Results 11  20
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62
Turbo Codes for Coherent FHSS with Partial Band Interference
 Proc. MILCOM '97
, 1997
"... In this paper, turbo codes are investigated in a slow frequencyhopped spread spectrum (FHSS) system with partialband jamming. In addition, fullband thermal noise is present. This paper focuses on the implemention of a modified turbo decoder for this model. We consider cases of known or unknown c ..."
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In this paper, turbo codes are investigated in a slow frequencyhopped spread spectrum (FHSS) system with partialband jamming. In addition, fullband thermal noise is present. This paper focuses on the implemention of a modified turbo decoder for this model. We consider cases of known or unknown channel state and variable number of bits per hop. Our approach is to modify the calculation of branch transition probabilities inherent in the decoder. Analytical bounds are derived and simulation is performed for coherent demodulation. The results drawn from this code are compared with a convolutional code. 1 Introduction Turbo codes are an exciting new channel coding scheme that achieve almost reliable data communication at signaltonoise ratios close to the Shannon limit. The results published in the inaugural paper by Berrou et al [2] were so good that they were met with much skepticism. Since then, however, these results have been reproduced and even improved. Consequently, much of t...
A codematched interleaver design for turbo codes
 IEEE Trans. on Communications
, 2002
"... Abstract—A codematched interleaver design for turbo codes in which a particular interleaver is constructed to match the code weight distribution is proposed. The design method is based on the code distance spectrum. The low weight paths in the code trellis which give large contributions to the erro ..."
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Cited by 13 (0 self)
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Abstract—A codematched interleaver design for turbo codes in which a particular interleaver is constructed to match the code weight distribution is proposed. The design method is based on the code distance spectrum. The low weight paths in the code trellis which give large contributions to the error probability in the signaltonoise ratio region of interest for practical communication systems are eliminated so that they do not appear in the overall code trellis after interleaving. The proposed interleaver improves the code error performance at moderate to high signaltonoise ratio and considerably increases the asymptotic slope of the error probability curves. Index Terms—Distance spectrum, interleaver design, relative contribution integral, turbo codes. I.
A Technique for Computing the Weight Spectrum of TurboCodes
 IEEE Comm. Letters
, 1999
"... We obtain an accurate and simple analytical approximation to the bit error probability of maximum likelihood decoding of parallel concatenated convolutional codes (turbocodes) by extending a result of [1], which investigates the weight enumerating function of terminated convolutional codes, to comp ..."
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Cited by 10 (0 self)
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We obtain an accurate and simple analytical approximation to the bit error probability of maximum likelihood decoding of parallel concatenated convolutional codes (turbocodes) by extending a result of [1], which investigates the weight enumerating function of terminated convolutional codes, to compute their conditional weight enumerating function. I.
Distribution of maxlog metrics for QAMbased BICM in fading channels
 IEEE Transactions on Communications
"... Abstract — In this letter we derive closedform expressions for the probability density functions (PDFs) of the bits ’ reliability metrics (Lvalues) in bitinterleaved coded modulation (BICM) transmission over fullyinterleaved fading channels. The expressions are valid for the relevant case of qua ..."
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Cited by 8 (5 self)
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Abstract — In this letter we derive closedform expressions for the probability density functions (PDFs) of the bits ’ reliability metrics (Lvalues) in bitinterleaved coded modulation (BICM) transmission over fullyinterleaved fading channels. The expressions are valid for the relevant case of quadrature amplitude modulation (QAM) with Gray mapping when the metrics are calculated via the socalled maxlog approximation. Using the developed expressions, the performance of coded BICM transmissions is efficiently evaluated, i.e., without resorting to otherwise required twodimensional numerical integration. The BICM capacity for different fading channels and constellation sizes is also evaluated.
Exploiting UEP in QAMbased BICM: Interleaver and code design
 IEEE Trans. Commun
, 2010
"... In this paper we formally analyze the interleaver and code design for QAMbased BICM transmissions using the binary reflected Gray code. We develop analytical bounds on the bit error rate and we use them to predict the performance of BICM when unequal error protection (UEP) is introduced by the cons ..."
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Cited by 8 (5 self)
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In this paper we formally analyze the interleaver and code design for QAMbased BICM transmissions using the binary reflected Gray code. We develop analytical bounds on the bit error rate and we use them to predict the performance of BICM when unequal error protection (UEP) is introduced by the constellation labeling. Based on these bounds the optimum design of interleaver and code is found, and numerical results for representative configurations are presented. When the new design is used, the improvements may reach 2 dB, and they are obtained without complexity increase. We also introduce the concept of generalized optimum distance spectrum convolutional codes, which are the optimum codes for this scenario.
New Iterative ("Turbo") Decoding Algorithms
 in Proc. International Symposium on Turbo Codes & Related Topics
, 1997
"... Decoding with feedback or iterative decoding is an efficient, lowcomplexity means for "information handover" in any parallel or serial concatenated coding scheme and in related applications. Invented twenty years ago, it has recently been payed considerable attention in the context of &qu ..."
