A simple turbo decoding scheme is proposed for partial-response (PR) channels by using high-rate parity-check codes as an outer error-correction code (ECC), The use of the simple parity codes enables a simplified and ...
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A simple turbo decoding scheme is proposed for partial-response (PR) channels by using high-rate parity-check codes as an outer error-correction code (ECC), The use of the simple parity codes enables a simplified and high-speed implementation of the a posterior probability (APP) decoder. Its key feature is an iterative decoding step for the parallel concatenation of two parity-check outer codes connected via an interleaver, The parity iterative decoding can provide the high-rate parity-check outer codes with superior correction capability for random error-events, so it can help to reduce the decoding latency, The combination of the serial turbo decoding for a modified E-2 PR ((MEPR)-P-2) channel and the parity iterative decoding demonstrated a coding gain of 4-5 dB at a bit error rate of 1.0E-5 for a coding rate of 8/9.
Turbo codes, with potential 4 to 5 dB coding gain over the conventional Viterbi detection schemes, are good candidates for the next generation detection/decoding schemes for magnetic recording systems. In this paper, ...
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Turbo codes, with potential 4 to 5 dB coding gain over the conventional Viterbi detection schemes, are good candidates for the next generation detection/decoding schemes for magnetic recording systems. In this paper, timing recovery is included in the evaluation of Turbo codes. Three timing recovery methods, namely voltage control oscillator (VCO) method, interpolated timing recovery (ITR) method and adaptive filter timing recovery (AFTR) method are examined for two turbo decoder architectures, full turbo and serial turbo. Bit error rate (BER) results from simulations suggest that full turbo decoder is more robust than the serial turbo decoder. For serial turbo decoder, error floor is seen earlier in VCO and ITR methods than AFTR method. Using s-random interleaver seems to be able to remove such error floor.
The partial response channel can be viewed as a rate-1 encoder in which the output alphabet differs from the input alphabet. in serially concatenated coding schemes, the partial response channel can serve as the inner...
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The partial response channel can be viewed as a rate-1 encoder in which the output alphabet differs from the input alphabet. in serially concatenated coding schemes, the partial response channel can serve as the inner encoder, Recent works on the application of turbo decoding techniques to partial response channels have used channel models to investigate system performance. While the models provided some insight into the performance of turbo decoding techniques, performance in a real system, with electronic and signal-dependent media noise, remained unknown. This paper will demonstrate the performance of turbo decoding techniques using real and modeled spinstand data. A simple serial concatenation system will be presented that uses as its outer code a single convolutional code and as its inner code the partial response channel. Significant gains will be shown over QMTR coded systems.
Recent work on the application of turbo decoding techniques to partial response channels has focused on additive white Gaussian noise channel models, Simulations using these ideal partial response channel models show ...
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Recent work on the application of turbo decoding techniques to partial response channels has focused on additive white Gaussian noise channel models, Simulations using these ideal partial response channel models show gains exceeding 5 dB over uncoded systems at bit error rates of 10(-5). Since the APP detectors of the turbo decoder assume uncorrelated Gaussian noise, the performance on more realistic channel models, using correlated noise, was unknown. In this work, we replace the white noise partial response channel model with the more realistic equalized Lorentzian channel model. Simulation results of the turbo decoding system with both channel models will be presented.
The performance and design of turbo codes using coherent BPSK signaling on the Rayleigh fading channel is considered. In low signal-to-noise regions, performance analysis uses simulations of typical turbo coding syste...
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The performance and design of turbo codes using coherent BPSK signaling on the Rayleigh fading channel is considered. In low signal-to-noise regions, performance analysis uses simulations of typical turbo coding systems. For higher signal-to-noise regions beyond simulation capabilities, an average upper bound is used in which the average is over all possible interleaving schemes. Fully interleaved and exponentially correlated Rayleigh channels are explored. Furthermore, the design issues relevant to turbo codes are examined for the correlated fading channel. Turbo interleaver design criteria are developed and architectural modifications are proposed for improved performance.
