% fsk_lib_ldpc_demo.m % % LDPC coded 4FSK modem demo, demonstrating soft dec using CML library functions fsk_lib; ldpc; % set up waveform function [states M] = modem_init(Rs,Fs,df) M = 4; states = fsk_init(Fs,Rs,M,P=8,nsym=100); states.tx_real = 0; states.tx_tone_separation = 250; states.ftx = -2.5*states.tx_tone_separation + states.tx_tone_separation*(1:M); states.fest_fmin = -Fs/2; states.fest_fmax = +Fs/2; states.fest_min_spacing = Rs/2; states.df = df; states.ber_valid_thresh = 0.1; states.ber_invalid_thresh = 0.2; end % Run a complete modem (freq and timing estimators running) at a % single Eb/No point. At low Eb/No the estimators occasionally fall % over so we get complete junk, we consider that case a packet error % and exclude it from the BER estimation. function [states uber cber cper] = modem_run_test(HRA, EbNodB = 10, num_frames=10, Fs=8000, Rs=100, df=0, plots=0) rand('seed',1); randn('seed',1); [states M] = modem_init(Rs, Fs, df); N = states.N; if plots; states.verbose = 0x4; end % set up LDPC code Hsize=size(HRA); Krate = (Hsize(2)-Hsize(1))/Hsize(2); states.rate = Krate; code_param = ldpc_init_user(HRA, modulation='FSK', mod_order=states.M, mapping='gray'); states.coden = code_param.coded_bits_per_frame; states.codek = code_param.data_bits_per_frame; % set up AWGN noise EcNodB = EbNodB + 10*log10(Krate); EcNo = 10^(EcNodB/10); variance = states.Fs/(states.Rs*EcNo*states.bitspersymbol); 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 % modulator and AWGN channel tx = fsk_mod(states, tx_bits); noise = sqrt(variance/2)*randn(length(tx),1) + j*sqrt(variance/2)*randn(length(tx),1); rx = tx + noise; % freq estimator and demod run_frames = floor(length(rx)/N)-1; st = 1; f_log = []; rx_bits = []; rx_filt = []; for f=1:run_frames % extract nin samples from input stream nin = states.nin; en = st + states.nin - 1; % due to nin variations it's possible to overrun buffer if en < length(rx) sf = rx(st:en); states = est_freq(states, sf, states.M); states.f = states.f2; [arx_bits states] = fsk_demod(states, sf); rx_bits = [rx_bits arx_bits]; rx_filt = [rx_filt abs(states.f_int_resample)]; f_log = [f_log; states.f]; st += nin; end end % count bit errors in test frames num_frames=floor(length(rx_bits)/code_param.coded_bits_per_frame); log_nerrs = []; num_frames_rx = 0; Tbits = Terrs = Tperr = Tpackets = 0; uber = cber = 0.5; cper = 1; for f=1:num_frames-1 st = (f-1)*code_param.coded_bits_per_frame + 1; en = (f+1)*code_param.coded_bits_per_frame; states = ber_counter(states, codeword_bits, rx_bits(st:en)); log_nerrs = [log_nerrs states.nerr]; if states.ber_state num_frames_rx++; end % Using sync provided by ber_counter() state machine for LDPC frame alignment if states.ber_state st_bit = (f-1)*code_param.coded_bits_per_frame + states.coarse_offset; st_symbol = (st_bit-1)/states.bitspersymbol + 1; en_symbol = st_symbol + code_param.coded_bits_per_frame/states.bitspersymbol - 1; %printf("coded_bits: %d bps: %d st_bit: %d st_symbol: %d en_symbol: %d\n", %code_param.coded_bits_per_frame, states.bitspersymbol, st_bit, st_symbol, en_symbol); % map FSK filter outputs to LLRs, then LDPC decode (see also fsk_cml_sam.m) symL = DemodFSK(1/states.v_est*rx_filt(:,st_symbol:en_symbol), states.SNRest, 1); llr = -Somap(symL); [x_hat, PCcnt] = MpDecode(llr, code_param.H_rows, code_param.H_cols, max_iterations=100, decoder_type=0, 1, 1); Niters = sum(PCcnt~=0); detected_data = x_hat(Niters,:); Nerrs = sum(xor(data_bits, detected_data(1:code_param.data_bits_per_frame))); Terrs += Nerrs; Tbits += code_param.data_bits_per_frame; if Nerrs Tperr++; end Tpackets++; end end if states.Terrs printf("Fs: %d Rs: %d df % 3.2f EbNo: %4.2f ftx: %3d frx: %3d\n",Fs, Rs, df, EbNodB, num_frames, num_frames_rx); uber = states.Terrs/states.Tbits; cber = Terrs/Tbits; cper = Tperr/Tpackets; printf(" Uncoded: nbits: %6d nerrs: %6d ber: %4.3f\n", states.Tbits, states.Terrs, uber); printf(" Coded..: nbits: %6d nerrs: %6d ber: %4.3f\n", Tbits, Terrs, cber); printf(" Coded..: npckt: %6d perrs: %6d per: %4.3f\n", Tpackets, Tperr, cper); end if plots figure(1); clf; ideal=ones(length(f_log),1)*states.ftx; plot((1:length(f_log)),ideal(:,1),'bk;ideal;') hold on; plot((1:length(f_log)),ideal(:,2:states.M),'bk'); hold off; hold on; plot(f_log(:,1), 'linewidth', 2, 'b;peak;'); plot(f_log(:,2:states.M), 'linewidth', 2, 'b'); hold off; xlabel('Time (frames)'); ylabel('Frequency (Hz)'); figure(2); clf; plot(log_nerrs); title('Errors per frame'); end end function freq_run_curve_peak_mask(HRA, num_frames=100) EbNodB = 4:10; m4fsk_ber_theory = [0.23 0.18 0.14 0.09772 0.06156 0.03395 0.01579 0.00591 0.00168 3.39E-4]; uber_log = []; cber_log = []; cper_log = []; for ne = 1:length(EbNodB) [states uber cber cper] = modem_run_test(HRA, EbNodB(ne), num_frames); uber_log = [uber_log uber]; cber_log = [cber_log cber]; cper_log = [cper_log cper]; end figure(1); clf; EbNodB_raw = EbNodB+10*log10(states.rate) semilogy(EbNodB_raw, m4fsk_ber_theory(round(EbNodB_raw+1)), 'linewidth', 2, 'bk+-;uber theory;'); grid; hold on; semilogy(EbNodB_raw, uber_log+1E-12, 'linewidth', 2, '+-;uber;'); semilogy(EbNodB, cber_log+1E-12, 'linewidth', 2, 'r+-;cber;'); semilogy(EbNodB, cper_log+1E-12, 'linewidth', 2, 'c+-;cper;'); hold off; xlabel('Eb/No (info bits, dB)'); ylabel('BER/PER'); axis([min(EbNodB_raw) max(EbNodB) 1E-4 1]); title(sprintf("%dFSK rate %3.1f (%d,%d) Ncodewords=%d NCodewordBits=%d Fs=%d Rs=%d", states.M, states.rate, states.coden, states.codek, num_frames, states.Tbits, states.Fs, states.Rs)); print("fsk_lib_ldpc.png", "-dpng") end % Choose simulation here --------------------------------------------------- init_cml(); load H_256_512_4.mat; HRA=H; more off; % single point [states uber cber cper] = modem_run_test(HRA, EbNodB=8); if cber == 0 printf("PASS\n"); end % curve %freq_run_curve_peak_mask(HRA, 200)