  This paper presents a stochastic algorithm for iterative error control
decoding. We show that the stochastic decoding algorithm is an approximation of
the sum-product algorithm. When the code's factor graph is a tree, as with
trellises, the algorithm approaches maximum a-posteriori decoding. We also
demonstrate a stochastic approximations to the alternative update rule known as
successive relaxation. Stochastic decoders have very simple digital
implementations which have almost no RAM requirements. We present example
stochastic decoders for a trellis-based Hamming code, and for a Block Turbo
code constructed from Hamming codes.