In this paper, turbo codes are investigated in a slow frequency-hopped spread spectrum (FH-SS) system with partial-band jamming. In addition, full-band thermal noise is present, The channel model is that of a partial-...
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In this paper, turbo codes are investigated in a slow frequency-hopped spread spectrum (FH-SS) system with partial-band jamming. In addition, full-band thermal noise is present, The channel model is that of a partial-band jammer in which a fraction of the frequency band is jammed and the remaining fraction is unjammed, This paper focuses on the implemention and performance of a modified turbo decoder for this model, We refer to the knowledge that each transmitted bit is jammed as channel state information. 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 original turbo decoder. For the cases with no side information and multiple bits per hop, we iteratively calculate channel state estimates, Analytical bounds are derived and simulation is performed for noncoherent demodulation. The performance of turbo codes is compared with a Reed-Solomon and a concatenated code comprised of a convolutional inner code and Reed-Solomon outer code.
We apply two reduced-computation variants of the BCJR algorithm to the decoding of serial and parallel cancatenated convolutional codes, One computes its recursions at only M states per trellis stage;one computes only...
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We apply two reduced-computation variants of the BCJR algorithm to the decoding of serial and parallel cancatenated convolutional codes, One computes its recursions at only M states per trellis stage;one computes only at states with values above a threshold, The threshold scheme is much more efficient, and it greatly reduces the computation of the BCJR algorithm, By computing only when the channel demands it, the threshold scheme reduces the turbo decoder computation to one-four nodes per trellis stage after the second iteration.
Recursive systematic convolutional encoders have been shown to play a crucial role in the design of turbo codes, We recall some properties of binary convolutional encoders and apply them to a search for good constitue...
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Recursive systematic convolutional encoders have been shown to play a crucial role in the design of turbo codes, We recall some properties of binary convolutional encoders and apply them to a search for good constituent convolutional codes of turbo codes. Tables of the ''best" recursive systematic convolutional encoders found are presented for various rates, together with the average bit-error probability performances of some turbo codes using them.
We present a unified graphical model framework for describing compound codes and deriving iterative decoding algorithms, After reviewing a variety of graphical models (Markov random fields, Tanner graphs, and Bayesian...
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We present a unified graphical model framework for describing compound codes and deriving iterative decoding algorithms, After reviewing a variety of graphical models (Markov random fields, Tanner graphs, and Bayesian networks), we derive a general distributed marginalization algorithm far functions described by factor graphs. From this general algorithm, Pearl's belief propagation algorithm is easily derived as a special case, We point out that recently developed iterative decoding algorithms for various codes, including "turbo decoding" of parallel-concatenated convolutional codes, may be viewed as probability propagation in a graphical model of the code, We focus on Bayesian network descriptions of codes, which give a natural input/state/output/channel description of a code and channel, and we indicate how iterative decoders can be developed for parallel- and serially concatenated coding systems, product codes, and low-density parity-check codes.
A soft-output Viterbi algorithm (SOVA) that can be used on trellis-coded modulation (TCM), rate-kin convolutional codes, and intersymbol interference (ISI) channels is proposed. The algorithm utilizes the postdetector...
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A soft-output Viterbi algorithm (SOVA) that can be used on trellis-coded modulation (TCM), rate-kin convolutional codes, and intersymbol interference (ISI) channels is proposed. The algorithm utilizes the postdetector architecture proposed by Berrou et nl, [6] to achieve low computational complexity. By starting with Battail's [4] generalized revision algorithm and rereferencing the "relative values" to the surviving path to each state, substantial simplifications are made possible. By comparing the revision operations dictated by the simplified revision equation for a rate-1/n convolutional code to the operations mandated by the rate-1/n postdetector algorithm presented by Berrou ef al,, it is possible to deduce the additional modifications necessary to produce a rate-k/n postdetector algorithm. Computer simulations suggest that the derived rate-k/n algorithm produces reasonably good a posteriori input probability estimates for rate-k/n convolutional codes and trellis codes. The algorithm may also be used for soft-output Viterbi equalization (SOVE) provided that the channel impairments are not too severe.
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