Results 1 - 10 of 456

"Turbo equalization": principles and new results

by Michael Tüchler, Ralf Kötter, Andrew Singer , 2000
"... Since the invention of \turbo codes" by Berrou et al. in 1993, the \turbo principle" has been adapted to several communication problems such as \turbo equalization", \turbo trellis coded modulation", and iterative multi user detection. In this paper we study the \turbo equalizati ..."
Abstract - Cited by 274 (25 self) - Add to MetaCart
Since the invention of \turbo codes" by Berrou et al. in 1993, the \turbo principle" has been adapted to several communication problems such as \turbo equalization", \turbo trellis coded modulation", and iterative multi user detection. In this paper we study the \turbo equalization" approach, which can be applied to coded data transmission over channels with intersymbol interference (ISI). In the original system invented by Douillard et al., the data is protected by a convolutional code and a receiver consisting of two trellis-based detectors are used, one for the channel (the equalizer) and one for the code (the decoder). It has been shown that iterating equalization and decoding tasks can yield tremendous improvements in bit error rate (BER). We introduce new approaches to combining equalization based on linear ltering with the decoding. The result is a receiver that is capable of improving BER performance through iterations of equalization and decoding in a manner similar to turbo ...
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Minimum mean squared error equalization using a priori information

by Michael Tüchler, Andrew C. Singer, Ralf Koetter - IEEE TRANS. SIGNAL PROCESSING , 2002
"... A number of important advances have been made in the area of joint equalization and decoding of data transmitted over intersymbol interference (ISI) channels. Turbo equalization is an iterative approach to this problem, in which a maximum a posteriori probability (MAP) equalizer and a MAP decoder e ..."
Abstract - Cited by 153 (12 self) - Add to MetaCart
A number of important advances have been made in the area of joint equalization and decoding of data transmitted over intersymbol interference (ISI) channels. Turbo equalization is an iterative approach to this problem, in which a maximum a posteriori probability (MAP) equalizer and a MAP decoder exchange soft information in the form of prior probabilities over the transmitted symbols. A number of reduced-complexity methods for turbo equalization have recently been introduced in which MAP equalization is replaced with suboptimal, low-complexity approaches. In this paper, we explore a number of low-complexity soft-input/soft-output (SISO) equalization algorithms based on the minimum mean square error (MMSE) criterion. This includes the extension of existing approaches to general signal constellations and the derivation of a novel approach requiring less complexity than the MMSE-optimal solution. All approaches are qualitatively analyzed by observing the mean-square error averaged over a sequence of equalized data. We show that for the turbo equalization application, the MMSE-based SISO equalizers perform well compared with a MAP equalizer while providing a tremendous complexity reduction.
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Iterative multiuser joint decoding: unified framework and asymptotic analysis

by Joseph Boutros, Giuseppe Caire - IEEE TRANS. INFORM. THEORY , 2002
"... We present a framework for iterative multiuser joint decoding of code-division multiple-access (CDMA) signals, based on the factor-graph representation and on the sum-product algorithm. In this framework, known parallel and serial, hard and soft interference cancellation algorithms are derived in a ..."
Abstract - Cited by 116 (3 self) - Add to MetaCart
We present a framework for iterative multiuser joint decoding of code-division multiple-access (CDMA) signals, based on the factor-graph representation and on the sum-product algorithm. In this framework, known parallel and serial, hard and soft interference cancellation algorithms are derived in a unified way. The asymptotic performance of these algorithms in the limit of large code block length can be rigorously analyzed by using density evolution. We show that, for random spreading in the large-system limit, density evolution is considerably simplified. Moreover, by making a Gaussian approximation of the decoder soft output, we show that the behavior of iterative multiuser joint decoding is approximately characterized by the stable fixed points of a simple one-dimensional nonlinear dynamical system.

The Factor Graph Approach to Model-Based Signal Processing

by Hans-Andrea Loeliger, et al. , 2007
"... ..."
Abstract - Cited by 89 (22 self) - Add to MetaCart
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EXIT charts of irregular codes

by M. Tüchler , J. Hagenauer , 2002
"... We study the convergence behavior of iterative decoding of a serially concatenated code. We rederive a existing analysis technique called EXIT chart [15] and show that for certain decoders the construction of an EXIT chart simplifies tremendously. The findings are extended such that simple irregula ..."
Abstract - Cited by 82 (6 self) - Add to MetaCart
We study the convergence behavior of iterative decoding of a serially concatenated code. We rederive a existing analysis technique called EXIT chart [15] and show that for certain decoders the construction of an EXIT chart simplifies tremendously. The findings are extended such that simple irregular codes can be constructed, which can be used to improve the converence of the iterative decoding algorithm significantly. An efficient and optimal optiamization algorithm is presented. Finally, some results on thresholds on the decoding convergence are outlined.

Turbo-BLAST for wireless communications: theory and experiments

by Mathini Sellathurai, Simon Haykin - IEEE Trans. Signal Processing , 2002
"... Abstract—TURBO-BLAST is a novel multitransmit multi-receive (MTMR) antenna scheme for high-throughput wireless communications. It exploits the following ideas: the Bell Labs layered space time (BLAST) architecture; random layered space-time (RLST) coding scheme by using independent block codes and r ..."
Abstract - Cited by 81 (1 self) - Add to MetaCart
Abstract—TURBO-BLAST is a novel multitransmit multi-receive (MTMR) antenna scheme for high-throughput wireless communications. It exploits the following ideas: the Bell Labs layered space time (BLAST) architecture; random layered space-time (RLST) coding scheme by using independent block codes and random space-time interleaving; sub-optimal turbo-like receiver that performs iterative decoding of the RLST codes and estimation of the channel matrix in an iterative and, most important, simple fashion. The net result is a new transceiver that is not only computationally efficient compared with the optimal maximum likelihood decoder, but it also yields a probability of error performance that is orders of magnitude smaller than traditional BLAST schemes for the same operating conditions. This paper also presents experimental results using real-life indoor channel measurements demonstrating the high-spectral efficiency of TURBO-BLAST. Index Terms—High-rate layered space-time methods, multi-transmit multireceive antennas, turbo principle. I.
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Turbo Equalization

