where N is the total number of VNs in the Tanner graph and [·]
is the nearest integer function.
Two extreme cases of (4) arise:
1) When b = s (symbolwise puncturing), Nlp
becomes minimum.
We puncture the minimum possible number of
VNs. But these VNs are punctured completely.
2) When b = 1(if allowable), Nlp
is the largest.We puncture
the maximum number of VNs. However, each of these
VNs undergoes the minimal puncturing.
Such conflicting cases can be investigated with the help of
the EXIT chart. The methods to obtain the VND and the CND
curves are discussed below.
VND Curve:
Let pv denote the probability that a VN is punctured. pv can
be expressed as