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Iterative Time-Variant Channel Estimation for 802.11p Using Generalized Discrete Prolate Spheroidal Sequences
- IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
, 2012
"... This paper deals with channel-estimation for orthogonal frequency division multiplexing (OFDM) in time-variant wireless propagation channels. We particularly consider the challenges of the IEEE 802.11p standard, the world-wide dominant system for vehicular communications. For historic reasons, 802.1 ..."
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Cited by 11 (7 self)
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This paper deals with channel-estimation for orthogonal frequency division multiplexing (OFDM) in time-variant wireless propagation channels. We particularly consider the challenges of the IEEE 802.11p standard, the world-wide dominant system for vehicular communications. For historic reasons, 802.11p uses a pilot pattern that is identical to the one used in 802.11a, which was initially designed for the estimation of indoor channels with no or little time variations. Therefore, this pilot pattern violates the sampling theorem for channels with both, large delay spread and large Doppler spread, as often occurs in vehicular communications. To remedy this problem, we design a robust iterative channel estimator based on a two-dimensional subspace spanned by generalized discrete prolate spheroidal sequences. Due to the tight subspace design the iterative receiver is able to converge to the same bit error rate as a receiver with perfect channel knowledge. Furthermore, we propose a backward compatible modification of the 802.11p pilot pattern such that the number of iterations sufficient for convergence can be reduced by a factor of two to three, strongly reducing implementation complexity.
Compressive sampling of swallowing accelerometry signals using time-frequency dictionaries based on modulated discrete prolate spheroidal sequences
- EURASIP Journal on Advances in Signal Processing
, 2012
"... Monitoring physiological functions such as swallowing often generates large volumes of sam-ples to be stored and processed, which can introduce computational constraints especially if remote monitoring is desired. In this paper, we propose a compressive sensing (CS) algorithm to alleviate some of th ..."
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Cited by 10 (2 self)
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Monitoring physiological functions such as swallowing often generates large volumes of sam-ples to be stored and processed, which can introduce computational constraints especially if remote monitoring is desired. In this paper, we propose a compressive sensing (CS) algorithm to alleviate some of these issues while acquiring dual-axis swallowing accelerometry signals. The proposed CS approach uses a time-frequency dictionary where the members are modulated dis-crete prolate spheroidal sequences (MDPSS). These waveforms are obtained by modulation and variation of discrete prolate spheroidal sequences (DPSS) in order to reflect the time-varying nature of swallowing acclerometry signals. While the modulated bases permit one to repre-sent the signal behavior accurately, the matching pursuit algorithm is adopted to iteratively decompose the signals into an expansion of the dictionary bases. To test the accuracy of the proposed scheme, we carried out several numerical experiments with synthetic test signals and dual-axis swallowing accelerometry signals. In both cases, the proposed CS approach based on the MDPSS yields more accurate representations than the CS approach based on DPSS. Specif-ically, we show that dual-axis swallowing accelerometry signals can be accurately reconstructed
Slepian-based two-dimensional estimation of time-frequency variant MIMO-OFDM channels
- IEEE Signal Process. Lett
, 2008
"... Abstract—A linear channel estimator for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems, based on a two-dimensional Slepian expansion, is presented. The estimator is meant to be part of an iterative receiver. We consider both estimation based on pilots o ..."
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Cited by 6 (0 self)
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Abstract—A linear channel estimator for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems, based on a two-dimensional Slepian expansion, is presented. The estimator is meant to be part of an iterative receiver. We consider both estimation based on pilots only and on pilots and data, the latter considered as a reference for the case when feedback from decoders is exploited. Performances are analyzed via computer simulations comparing the relative minimum square error (RMMSE) of an analogous one-dimensional estimator and the proposed extension. Index Terms—Channel estimation, discrete prolate spheroidal sequences, iterative receivers, multiple-input multiple-output (MIMO) channels, orthogonal frequency-division multiplexing (OFDM) systems. I.