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Cited by 7 (2 self)
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Decoding with feedback or iterative decoding is an efficient, lowcomplexity means for "information handover" in any parallel or serial concatenated coding scheme and in related applications. Invented twenty years ago, it has recently been payed considerable attention in the context of "Turbo Codes". Iterative decoding has been justified intuitively, but many question remain and perhaps will resist.
On the performance of Turbo codes
 Proceedings of IEEE Military Communications Conference
, 1998
"... The performance of the turbo code is sensitive to its code structure, which is made up of code rate, constraint length, tap connection, block size, interleaving pattern and number of decoding iterations. In this paper, mitigation techniques that can lower the error floor are adopted in both encoder ..."
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Cited by 7 (0 self)
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The performance of the turbo code is sensitive to its code structure, which is made up of code rate, constraint length, tap connection, block size, interleaving pattern and number of decoding iterations. In this paper, mitigation techniques that can lower the error floor are adopted in both encoder and decoder. Optimum tap connections are listed for codes with constraint lengths 3, 4, and 5. Performance variations achieved by changing different parameters are investigated. Simulation results show that (1) using 10 decoding iterations is adequate; (2) the Srandom interleaving provides the best performance among the interleaves investigated; (3) using codes with constraint lengths greater than 3 does not buy any additional coding gain for short block size (in the vicinity of 100); (4) for block size greater than 500, no significant improvement is noticed by increasing the constraint length from 4 to 5 in the range of bit error rate (BER) < 1o–6; and (5) the punctured rate 1/2 code structure degrades the performance by only 0.5 to 0.7 dB in comparison with the classic rate 1/3 turbo code for constraint lengths 3,4, and 5. 1
Design and Performance Analysis of Turbo Codes on Rayleigh Fading Channels
 in Proc., CISS
, 1996
"... The performance of turbo codes using coherent BSPK signaling on the Rayleigh fading channels is considered. The analysis relies on simulations of typical turbo coding systems for performance analysis in regions of low signaltonoise. For higher signalto noise regions beyond simulation capabilities ..."
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The performance of turbo codes using coherent BSPK signaling on the Rayleigh fading channels is considered. The analysis relies on simulations of typical turbo coding systems for performance analysis in regions of low signaltonoise. For higher signalto noise regions beyond simulation capabilities, an average upper bound is used, where the average is over all possible interleaving schemes. Attention is given to performance and design of turbo codes on fullyinterleaved and correlated fading channels. 1 Introduction For wireless applications on fading channels, channel coding is an important tool for improving communications reliability. In this paper, we examine the "turbo" error correcting coding technique [1], over fullyinterleaved and correlated Rayleigh slowfading channels. We illustrate the achievable performance of these codes and discuss issues related to optimizing turbo codes for fading channels. The organization of the paper includes a brief overview of turbo codes follo...
A novel technique for the evaluation of the transfer function of punctured turbo codes
 in Proc. ICC’06
, 2006
"... Turbo codes, in the form of parallel concatenated convolutional codes, consist of two recursive systematic convolutional encoders separated by an interleaver. Due to the presence of the interleaver, each constituent convolutional encoder accepts as input a block of information bits with a size equal ..."
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Cited by 7 (7 self)
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Turbo codes, in the form of parallel concatenated convolutional codes, consist of two recursive systematic convolutional encoders separated by an interleaver. Due to the presence of the interleaver, each constituent convolutional encoder accepts as input a block of information bits with a size equal to that of the interleaver rather than a continuous stream of information bits. By determining the transfer function of each terminated constituent convolutional code, which can be seen as a convolutional block code, an upper bound to the bit error rate performance of the turbo code is readily calculated. In this paper, we briefly present the conventional techniques for evaluating the transfer function of the convolutional block code and we propose a novel technique, according to which the state diagram of the convolutional code is modified so as to allow the direct evaluation of the transfer function of the convolutional block code. 1
Serially Concatenated Systems: An Iterative Decoding Approach with Application to Continuous Phase Modulation
, 1999
"... Iterative methods for concatenated coding and modulation in digital communication systems are considered. It is assumed that the code and modulation can be described by finitestate machines (FSM). An iterative decoder for such a system typically consists of a posteriori probability (APP) algorithms ..."
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Cited by 6 (0 self)
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Iterative methods for concatenated coding and modulation in digital communication systems are considered. It is assumed that the code and modulation can be described by finitestate machines (FSM). An iterative decoder for such a system typically consists of a posteriori probability (APP) algorithms for the constituent FSMs. Starting with a detailed examination of these algorithms, it is found that their initialization values can be formally justified. Then, possible iterative methods such as fixpoint iteration, Jacobi overrelaxation, damped substitution, and Newton's method are presented and evaluated. The result is that fixpoint iteration seems to be the best choice in most situations. As an