Likewise, the columns of the parity check matrices H
,
H
2
associated with G
1
, G
each form a basis for their null
spaces of dimensions (N − K
2
1
) and (N − K
), respectively.
A necessary condition to prevent G from having a rank
smaller than K
1
+ K
2
is that H
1
, H
2
2
cannot have more than
(N − K
) linear independent parity check equations
in common. Based on these considerations, we propose the
following design strategy. First, randomly generate a matrix
M ∈{0, 1}
1
− K
2
of full rank N, according to a given row
and column degree distribution. This matrix is then partitioned
into three submatrices
N×N
1