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Search Results: 1 - 10 of 1256 matches for " Gerd Ascheid "
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MIMO APP Receiver Processing with Performance-Determined Complexity
Konstantinos Nikitopoulos,Gerd Ascheid
Mathematics , 2010,
Abstract: Typical receiver processing, targeting always the best achievable bit error rate performance, can result in a waste of resources, especially, when the transmission conditions are such that the best performance is orders of magnitude better than the required. In this work, a processing framework is proposed which allows adjusting the processing requirements to the transmission conditions and the required bit error rate. It applies a-posteriori probability receivers operating over multiple-input multiple-output channels. It is demonstrated that significant complexity savings can be achieved both at the soft, sphere-decoder based detector and the channel decoder with only minor modifications.
Complexity Adjusted Soft-Output Sphere Decoding by Adaptive LLR Clipping
Konstantinos Nikitopoulos,Gerd Ascheid
Mathematics , 2010, DOI: 10.1109/LCOMM.2011.061011.110516
Abstract: A-posteriori probability (APP) receivers operating over multiple-input, multiple-output channels provide enhanced bit error rate (BER) performance at the cost of increased complexity. However, employing full APP processing over favorable transmission environments, where less efficient approaches may already provide the required performance at a reduced complexity, results in unnecessary processing. For slowly varying channel statistics substantial complexity savings can be achieved by simple adaptive schemes. Such schemes track the BER performance and adjust the complexity of the soft output sphere decoder by adaptively setting the related log-likelihood ratio (LLR) clipping value.
Approximate MIMO Iterative Processing with Adjustable Complexity Requirements
Konstantinos Nikitopoulos,Gerd Ascheid
Mathematics , 2011, DOI: 10.1109/TVT.2011.2179324
Abstract: Targeting always the best achievable bit error rate (BER) performance in iterative receivers operating over multiple-input multiple-output (MIMO) channels may result in significant waste of resources, especially when the achievable BER is orders of magnitude better than the target performance (e.g., under good channel conditions and at high signal-to-noise ratio (SNR)). In contrast to the typical iterative schemes, a practical iterative decoding framework that approximates the soft-information exchange is proposed which allows reduced complexity sphere and channel decoding, adjustable to the transmission conditions and the required bit error rate. With the proposed approximate soft information exchange the performance of the exact soft information can still be reached with significant complexity gains.
On the Performance of Quasiorthogonal STBC with Relay Selection and Phase Rotation Techniques for Decode and Forward Cooperative Communications
Nikorn Sutthisangiam,Chaiyod Pirak,Gerd Ascheid
International Journal of Distributed Sensor Networks , 2013, DOI: 10.1155/2013/795050
A Modified Levenberg-Marquardt Method for the Bidirectional Relay Channel
Guido Dartmann,Ehsan Zandi,Gerd Ascheid
Computer Science , 2013,
Abstract: This paper presents an optimization approach for a system consisting of multiple bidirectional links over a two-way amplify-and-forward relay. It is desired to improve the fairness of the system. All user pairs exchange information over one relay station with multiple antennas. Due to the joint transmission to all users, the users are subject to mutual interference. A mitigation of the interference can be achieved by max-min fair precoding optimization where the relay is subject to a sum power constraint. The resulting optimization problem is non-convex. This paper proposes a novel iterative and low complexity approach based on a modified Levenberg-Marquardt method to find near optimal solutions. The presented method finds solutions close to the standard convex-solver based relaxation approach.
Dual-Polarized Ricean MIMO Channels: Modeling and Performance Assessment
Adrian Ispas,Xitao Gong,Christian Schneider,Gerd Ascheid,Reiner Thom?
Mathematics , 2012, DOI: 10.1109/TCOMM.2013.082813.120976
Abstract: In wireless communication systems, dual-polarized (DP) instead of single-polarized (SP) multiple-input multiple-output (MIMO) transmission is used to improve the spectral efficiency under certain conditions on the channel and the signal-to-noise ratio (SNR). In order to identify these conditions, we first propose a novel channel model for DP mobile Ricean MIMO channels for which statistical channel parameters are readily obtained from a moment-based channel decomposition. Second, we derive an approximation of the mutual information (MI), which can be expressed as a function of those statistical channel parameters. Based on this approximation, we characterize the required SNR for a DP MIMO system to outperform an SP MIMO system in terms of the MI. Finally, we apply our results to channel measurements at 2.53 GHz. We find that, using the proposed channel decomposition and the approximation of the MI, we are able to reproduce the (practically relevant) SNR values above which DP MIMO systems outperform SP MIMO systems.