Low-complexity MIMO multiuser receiver: A joint antenna detection scheme for time-varying channels
- IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, to be published. Andreas F. Molisch (S’89, M’95, SM00, F’05) is Professor of Electrical Engineering at the University of Southern
, 2008
"... Abstract—This paper deals with the uplink of a wireless multiple-input multiple-output (MIMO) communication system based on multicarrier (MC) code division multiple access (CDMA). We focus on time-varying channels for users moving at vehicular speeds. The optimal maximum a posteriori (MAP) receiver ..."
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Cited by 4 (3 self)
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Abstract—This paper deals with the uplink of a wireless multiple-input multiple-output (MIMO) communication system based on multicarrier (MC) code division multiple access (CDMA). We focus on time-varying channels for users moving at vehicular speeds. The optimal maximum a posteriori (MAP) receiver for such a system is prohibitively complex and can be approximated using iterative linear minimum mean-square error (LMMSE) multiuser detection and parallel interference cancellation (PIC). For time-varying channels, two LMMSE filters for channel estimation and multiuser detection need to be computed at every time instant, making implementation in a real-time system difficult. We develop a novel low-complexity receiver that exploits the multiple antenna structure of the system and performs joint iterative multiuser detection and channel estimation. Our receiver algorithms are based on the Krylov subspace method, which solves a linear system with low complexity, trading accuracy for efficiency. The computational complexity of the channel estimator can be reduced by one order of magnitude. For multiuser detection, a PIC scheme in the user space, i.e., after the matched filter, allows simultaneous detection of all users as well as drastic computational complexity reduction by more than one order of magnitude. Index Terms—Joint antenna detection, Krylov subspace method, low-complexity receiver, multiple-input multiple-output (MIMO), orthogonal frequency-division multiplexing (OFDM), time-varying channel. I.
Low-Complexity Doubly Selective Channel Simulation Using Multidimensional Discrete Prolate Spheroidal Sequences
- In Proc. IST Mobile and Wireless Communications
, 2006
"... This paper presents a low-complexity algorithm for the simulation of time-variant frequency-selective geometry based channel models. The algorithm approximately calculates the time-variant transfer function of the channel in the subspace spanned by multidimensional discrete prolate spheroidal (DPS) ..."
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Cited by 1 (1 self)
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This paper presents a low-complexity algorithm for the simulation of time-variant frequency-selective geometry based channel models. The algorithm approximately calculates the time-variant transfer function of the channel in the subspace spanned by multidimensional discrete prolate spheroidal (DPS) sequences. The only parameters of the subspace are the maximum Doppler shift and the maximum delay of the channel as well as the channel bandwidth and the observed time interval.
Slepian-Based Serial Estimation of Time-Frequency Variant Channels for MIMO-OFDM Systems
"... Abstract—This paper proposes a low-complexity twodimensional channel estimator for MIMO-OFDM systems derived from a time-frequency variant channel estimator previously proposed. The estimator exploits both time and frequency correlations of the wireless channel via use of Slepian-basis expansions. T ..."
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Abstract—This paper proposes a low-complexity twodimensional channel estimator for MIMO-OFDM systems derived from a time-frequency variant channel estimator previously proposed. The estimator exploits both time and frequency correlations of the wireless channel via use of Slepian-basis expansions. The computational saving comes from replacing a two-dimensional Slepian-basis expansion with two seriallyconcatenated one-dimensional Slepian-basis expansions. Performance in terms of Normalized Mean Square Error (NMSE) vs. Signal-to-Noise Ratio (SNR) have been analyzed via numerical simulations and compared with the original estimator. The analysis of the performance takes into account the impact of both system and channel parameters. I.
(Mobile Communications) eingereicht an der
"... This thesis collects my research results obtained throughout the last eight years at FTW Telecommunications Research Center Vienna. During this time I had the pleasure to work with and advice a group of talented researchers that pursuit their PhD degree within my different research projects at FTW. ..."
