The concatenation of an equalizer and a Viterbi decoder is a powerful means for improving receiver performance in wireless communication systems. A soft-output equalizer increases the impact of this combination by ena...
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The concatenation of an equalizer and a Viterbi decoder is a powerful means for improving receiver performance in wireless communication systems. A soft-output equalizer increases the impact of this combination by enabling the use of. soft-decision Viterbi decoding, It is well known that the maximum a posteriori (map) algorithm provides optimal reliability information, but at the cost of substantial complexity. This paper contains the results of an investigation into the design and performance of soft-output adaptive equalization techniques based on suboptimum trellis-based soft-output decoding algorithms. It is shown that the performance improvement relative to hard output equalizers is substantial, while the cost in terms of complexity is modest. A time-division multiple-access (TDMA) cellular system is used as the basis for comparisons. Simulation results and a complexity analysis are presented.
A new type of recursive algorithm for decoding turbo codes is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion and has lower computational complexi...
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A new type of recursive algorithm for decoding turbo codes is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion and has lower computational complexity. The number of variables to be stored increases linearly with the decoding delay. For iterative decoding, the extrinsic information given by the new algorithm is also described. This algorithm can be used in continuous decoding for both recursive and non-recursive encoder.
Although the reduced-state technique has been widely used in Viterbi equalisers, its application to maximum a posteriori probability (map) equalisers is not satisfactory because it cannot operate due to the backward r...
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Although the reduced-state technique has been widely used in Viterbi equalisers, its application to maximum a posteriori probability (map) equalisers is not satisfactory because it cannot operate due to the backward recursion of the conventional map algorithm. A new kind of map algorithm is proposed in which the forward and backward recursions are exactly symmetric. The reduced-state technique can thus be applied to both forward and backward recursions and a gain in performance is achieved over that of conventional reduced-state map equalisers at the cost of double the computational overhead.
For binary codes, Fossorier et al. have shown that the soft-output Viterbi algorithm (SOVA) becomes equivalent to the Max-Log-maximum a posteriori (map) algorithm after a modification. In this letter, we generalize su...
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For binary codes, Fossorier et al. have shown that the soft-output Viterbi algorithm (SOVA) becomes equivalent to the Max-Log-maximum a posteriori (map) algorithm after a modification. In this letter, we generalize such modified SOVA to nonbinary cases, motivated by the fact that the performance gap between the original SOVA and the Max-Log-map algorithm broadens in these cases. The equivalence between the two algorithms is proved in a more compact form. The modified SOVA requires only add-compare-select operations and is well suited for high-speed parallel implementation.
A novel type of recursive algorithm for decoding turbo codes with a convolutional interleaver is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion w...
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A novel type of recursive algorithm for decoding turbo codes with a convolutional interleaver is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion which can be performed in parallel, and the number of variables to be stored does not increase with decoding delay. This algorithm can be used in continuous decoding for both recursive and nonrecursive encoders. Simulation results of demonstrating its performance are presented.
In this paper, we consider the applicability of turbo code for future third generation (3G) mobile telecommunication systems. Futhermore, we propose a simple method of estimating the channel variance which is necessar...
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In this paper, we consider the applicability of turbo code for future third generation (3G) mobile telecommunication systems. Futhermore, we propose a simple method of estimating the channel variance which is necessary for the map (Maximum A Posteriori) decoding algorithm. We compare the performance of turbo code with a known channel variance, conventional variance estimate and variance estimated by our proposed technique. We show that our variance estimation scheme is adequate for 3G WB-CDMA mobile systems without degradation of turbo code performance.
This paper investigates the use of a maximum a posteriori probability (map) algorithm to realize soft-output equalization in a concatenated equalization and trellis-coded modulation (TCM) decoding-based wireless commu...
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This paper investigates the use of a maximum a posteriori probability (map) algorithm to realize soft-output equalization in a concatenated equalization and trellis-coded modulation (TCM) decoding-based wireless communication system. Specifically, we first begin with a general map algorithm and then focus on studying Bahl's map and Lee's map algorithms. We then propose a modified version of Lee's map algorithm which is much simpler than the original, in terms of complexity, and is more practical. In particular, a very simple channel estimation method which employs orthogonal training sequences is proposed. In order to improve the system performance, equal-gain combining and selection diversity will be also considered. Finally, we compare the performance of the map algorithm-based equalization with our previously proposed equalization scheme, which combines decision feedback equalization and TCM.
Symbol-by-symbol maximum a posteriori (map) decoding algorithms for nonbinary block and convolutional codes over an extension field GF (p(a)) are presented. Equivalent map decoding rules employing the dual code are gi...
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Symbol-by-symbol maximum a posteriori (map) decoding algorithms for nonbinary block and convolutional codes over an extension field GF (p(a)) are presented. Equivalent map decoding rules employing the dual code are given which are computationally more efficient for high-rate codes. It is shown that these algorithms meet all requirements needed for iterative decoding as the output of the decoder can be split into three independent estimates: soft channel value, a priori term and extrinsic value. The discussed algorithms are then applied to a parallel concatenated coding scheme with nonbinary component codes in conjunction with orthogonal signaling.
For binary codes, Fossorier et al. (1998), have shown that the soft-output Viterbi algorithm (SOVA) becomes equivalent to the max-log-maximum a posteriori (map) algorithm after a modification. In this letter, such mod...
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Turbo codes have fascinated many coding researchers because of their near-Shannon-limit error correction performance. In this paper, we discuss multi-dimensional turbo codes which are parallel concatenation of multipl...
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Turbo codes have fascinated many coding researchers because of their near-Shannon-limit error correction performance. In this paper, we discuss multi-dimensional turbo codes which are parallel concatenation of multiple constituent codes. The average upper bound to bit error probability of multidimensional turbo codes is derived. The bound shows that the interleaver gains of this kind of codes are larger than that of conventional two-dimensional turbo codes. Simplified structures of multi-dimensional turbo encoder and decoder are proposed for easier implementation. Simulation results show that for a given interleaver size, by increasing the dimension, great performance improvement can be obtained.
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