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% fsk_lib_ldpc_tx.m
%
% LDPC coded 4FSK modem tx, generates a 8 kHz 16 bit short real valued sample file
function fsk_lib_ldpc_tx(filename, num_frames=10, Rs=100, coderate=0.5, EbNodB=100)
fsk_lib_ldpc;
% set up LDPC code
init_cml();
if coderate == 0.5
load H_256_512_4.mat;
elseif coderate == 0.75
load HRAa_1536_512.mat; H=HRA;
else
disp("unknown code rate");
end
[states code_param] = fsk_lib_ldpc_init (H, Rs, Fs=8000);
n = code_param.coded_bits_per_frame; k = code_param.data_bits_per_frame;
rand('seed',1);
data_bits = round(rand(1,code_param.data_bits_per_frame)); tx_bits = [];
for f=1:num_frames
codeword_bits = LdpcEncode(data_bits, code_param.H_rows, code_param.P_matrix);
tx_bits = [tx_bits codeword_bits];
end
tx = fsk_mod(states, tx_bits);
% set up (optional) AWGN noise
EcNodB = EbNodB + 10*log10(states.rate);
EcNo = 10^(EcNodB/10);
variance = states.Fs/(states.Rs*EcNo*states.bitspersymbol);
% note real noise
noise = sqrt(variance/2)*randn(length(tx),1);
rx = tx + noise;
frx=fopen(filename,"wb"); fwrite(frx, states.amp_scale*rx, "short"); fclose(frx);
printf("Fs: %d Rs: %d rate %4.2f (%d,%d) EbNodB: %3.1f EcNodB: %3.1f frames transmitted: %3d\n",
Fs, Rs, coderate, n, k, EbNodB, EcNodB, num_frames);
end
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