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Raptor Codes

20.1  Evolution of Raptor Codes

The second class of Fountain codes is the Raptor code (‘raptor’ derived from rapid tornado), which was necessitated due to the fact that in many applications a universal Fountain code must be constructed that has a constant average weight of an output symbol and operates on a fast decoding algorithm. The basic idea behind Raptor codes is a pre-coding of the input symbols prior to the application of an appropriate LT code. We will design a class of universal Raptor codes with linear time encoder and decoder for which the probability of decoding failure converges to zero polynomially fast as the number of input symbols increases. With proper bounds on the error probability, a finite length Raptor ...

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