. Although we restrict the analysis to a two player game, analogous concepts can be used to design decentralized algorithms for scenarios with more players.
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| 8. |
- Devarakota, Pandu R, et al.
(författare)
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Confidence estimation in classification decision : A method for detecting unseen patterns
- 2007
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Ingår i: Proceedings of the Sixth International Conference on Advances in Pattern Recognition. - SINGAPORE : WORLD SCIENTIFIC PUBL CO PTE LTD. ; , s. 290-294
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The classification task for a real world application shall include a confidence estimation to handle unseen patterns i.e., patterns which were not considered during the learning stage of a classifier. This is important especially for safety critical applications where the goal is to assign these situations as "unknown" before they can lead to a false classification. Several methods were proposed in the past which were based on choosing a threshold on the estimated class membership probability. In this paper we extend the use of Gaussian mixture model (GMM)to estimate the uncertainty of the estimated class membership probability in terms of confidence interval around the estimated class membership probability. This uncertainty measure takes into account the number of training patterns available in the local neighborhood of a test pattern. Accordingly, the lower bound of the confidence interval or the number of training samples around a test pattern, can be used to detect the unseen patterns. Experimental results on a real-world application are discussed.
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| 9. |
- Garcia, Frederic, et al.
(författare)
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A new 1-D colour model and its application to image filtering
- 2011
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Ingår i: ISPA 2011 - 7th International Symposium on Image and Signal Processing and Analysis. ; , s. 134-138
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Konferensbidrag (refereegranskat)abstract
- This paper introduces a new 1-D model to encodecoloured images for an efficient subsequent processing. Thisrepresentation is equivalent to, but more compact than, the 3-DHCL conical representation. It consists in gathering all the hue,chroma and luminance information in one component, namely,the cumulative spiral angle, where the spirals in question aredefined as a sampling of the solid HCL cone. We use theproposed model for joint bilateral upsampling of low-resolutiondepth maps. The results show that, in addition to preserving theperceptual properties of the HCL colour representation, usingthe proposed model leads to a solution that is more accuratethan when using grayscale images.
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