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Dynamic look-up-table-based maximum a posterior probability algorithm

WIRELESS PERSONAL COMMUNICATIONS 2008年第3期46卷 317-328页

作者： Kahveci, Salim Kaya, Ismail Turk, Kadir KTU Dept Elect & Elect Engn Trabzon Turkey

In this paper, a Look-Up-Table (LUT) based calculation for implementing log-likelihood ratio (LLR) of the Maximum a Posterior (map) decoder is introduced and analysed. In the region of low signal to noise ratio, the analysed performances of turbo coding have been found very satisfying. However, when implementing the map turbo decoder, the required calculation for LLR is too complex prohibiting its applications. In order to reduce the complexity a dynamic-LUT based simplification is proposed whereas a static-LUT never converge the expectations, since the limited size and resolution of LUT dramatically degrade the performance. In order to maintain simplicity for a high performance implementation, a dynamic LUT, which has partial resolutions in separate decision regions and being re-calculated for further iterations of decoding, is proposed. One of the most important results obtained is that our proposed dynamic-LUT based map algorithm removes "ln(center dot)" process, which is the natural logarithm in LLR's calculation. Therefore, it reduces high computational complexity in the map algorithm with some reasonable performance degradations.

关键词： bluetooth map algorithm LUT

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On the iterative approximation of optimal joint source-channel decoding

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 2001年第9期19卷 1662-1670页

作者： Görtz, N Univ Kiel Fac Engn Inst Circuits & Syst Theory Kiel Germany

Joint source-channel decoding is formulated as an estimation problem. The optimal solution is stated and it is shown that it is not feasible in many practical systems due to its complexity. Therefore, a novel iterative procedure for the approximation of the optimal solution is introduced, which is based on the principle of iterative decoding of turbo codes. New analytical expressions for different types of information in the optimal algorithm are used to derive the iterative approximation. A direct comparison of the performances of the optimal algorithm and its iterative approximation is given for a simple transmission system with "short" channel codewords. Furthermore, the performance of iterative joint source-channel decoding is investigated for a more realistic system.

关键词： concatenated codes iterative decoding joint source-channel coding map algorithm soft-in/soft-out decoding turbo (de)coding

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A low-memory intensive decoding architecture for double-binary convolutional turbo code

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TURKISH JOURNAL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCES 2014年第1期22卷 202-213页

作者： Zhan, Ming Zhou, Liang Wu, Jun Univ Elect Sci & Technol China Natl Key Lab Sci & Technol Commun Chengdu 610054 Peoples R China Southwest Univ Sch Elect & Informat Engn Chongqing Peoples R China Waseda Univ Global Informat & Telecommun Inst Tokyo Japan

Memory accesses take a large part of the power consumption in the iterative decoding of double-binary convolutional turbo code (DB-CTC). To deal with this, a low-memory intensive decoding architecture is proposed for DB-CTC in this paper. The new scheme is based on an improved maximum a posteriori probability algorithm, where instead of storing all of the state metrics, only a part of these state metrics is stored in the state metrics cache (SMC), and the memory size of the SMC is thus reduced by 25%. Owing to a compare-select{recalculate processing (CSRP) module in the proposed decoding architecture, the unstored state metrics are recalculated by simple operations, while maintaining near optimal decoding performance.

关键词： Branch metrics computational complexity map algorithm state metrics cache

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Trellis-based soft-output adaptive equalization techniques for TDMA cellular systems

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2000年第1期49卷 83-94页

作者： Park, JI Wicker, SB Owen, HL Korean Mil Acad Dept Elect Engn Seoul 139799 South Korea Cornell Univ Sch Elect Engn Ithaca NY 14853 USA Georgia Inst Technol Sch Elect & Comp Engn Atlanta GA 30332 USA

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.

关键词： adaptive equalization fading channel map algorithm modified-map algorithm soft output SOVA SSA TDMA Viterbi decoder

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Low-Complexity Soft-Decision Detection for Combating DFE Burst Errors in IM/DD Links

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2024年第5期42卷 1395-1408页

作者： Wu, Kaiquan Liga, Gabriele Riani, Jamal Alvarado, Alex Eindhoven Univ Technol Dept Elect Engn Informat & Commun Theory Lab Signal Proc Syst Grp NL-5600 MB Eindhoven Netherlands Marvell Technol Santa Clara CA 95054 USA

The deployment of non-binary pulse amplitude modulation (PAM) and soft decision (SD)-forward error correction (FEC) in future intensity-modulation (IM)/direct-detection (DD) links is inevitable. However, high-speed IM/DD links suffer from inter-symbol interference (ISI) due to bandwidth-limited hardware. Traditional approaches to mitigate the effects of ISI are filters and trellis-based algorithms targeting symbol-wise maximum a posteriori (map) detection. The former approach includes decision-feedback equalizer (DFE), and the latter includes Max-Log-map (MLM) and soft-output Viterbi algorithm (SOVA). Although DFE is easy to implement, it introduces error propagation (EP). Such burst errors distort the log-likelihood ratios (LLRs) required by SD-FEC, causing performance degradation. On the other hand, MLM and SOVA provide near-optimum performance, but their complexity is very high for high-order PAM. In this article, we consider a one-tap partial response channel model, which is relevant for high-speed IM/DD links. We propose to combine DFE with either MLM or SOVA in a low-complexity architecture. The key idea is to allow MLM or SOVA to detect only 3 typical DFE symbol errors, and use the detected error information to generate LLRs in a modified demapper. The proposed structure enables a tradeoff between complexity and performance: i) the complexity of MLM or SOVA is reduced and ii) the decoding penalty due to EP is mitigated. Compared to SOVA detection, the proposed scheme can achieve a significant complexity reduction of up to 94% for PAM-8 transmission. Simulation and experimental results show that the resulting SNR loss is roughly $0.3\!\sim\! 0.4$ dB for PAM-4, and becomes marginal 0.18 dB for PAM-8.

