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Turbo Codes

  • Giovanni CancellieriEmail author
Chapter
Part of the Signals and Communication Technology book series (SCT)

Abstract

Recursive systematic convolutional codes are studied from the point of view of their capability in transforming low-weight information sequences into high-weight output sequences. The basic principle of a turbo code, constructed by means of two recursive systematic convolutional codes in parallel concatenation, is presented. The importance of the role of the interleaver is stressed. The interleaver coding gain and the concept of effective minimum distance are discussed. The phenomenon of spectral thinning is described. The possibility of employing puncturation for increasing the code rate is taken into account. A statistical prediction of turbo code performance is developed, exploiting the model of a uniform interleaver. The presence of a BER floor is considered, and some solutions for lowering it are proposed. The possibility of not terminating one of the two component codes is examined, with the purpose of increasing the code rate. The generator matrix of a turbo code is calculated, taking into account some very simple deterministic interleavers. A description of the decoding algorithm is outlined, with particular attention to its time latency, imposed by the number of iterations. A variant of turbo codes consisting of a serial concatenation is introduced. It typically shows a smaller interleaver gain, but also a less pronounced BER floor. Finally a turbo product code is described, based on two convolutional codes forming a product scheme with or without interleaver. The parity check matrices of some turbo code arrangements are presented.

Keywords

Code Rate Block Code LDPC Code Code Word Turbo Code 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  1. 1.Information EngineeringPolytechnic University of MarcheAnconaItaly

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