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% qam16.m
% David Rowe May 2020
%
% Octave QAM16 functions
1;
function symbol = qam16_mod(constellation, four_bits)
bits_decimal = sum(four_bits .* [8 4 2 1]);
symbol = constellation(bits_decimal+1);
endfunction
function four_bits = qam16_demod(constellation, symbol, amp_est=1)
assert (amp_est != 0);
symbol /= amp_est;
dist = abs(symbol - constellation(1:16));
[tmp decimal] = min(dist);
four_bits = zeros(1,4);
for i=1:4
four_bits(1,5-i) = bitand(bitshift(decimal-1,1-i),1);
end
endfunction
function test_qam16_mod_demod(constellation)
for decimal=0:15
tx_bits = zeros(1,4);
for i=1:4
tx_bits(1,5-i) = bitand(bitshift(decimal-1,1-i),1);
end
symbol = qam16_mod(constellation, tx_bits);
rx_bits = qam16_demod(constellation,symbol);
assert(tx_bits == rx_bits);
end
endfunction
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