关键词： Direct detection decision-feedback equalizer intensity modulation map algorithm pulse amplitude modulation soft-decision decoding soft-output Viterbi algorithm

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Turbo Code with Modified LLR and Performance Analysis for Bluetooth Packets in Indoor Environments

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WIRELESS PERSONAL COMMUNICATIONS 2010年第2期54卷 277-287页

作者： Kahveci, Salim Kaya, Ismail Karadeniz Tech Univ Dept Elect & Elect Engn TR-61080 Trabzon Turkey

Most of the restrictions in indoor environments do not exist for outdoor sites. The main limitations for indoors are the attenuation of walls and the multipath fading effects. The signal propagation is limited by the standard free space path loss in outdoor environments or free space. The loss in free space is usually equal to the range squared whereas the loss exponent for indoors is more like the 4th power. This study investigates the performance of turbo codes with modified Maximum-A-Posteriori (map) decoding algorithm for Bluetooth data packets in indoor environments over the frequency selective Rayleigh fading channels;which are also called as indoor wireless communication channels. In order to reduce the computational complexity of turbo decoders, map algorithm is modified in this study. Bit error rate (BER) versus energy of bit-to-noise ratio (E (b) /N (o) ) of modified map algorithms for Bluetooth data packets at 2.4 GHz industrial-scientific-medical (ISM) band are evaluated by means of computer simulations. Thus, modified logarithmic likelihood ratio (LLR) method can significantly reduce the computational complexity of the map algorithm. Furthermore, the performances of different types of forward error correction (FEC) coding for Bluetooth data packets are compared in the study.

关键词： Bluetooth FEC Turbo codes map algorithm

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A Flexible LDPC/Turbo Decoder Architecture

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JOURNAL OF SIGNAL PROCESSING SYSTEMS FOR SIGNAL IMAGE AND VIDEO TECHNOLOGY 2011年第1期64卷 1-16页

作者： Sun, Yang Cavallaro, Joseph R. Rice Univ Dept Elect & Comp Engn Houston TX 77005 USA

Low-density parity-check (LDPC) codes and convolutional Turbo codes are two of the most powerful error correcting codes that are widely used in modern communication systems. In a multi-mode baseband receiver, both LDPC and Turbo decoders may be required. However, the different decoding approaches for LDPC and Turbo codes usually lead to different hardware architectures. In this paper we propose a unified message passing algorithm for LDPC and Turbo codes and introduce a flexible soft-input soft-output (SISO) module to handle LDPC/Turbo decoding. We employ the trellis-based maximum a posteriori (map) algorithm as a bridge between LDPC and Turbo codes decoding. We view the LDPC code as a concatenation of n super-codes where each super-code has a simpler trellis structure so that the map algorithm can be easily applied to it. We propose a flexible functional unit (FFU) for map processing of LDPC and Turbo codes with a low hardware overhead (about 15% area and timing overhead). Based on the FFU, we propose an area-efficient flexible SISO decoder architecture to support LDPC/Turbo codes decoding. Multiple such SISO modules can be embedded into a parallel decoder for higher decoding throughput. As a case study, a flexible LDPC/Turbo decoder has been synthesized on a TSMC 90 nm CMOS technology with a core area of 3.2 mm(2). The decoder can support IEEE 802.16e LDPC codes, IEEE 802.11n LDPC codes, and 3GPP LTE Turbo codes. Running at 500 MHz clock frequency, the decoder can sustain up to 600 Mbps LDPC decoding or 450 Mbps Turbo decoding.

关键词： SISO decoder LDPC decoder Turbo decoder Error correcting codes map algorithm Reconfigurable architecture

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Performance of turbo code in WB-CDMA radio links with estimated channel variance

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IEICE TRANSACTIONS ON COMMUNICATIONS 1998年第12期E81B卷 2514-2518页

作者： Lee, HW Park, CS Yun, YS Hwang, SK SAMSUNG ELECT CO LTD IMT Syst Dev Grp 2000 Telecommun R&D Ctr Bundang Gu Kyungki Do 463050 South Korea Korea Adv Inst Sci & Technol Dept Elect Engn Commun Network Lab Yoosung Gu Taejon 305701 South Korea

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.

关键词： turbo code convolutional code Reed-Solomon code map algorithm WB-CDMA

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On SOVA for nonbinary codes

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IEEE COMMUNICATIONS LETTERS 1999年第12期3卷 335-337页

作者： Ling, C Wu, XF Yi, XX Nanjing Inst Commun Engn Nanjing 210016 Peoples R China

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.

关键词： map algorithm soft-input soft-output decoding SOVA

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A soft-output Viterbi equalizer employing expanded memory length in a trellis

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IEICE TRANSACTIONS ON COMMUNICATIONS 1997年第2期E80B卷 381-385页

作者： Nagayasu, T Kubo, H Murakami, K Fujino, T Information Technology R and D Center Mitsubishi Electric Corporation Kamakura-shi 247 Japan

This paper presents a novel approach to a soft-output equalizer, which makes a symbol-by-symbol soft-decision based on a posteriori probabilities (APP's) criterion in the presence of intersymbol interference. The authors propose a soft-output Viterbi equalizer (SOVE) employing expanded memory length in a trellis of the Viterbi algorithm with small arithmetic complexity. The proposed equalizer gives suboptimum soft-decision closer to that of a equalizer with the maximum a posteriori probabilities (map) algorithm than the conventional SOVE.

关键词： soft-output Viterbi equalizer map algorithm Viterbi algorithm soft-decision intersymbol interference

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