From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Fri, 24 Mar 2017 03:05:29 +0000 (+0000)
Subject: can now simulate avergaing three carriers, about to speed up for longer tests
X-Git-Url: http://git.whiteaudio.com/gitweb/?a=commitdiff_plain;h=f4e24235fc112f58fec227b799820b298a01f419;p=freetel-svn-tracking.git

can now simulate avergaing three carriers, about to speed up for longer tests

git-svn-id: https://svn.code.sf.net/p/freetel/code@3083 01035d8c-6547-0410-b346-abe4f91aad63
---

diff --git a/codec2-dev/octave/bpsk_hf.m b/codec2-dev/octave/bpsk_hf.m
index a117c1ae..432850ff 100644
--- a/codec2-dev/octave/bpsk_hf.m
+++ b/codec2-dev/octave/bpsk_hf.m
@@ -1,66 +1,153 @@
 % bpsk_hf.m
 % David Rowe Mar 2017
 %
-% Rate Rs BPSk simulation to explore phase over multiple carriers in HF channel
+% Rate Rs BPSK simulation to explore phase over multiple carriers in HF channel
 
 1;
 
 function sim_out = run_sim(sim_in)
-  Rs = 50;
+  Rs = 100;
 
   Nbits = sim_in.Nbits;
   EbNodB = sim_in.EbNodB;
   verbose = sim_in.verbose;
+  hf_en = sim_in.hf_en;
+  Nc = sim_in.Nc;          % Number of cols, aka number of carriers
+  Nr = Nbits/Nc;           % Number of rows to get Nbits total
+
+  assert(Nbits/Nc == floor(Nbits/Nc), "Nbits/Nc must be an integer");
+  
+  % set up HF model
+
+  if hf_en
+
+    % some typical values
+
+    dopplerSpreadHz = 1.0; path_delay = 1E-3*Rs;
+
+    spread1 = doppler_spread(dopplerSpreadHz, Rs, Nr*2);
+    spread2 = doppler_spread(dopplerSpreadHz, Rs, Nr*2);
+    hf_gain = 1.0/sqrt(var(spread1)+var(spread2));
+    % printf("nsymb: %d lspread1: %d\n", nsymb, length(spread1));
+  end
+  
+  % simulate for each Eb/No point
 
   for nn=1:length(EbNodB)
+    rand('seed',1);
+    randn('seed',1);
+
     EbNo = 10 .^ (EbNodB(nn)/10);
     variance = 1/(EbNo/2);
-    noise = sqrt(variance)*(0.5*randn(1,Nbits) + j*0.5*randn(1,Nbits));
+    noise = sqrt(variance)*(0.5*randn(Nr,Nc) + j*0.5*randn(Nr,Nc));
 
-    tx = zeros(1,Nbits);
-    rx = zeros(1,Nbits);
-    tx_bits = rand(1,Nbits) > 0.5;
+    tx_bits = rand(Nr,Nc) > 0.5;
     tx = 1 - 2*tx_bits;
-    rx = tx + noise;
 
+    rx = tx;
+
+    if hf_en
+
+      % simplified rate Rs simulation model that doesn't include
+      % ISI, just freq filtering.  We assume perfect phase estimation
+      % so it's just amplitude distortion.
+      
+      % Note Rs carrier spacing, sample rate is Rs
+
+      hf_model = zeros(Nr,Nc); phase_est = zeros(1,Nr);
+      for i=1:Nr
+        for c=1:Nc
+          w = 2*pi*c*Rs/Rs; 
+          hf_model(i,c) = hf_gain*(spread1(i) + exp(-j*w*path_delay)*spread2(i));
+        end
+
+        if sim_in.av_phase
+
+          % Simulate obtaining phase est by averaging hf channel model
+          % samples at carrier frequencies adjacent to each carrier.
+          % In case of edge carriers we sample HF channel model to one
+          % side of carrier for now, for a real world estimate we'd
+          % need to interpolate phase to edge carriers somehow
+
+          for c=1:Nc
+            phase_sum = 0;
+            for cc = c-1:c+1
+              w = 2*pi*cc*Rs/Rs; 
+              ahf_model = hf_gain*(spread1(i) + exp(-j*w*path_delay)*spread2(i));
+              phase_sum += ahf_model;
+            end
+            phase_est(i,c) = angle(phase_sum); 
+          end
+          for c=1:Nc
+            rx(i,c) = rx(i,c) .* hf_model(i,c) * exp(-j*phase_est(i,c));
+          end
+
+        else
+
+          % just apply amplitude fading, assume we have ideal phase est
+
+          for c=1:Nc
+            rx(i,c) = rx(i,c) .* abs(hf_model(i,c));
+          end
+        end
+      end
+    end
+
+    rx += noise;
     rx_bits = real(rx) < 0;
     errors = xor(tx_bits, rx_bits);
-    Nerrs = sum(errors);                                         
-    printf("EbNodB: %3.2f BER: %4.3f Nbits: %d Nerrs: %d\n", EbNodB(nn), Nerrs/Nbits, Nbits, Nerrs);
+    Nerrs = sum(errors);
+    printf("EbNodB: %3.2f BER: %4.3f Nbits: %d Nerrs: %d\n", EbNodB(nn), sum(Nerrs)/Nbits, Nbits, sum(Nerrs));
 
     if verbose
       figure(1); clf; 
       plot(rx,'+');
       axis([-2 2 -2 2]);
+      figure(2); clf; 
+      plot(abs(hf_model));
+      figure(3); clf; 
+      plot(angle(hf_model));
+      hold on; plot(phase_est,'+'); hold off;
     end
 
-    sim_out.ber(nn) = Nerrs/Nbits;
+    sim_out.ber(nn) = sum(Nerrs)/Nbits;
   end
 endfunction
 
 
 function run_curves
   sim_in.verbose = 0;
-  sim_in.Nbits = 10000;
-  sim_in.EbNodB = 0:6;
+  sim_in.Nbits = 12000;
+  sim_in.EbNodB = 2:8;
+  sim_in.hf_en = 1;
+  sim_in.Nc = 3;
 
-  bpsk_out = run_sim(sim_in);
+  sim_in.av_phase = 0;
+  bpsk_hf = run_sim(sim_in);
+
+  sim_in.av_phase = 1;
+  bpsk_hf_av_phase = run_sim(sim_in);
 
   figure(3); clf;
-  semilogy(sim_in.EbNodB, bpsk_out.ber,'b+-;BPSK;');
+  semilogy(sim_in.EbNodB, bpsk_hf.ber,'b+-;BPSK HF;');
+  hold on;
+  semilogy(sim_in.EbNodB, bpsk_hf_av_phase.ber,'g+-;BPSK HF average phase;');
+  hold off;
   xlabel('Eb/No (dB)');
   ylabel('BER');
   grid;
   legend('boxoff');
-  title('Coherent BPSK');
 
 end
 
 
 function run_single
-  sim_in.Nbits = 1000;
-  sim_in.EbNodB = 4;
-  sim_in.verbose = 1;
+  sim_in.Nbits = 3000;
+  sim_in.EbNodB = 6;
+  sim_in.verbose = 0;
+  sim_in.hf_en = 1;
+  sim_in.Nc = 3;
+  sim_in.av_phase = 1;
 
   run_sim(sim_in);
 end
@@ -68,8 +155,6 @@ end
 
 format;
 more off;
-rand('seed',1);
-randn('seed',1);
 
 run_single
 %run_curves