Modified augmented belief propagation for general memoryless channels

In this paper, we propose an efficient implementation of the augmented belief propagation (ABP) algorithm for low-density parity-check codes over general memoryless channels. ABP is a multistage BP based decoder that uses a backtracking processing when decoding fails. The algorithm proceeds in two main steps, namely a symbol selection step and an augmented decoding step. The former is based on a criterion related both to the stopping subgraph connectivity and to the input reliability, while the latter can be either implemented using a list based or a greedy approach. Compared to the original implementation, we consider a different approach for both steps. First, the proposed node selection is only based on the dynamic of sign changes of the extrinsic messages at the variable nodes output. This enables us to consider indifferently general memoryless channels, while still taking into account the graph irregularity. Then, we propose a simple yet efficient implementation of the augmented decoding procedure based on pruning of the branching tree The proposed algorithm shows near maximum likelihood decoding performance while decreasing the overall complexity (computation and memory) of the original algorithm. Moreover, complexity-performance trade-off is an built-in feature for this kind of algorithm

On the Impact of Link Layer Retransmissions on TCP for Aeronautical Communications

In this article, we evaluate the impact of link layer retransmissions on the performance of TCP in the context of aeronautical communications.We present the architecture of aeronautical networks, which is manly driven by an important channel access delay, and the various retransmission strategies that can be implemented at both link and transport layers. We consider a worst case scenario to illustrate the benefits provided by the ARQ scheme at the link layer in terms of transmission delay.We evaluate the trade-off between allowing a fast data transmission and a low usage of satellite capacity by adjusting link layer parameters

Blind frame synchronization of Reed-salomon codes

International audienceWe consider in this paper the problem of blind frame synchronization of systems using reed-Solomon (RS) codes and other related families. We present first of all three techniques of blind frame synchronization based on the non-binary parity check matrix of RS codes. While the first two techniques involve the calculation of hard and soft values of the syndrome elements respectively, the third one perform an adaptation step of the parity check matrix before applying the soft criterion. Although RS codes are constructed from non-binary symbols, we show in this paper that it is also possible to synchronize them using the binary image expansion of their parity check matrix. Simulation results show that the synchronization algorithm based on the adaptation of the binary parity check matrix of RS codes has the best synchronization performance among all other techniques. Furthermore, the Frame Error Rate (FER) curves obtained after synchronization and decoding are very close to the perfect synchronization curves

Asymptotic Analysis and Design of LDPC Codes for Laurent-based Optimal and Suboptimal CPM Receivers

International audienceIn this paper, we derive an asymptotic analysis for a capacity approaching design of serially concatenated turbo schemes with low density parity check (LDPC) codes and continuous phase modulation (CPM) based on Laurent decomposition. The proposed design is based on extrinsic mutual information evolution and Gaussian approximation. By inserting partial interleavers between LDPC and CPM and allowing degree-1 variable nodes under a certain constraint we show that designed rates are very close to the maximum achievable rates. Furthermore, we discuss the selection of low complexity receivers that works with the same optimized profiles

Design of Unstructured and Protograph-Based LDPC Coded Continuous Phase Modulation

In this paper, we derive an asymptotic analysis and optimization of coded CPM systems using both unstructured and protograph-based LDPC codes ensembles. First, we present a simple yet effective approach to design unstructured LDPC codes : by inserting partial interleavers between LDPC and CPM, and allowing degree-1 and degree-2 variable nodes in a controlled pattern, we show that designed codes perform that can operate very close to the maximum achievable rates. Finally, the extension to protograph based codes is discussed. We provide some simple rules to design good protograph codes with good threshold properties

Embedding Protection Inside H.264/AVC and SVC Streams

A backward compatible error-protection mechanism embedded into the H.264 (AVC or SVC) syntax is described. It consists of the addition into the H.264 bitstream of supplementary network abstraction layer (NAL) units that contain forward error-correction (FEC) data generated by a block error-correction code. The proposed mechanism allows to leave the original information bits and NAL units intact and does not rely on any side information or extra signalling coming from lower layers, ensuring backward compatibility with the standard syntax. Simulation results obtained with Reed-Solomon and Low-density parity check error-correcting codes show significant improvements for both erroneous and lossy transmission channel configurations.</p

Non Binary LDPC Coded Orthogonal Modulation Schemes based on Non Binary Multilevel Coding

International audienceExisting error correcting schemes approaching the capacity of orthogonal modulations are mainly resorting to optimized bit-interleaved coded modulation (BICM) schemes with mandatory iterative decoding or to non binary coded coding schemes for which the field order is matched to the modulation order. The latter approach is efficient especially for short codeword lengths but suffers from a high complexity for high modulation orders. In this paper, we study properties of multi-level coding (MLC) schemes for high order orthogonal modulations and propose to consider non binary MLC to naturally address layer reduction. Design of non binary LDPC codes for non binary MLC is then investigated for both the Gaussian and Rayleigh fading channels showing good performance in both asymptotic and finite length regimes

LDPC Codes with Low Error Floors and Efficient Encoders

International audienceThis work presents low-density parity-check (LDPC) codes with low error floors, close to capacity performance and highly efficient encoders targeting high throughput applications such as free-space optical downlinks from low earth orbit (LEO) satellites to ground. We devise a code design strategy to find suitable protograph LDPC code ensembles and discuss an field-programmable gate array (FPGA) implementation of the obtained codes. In addition to having competitive decoding performance, the proposed codes have advantages in terms of encoding complexity. An FPGA prototype highlights significant improvements in resource utilization by a factor of around 10 compared to standardized DVB-S2 and CCSDS solutions

Schémas de modulations orthogonales avec codage multi-étages basés sur des codes polaires

International audienceWe investigate MLC (Multilevel Coding) schemes for orthogonal modulations based on polar codes using Monte-Carlo method over a Gaussian channel and over coherent and non coherent regimes.Nous nous intéressons aux schémas MLC (Multilevel Coding) pour les modulations orthogonales en utilisant des codes polaires construits par méthode de Monte-Carlo pour un canal Gaussien cohérent et non cohérent

Extrinsic distortion based Source-Channel allocation for Wireless JPEG2000 transcoding systems

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