commit dafb33700eb7dee6ece776cd6b548721c28c9bd5
author Thomas Tsou <tom@tsou.cc> Wed Sep 18 16:21:26 2013 -0400
committer Thomas Tsou <tom@tsou.cc> Fri Oct 18 13:10:17 2013 -0400
tree c2f5918b0f65b2fd41d9a6c278e7faf23bcf6727
parent 0e44ab360ef53b0d3d28228fe1e71aa99181ded7

Transceiver52M: Reduce RACH and TSC correlation windows

Start the correlation search window at 4 symbols before
the expected correlation peak. End the search at 10
symbols and 4 + maximum expected delay for RACH and TSC
bursts respectively.

This change lowers receive side cpu utilization while
maintaining reasonable timing jitter and accuracy tolerance.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

Transceiver52M/sigProcLib.cpp

diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 2350abb..7598156 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -1215,8 +1215,8 @@
  *
  * Correlation window parameters:
  *   target: Tail bits + RACH length (reduced from 41 to a multiple of 4)
- *   head: Search 8 symbols before target 
- *   tail: Search 8 symbols after target
+ *   head: Search 4 symbols before target 
+ *   tail: Search 10 symbols after target
  */
 int detectRACHBurst(signalVector &rxBurst,
 		    float thresh,
@@ -1234,8 +1234,8 @@
     return -1;
 
   target = 8 + 40;
-  head = 8;
-  tail = head;
+  head = 4;
+  tail = 10;
 
   start = (target - head) * sps - 1;
   len = (head + tail) * sps;
@@ -1268,8 +1268,8 @@
  *
  * Correlation window parameters:
  *   target: Tail + data + mid-midamble + 1/2 remaining midamblebits
- *   head: Search 8 symbols before target
- *   tail: Search 8 symbols + maximum expected delay
+ *   head: Search 4 symbols before target
+ *   tail: Search 4 symbols + maximum expected delay
  */
 int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
                         int sps, complex *amp, float *toa, unsigned max_toa,
@@ -1285,8 +1285,8 @@
     return -1;
 
   target = 3 + 58 + 16 + 5;
-  head = 8;
-  tail = head + max_toa;
+  head = 4;
+  tail = 4 + max_toa;
 
   start = (target - head) * sps - 1;
   len = (head + tail) * sps;