-% fsk_horus.txt
+% fsk_horus.m
% David Rowe 10 Oct 2015
%
% Experimental near space balloon FSK demodulator
% Assume high SNR, but fades near end of mission can wipe out a few bits
% So low SNR perf not a huge issue
%
-% [ ] processing buffers of 1 second
+% [X] processing buffers of 1 second
% + 8000 samples input
% + keep 30 second sliding window to extract packet from
% + do fine timing on this
% [X] estimate frequency of two tones
% + this way we cope with variable shift and drift
-% [ ] estimate amplitudes and equalise, or limit
+% + starts to lose it at 8 Eb/No = 8db. Maybe wider window?
+% [X] estimate amplitudes and equalise, or limit
+% + not needed - tones so close in freq unlikely to be significant ampl diff
+% across SSB rx filter
% [X] Eb/No point 8dB, 2% ish
% [X] fine timing and sample slips, +/- 1000ppm (0.1%) clock offset test
% [ ] bit flipping against CRC
% [ ] implement CRC
-% [ ] frame sync
-% [ ] compare to fldigi
-% [ ] test over range of f1/f2, shifts (varying), timing offsets, clock offsets, Eb/No
+% [X] frame sync
+% [X] compare to fldigi
+% + in AWGN channel 3-4dB improvement. In my tests fldigi can't decode
+% with fading model, requires Eb/No > 40dB, this demo useable at Eb/No = 20dB
+% [ ] test over range of f1/f2, shifts, timing offsets, clock offsets, Eb/No
+% [X] +/- 1000ppm clock offset OK at Eb/No = 10dB, starts to lose it at 8dB
+% [X] tone freq est starts to lose it at 8dB in awgn. Maybe wider window?
+% [ ] low snr detection of $$$$$$
+% + we might be able to pick up a "ping" at very low SNRs to help find baloon on ground
+% [ ] streaming, indicator of audio freq, i.e. speaker output
1;
states.uw = [mapped_db zeros(1,npad) mapped_db zeros(1,npad) mapped_db zeros(1,npad) mapped_db zeros(1,npad) mapped_db zeros(1,npad)];
- states.uw_thresh = 5*7 - 2; % allow 2 bit errors when looking for UW
+ states.uw_thresh = 5*7 - 4; % allow 24bit errors when looking for UW
+
+ states.df = 0;
endfunction
tx = zeros(states.Ts*length(tx_bits),1);
tx_phase = 0;
Ts = states.Ts;
- f1 = 1500; f2 = 1900;
+ Fs = states.Fs;
+ f1 = 1000; f2 = 1400;
+ df = states.df; % tone freq change in Hz/s
for i=1:length(tx_bits)
if tx_bits(i) == 0
- tx_phase_vec = tx_phase + (1:Ts)*2*pi*f1/states.Fs;
+ tx_phase_vec = tx_phase + (1:Ts)*2*pi*f1/Fs;
else
- tx_phase_vec = tx_phase + (1:Ts)*2*pi*f2/states.Fs;
+ tx_phase_vec = tx_phase + (1:Ts)*2*pi*f2/Fs;
end
tx((i-1)*Ts+1:i*Ts) = 2.0*cos(tx_phase_vec);
tx_phase -= floor(tx_phase/(2*pi))*2*pi;
+ f1 += df*Ts/Fs; f2 += df*Ts/Fs;
end
endfunction
function run_sim
frames = 100;
- EbNodB = 10;
- timing_offset = 0.0;
- test_frame_mode = 1;
+ EbNodB = 20;
+ timing_offset = 0.0; % see resample() for clock offset below
+ test_frame_mode = 4;
+ fading = 1; % modulates tx power at 5Hz with 20dB fade depth,
+ % to simulate balloon rotating at end of mission
+ df = 1; % tx tone freq drift in Hz/s
more off
rand('state',1);
P = states.P;
Rs = states.Rs;
nsym = states.nsym;
+ Fs = states.Fs;
+ states.df = df;
EbNo = 10^(EbNodB/10);
variance = states.Fs/(states.Rs*EbNo);
tx_bits(1:2:length(tx_bits)) = 1;
end
+ if test_frame_mode == 4
+
+ % load up a horus msg from disk and modulate that
+
+ test_frame = load("horus_msg.txt");
+ ltf = length(test_frame);
+ ntest_frames = ceil((frames+1)*nsym/ltf);
+ tx_bits = [];
+ for i=1:ntest_frames
+ tx_bits = [tx_bits test_frame];
