in the decoding of later layers in the first iteration.
Hence, for these layers, the a posteriori messages computed
from the previous layer are the v-to-c messages of the
current layer. Starting from the second decoding iteration, the
c-to-v messages of the same layer from the previous iteration
need to be subtracted from the a posteriori messages to generate
the v-to-c messages according to (3). Storing the c-to-v messages
of each layer requires a RAM A, which is significantly
larger than a RAM E when