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Diffstat (limited to 'octave/fsk_llr_test.m')
| -rw-r--r-- | octave/fsk_llr_test.m | 294 |
1 files changed, 294 insertions, 0 deletions
diff --git a/octave/fsk_llr_test.m b/octave/fsk_llr_test.m new file mode 100644 index 0000000..3c21c64 --- /dev/null +++ b/octave/fsk_llr_test.m @@ -0,0 +1,294 @@ +% fsk_llr_test.m +% +% 2/4FSK simulation to develop LLR estimation algorithms for 4FSK/LDPC modems +% Modified version of David's fsk_llr.m; Bill + +#{ + TODO + The 'v' param of the Ricean pdf is the signal-only amplitude: genie value=16 + In practice, given varying input levels, this value needs to be estimated. + + A small scaling factor seems to improve 2FSK performance -- probably the 'sig' + estimate can be improved. + + Only tested with short code -- try a longer one! + + Simulation should be updated to exit Eb after given Nerr reached + +#} + +ldpc; + +% define Rician pdf +function y = rice(x,v,s) + s2 = s*s; + y = (x / s2) .* exp(-0.5 * (x.^2 + v.^2)/s2) .* besseli(0, x*v/s2); +endfunction + +function plot_pdf(v,s) + x=(0:0.1:2*v); + y= rice(x, v, s); + figure(201); hold on + plot(x,y,'g'); + %title('Rician pdf: signal carrier') + y= rice(x, 0, s); + plot(x,y,'b'); + title('Rician pdf: signal and noise-only carriers') + pause(0.01); +endfunction + +% single Eb/No point simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +function [raw_ber rx_filt rx_bits tx_symbols demapper sig_est ] = run_single(tx_bits, M, EcNodB, plt=0) + % Ec/N0 is per channel bit + bps = log2(M); % bits per symbol + Ts = 16; % length of each symbol in samples + + if length(tx_bits)==1 + Nbits = tx_bits; + tx_bits = randi(2,1,Nbits)-1; % make random bits + endif + + Nbits = length(tx_bits); + Nsymbols = Nbits/log2(M); + tx_symbols = zeros(1,Nsymbols); + + mapper = bps:-1:1; + % look up table demapper from symbols to bits (hard decision) + demapper=zeros(M,bps); + for m=1:M + for b=1:bps + if bitand(m-1,b) demapper(m,bps-b+1) = 1; end + end + end + + % continuous phase mFSK modulator + + w(1:M) = 2*pi*(1:M)/Ts; + tx_phase = 0; + tx = zeros(1,Ts*Nsymbols); + + for s=1:Nsymbols + bits_for_this_symbol = tx_bits(bps*(s-1)+1:bps*s); + symbol_index = bits_for_this_symbol * mapper' + 1; + tx_symbols(s) = symbol_index; + assert(demapper(symbol_index,:) == bits_for_this_symbol); + for k=1:Ts + tx_phase += w(symbol_index); + tx((s-1)*Ts+k) = exp(j*tx_phase); + end + end + + % AWGN channel noise + + + EsNodB = EcNodB + 10*log10(bps) + EsNo = 10^(EsNodB/10); + variance = Ts/EsNo; + noise = sqrt(variance/2)*(randn(1,Nsymbols*Ts) + j*randn(1,Nsymbols*Ts)); + rx = tx + noise; + + if plt==2, % check the Spectrum + [psd,Fpsd] =pwelch(rx,128,0.5,128,Ts); + figure(110); plot(Fpsd,10*log10(psd)); + title('Rx Signal: PSD '); + xlabel('Freq/Rs'); + %figure(111);plot(unwrap(arg(tx))); + pause(0.01); + endif + + + % integrate and dump demodulator + + rx_bits = zeros(1,Nbits); + rx_filt = zeros(Nsymbols,M); + rx_pows = zeros(1,M); + rx_nse_pow = 0.0; rx_sig_pow =0.0; + for s=1:Nsymbols + arx_symb = rx((s-1)*Ts + (1:Ts)); + for m=1:M + r= sum(exp(-j*w(m)*(1:Ts)) .* arx_symb); + rx_pows(m)= r * conj(r); + rx_filt(s,m) = abs(r); + end + [tmp symbol_index] = max(rx_filt(s,:)); + rx_sig_pow = rx_sig_pow + rx_pows(symbol_index); + rx_pows(symbol_index)=[]; + rx_nse_pow = rx_nse_pow + sum(rx_pows)/(M-1); + rx_bits(bps*(s-1)+1:bps*s) = demapper(symbol_index,:); + end + % using Rxpower = v^2 + sigmal^2 + + rx_sig_pow = rx_sig_pow/Nsymbols; + rx_nse_pow = rx_nse_pow/Nsymbols; + sig_est = sqrt(rx_nse_pow/2) % for Rayleigh: 2nd raw moment = 2 .sigma^2 + Kest = rx_sig_pow/(2.0*sig_est^2) -1.0 + + Nerrors = sum(xor(tx_bits, rx_bits)); + raw_ber = Nerrors/Nbits; + printf("EcNodB: %4.1f M: %2d Uncoded Nbits: %5d Nerrors: %4d (Raw) BER: %1.3f\n", ... + EcNodB, M, Nbits, Nerrors, raw_ber); + if plt==1, plot_hist(rx_filt,tx_symbols, M); end + +endfunction + + +% Plot histograms of Rx filter outputs +function plot_hist(rx_filt,tx_symbols, M) + % more general version of previous fn; - plots histograms for any Tx patterns + Smax = 36; + X = 0:Smax-1; + H = zeros(1,Smax); H2 = zeros(1,Smax); s2=0.0; + for m = 1:M + ind = tx_symbols==m; + ind2 = tx_symbols~=m; + H= H+ hist(rx_filt(ind,m),X); + H2= H2+ hist(rx_filt(ind2,m),X); + x=rx_filt(ind2,m); + s2 =s2 + sum(x(:).