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