Complexity-Efficient Enumeration Techniques for Soft-Input, Soft-Output Sphere Decoding
Konstantinos Nikitopoulos,Dan Zhang,I-Wei Lai,Gerd Ascheid
Computer Science , 2009, DOI: 10.1109/LCOMM.2010.04.092230
Abstract: In this paper two complexity efficient soft sphere-decoder modifications are proposed for computing the max-log LLR values in iterative MIMO systems, which avoid the costly, typically needed, full enumeration and sorting (FES) procedure during the tree traversal without compromising the max-log performance. It is shown that despite the resulting increase in the number of expanded nodes, they can be more computationally efficient than the typical soft sphere decoders by avoiding the unnecessary complexity of FES.
A Non-Alternating Algorithm for Joint BS-RS Precoding Design in Two-Way Relay Systems
Ehsan Zandi,Guido Dartmann,Gerd Ascheid,Rudolf Mathar
Computer Science , 2013,
Abstract: Cooperative relay systems have become an active area of research during recent years since they help cellular networks to enhance data rate and coverage. In this paper we develop a method to jointly optimize precoding matrices for amplify-and-forward relay station and base station. Our objective is to increase max-min SINR fairness within co-channel users in a cell. The main achievement of this work is avoiding any tedious alternating optimization for joint design of RS/BS precoders, in order to save complexity. Moreover, no convex solver is required in this method. RS precoding is done by transforming the underlying non-convex problem into a system of nonlinear equations which is then solved using Levenberg-Marquardt algorithm. This method for RS precoder design is guaranteed to converge to a local optimum. For the BS precoder a low-complexity iterative method is proposed. The efficiency of the joint optimization method is verified by simulations.
Analysis of the Local Quasi-Stationarity of Measured Dual-Polarized MIMO Channels
Adrian Ispas,Christian Schneider,Gerd Ascheid,Reiner Thom?
Computer Science , 2014, DOI: 10.1109/TVT.2014.2358942
Abstract: It is common practice in wireless communications to assume strict or wide-sense stationarity of the wireless channel in time and frequency. While this approximation has some physical justification, it is only valid inside certain time-frequency regions. This paper presents an elaborate characterization of the non-stationarity of wireless dual-polarized channels in time. The evaluation is based on urban macrocell measurements performed at 2.53 GHz. In order to define local quasi-stationarity (LQS) regions, i.e., regions in which the change of certain channel statistics is deemed insignificant, we resort to the performance degradation of selected algorithms specific to channel estimation and beamforming. Additionally, we compare our results to commonly used measures in the literature. We find that the polarization, the antenna spacing, and the opening angle of the antennas into the propagation channel can strongly influence the non-stationarity of the observed channel. The obtained LQS regions can be of significant size, i.e., several meters, and thus the reuse of channel statistics over large distances is meaningful (in an average sense) for certain algorithms. Furthermore, we conclude that, from a system perspective, a proper non-stationarity analysis should be based on the considered algorithm.
A Scalable VLSI Architecture for Soft-Input Soft-Output Depth-First Sphere Decoding
Ernst Martin Witte,Filippo Borlenghi,Gerd Ascheid,Rainer Leupers,Heinrich Meyr
Computer Science , 2009, DOI: 10.1109/TCSII.2010.2056014
Abstract: Multiple-input multiple-output (MIMO) wireless transmission imposes huge challenges on the design of efficient hardware architectures for iterative receivers. A major challenge is soft-input soft-output (SISO) MIMO demapping, often approached by sphere decoding (SD). In this paper, we introduce the - to our best knowledge - first VLSI architecture for SISO SD applying a single tree-search approach. Compared with a soft-output-only base architecture similar to the one proposed by Studer et al. in IEEE J-SAC 2008, the architectural modifications for soft input still allow a one-node-per-cycle execution. For a 4x4 16-QAM system, the area increases by 57% and the operating frequency degrades by 34% only.
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