^2)/length(x); + end + disp('noise RMS is '); sqrt(s2/4) + figure(1); clf; plot(X,H); + title([num2str(M) 'FSK pdf for rx=tx symbol']) + figure(2); clf; plot(X,H2); + title([num2str(M) 'FSK pdf for rx!=tx symbol']) + pause(0.1); + +endfunction + +% 2FSK SD -> LLR mapping that we used for Wenet SSTV system +function llr = sd_to_llr(sd, HD=0) % original 2FSK + HD option + sd = sd / mean(abs(sd)); + x = sd - sign(sd); + sumsq = sum(x.^2); + summ = sum(x); + mn = summ/length(sd); + estvar = sumsq/length(sd) - mn*mn; + estEsN0 = 1/(2* estvar + 1E-3); + if HD==0, + llr = 4 * estEsN0 * sd; + else + llr = 4 * estEsN0 * sign(sd); + endif +endfunction + + +% single point LDPC encoded frame simulation, using 2FSK as a tractable starting point +% Note: ~/cml/matCreateConstellation.m has some support for FSK - can it do 4FSK? + +%%%%%%%%%%%%%%%%%%%%%%%%% + function [Nerrors raw_ber EcNodB] = run_single_ldpc(M, Ltype, Nbits,EbNodB, plt=0) + + disp([num2str(M) 'FSK coded test ... ']) + if M==2 + bps = 1; modulation = 'FSK'; mod_order=2; mapping = 'gray'; + elseif M==4 + bps = 2; modulation = 'FSK'; mod_order=4; mapping = 'gray'; + else + error('sorry - bad value of M!'); + endif + decoder_type = 0; max_iterations = 100; + + load H_256_768_22.txt + Krate = 1/3; + EcNodB = EbNodB + 10*log10(Krate); + code_param = ldpc_init_user(H_256_768_22, modulation, mod_order, mapping); + Nframes = floor(Nbits/code_param.data_bits_per_frame) + Nbits = Nframes*code_param.data_bits_per_frame + + % Encoder + data_bits = round(rand(1,code_param.data_bits_per_frame)); + tx_bits = []; + for f=1:Nframes; + codeword_bits = LdpcEncode(data_bits, code_param.H_rows, code_param.P_matrix); + tx_bits = [tx_bits codeword_bits]; + end + %tx_bits = zeros(1,length(tx_bits)); + + % modem/channel simulation + [raw_ber rx_filt rx_bits tx_symbols demapper sig_est ] = run_single(tx_bits,M,EcNodB, 0 ); + + % Decoder + Nerrors = 0; + for f=1:Nframes + st = (f-1)*code_param.coded_bits_per_frame/bps + 1; + en = st + code_param.coded_bits_per_frame/bps - 1; + + if or(Ltype==1, Ltype==3) + if bps==1, + sd = rx_filt(st:en,1) - rx_filt(st:en,2); + % OR ind = rx_filt(st:en,1) > rx_filt(st:en,2); + % llr = ind'*2 -1; % this works but use SNR scaling + if Ltype==3, HD=1; else, HD = 0; endif + llr = sd_to_llr(sd, HD)'; + endif + if bps==2, + if Ltype==3, + llr = mfsk_hd_to_llrs(rx_filt(st:en,:), demapper); + else + error('Ltype =1 not provided for coded 4FSK'); + endif + endif + endif + if Ltype==2, % SDs are converted to LLRs + v=16; + if plt==1, plot_pdf(v, sig_est); endif + llr = mfsk_sd_to_llrs(rx_filt(st:en,:), demapper, v, sig_est); + endif + + [x_hat, PCcnt] = MpDecode(llr, code_param.H_rows, code_param.H_cols, ... + max_iterations, decoder_type, 1, 1); + Niters = sum(PCcnt!=0); + detected_data = x_hat(Niters,:); + Nerrors += sum(xor(data_bits, detected_data(1:code_param.data_bits_per_frame))); + endfor + ber = Nerrors/Nbits; + printf("EbNodB: %4.1f Coded Nbits: %5d Nerrors: %4d BER: %1.3f\n", EbNodB, Nbits, Nerrors, ber); +endfunction + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +%rand('seed',1); +%randn('seed',1); +format short +more off +init_cml(); + +% store results in array "res" and plot afterwards +% comment the following line if you want to retain prev sims +nrun = 0; clear res; + +Nbits = 20000; plt=0; + +#{ +disp(' uncoded runs') +for M= [2 4] +for Eb = [6:10] + raw_ber = run_single(Nbits, M, Eb, plt) % 2fsk coded + nrun = nrun+1; res(nrun,:) = [Eb Eb M -1 Nbits -1 raw_ber] +endfor +endfor +#} + +disp(' coded runs '); + +M=2, +for Ltype = [1 2 3] +for Eb = [7: 0.5: 9] + [Nerr raw_ber Ec] = run_single_ldpc(M, Ltype, Nbits, Eb, plt) + nrun = nrun+1; res(nrun,:) = [Eb Ec M Ltype Nbits Nerr raw_ber] +endfor +endfor + +M=4, %v=16; +for Ltype = [2 3] +for Eb = [8.0 8.3 8.6 ] + [Nerr raw_ber Ec] = run_single_ldpc(M, Ltype, Nbits, Eb, plt) + nrun = nrun+1; res(nrun,:) = [Eb Ec M Ltype Nbits Nerr raw_ber] +endfor +endfor + + +date = datestr(now) +save 'mfsk_test_res.mat' res date + |