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Diffstat (limited to 'octave/fdmdv_demod_coh.m')
| -rw-r--r-- | octave/fdmdv_demod_coh.m | 253 |
1 files changed, 253 insertions, 0 deletions
diff --git a/octave/fdmdv_demod_coh.m b/octave/fdmdv_demod_coh.m new file mode 100644 index 0000000..9f00574 --- /dev/null +++ b/octave/fdmdv_demod_coh.m @@ -0,0 +1,253 @@ +% fdmdv_demod_coh.m +% +% Demodulator function for FDMDV modem (Octave version). Requires +% 8kHz sample rate raw files as input. This version uses experimental +% pseudo coherent demodulation. +% +% Copyright David Rowe 2013 +% This program is distributed under the terms of the GNU General Public License +% Version 2 +% + +function fdmdv_demod_coh(rawfilename, nbits, pngname) + + fdmdv; % include modem code + + modulation = 'dqpsk'; + + fin = fopen(rawfilename, "rb"); + gain = 1000; + frames = nbits/(Nc*Nb); + + prev_rx_symbols = ones(Nc+1,1); + foff_phase = 1; + + % BER stats + + total_bit_errors = 0; + total_bits = 0; + bit_errors_log = []; + sync_log = []; + test_frame_sync_log = []; + test_frame_sync_state = 0; + + % SNR states + + sig_est = zeros(Nc+1,1); + noise_est = zeros(Nc+1,1); + + % logs of various states for plotting + + rx_symbols_log = []; + rx_timing_log = []; + foff_log = []; + rx_fdm_log = []; + snr_est_log = []; + + % misc states + + nin = M; % timing correction for sample rate differences + foff = 0; + track_log = []; + track = 0; + fest_state = 0; + + % pseudo coherent demod states + + rx_symbols_ph_log = []; + prev_rx_symbols_ph = ones(Nc+1,1); + rx_phase_offsets_log = []; + phase_amb_log = []; + + % Main loop ---------------------------------------------------- + + for f=1:frames + + % obtain nin samples of the test input signal + + for i=1:nin + rx_fdm(i) = fread(fin, 1, "short")/gain; + end + + rx_fdm_log = [rx_fdm_log rx_fdm(1:nin)]; + + % frequency offset estimation and correction + + [pilot prev_pilot pilot_lut_index prev_pilot_lut_index] = get_pilot(pilot_lut_index, prev_pilot_lut_index, nin); + [foff_coarse S1 S2] = rx_est_freq_offset(rx_fdm, pilot, prev_pilot, nin); + + if track == 0 + foff = foff_coarse; + end + foff_log = [ foff_log foff ]; + foff_rect = exp(j*2*pi*foff/Fs); + + for i=1:nin + foff_phase *= foff_rect'; + rx_fdm(i) = rx_fdm(i)*foff_phase; + end + + % baseband processing + + rx_baseband = fdm_downconvert(rx_fdm, nin); + rx_filt = rx_filter(rx_baseband, nin); + + [rx_symbols rx_timing] = rx_est_timing(rx_filt, rx_baseband, nin); + rx_timing_log = [rx_timing_log rx_timing]; + + nin = M; + if rx_timing > 2*M/P + nin += M/P; + end + if rx_timing < 0; + nin -= M/P; + end + + rx_symbols_log = [rx_symbols_log rx_symbols.*(conj(prev_rx_symbols)./abs(prev_rx_symbols))*exp(j*pi/4)]; + + % coherent phase offset estimation ------------------------------------ + + [rx_phase_offsets ferr] = rx_est_phase(rx_symbols); + rx_phase_offsets_log = [rx_phase_offsets_log rx_phase_offsets]; + phase_amb_log = [phase_amb_log phase_amb]; + rx_symbols_ph = rx_symbols_mem(:,floor(Nph/2)+1) .* exp(-j*(rx_phase_offsets + phase_amb)); + rx_symbols_ph_log = [rx_symbols_ph_log rx_symbols_ph .* exp(j*pi/4)]; + rx_symbols_ph = -1 + 2*(real(rx_symbols_ph .* exp(j*pi/4)) > 0) + j*(-1 + 2*(imag(rx_symbols_ph .