mirror of https://github.com/drowe67/codec2.git
60 lines
1.2 KiB
Matlab
60 lines
1.2 KiB
Matlab
% gp_interleaver.m
|
|
%
|
|
% David Rowe May 2017
|
|
%
|
|
% Golden Prime Interleaver. My interprestation of "On the Analysis and
|
|
% Design of Good Algebraic Interleavers", Xie et al,eq (5).
|
|
|
|
1;
|
|
|
|
% return 1 if prime
|
|
function ret = is_prime(x)
|
|
for i=2:x-1
|
|
if mod(x,i) == 0
|
|
ret = 0;
|
|
return;
|
|
end
|
|
end
|
|
ret = 1;
|
|
end
|
|
|
|
function x = next_prime(x)
|
|
x++;
|
|
while is_prime(x) == 0
|
|
x++;
|
|
end
|
|
end
|
|
|
|
% Choose b for Golden Prime Interleaver. b is chosen to be the
|
|
% closest integer, which is relatively prime to N, to the Golden
|
|
% section of N.
|
|
|
|
function b = choose_interleaver_b(Nbits)
|
|
b = floor(Nbits/1.62);
|
|
b = next_prime(b);
|
|
assert(gcd(b,Nbits) == 1, "b and Nbits must be co-prime");
|
|
end
|
|
|
|
|
|
function interleaved_frame = gp_interleave(frame)
|
|
Nbits = length(frame);
|
|
b = choose_interleaver_b(Nbits);
|
|
interleaved_frame = zeros(1,Nbits);
|
|
for i=1:Nbits
|
|
j = mod((b*(i-1)), Nbits);
|
|
interleaved_frame(j+1) = frame(i);
|
|
end
|
|
endfunction
|
|
|
|
|
|
function frame = gp_deinterleave(interleaved_frame)
|
|
Nbits = length(interleaved_frame);
|
|
b = choose_interleaver_b(Nbits);
|
|
frame = zeros(1,Nbits);
|
|
for i=1:Nbits
|
|
j = mod((b*(i-1)), Nbits);
|
|
frame(i) = interleaved_frame(j+1);
|
|
end
|
|
endfunction
|
|
|