+ end
+ end
+
tx = fsk_horus_mod(states, tx_bits);
- tx = resample(tx, 1000, 1001); % simulated sample clock offset
+ tx = resample(tx, 1000, 1000); % simulated 1000ppm sample clock offset
+
+ if fading
+ ltx = length(tx);
+ tx = tx .* (1.1 + cos(2*pi*5*(0:ltx-1)/Fs))'; % min amplitude 0.1, -20dB fade, max 3dB
+ end
noise = sqrt(variance/2)*(randn(length(tx),1) + j*randn(length(tx),1));
rx = tx + noise;
+ % dump simulated rx file
+ ftx=fopen("fsk_horus_rx.raw","wb"); rxg = rx*5000; fwrite(ftx, rxg, "short"); fclose(ftx);
+
timing_offset_samples = round(timing_offset*states.Ts);
st = 1 + timing_offset_samples;
rx_bits_buf = zeros(1,2*nsym);
nerr_log = [];
f1_int_resample_log = [];
f2_int_resample_log = [];
+ f1_log = f2_log = [];
for f=1:frames
x_log = [x_log states.x];
f1_int_resample_log = [f1_int_resample_log abs(states.f1_int_resample)];
f2_int_resample_log = [f2_int_resample_log abs(states.f2_int_resample)];
+ f1_log = [f1_log states.f1];
+ f2_log = [f2_log states.f2];
% frame sync based on min BER
subplot(212)
plot(nerr_log)
title('num bit errors each frame')
+
+ figure(4)
+ clf
+ plot(real(rx(1:Fs)))
+ title('rx signal at demod input')
+
+ figure(5)
+ clf
+ plot(f1_log)
+ hold on;
+ plot(f2_log,'g');
+ hold off;
+ title('tone frequencies')
+ axis([1 frames 0 Fs/2])
endfunction
printf("frame sync and data extraction...\n");
- % Now perform frame sync and extract ASCII text --------------------------------------------------------
+ % Now perform frame sync and extract ASCII text -------------------------------------------
% use UWs to delimit start and end of data packets
% RS232 idle bits stuck into it anywhere, ie "bit fields" don't
% change dynamically.
+ % dump msg bits so we can use them as a test signal
+ %msg = rx_bits_log(st:uw_loc-1);
+ %save -ascii horus_msg.txt msg
+
str = [];
st += length(states.uw); % first bit of first char
for i=st:nfield+npad:uw_loc
field = rx_bits_log(i:i+nfield-1);
ch_dec = field * (2.^(0:nfield-1))';
+ % filter out unlikely characters that bit errors may introduce, and ignore \n
+ if (ch_dec > 31) && (ch_dec < 91)
+ str = [str char(ch_dec)];
+ else
+ str = [str char(32)]; % space is "non sure"
+ end
%printf("i: %d ch_dec: %d ch: %c\n", i, ch_dec, ch_dec);
- str = [str char(ch_dec)];
end
- printf("%s", str);
+ printf("%s\n", str);
end
endwhile
endfunction
+
% run test functions from here during development
%run_sim
-rx_bits = demod_file("~/Desktop/vk5arg-3-1.wav");
-
-
-% [X] fixed test frame
-% [X] frame sync on that
-% [X] measure BER, and bits decoded
-% [X] test with sample clock slip
-% [X] test at Eb/No point
-% [X] try to match bits with real data
-% [X] look for UW
-% [ ] try big amplitude fades at a few Hz to simulate spinning, see if timing loses it
-% [ ] streaming I/O
+%rx_bits = demod_file("~/Desktop/vk5arg-3.wav");
+%rx_bits = demod_file("~/Desktop/fsk_horus_10dB_1000ppm.wav");
+%rx_bits = demod_file("~/Desktop/fsk_horus_6dB_0ppm.wav");
+rx_bits = demod_file("fsk_horus_rx.raw");
+%rx_bits = demod_file("~/Desktop/fsk_horus_20dB_0ppm_20dBfade.wav");
+
+% streaming version: take a buffer of say 1 sec. demo to bits. Add to buffer
+% of bits. When two UWs found, demod and dump txt. Shift buffer back that far.
+% how long to make buffer? How to dunmp diagnostics? printf f1, f2, clock offset est
projects / freetel-svn-tracking.git / commitdiff