* exp(j*pi/4)) > 0)); + + % Std differential (used for freq offset est and BPSK sync) and pseudo coherent detection ----------------------- + + [rx_bits_unused sync f_err pd ] = qpsk_to_bits(prev_rx_symbols, rx_symbols, modulation); + [rx_bits sync_unused ferr_unused pd_unused] = qpsk_to_bits(prev_rx_symbols_ph, rx_symbols_ph, 'dqpsk'); + + foff -= 0.5*f_err; + prev_rx_symbols = rx_symbols; + prev_rx_symbols_ph = rx_symbols_ph; + sync_log = [sync_log sync]; + + [sig_est noise_est] = snr_update(sig_est, noise_est, pd); + snr_est = calc_snr(sig_est, noise_est); + snr_est_log = [snr_est_log snr_est]; + + % freq est state machine + + [track fest_state] = freq_state(sync, fest_state); + track_log = [track_log track]; + + % count bit errors if we find a test frame + + [test_frame_sync bit_errors] = put_test_bits(test_bits, rx_bits); + if (test_frame_sync == 1) + total_bit_errors = total_bit_errors + bit_errors; + total_bits = total_bits + Ntest_bits; + bit_errors_log = [bit_errors_log bit_errors/Ntest_bits]; + else + bit_errors_log = [bit_errors_log 0]; + end + + % test frame sync state machine, just for more informative plots + + next_test_frame_sync_state = test_frame_sync_state; + if (test_frame_sync_state == 0) + if (test_frame_sync == 1) + next_test_frame_sync_state = 1; + test_frame_count = 0; + end + end + + if (test_frame_sync_state == 1) + % we only expect another test_frame_sync pulse every 4 symbols + test_frame_count++; + if (test_frame_count == 4) + test_frame_count = 0; + if ((test_frame_sync == 0)) + next_test_frame_sync_state = 0; + end + end + end + test_frame_sync_state = next_test_frame_sync_state; + test_frame_sync_log = [test_frame_sync_log test_frame_sync_state]; + + end + + % --------------------------------------------------------------------- + % Print Stats + % --------------------------------------------------------------------- + + ber = total_bit_errors / total_bits; + + printf("%d bits %d errors BER: %1.4f\n",total_bits, total_bit_errors, ber); + + % --------------------------------------------------------------------- + % Plots + % --------------------------------------------------------------------- + + xt = (1:frames)/Rs; + secs = frames/Rs; + + figure(1) + clf; + [n m] = size(rx_symbols_log); + plot(real(rx_symbols_log(1:Nc+1,15:m)),imag(rx_symbols_log(1:Nc+1,15:m)),'+') + axis([-2 2 -2 2]); + title('Scatter Diagram'); + + figure(2) + clf; + subplot(211) + plot(xt, rx_timing_log) + title('timing offset (samples)'); + subplot(212) + plot(xt, foff_log, '-;freq offset;') + hold on; + plot(xt, track_log*75, 'r;course-fine;'); + hold off; + title('Freq offset (Hz)'); + grid + + figure(3) + clf; + subplot(211) + [a b] = size(rx_fdm_log); + xt1 = (1:b)/Fs; + plot(xt1, rx_fdm_log); + title('Rx FDM Signal'); + subplot(212) + spec(rx_fdm_log,8000); + title('FDM Rx Spectrogram'); + + figure(4) + clf; + subplot(311) + stem(xt, sync_log) + axis([0 secs 0 1.5]); + title('BPSK Sync') + subplot(312) + stem(xt, bit_errors_log); + title('Bit Errors for test frames') + subplot(313) + plot(xt, test_frame_sync_log); + axis([0 secs 0 1.5]); + title('Test Frame Sync') + + figure(5) + clf; + plot(xt, snr_est_log); + title('SNR Estimates') + + figure(6) + clf; + [n m] = size(rx_symbols_ph_log); + plot(real(rx_symbols_ph_log(1:Nc+1,15:m)),imag(rx_symbols_ph_log(1:Nc+1,15:m)),'+') + %plot(real(rx_symbols_ph_log(2,15:m)),imag(rx_symbols_ph_log(2,15:m)),'+') + axis([-2 2 -2 2]); + title('Scatter Diagram - after phase correction'); + + figure(7) + clf; + subplot(211) + plot(rx_phase_offsets_log(1,:)) + subplot(212) + plot(phase_amb_log(1,:)) + title('Rx Phase Offset Est') + +endfunction |