Applications of graph-based codes in networks: analysis of capacity and design of improved algorithms

Capacity;Improved MP decoder;LDPC codes;Rateless codes;Finite-buffer networks;Graph-based codes;Network codes

Vellambi, Badri Narayanan ; Electrical and Computer Engineering

University:Georgia Institute of Technology

Department:Electrical and Computer Engineering

关键词: Capacity;    Improved MP decoder;    LDPC codes;    Rateless codes;    Finite-buffer networks;    Graph-based codes;    Network codes;   

Others  :  https://smartech.gatech.edu/bitstream/1853/37091/1/vellambi_badri_narayanan_200812_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

The conception of turbo codes by Berrou et al. has created a renewed interest in modern graph-based codes. Several encouraging results that have come to light since then have fortified the role these codes shall play as potential solutions for present and future communication problems.This work focuses on both practical and theoretical aspects of graph-based codes. Thethesis can be broadly categorized into three parts. The first part of the thesis focuses onthe design of practical graph-based codes of short lengths. While both low-density parity-checkcodes and rateless codes have been shown to be asymptotically optimal under the message-passing (MP) decoder, the performance of short-length codes from these families under MP decoding is starkly sub-optimal. This work first addresses thestructural characterization of stopping sets to understand this sub-optimality. Using thischaracterization, a novel improved decoder that offers several orders of magnitude improvement in bit-error rates is introduced. Next, a novel scheme for the design of a good rate-compatible family of punctured codes is proposed.The second part of the thesis aims at establishing these codes as a good tool to developreliable, energy-efficient and low-latency data dissemination schemes in networks. The problems of broadcasting in wireless multihop networks and that of unicast in delay-tolerant networks are investigated. In both cases, rateless coding is seen to offer an elegant means of achieving the goals of the chosen communication protocols. It was noticed that the ratelessness and the randomness in encoding process make this schemespecifically suited to such network applications.The final part of the thesis investigates an application of a specific class of codes callednetwork codes to finite-buffer wired networks. This part of the work aims at establishing a framework for the theoretical study and understanding of finite-buffer networks. Theproposed Markov chain-based method extends existing results to develop an iterativeMarkov chain-based technique for general acyclic wired networks. The framework not only estimates the capacity of such networks, but also provides a means to monitor network traffic and packet drop rates on various links of the network.