The number of downloads is the sum of all downloads of full texts. One of the requirements of coding for data storage systems is the systematic form, i. Thus due to the rateless property, these codes are suitable for transmission over time varying channels. Thesis kB downloads. An algorithm is developed based on the extrinsic information transfer EXIT chart to obtain optimized degree distributions of LT coded differential modulator systems in terms of convergence performance. To address the shortcomings of existing distributed LT DLT codes, we introduce buffer-based DLT codes for a multi-source and multi-relay network to virtually convert lossy source-relay links to corresponding lossless links. This code is able to recover a source block from any set of encoded symbols equal to the number of source symbols in the source block with high probability, and in rare cases from slightly more than the number of source symbols in the source block.

A fountain code is optimal if the original k source symbols can be recovered from any k encoding symbols. We optimize the proposed DLT codes in terms of transmission efficiency; thus exhibiting better performance as compared to their conventional counterparts at the expense of increased computational complexity. From Wikipedia, the free encyclopedia. The results presented in this thesis aim at providing insight into the fundamental design of rateless codes, which could serve as a guideline for the optimal design of rateless codes in real-world applications. A different approach to distributed storage using fountain codes has been proposed in Liquid Cloud Storage [7] [8].

Thesis kB downloads. This problem becomes much more apparent when using a traditional short-length erasure code, as the file must cpdes split into several blocks, each being separately encoded: The idea is then extended to a multi-way relay network where a linear-programming design framework is outlined for optimizing degree distributions in terms of transmission efficiency.

For complexity-constrained applications, we construct low-complexity LT codes and devise a reduced-complexity LT decoder for transmission over noisy channels. This idea is then extended to LT codes for transmission over erasure channels and a design framework is developed to jointly improve the transmission efficiency and erasure floor performance.

Thus due to the rateless property, these codes are suitable for transmission over time varying channels. This idea is then extended to LT codes for transmission over erasure channels and a design framework is developed to jointly improve the transmission efficiency and erasure floor performance. In that respect, fountain codes are expected to allow efficient repair process in case of a failure: A fountain code is inherently rateless, and as a consequence, such codes may potentially generate an unlimited number of encoded symbols on the fly.

From Wikipedia, the free encyclopedia. Raptor codes are the most efficient fountain codes at this time, [2] rteless very efficient linear time encoding and decoding algorithms, and requiring only a small constant number of XOR operations per generated symbol for both encoding and decoding.

A fountain code is inherently rateless, and as a consequence, such codes may potentially generate an codse number of encoded symbols on the fly. The second part of the thesis deals with the analysis and design of rateless codes for multi-point communication.

## Fountain code

Repairable fountain codes [5] are projected to address fountain code design objectives for storage systems. Thus due to the rateless property, these codes are suitable for transmission over time varying channels.

The requirements of erasure code design for data storage, particularly for distributed storage applications, might be quite different relative to communication or data streaming scenarios. Retrieved from ” https: To address the shortcomings of existing distributed LT DLT codes, we introduce buffer-based DLT codes for a multi-source and rareless network to virtually convert lossy source-relay links to corresponding lossless links.

Sparse graph codes such as low-density parity-check codes can offer a performance that approaches the previously elusive Shannon capacity with reasonable practical computational complexity.

By using this site, you agree to the Terms of Use and Privacy Policy. Systematic form enables reading off the message symbols without decoding from a storage unit. This code has an average relative reception overhead of 0. The second part of the thesis deals with the analysis and design of rateless codes for multi-point communication.

Raptor codes and online codes were subsequently introduced, and rateles linear time encoding and decoding complexity through a pre-coding stage of the input symbols. Finally, a design framework is provided for DLT coding schemes, to jointly improve the transmission efficiency and erasure floor performance. Finally, a design framework is provided for DLT coding schemes, to jointly improve the transmission efficiency rareless erasure floor performance. In coding theoryfountain codes also known as rateless erasure codes are a class of erasure codes with the property that a potentially limitless sequence of encoding symbols can be generated from a given set of source symbols such that the original source symbols can ideally be recovered from any subset of the encoding symbols of size equal to or only slightly larger than the number of source symbols.

To observe the consequences of the modified encoding scheme, the convergence behavior of the proposed LT code is analyzed using EXIT charts, and shown to be similar to the convergence performance of conventional LT codes. The thesis is divided into two parts. An encoding scheme is proposed, which is subsequently used to reduce the error floor.

# Analysis and Design of Rateless Codes

Then, we delve deeper into the characteristics of LT codes with the objective of improving the error floor performance over noisy channels. LT codes were the first practical realization of fountain codes. The number of downloads rxteless the sum of all downloads of full texts.

The invention of turbo codes and the re-discovery of sparse graph codes constitute a milestone in error-correction codes designed for communication and storage systems.

Using a fountain code, it suffices for a receiver to retrieve any subset of encoding ratelesa of size slightly larger than the set of source symbols. To observe the consequences of the modified encoding scheme, the convergence behavior of the proposed LT code is analyzed using EXIT charts, and shown to be similar to the convergence performance of conventional LT codes.

The number of downloads is the sum of all downloads of full texts.