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ABSTRACT: This paper deals with a posteriori probability (APP) decoding of high-rate convolutional codes, using the dual code's trellis. After deriving the dual APP (DAPP) algorithm from the APP relation, its trellis-based implementation is addressed. The challenge involved in practical implementation of a DAPP decoder is then highlighted. Metric representation schemes similar to the log domain used for log-APP decoding are shown to be unattractive for DAPP decoding due to quantization requirements. After explaining the nature of the DAPP metrics, an arc hyperbolic tangent (AHT) scheme is proposed and its equivalent arithmetic operations derived. By using an efficient approximation, an addition is translated to an addition in the AHT domain. Efficient techniques for normalization and extrinsic log-likelihood ratio (LLR ) calculation are presented which reduce implementation complexity significantly. Simulation results with different high-rate codes are given to show that the AHT-DAPP decoder performs similarly to a log-APP decoder and at the same time performs better than a decoder for a punctured code. A fully fixed-point model of an AHT-DAPP decoder is shown to perform close to an optimum decoder. The decoding complexity of the log-APP and AHT-DAPP decoders are listed and compared for several rate-k/(k+1) codes. It is shown that an AHT-DAPP decoder starts to be less complex from a code rate of 7/8 . When compared against a max-log-APP decoder, the AHT-DAPP decoder is less complex at a code rate of 9/10 and above.
IEEE Transactions on Information Theory 02/2010; · 3.01 Impact Factor
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ABSTRACT: For high rate k/n convolutional codes (k/n > 0.5), a trellis based implementation of a posteriori probability (APP) decoders is less complex on the dual code trellis owing to its branch complexity (2<sup>n-k</sup> ) being lower than the code trellis (2<sup>k</sup>). The log scheme used for APP decoders is not attractive for practical implementation owing to heavy quantisation requirements. As an alternative, presented is an arc hyperbolic tangent (AHT) scheme for implementing the dual- APP decoder. The trellis based implementation of this AHT dual APP decoder is discussed and some fundamental differences between primal APP and dual APP decoders that have an effect on a quantised implementation are reported.
Electronics Letters 02/2008; · 0.96 Impact Factor
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ABSTRACT: An a posteriori probability (APP) decoder working on the trellis of the dual code is preferred if the code rate is high. However, a hardware realisation of this decoder is quite complex due to very fine quantisation requirements. This paper explains the nature of the metrics in this dual-APP decoder and points out the underlying reason behind the unsuitability of a traditional log domain approach. We propose a new metric representation scheme and discuss the arithmetic operations involved for a trellis based implementation. Simulation results are given, showing a better performance tradeoff of the proposed scheme against quantisation
Vehicular Technology Conference, 2006. VTC 2006-Spring. IEEE 63rd; 06/2006
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ABSTRACT: A technique of using a non-uniform 16QAM modulation combined with bit interleaved coded modulation and a new iterative decoding (BICM-ID) scheme is investigated. Simulation results of a parallel concatenated convolutional code shows a gain of 0.95 dB at a BER of 10<sup>-5</sup> compared to conventional uniform 16QAM modulation in a linear channel. For a nonlinear satellite channel, this scheme offers a gain of 1.2 dB at the same BER compared to a uniform constellation.
Electronics Letters 05/2006; · 0.96 Impact Factor
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ABSTRACT: Amplitude phase shift keying (APSK) modulation presents an attractive scheme to overcome nonlinearity effects on nonlinear channels compared to conventional square quadrature amplitude modulation (QAM). In this paper, we investigate the performance of a bit interleaved coded modulation with iterative decoding (BICM-ID) system in which APSK modulation is used to achieve a spectral efficiency of 3 bit/s/Hz. A new iterative receiver is proposed where an extra soft-demapper is used between the two soft input soft output (SISOs) decoders. Extrinsic information exchange for the data and parity bits is optimised according to an appropriate iteration scheduling. Simulation results show a gain of 0.15 dB at a bit error rate (BER) of 10<sup>-4</sup> with this new iterative decoding scheme and the optimised constellation over a nonlinear satellite channel
Communications Theory Workshop, 2006. Proceedings. 7th Australian; 03/2006
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ABSTRACT: Tail-biting codes are suitable for high rate codes of short block length as they do not introduce any rate loss and have a simpler a posteriori Probability (APP) decoder structure than block codes. For such high rate codes, an APP algorithm working on the trellis of the dual code is preferred since the branch complexity is much less compared to the original code trellis. However, the nature of the metrics in a dual-APP decoder makes a hardware realisation quite complex, due to very fine quantisation requirements. This paper points out the problems associated with a traditional log domain approach and proposes a new metric representation scheme. The arithmetic operations involved in a trellis based implementation are discussed. The proposed scheme is applied to a sub optimum decoder for tail-biting codes and simulation results are given.
