Contents lists available at ScienceDirect Int. J. Electron. Commun. (AEÜ) journal homepage: www.elsevier.com/locate/aeue Regular paper Modification of extrinsic information for parallel concatenated Gallager/ Convolutional code to improve performance/complexity trade-offs Brahim Oudjani a,b,c, ⁎ , Hicham Tebbikh c , Noureddine Doghmane d a Department of Electronic, Badji Mokhtar University, BP 12, Annaba 23000, Algeria b Research Center in Industrial Technologies (CRTI), B.O. Box 64, Cheraga 16000, Algiers, Algeria c Laboratory of Automatics and Informatics of Guelma (LAIG), University 08 Mai 45, BP 401, Guelma 24000, Algeria d Laboratory of Automatics and Signals of Annaba (LASA), Badji Mokhtar University, BP 12, Annaba 23000, Algeria ARTICLE INFO Keywords: Computation complexity Convolutional code Extrinsic information LDPC Parallel concatenation Turbo code ABSTRACT To benefit the properties of both Low-Density Parity-Check (LDPC) and Turbo Convolutional Codes ( TCC), we propose a practical concatenated Gallager/Convolutional code in a turbo coding way. The modified code creates a balance between the advantages and the disadvantages of LDPC and TCC in terms of the overall complexity and latency. This will be done through two different component SISO decoders; LDPC and convolutional code of the same rate 1/2 without interleaver. Since the two SISO decoders are different in nature, they exchange ex- trinsic information that will be easily adapted to each other. The study of computation complexity and decoding performance over an AWGN channel indicates that such approach leads to excellent performance because of several factors. The proposed approach achieves a trade-off between waterfall and error floor regions. It reduces complexity decoding compared to TCC and D 3 - TCC . It provides a better coding gain over LDPC and PCGC (Parallel Concatenated Gallager Codes). These features will ensure optimal outcomes and cost-performance ratio, and thus, this trend can be the best choice for today's communication systems. 1. Introduction In most practical wireless communication systems, especially in deep space communications and in next generation mobile commu- nications, a powerful channel coding technique is needed to improve the robustness of data transmission over a very noisy channel. The conception of such code depends on specified criteria. In terms of performance, there are two most crucial facts: the good convergence in waterfall region and the very low error floor. In terms of complexity, also there are two facts to be considered: The low computational complexity of the decoding algorithms and the least number of itera- tions for reaching the desired performance. Most powerful codes have been developed specifically to investigate the rules for channel coding conception regarding the criteria described above. Unfortunately, cer- tain codes are good for a criterion but bad for another. Among these codes, we find the powerful TCC by Berrou et al. [1,2], which are the first codes to reach the limit prophesied by Shannon. Due to their iterative decoding nature, it is difficult to get a very low bit error rate (BER) in all range of signal-to-noise ratio (SNR) because of its error floor phenomenon [3]. However, researchers continually aimed to re- duce error floor region of turbo codes; thus, Three-dimensional turbo code ( D 3 - TCC ) was proposed in [4,5]. Unfortunately, this was at the cost of a slight increase in decoding complexity compared to classical turbo codes. In [6,7], authors have proposed other methods to reducing error floors of classical turbo codes. However, the decoding complexity, the interleaving process and latency make TCC unsuitable for some situations. Several works, such as [8,9], aimed to reduce interleaving complexity to gain high-speed decoding, reduced storage requirements and reduced power consumption. Hyeji et al. [10] proposed a new cyclic redundancy check ( CRC ) stopping criteria unit to reduce the average number of TCC iterations. For very short frame TCC, [11] have designed an efficient early stopping scheme. On another hand, the ad- vances in LDPC codes by Mackay [12,13] overcome TCC in terms of performance and error floor in the higher SNR, leaving TCC suited for only lower SNR. The communication systems which chose LDPC codes over TCC added additional external error correction code to correct the occasional errors that have overstepped the LDPC code. For example, recent digital video broadcasting standards such as DVB - S2 [14] use a BCH external code to eliminate occasional errors of LDPC decoding. Better performance is obtained with the use of TCC as an outer code with LDPC inner code. Although this serial concatenation has been proven effective for deep space communications [15], it increases the https://doi.org/10.1016/j.aeue.2017.10.033 Received 26 April 2017; Accepted 26 October 2017 ⁎ Corresponding author at: Department of Electronic, Badji Mokhtar University, BP 12, Annaba 23000, Algeria. E-mail addresses: oudjani@gmail.com (B. Oudjani), tebbikh@yahoo.com (H. Tebbikh), ndoghmane@univ-annaba.org (N. Doghmane). Int. J. Electron. Commun. (AEÜ) 83 (2018) 484–491 1434-8411/ © 2017 Elsevier GmbH. All rights reserved. MARK