% ofdm_acquisition.m % David Rowe Jan 2021 % % Simulations used for development of HF data modem burst mode acquisition % % To run headless on a server: % % DISPLAY=\"\" octave-cli --no-gui -qf ofdm_acquisition.m > 210218.txt & ofdm_lib; channel_lib; % Build a vector of Tx bursts in noise, one burst occurs every padded_burst_len samples function [rx tx_preamble tx_postamble burst_len padded_burst_len ct_targets states] = generate_bursts(sim_in) config = ofdm_init_mode(sim_in.mode); states = ofdm_init(config); ofdm_load_const; tx_preamble = states.tx_preamble; tx_postamble = states.tx_postamble; Nbursts = sim_in.Nbursts; tx_bits = create_ldpc_test_frame(states, coded_frame=0); tx_burst = [tx_preamble ofdm_mod(states, tx_bits) tx_postamble]; burst_len = length(tx_burst); tx_burst = ofdm_hilbert_clipper(states, tx_burst, tx_clip_en=0); padded_burst_len = Fs+burst_len+Fs; tx = []; ct_targets = []; for f=1:Nbursts % 100ms of jitter in the burst start point jitter = floor(rand(1,1)*0.1*Fs); tx_burst_padded = [zeros(1,Fs+jitter) tx_burst zeros(1,Fs-jitter)]; ct_targets = [ct_targets Fs+jitter]; tx = [tx tx_burst_padded]; end % adjust channel simulator SNR setpoint given (burst on length)/(sample length) ratio mark_space_SNR_offset = 10*log10(burst_len/padded_burst_len); SNRdB_setpoint = sim_in.SNR3kdB + mark_space_SNR_offset; %printf("SNR3kdB: %f Burst offset: %f\n", sim_in.SNR3kdB, mark_space_SNR_offset) rx = channel_simulate(Fs, SNRdB_setpoint, sim_in.foff_Hz, sim_in.channel, tx); % optional BPF if strcmp(sim_in.mode,"datac4") || strcmp(sim_in.mode,"datac13") [rx delay_samples] = ofdm_complex_bandpass_filter(states, sim_in.mode, rx); l = length(rx); rx = [rx(delay_samples:l) zeros(1,delay_samples)]; end endfunction function results = evaluate_candidate(states, det, i, Nsamperburstpadded, ct_target, foff_Hz, ttol_samples, ftol_hz) results.candidate = 0; if det.timing_mx > states.timing_mx_thresh % OK we have located a candidate peak % re-base ct_est to be wrt start of current burst reference frame ct_est = det.ct_est - (i-1)*Nsamperburstpadded; delta_ct = abs(ct_est-ct_target); delta_foff = det.foff_est-foff_Hz; ok = (abs(delta_ct) < ttol_samples) && (abs(delta_foff) < ftol_hz); results.candidate = 1; results.ct_est = ct_est; results.delta_ct = delta_ct; results.delta_foff = delta_foff; results.ok = ok; end endfunction % test frame by frame acquisition algorithm function Pa = frame_by_frame_acquisition_test(mode="datac1", Ntests=10, channel="awgn", SNR3kdB=100, foff_Hz=0, verbose_top=0) sim_in.SNR3kdB = SNR3kdB; sim_in.channel = channel; sim_in.foff_Hz = foff_Hz; sim_in.mode = mode; sim_in.Nbursts = Ntests; [rx tx_preamble tx_postamble Nsamperburst Nsamperburstpadded ct_targets states] = generate_bursts(sim_in); states.verbose = bitand(verbose_top,3); ofdm_load_const; timing_mx_log = []; ct_log = []; delta_ct_log = []; delta_foff_log = []; state_log = []; % allowable tolerance for acquistion ftol_hz = 2; % we can sync up on this (todo: make mode selectable) ttol_samples = 0.006*Fs; % CP length (todo: make mode selectable) target_acq = zeros(1,Ntests); state = 'acquisition'; for n=1:Nsamperframe:length(rx)-2*Nsamperframe pre = burst_acquisition_detector(states, rx, n, tx_preamble); post = burst_acquisition_detector(states, rx, n, tx_postamble); % adjust time reference for this simulation pre.ct_est += n; post.ct_est += n; timing_mx_log = [timing_mx_log [pre.timing_mx; post.timing_mx]]; % state machine to simulate acquisition/demod processing next_state = state; if strcmp(state,'acquisition') state_log = [state_log 0]; % work out what burst we are evaluating i = ceil(n/Nsamperburstpadded); % i-th burst we are evaluating w = (i-1)*Nsamperburstpadded; % offset of burst in s() for plotting purposes ct_target_pre = ct_targets(i); ct_target_post = ct_targets(i) + Nsamperburst - length(tx_preamble); pre_eval = evaluate_candidate(states, pre, i, Nsamperburstpadded, ct_target_pre, foff_Hz, ttol_samples, ftol_hz); post_eval = evaluate_candidate(states, post, i, Nsamperburstpadded, ct_target_post, foff_Hz, ttol_samples, ftol_hz); if