From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Thu, 22 Mar 2018 07:11:41 +0000 (+0000)
Subject: normalised correlation of coarse timing, to assist with initial sync at different... 
X-Git-Url: http://git.whiteaudio.com/gitweb/?a=commitdiff_plain;h=2d5018b56f72cb492f35e19b46352689d5a69561;p=freetel-svn-tracking.git

normalised correlation of coarse timing, to assist with initial sync at different rx levels

git-svn-id: https://svn.code.sf.net/p/freetel/code@3424 01035d8c-6547-0410-b346-abe4f91aad63
---

diff --git a/codec2-dev/octave/ofdm_dev.m b/codec2-dev/octave/ofdm_dev.m
index 48059ade..520eb1fc 100644
--- a/codec2-dev/octave/ofdm_dev.m
+++ b/codec2-dev/octave/ofdm_dev.m
@@ -849,7 +849,7 @@ function [delta_ct delta_foff] = acquisition_test(Ntests=10, EbNodB=100, foff_hz
   sim_in.Tcp = 0.002; 
   sim_in.Rs = 1/Ts; sim_in.bps = 2; sim_in.Nc = 16; sim_in.Ns = 8;
 
-  sim_in.Nsec = Ntests*(sim_in.Ns+1)/sim_in.Rs;
+  sim_in.Nsec = (Ntests+1)*(sim_in.Ns+1)/sim_in.Rs;
 
   sim_in.EbNodB = EbNodB;
   sim_in.verbose = 0;
@@ -861,8 +861,8 @@ function [delta_ct delta_foff] = acquisition_test(Ntests=10, EbNodB=100, foff_hz
   sim_in.ldpc_en = 0;
   
   [sim_out rx states] = run_sim(sim_in);
-
-  states.verbose = 0;
+  
+  states.verbose = 2;
   
   % set up acquistion 
 
@@ -906,7 +906,7 @@ function [delta_ct delta_foff] = acquisition_test(Ntests=10, EbNodB=100, foff_hz
     en = 2.5*Nsamperframe - 1;
     ct_target = Nsamperframe/2;
 
-    for w=1:Nsamperframe:length(rx)-3*Nsamperframe
+    for w=1:Nsamperframe:length(rx)-4*Nsamperframe
       %st = w+0.5*Nsamperframe; en = st+2*Nsamperframe-1;
       %[ct_est foff_est] = coarse_sync(states, rx(st:en), rate_fs_pilot_samples);
       [ct_est foff_est] = coarse_sync(states, rx(w+st:w+en), rate_fs_pilot_samples);
@@ -1010,5 +1010,5 @@ init_cml('/home/david/Desktop/cml/');
 %run_single 
 %run_curves
 %run_curves_estimators
-acquisition_histograms(0, 0)
-%acquisition_test(10, 4, 5)
+%acquisition_histograms(0, 0)
+acquisition_test(10, -3, 5)
diff --git a/codec2-dev/octave/ofdm_lib.m b/codec2-dev/octave/ofdm_lib.m
index a71481da..bd0303b9 100644
--- a/codec2-dev/octave/ofdm_lib.m
+++ b/codec2-dev/octave/ofdm_lib.m
@@ -71,13 +71,16 @@ function [t_est foff_est] = coarse_sync(states, rx, rate_fs_pilot_samples)
     Ncorr = length(rx) - (Nsamperframe+Npsam) + 1;
     assert(Ncorr > 0);
     corr1 = corr2 = zeros(1,Ncorr);
+    av_level = Npsam*sqrt(rx*rx')/Ncorr + 1E-12;
     for i=1:Ncorr
-      corr1(i)   = rx(i:i+Npsam-1) * rate_fs_pilot_samples';
-      corr2(i)  += rx(i+Nsamperframe:i+Nsamperframe+Npsam-1) * rate_fs_pilot_samples';
+      rx1      = rx(i:i+Npsam-1); rx2 = rx(i+Nsamperframe:i+Nsamperframe+Npsam-1);
+      corr1(i) = rx1 * rate_fs_pilot_samples';
+      corr2(i) = rx2 * rate_fs_pilot_samples';
     end
 
-    corr = abs(corr1) + abs(corr2);
+    corr = (abs(corr1) + abs(corr2))/av_level;
     [mx t_est] = max(corr);
+    printf("   max: %f t_est: %d\n", mx, t_est);
 
     #{
     % original freq offset est code that never made it into C.  Have some concerns about CPU
@@ -110,6 +113,7 @@ function [t_est foff_est] = coarse_sync(states, rx, rate_fs_pilot_samples)
       %printf("t_est: %d\n", t_est);
       figure(7); clf;
       plot(abs(corr))
+      axis([1 Ncorr 0 2])
       #{
       figure(8)
       plot(C)
@@ -305,7 +309,7 @@ function [rx_bits states aphase_est_pilot_log rx_np rx_amp] = ofdm_demod(states,
 
   % update timing estimate --------------------------------------------------
 
-  delta_t = 0;
+  delta_t = coarse_foff_est_hz = 0;
   if timing_en
     % update timing at start of every frame