Calculation of Mutual Information between Messages in Loops of a Tanner Graph

This paper introduces a method for calculating the mutual information between the messages sent to a loop and returning from a loop in a Tanner graph. This mutual information is defined as the difference between the cases when the loop is open and the loop is closed. The proposed method suggests to track the change of information in each node in the loop. The paper explains in detail how to calculate the amount of information change in a node