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This thesis collects my research results obtained throughout the last eight years at FTW Telecommunications Research Center Vienna. During this time I had the pleasure to work with and advice a group of talented researchers that pursuit their PhD degree within my different research projects at FTW. I want to thank, in chronological order, Florian Kaltenberger, Nicolai Czink, Charlotte Dumard, Laura Bernadó, and Paolo Castiglione for the fruitful collaboration. I would also like to thank Alexander Paier and Sebastian Caban for the joint work during their time
9 Multi-User MIMO Receiver Processing for Time-Varying Channels
"... Wireless broadband communications for mobile users at vehicular speed is the cornerstone of future 4th generation systems. This chapter deals with joint iterative channel estimation and multi-user detection for the uplink of a multi-carrier (MC) code division multiple access (CDMA) system. MC-CDMA i ..."
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Wireless broadband communications for mobile users at vehicular speed is the cornerstone of future 4th generation systems. This chapter deals with joint iterative channel estimation and multi-user detection for the uplink of a multi-carrier (MC) code division multiple access (CDMA) system. MC-CDMA is based on orthogonal frequency division multiplexing
Cooperative Space-Time Coded OFDM with Timing Errors and Carrier Frequency Offsets
"... Abstract—The use of distributed space-time codes in cooperative communications promises to increase the rate and reliability of data transmission. These gains were mostly demonstrated for ideal scenarios, where all the nodes are perfectly synchronized. Considering a cooperative uplink scenario with ..."
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Abstract—The use of distributed space-time codes in cooperative communications promises to increase the rate and reliability of data transmission. These gains were mostly demonstrated for ideal scenarios, where all the nodes are perfectly synchronized. Considering a cooperative uplink scenario with asynchronous nodes, the system suffers from two effects: timing errors and individual carrier frequency offsets. In effect, timing errors can completely cancel the advantages introduced by space-time codes, while individual carrier frequency offsets provide a great challenge to receivers. Indeed, in cooperative communications, frequency offsets are perceived as a time-variant channel, even if the individual links are static. We show that using OFDM, space-time codes (STCs) become robust to timing errors. Channel estimation and tracking takes care of frequency offsets. Our simulations demonstrate that the bit error rate (BER) performance improves by an order of magnitude, when using a cooperative system design, which takes these two effects into account. Index Terms—OFDM, Block codes, distributed space-time code, virtual MIMO, diversity methods, cooperative systems,
Open Access
"... Protein conjugated with aldehydes derived from lipid peroxidation as an independent parameter of the carbonyl stress in the kidney damage Rafael Medina-Navarro 1 * , Renato Nieto-Aguilar 1,3 and Cleto Alvares-Aguilar 2 Background: One of the well-defined and characterized protein modifications usual ..."
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Protein conjugated with aldehydes derived from lipid peroxidation as an independent parameter of the carbonyl stress in the kidney damage Rafael Medina-Navarro 1 * , Renato Nieto-Aguilar 1,3 and Cleto Alvares-Aguilar 2 Background: One of the well-defined and characterized protein modifications usually produced by oxidation is carbonylation, an irreversible non-enzymatic modification of proteins. However, carbonyl groups can be introduced into proteins by non-oxidative mechanisms. Reactive carbonyl compounds have been observed to have increased in patients with renal failure. In the present work we have described a procedure designed as aldehyde capture to calculate the protein carbonyl stress derived solely from lipid peroxidation. Methods: Acrolein-albumin adduct was prepared as standard at alkaline pH. Rat liver microsomal membranes and serum samples from patients with diabetic nephropathy were subjected to the aldehyde capture procedure and aldol-protein formation. Before alkalinization and incubation, samples were precipitated and redisolved in 6M guanidine. The absorbances of the samples were read with a spectrophotometer at 266 nm against a blank of guanidine.