pre_eval.candidate if pre_eval.ok == 0 target_acq(i) = -1; % flag bad candidate end if pre_eval.ok && (target_acq(i) == 0) target_acq(i) = 1; % flag a successful acquisition next_state = "demod"; modem_frame = 0; end delta_ct_log = [delta_ct_log pre_eval.delta_ct]; delta_foff_log = [delta_foff_log pre_eval.delta_foff]; ct_log = [ct_log w+pre_eval.ct_est]; if states.verbose printf("Pre i: %2d n: %8d ct_est: %6d delta_ct: %6d foff_est: %5.1f timing_mx: %3.2f Acq: %2d\n", i, n, pre_eval.ct_est, pre_eval.delta_ct, pre.foff_est, pre.timing_mx, target_acq(i)); end end if post_eval.candidate if post_eval.ok == 0 target_acq(i) = -1; % flag bad candidate end if post_eval.ok && (target_acq(i) == 0) target_acq(i) = 1; % flag a successful acquisition next_state = "demod"; modem_frame = Np-2; end delta_ct_log = [delta_ct_log post_eval.delta_ct]; delta_foff_log = [delta_foff_log post_eval.delta_foff]; ct_log = [ct_log w+post_eval.ct_est]; if states.verbose printf("Post i: %2d n: %8d ct_est: %6d delta_ct: %6d foff_est: %5.1f timing_mx: %3.2f Acq: %2d\n", i, n, post_eval.ct_est, post_eval.delta_ct, post.foff_est, post.timing_mx, target_acq(i)); end end end if strcmp(state, "demod") state_log = [state_log 1]; modem_frame++; if modem_frame > states.Np next_state = "acquisition"; end end state = next_state; end if bitand(verbose_top,8) figure(1); clf; plot(timing_mx_log(1,:),'+-;preamble;'); hold on; plot(timing_mx_log(2,:),'o-;postamble;'); plot(0.45+0.1*state_log,'-g;state;'); title('mx log'); axis([0 length(timing_mx_log) 0 1.0]); grid; hold off; figure(4); clf; plot(real(rx)); axis([0 length(rx) -3E4 3E4]); hold on; plot(ct_log,zeros(1,length(ct_log)),'r+','markersize', 25, 'linewidth', 2); hold off; figure(5); clf; plot_specgram(rx, Fs, 500, 2500); all_mx = [ timing_mx_log(1,:) timing_mx_log(2,:)]; figure(6); clf; [nn xx] = hist(all_mx); semilogy(xx,nn+1); grid; figure(7); clf; cdf = empirical_cdf(0:0.1:1,all_mx); plot(0:0.1:1, cdf); grid; end Pacq = length(find(target_acq == 1))/Ntests; Pfalse_acq = length(find(target_acq == -1))/Ntests; printf("%s %s SNR: %3.1f foff: %3.1f P(acq) = %3.2f P(false_acq) = %3.2f\n", mode, channel, SNR3kdB, foff_Hz, Pacq, Pfalse_acq); endfunction % test frame by frame across modes, channels, and SNR (don't worry about sweeping freq) function acquistion_curves_frame_by_frame_modes_channels_snr(Ntests=5, quick_test=0) modes={'datac0', 'datac1', 'datac3'}; if quick_test Ntests = 5; channels={'awgn','mpp'}; SNR = [0 5]; else channels={'awgn', 'mpm', 'mpp', 'notch'}; SNR = [ -10 -5 -3.5 -1.5 0 1.5 3.5 5 7.5 10 15]; end cc = ['b' 'g' 'k' 'c' 'm' 'r']; pt = ['+' '*' 'x' 'o' '+' '*']; for i=1:length(modes) figure(i); clf; hold on; title(sprintf("%s P(acquisition)", modes{i})); end for m=1:length(modes) figure(m); for c=1:length(channels) Pa_log = []; for s=1:length(SNR) Pa = frame_by_frame_acquisition_test(modes{m}, Ntests, channels{c}, SNR(s), foff_hz=0, verbose=1); Pa_log = [Pa_log Pa]; end l = sprintf('%c%c-;%s;', cc(c), pt(c), channels{c}); plot(SNR, Pa_log, l, 'markersize', 10); end end for i=1:length(modes) figure(i); grid; xlabel('SNR3k dB'); legend('location', 'southeast'); xlim([min(SNR)-2 max(SNR)+2]); ylim([0 1.1]); print('-dpng', sprintf("%s_ofdm_dev_acq_curves_fbf_%s.png", datestr(clock(),"yyyy-mm-dd"), modes{i})); end endfunction % main starts here ----------------------------------------- format; more off; pkg load signal; graphics_toolkit ("gnuplot"); randn('seed',1); % --------------------------------------------------------- % choose simulation to run here % --------------------------------------------------------- if exist("ctest","var") % simple tests to run as part of ctests frame_by_frame_acquisition_test("datac0", Ntests=5, 'mpp', SNR3kdB=5, foff_hz=0, verbose=1+8); else % other development work here frame_by_frame_acquisition_test("datac13", Ntests=100, 'mpp', SNR3kdB=-4, foff_hz=0, verbose=1+8); %acquistion_curves_frame_by_frame_modes_channels_snr(Ntests=50, quick_test=0) end