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% 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;
% 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)
p = primes(Nbits);
i = 1;
while(p(i) < Nbits/1.62)
i++;
end
b = p(i);
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
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