find_qc_ldpc.m

Generates Alist format files for SFT LDPC codes

function [m_found,a,b,j_found,k_found] = find_QC_LDPC(rate,N,max)

difference = 10;

rate_lowerbound = 1 - rate;
N_lowerbound = N - difference;
N_upperbound = N + difference;
previous_rate = 1;

for m = 1:max
    if isprime(m) ~= 1
        continue;
    end
    k_lower = floor(N_lowerbound/m);
    k_upper = ceil(N_upperbound/m);
    
    for k =k_lower:k_upper
        a_found = 0;
        b_found = 0;
        j_lower = ceil(k * (1 - rate));
        for j = j_lower:m
            b_found = find_order(j,m);
            a_found = find_order(k,m);
            if( (a_found * b_found) > 0 && (a_found ~= -1) && (b_found ~= -1))
                rate_found = 1 - j/k;
                if rate_found < previous_rate
                    b = b_found;
                    a = a_found;
                    m_found = m;
                    previous_rate = rate_found;
                    j_found = j;
                    k_found = k;
                end
            end
        end
    end
end