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15.3 Compressive Modulation (CM) for Sparse Binary Sources 327
represented by bipartite graphs too, where variable nodes are source bits and check
nodes are RP symbols. We refer to Brink et al. [385, 386] for further details on ex-
trinsic information processing.
As it is difficult to obtain a closed-form expression for the extrinsic information
transfer in RP decoding, we measure the mutual information after each iteration of
decoder processing. We use the notation by Brink [385] and write I
A
for the average
mutual information between the bits and the a priori probabilities. Similarly, we write
I
E
for the average mutual information between the ...