Communications Theory Workshop, 2006. Proceedings. 7th Australian; 03/2006
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ABSTRACT: We recently proposed a new class of turbo-like codes called parallel data convolutional codes (PDCCs). The distinct characteristics of PDCCs include parallel data input bits and a self-iterative soft-in/soft-out a posteriori probability (APP) decoder. In this paper, we analyse this turbo-like code by means of the extrinsic information transfer chart (EXIT chart). Our results show that the threshold E<sub>b</sub>/N<sub>0</sub> point for a rate 1/2 8-state PDCC is 0.6 dB, which is the same as the threshold point for a punctured rate 1/2 16-state parallel concatenated convolutional code (turbo code).
Intelligent Signal Processing and Communication Systems, 2005. ISPACS 2005. Proceedings of 2005 International Symposium on; 01/2006
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ABSTRACT: We propose a new class of parallel data convolutional codes (PDCCs) in this paper. The PDCC encoders inputs are composed of an original block of data and its interleaved version. A novel single self-iterative soft-in/soft-out a posteriori probability (APP) decoder structure is proposed for the decoding of the PDCCs. Simulation results are presented to compare the performance of PDCCs to that of parallel concatenated convolutional codes (PCCCs)
Communications Theory Workshop, 2005. Proceedings. 6th Australian; 03/2005
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ABSTRACT: This paper investigates the effects of the nonequiprobable distribution of a high bandwidth efficiency M-ary QAM signal constellation on the error performance for nonlinear channels. A simple nonlinear channel model where the phase and amplitude of the transmitted samples are distorted by a nonlinear function with additive white Gaussian noise (AWGN) in the downlink was simulated. Simulation results for binary turbo coded modulation (TCM) show a 3 dB improvement when the distribution of the signal constellation is nonequiprobable
Communications Theory Workshop, 2005. Proceedings. 6th Australian; 03/2005
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ABSTRACT: For high rate codes, an a posteriori probability (APP) algorithm working on the dual code is preferable. The challenge involved in log domain implementation of this algorithm due to the presence of negative valued metrics is highlighted. To represent these metrics, a new representation system is proposed in place of the existing sign-magnitude representation. A generalised model of a trellis based implementation is presented, over which the log domain implementation of two approaches, one based on likelihood ratios (LRs) and the other based on reflection coefficients (RCs) are compared in complexity. It is found that the approach based on LRs is less complex
Communications Theory Workshop, 2005. Proceedings. 6th Australian; 03/2005
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ABSTRACT: We investigate the capacity of various intersymbol interference (ISI) channels with additive white Gaussian noise (AWGN). Previous papers showed a minimum E<sub>b</sub>/N<sub>0</sub> of -4.6 dB, 3 dB below the capacity of a flat channel, is obtained using water-pouring capacity formulas for the 1+D channel. However, these papers did not take into account that the channel power gain can be greater than one when water-pouring is used. We present a generic power normalization method of the channel frequency response, namely, peak bandwidth normalization (PBN), to facilitate the fair capacity comparison of various ISI channels. Three types of ISI channel, i.e., adder channels, RC channels, and magnetic recording channels, are examined. By using our channel power gain normalization, the capacity curves of these ISI channels are shown.
IEEE Transactions on Information Theory 10/2003; · 3.01 Impact Factor
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ABSTRACT: Iterative decoding of JPEG images does not perform well due to the poor distance property of the original JPEG Huffman codes. We propose a symmetric RVLC with large free distance which can dramatically improve the system performance when iterative decoding is performed. Simulation results indicate up to 4 dB coding gain is achievable.
