Forward Error Correction Solution Research Articles

Considerations on the Use of Digital Signal Processing in Future Optical Access Networks

In this invited article, we address the impacts of the rise of signal processing for increased capacity per wavelength and better receiver sensitivities in next generation optical access networks. We start by recalling the main channel limitations of currently deployed intensity modulated, directly detected, passive optical networks. Then, with the intention of providing a benchmarking of signal processing approaches used in communication systems other than optical access, we provide a historic perspective on how digital signal processing emerged in copper access systems, and we evaluate powerful techniques envisaged for future mobile generation in both air interface and radio access networks. We also assess signal processing in light of multi-vendor interoperability by providing insights on burst mode operation and the needed protocol and monitoring procedures. Interoperability with regard to optical transceivers is also considered. Last but not least, we evaluate power consumption of digital signal processing and forward error correction solutions used in disruptive, coherent transmission approaches.

Design of Finite-Length Precoded EWF Codes for Scalable Video Streaming

Expanding window fountain (EWF) codes, which can provide unequal erasure protection property, are used as an efficient application-layer forward error correction solution for scalable multimedia data transmission over packet networks. Similar to Raptor codes, precoded EWF codes can provide linear coding complexity. However, only when the information length is large, the precoded EWF codes in previous literatures can achieve good performance. In this paper, we carefully investigate how to choose code rates of precodes and degree distributions of EWF codes for different information lengths. Our proposed precoded EWF coding scheme can achieve superior performance compared to the previous scheme for small and moderate information lengths. Simulation results for the scalable video coding extension of the H.264/AVC standard show that, compared with the previous scheme, our proposed scheme requires a smaller reception overhead to recover the base layer.

Low-Complexity Soft-Decision Concatenated LDGM-Staircase FEC for High-Bit-Rate Fiber-Optic Communication

A concatenated soft-decision forward error correction (FEC) scheme consisting of an inner low-density generator-matrix (LDGM) code and an outer staircase code is proposed. The soft-decision LDGM code is used for error reduction, while the majority of bit errors are corrected by the low-complexity hard-decision staircase code. Decoding complexity of the concatenated code is quantified by a score based on the number of edges in the LDGM code Tanner graph, the number of decoding iterations, and the number of staircase code decoding operations. The inner LDGM ensemble is designed by solving an optimization problem, which minimizes the product of the average node degree and an estimate of the required number of decoding iterations. A search procedure is used to find the inner and outer code pair with lowest complexity. The design procedure results in a Pareto-frontier characterization of the tradeoff between net coding gain and complexity for the concatenated code. Simulations of code designs at $\text{20}\%$ overhead showed that the proposed scheme achieves net coding gains equivalent to existing soft-decision FEC solutions, with up to $\text{57}\%$ reduction in complexity.

Modeling and Analysis of Frame-Level Forward Error Correction for MPEG Video over Burst-Loss Channels

Forward error correction (FEC) is a common error control technique to improve the quality of video streaming over lossy channels. To optimize the data recovery performance, frame-level FEC schemes have been proposed for streaming video to maximize playable frame rate (PFR) within transmission rate constraint on a random binary symmetric channel (BSC). However, burst loss is a commonplace in current Internet architecture, and the FEC efficacy c an be degraded since the burst data losses easily exceed the error correction capacity of FEC. Accordingly, an estimated video quality model over burst loss channels is proposed in this paper to evaluate the impact of burst loss for FEC-based video applications. In addition to th e model analysis, the simulation experiments on the NS-2 network simulator are conducted at a given estimate of the packet loss probability and average burst length. The results suggest a useful reference in designing the FEC scheme for video applications, and as the video coding and channel parameters are given, the proposed model can provide the optimal FEC solution to achieve a better reconstructed video quality than the FEC model based on a random BSC channel.

Layer-Aware Forward Error Correction for Mobile Broadcast of Layered Media

The bitstream structure of layered media formats such as scalable video coding (SVC) or multiview video coding (MVC) opens up new opportunities for their distribution in Mobile TV services. Features like graceful degradation or the support of the 3-D experience in a backwards-compatible way are enabled. The reason is that parts of the media stream are more important than others with each part itself providing a useful media representation. Typically, the decoding of some parts of the bitstream is only possible, if the corresponding more important parts are correctly received. Hence, unequal error protection (UEP) can be applied protecting important parts of the bitstream more strongly than others. Mobile broadcast systems typically apply forward error correction (FEC) on upper layers to cope with transmission errors, which the physical layer FEC cannot correct. Today's FEC solutions are optimized to transmit single layer video. The exploitation of the dependencies in layered media codecs for UEP using FEC is the subject of this paper. The presented scheme, which is called layer-aware FEC (LA-FEC), incorporates the dependencies of the layered video codec into the FEC code construction. A combinatorial analysis is derived to show the potential theoretical gain in terms of FEC decoding probability and video quality. Furthermore, the implementation of LA-FEC as an extension of the Raptor FEC and the related signaling are described. The performance of layer-aware Raptor code with SVC is shown by experimental results in a DVB-H environment showing significant improvements achieved by LA-FEC.

Scalable Video Multicast Using Expanding Window Fountain Codes

Fountain codes were introduced as an efficient and universal forward error correction (FEC) solution for data multicast over lossy packet networks. They have recently been proposed for large scale multimedia content delivery in practical multimedia distribution systems. However, standard fountain codes, such as LT or Raptor codes, are not designed to meet unequal error protection (UEP) requirements typical in real-time scalable video multicast applications. In this paper, we propose recently introduced UEP expanding window fountain (EWF) codes as a flexible and efficient solution for real-time scalable video multicast. We demonstrate that the design flexibility and UEP performance make EWF codes ideally suited for this scenario, i.e., EWF codes offer a number of design parameters to be ldquotunedrdquo at the server side to meet the different reception criteria of heterogeneous receivers. The performance analysis using both analytical results and simulation experiments of H.264 scalable video coding (SVC) multicast to heterogeneous receiver classes confirms the flexibility and efficiency of the proposed EWF-based FEC solution.

Layered unequal loss protection with pre-interleaving for fast progressive image transmission over packet-loss channels

Most existing unequal loss protection (ULP) schemes do not consider the minimum quality requirement and usually have high computation complexity. In this research, we propose a layered ULP (L-ULP) scheme to solve these problems. In particular, we use the rate-based optimal solution with a local search to find the average forward error correction (FEC) allocation and use the gradient search to find the FEC solution for each layer. Experimental results show that the executing time of L-ULP is much faster than the traditional ULP scheme but the average distortion is worse. Therefore, we further propose to combine the L-ULP with the pre-interleaving to have an improved L-ULP (IL-ULP) system. By using the pre-interleaving, we are able to delay the occurrence of the first unrecoverable loss in the source bitstream and thus improve the loss resilience performance. With the better loss resilience performance in the source bitstream, our proposed IL-ULP scheme is allowed to have a weaker FEC protection and allocate more bits to the source coding which leads to the improvement of overall performance. Experimental results show that our proposed IL-ULP scheme even outperforms the global optimal result obtained by any traditional ULP scheme while the complexity of IL-ULP is almost the same as L-ULP.