by Ralf Koetter, Andrew C. Singer, Michael Tüchler - IEEE Signal Processing Mag , 2004
"... Capitalizing on the tremendous performance gains of turbo codes and the turbo decoding algorithm, turbo equalization is an iterative equalization and decoding technique that can achieve equally impressive performance gains for communication systems that send digital data over channels that require e ..."
Abstract - Cited by 69 (4 self) - Add to MetaCart
Capitalizing on the tremendous performance gains of turbo codes and the turbo decoding algorithm, turbo equalization is an iterative equalization and decoding technique that can achieve equally impressive performance gains for communication systems that send digital data over channels that require equalization, i.e. those which suffer from intersymbol interference (ISI). In this paper, we discuss the turbo equalization approach to coded data transmission over ISI channels, with an emphasis on the basic ideas and some of the practical details. The original system introduced by Douillard, et al., can be viewed as an extension of the turbo decoding algorithm by considering the effect of the ISI channel as another form of error protection, i.e. as a rate-1 convolutional code.
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Minimum mean-squared error iterative successive parallel arbitrated decision feedback detectors for DS-CDMA systems

by Rodrigo C. De Lamare, Raimundo Sampaio-neto - in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process , 2008
"... Abstract—In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, p ..."
Abstract - Cited by 62 (51 self) - Add to MetaCart
Abstract—In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, parallel and iterative interference cancellation structures. A novel efficient DF structure that employs successive cancellation with parallel arbitrated branches and a near-optimal low complexity user ordering algorithm are presented. The proposed DF receiver structure and the ordering algorithm are then combined with iterative cascaded DF stages for mitigating the deleterious effects of error propagation for convolutionally encoded systems with both Viterbi and turbo decoding as well as for uncoded schemes. We mathematically study the relations between the MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback. Simulation results for an uplink scenario assess the new iterative DF detectors against linear receivers and evaluate the effects of error propagation of the new cancellation methods against existing ones. Index Terms—DS-CDMA systems, multiuser detection, decision feedback structures, iterative detection, iterative decoding. I.
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Iterative Multiuser Joint Decoding: Optimal Power Allocation and Low-Complexity Implementation

by Giuseppe Caire, Ralf Müller, Toshiyuki Tanaka , 2002
"... We consider a canonical model for coded CDMA with random spreading, where the receiver makes use of iterative Belief-Propagation (BP) joint decoding. We provide simple Density-Evolution analysis in the large-system limit (large number of users) of the performance of the exact BP decoder and of so ..."
Abstract - Cited by 62 (11 self) - Add to MetaCart
We consider a canonical model for coded CDMA with random spreading, where the receiver makes use of iterative Belief-Propagation (BP) joint decoding. We provide simple Density-Evolution analysis in the large-system limit (large number of users) of the performance of the exact BP decoder and of some suboptimal approximations based on Interference Cancellation (IC). Based on this analysis, we optimize the received user SNR distribution in order to maximize the system spectral efficiency for given user channel codes, channel load (users per chip) and target user bit-error rate. The optimization of the received SNR distribution is obtained by solving a simple linear program and can be easily incorporated into practical power control algorithms. Remarkably, under the optimized SNR assignment the suboptimal Minimum Mean-Square Error (MMSE) IC-based decoder performs almost as well as the more complex exact BP decoder. Moreover, for a large class of commonly used convolutional codes we observe that the optimized SNR distribution consists of a finite number of discrete SNR levels. Based on this observation, we provide a low-complexity approximation of the MMSE-IC decoder that suffers from very small performance degradation while attaining considerable savings in complexity. As

Downlink capacity of interference-limited MIMO systems with joint detection

by Huaiyu Dai, Andreas F. Molisch, Senior Member, H. Vincent Poor - IEEE Trans. Wireless Commun , 2004
"... The capacity of downlink cellular multiple-input multiple-output (MIMO) cellular systems, where co-channel interference is the dominant channel impairment, is investigated in this paper, mainly from a signal-processing perspective. Turbo space-time multiuser detection (ST MUD) is employed for intrac ..."
Abstract - Cited by 60 (7 self) - Add to MetaCart
The capacity of downlink cellular multiple-input multiple-output (MIMO) cellular systems, where co-channel interference is the dominant channel impairment, is investigated in this paper, mainly from a signal-processing perspective. Turbo space-time multiuser detection (ST MUD) is employed for intracell communications, and is shown to closely approach the ultimate capacity limits in Gaussian ambient noise for an isolated cell. Then it is combined with various multiuser detection methods for combating intercell interference. Among various multiuser detection techniques examined, linear minimum-mean-square-error (MMSE) MUD and successive interference cancellation are shown to be feasible and effective. Based on these two multiuser detection schemes, one of which may outperform the other for different settings, an adaptive detection scheme is developed, which together with a Turbo ST MUD structure offers substantial performance gain over the well known V-BLAST techniques with coding in this interference-limited cellular environment. The obtained multiuser capacity is excellent in high to medium signal-to-interference ratio scenario. Nonetheless, numerical results also indicate that a further increase in system complexity, using base-station cooperation, could lead to further significant increases of the system capacity. The asymptotic multicell MIMO capacity with linear MMSE MUD preprocessing is also derived, and this analysis agrees well with the simulation results.
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