Information Theory, 2003. Proceedings. IEEE International Symposium on; 08/2003
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ABSTRACT: We investigate the capacity of various ISI channels with adaptive white Gaussian noise. Previous papers showed a minimum E<sub>b</sub>/N<sub>0</sub> of -4.6 dB, 3 dB below the capacity of a flat channel, is obtained using water pouring capacity formulas for the 1 + D channel. However, these papers did not take it into account that the channel power gain can be greater than one when water pouring is used. We present a generic power normalisation method of the channel frequency response, namely peak bandwidth normalisation, to facilitate the pair capacity comparison of various ISI channels. Three types of ISI channel, i.e., adder channels, RC channels and magnetic recording channels, are examined. By using our channel power gain normalisation, the capacity curves of these ISI channels are shown.
Communications, 2003. ICC '03. IEEE International Conference on; 06/2003
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ABSTRACT: An investigation of unequal error protection (UEP) methods applied
to JPEG image transmission using turbo codes is presented. The JPEG
image is partitioned into two groups, i.e., DC components and AC
components according to their respective sensitivity to channel noise.
The highly sensitive DC components are better protected with a lower
coding rate, while the less sensitive AC components use a higher coding
rate. Simulation results are given to demonstrate how the UEP schemes
outperforms the equal error protection (EEP) scheme in terms of bit
error rate (BER) and peak signal to noise ratio (PSNR)
Information Theory Workshop, 2001. Proceedings. 2001 IEEE; 02/2001
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ABSTRACT: This paper describes a new class of codes, chaotic turbo codes. They were born from a symbiosis between a chaotic digital encoder and a turbo code. This paper investigates the most important properties of both chaotic digital encoders and turbo encoders in order to understand how the two complement each other. A chaotic turbo encoder is then described and initial results are presented
Information Theory, 2000. Proceedings. IEEE International Symposium on; 02/2000
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ABSTRACT: The performance of turbo codes can be improved by choosing the
best constituent encoder. Previous lists of the best constituent codes
were found based on maximising the input weight, two effective free
distance d<sub>2</sub>. We show that minimising the number of nearest
neighbours N<sub>2</sub> is also an important requirement. If there are
multiple codes having the same d<sub>2</sub> and N<sub>2</sub>, we show
that the minimum distance d<sub>min</sub> can be a useful criteria to
identify the best code. A list of generator polynomials suitable for
turbo codes are presented in this paper which satisfy the criteria
mentioned above. The previously published results are also extended to
include larger memory
Global Telecommunications Conference, 1998. GLOBECOM 98. The Bridge to Global Integration. IEEE; 02/1998
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ABSTRACT: A coding scheme, termed turbo-codes was proposed, which achieves
results very close to the Shannon-limit. The encoding and decoding of
turbo-codes is reviewed. In particular, a comparison of the current
methods used for terminating the trellis of the turbo-code are
described. A novel approach to termination of the code is introduced
which removes the need to transmit tail bits across the channel. A
reduction in transmitted symbols by 2 percent is achieved for PCS CDMA
type applications. Simulations confirm that the novel approach is better
in terms of BER than other methods of termination
Personal, Indoor and Mobile Radio Communications, 1996. PIMRC'96., Seventh IEEE International Symposium on; 11/1996
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S.S. Pietrobon
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ABSTRACT: New upper and lower bounds and approximations on the sequence,
event, first event, and bit-error probabilities of convolutional codes
are presented. Each of these probabilities are precisely defined and the
relationship between them described. Some of the new bounds and
approximations are found to be very close to computer simulations at
very high error ratios. Simple modifications to the traditional union
upper bound are also described for both hard- and soft-decision channels
that allow better performance estimates to be made
IEEE Transactions on Information Theory 10/1996; · 3.01 Impact Factor
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ABSTRACT: A new bandwidth efficient interleaver is described for turbo codes when used to decode short frames of data using the MAP algorithm. Applications in rate compatible turbo codes and encryption are presented
Information Theory, 1995. Proceedings., 1995 IEEE International Symposium on; 10/1995
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ABSTRACT: Turbo codes can easily be used when two error protection levels
are needed. The same encoder and decoder is used to achieve this unequal
error protection. This will allow turbo codes to be used for channels
where some information bits are more sensitive to errors than others,
and at the same time where powerful codes are required (e.g. a mobile
satellite channel)
Electronics Letters 04/1995; · 0.96 Impact Factor
