From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Mon, 19 Oct 2015 07:37:34 +0000 (+0000)
Subject: ideal mFSK sim for m=4 working and getting sensible results
X-Git-Url: http://git.whiteaudio.com/gitweb/?a=commitdiff_plain;h=2fcf934a57bf8180e9f897d5fb2c2281290fe467;p=freetel-svn-tracking.git

ideal mFSK sim for m=4 working and getting sensible results

git-svn-id: https://svn.code.sf.net/p/freetel/code@2453 01035d8c-6547-0410-b346-abe4f91aad63
---

diff --git a/codec2-dev/octave/mfsk.m b/codec2-dev/octave/mfsk.m
new file mode 100644
index 00000000..0414b5e6
--- /dev/null
+++ b/codec2-dev/octave/mfsk.m
@@ -0,0 +1,199 @@
+% mfsk.m
+% David Rowe Nov 2015
+
+% Simulation to test m=2 and m=4 FSK demod
+
+
+1;
+
+function sim_out = fsk_ber_test(sim_in)
+  Fs        = 96000;
+  M         = sim_in.M;
+  Rs        = sim_in.Rs;
+  Ts        = Fs/Rs;
+  verbose   = sim_in.verbose;
+
+  nbits     = sim_in.nbits;
+  nsym      = sim_in.nbits*2/M;
+  nsam      = nsym*Ts;
+  EsNodB    = sim_in.EbNodB + 10*log10(M/2);
+
+  % printf("M: %d nbits: %d nsym: %d\n", M, nbits, nsym);
+
+  if M == 2
+    f(1) = -Rs/2;
+    f(2) =  Rs/2;
+  end
+  if M == 4
+    f(1) = -3*Rs/2;
+    f(2) = -Rs/2;
+    f(3) =  Rs/2;
+    f(4) =  3*Rs/2;
+  end
+
+  % simulate over a range of Eb/No values
+
+  for ne = 1:length(EsNodB)
+    Nerrs = Terrs = Tbits = 0;
+
+    aEsNodB = EsNodB(ne);
+    EsNo = 10^(aEsNodB/10);
+    variance = Fs/(Rs*EsNo);
+
+    % Modulator -------------------------------
+
+    tx_bits = round(rand(1, nbits));
+    tx = zeros(1,nsam);
+    tx_phase = 0;
+
+    for i=1:nsym
+      if M == 2
+        tone = tx_bits(i) + 1;
+      else
+        tone = (tx_bits(2*(i-1)+1:2*i) * [2 1]') + 1;
+      end
+
+      tx_phase_vec = tx_phase + (1:Ts)*2*pi*f(tone)/Fs;
+      tx((i-1)*Ts+1:i*Ts) = exp(j*tx_phase_vec);
+      tx_phase = tx_phase_vec(Ts) - floor(tx_phase_vec(Ts)/(2*pi))*2*pi;
+    end
+  
+    % Channel ---------------------------------
+
+    % We use complex (single sided) channel simulation, as it's convenient
+    % for the FM simulation.
+
+    noise = sqrt(variance/2)*(randn(1,nsam) + j*randn(1,nsam));
+    rx    = tx + noise;
+    if verbose > 1
+      printf("EbNo: %f Eb: %f var No: %f EbNo (meas): %f\n", 
+      EbNo, var(tx)*Ts/Fs, var(noise)/Fs, (var(tx)*Ts/Fs)/(var(noise)/Fs));
+    end
+ 
+    % Demodulator -----------------------------
+
+    % non-coherent FSK demod
+
+    rx_bb = rx;
+    dc = zeros(M,nsam);
+    for m=1:M
+      dc(m,:) = rx_bb .* exp(-j*(0:nsam-1)*2*pi*f(m)/Fs);
+    end
+
+    rx_bits = zeros(1, nsym);
+    for i=1:nsym
+      st = (i-1)*Ts+1;
+      en = st+Ts-1;
+      for m=1:M
+        int(m,i) = abs(sum(dc(m,st:en)));
+      end
+      if m == 2
+        rx_bits(i) = int(1,i) < int(2,i);
+      else
+        [max_amp tone] = max([int(1,i) int(2,i) int(3,i) int(4,i)]);
+        if tone == 1
+          rx_bits(2*(i-1)+1:2*i) = [0 0];
+        end
+        if tone == 2
+          rx_bits(2*(i-1)+1:2*i) = [0 1];
+        end
+        if tone == 3
+          rx_bits(2*(i-1)+1:2*i) = [1 0];
+        end
+        if tone == 4
+          rx_bits(2*(i-1)+1:2*i) = [1 1];
+        end
+     end
+    end
+  
+    error_positions = xor(rx_bits, tx_bits);
+    Nerrs = sum(error_positions);
+    Terrs += Nerrs;
+    Tbits += length(error_positions);
+
+    TERvec(ne) = Terrs;
+    BERvec(ne) = Terrs/Tbits;
+
+    if verbose > 1
+      figure(2)
+      clf
+      Rx = 10*log10(abs(fft(rx)));
+      plot(Rx(1:Fs/2));
+      axis([1 Fs/2 0 50]);
+
+      figure(3)
+      clf;
+      subplot(211)
+      plot(real(rx_bb(1:Ts*20)))
+      subplot(212)
+      Rx_bb = 10*log10(abs(fft(rx_bb)));
+      plot(Rx_bb(1:3000));
+      axis([1 3000 0 50]);
+
+      figure(4);
+      subplot(211)
+      stem(abs(mark_int(1:100)));
+      subplot(212)
+      stem(abs(space_int(1:100)));   
+    end
+
+    if verbose
+      printf("EbNo (db): %3.2f Terrs: %d BER: %4.3f \n", aEsNodB - 10*log10(M/2), Terrs, Terrs/Tbits);
+    end
+  end
+
+  sim_out.TERvec = TERvec;
+  sim_out.BERvec = BERvec;
+endfunction
+
+
+function run_fsk_curves
+  sim_in.M         = 2;
+  sim_in.Rs        = 1200;
+  sim_in.nbits     = 12000;
+  sim_in.EbNodB    = 0:2:20;
+  sim_in.verbose   = 1;
+  
+  EbNo  = 10 .^ (sim_in.EbNodB/10);
+  fsk_theory.BERvec = 0.5*exp(-EbNo/2); % non-coherent BFSK demod
+  fsk2_sim = fsk_ber_test(sim_in);
+
+  sim_in.M = 4;
+  fsk4_sim = fsk_ber_test(sim_in);
+
+  % BER v Eb/No curves
+
+  figure(1); 
+  clf;
+  semilogy(sim_in.EbNodB, fsk_theory.BERvec,'r;2FSK theory;')
+  hold on;
+  semilogy(sim_in.EbNodB, fsk2_sim.BERvec,'g;2FSK sim;')
+  semilogy(sim_in.EbNodB, fsk4_sim.BERvec,'b;4FSK sim;')
+  hold off;
+  grid("minor");
+  axis([min(sim_in.EbNodB) max(sim_in.EbNodB) 1E-4 1])
+  legend("boxoff");
+  xlabel("Eb/No (dB)");
+  ylabel("Bit Error Rate (BER)")
+
+end
+
+
+function run_fsk_single
+  sim_in.M         = 4;
+  sim_in.Rs        = 1200;
+  sim_in.nbits     = 5000;
+  sim_in.EbNodB    = 8;
+  sim_in.verbose   = 1;
+
+  fsk_sim = fsk_ber_test(sim_in);
+endfunction
+
+
+rand('state',1); 
+randn('state',1);
+graphics_toolkit ("gnuplot");
+
+run_fsk_curves
+%run_fsk_single
+