From f775720a830b100e1ed0286b2f879d13be70ca75 Mon Sep 17 00:00:00 2001
From: Ben Reynwar <ben@reynwar.net>
Date: Mon, 30 Apr 2012 09:17:40 -0700
Subject: Fully gray-coding QAM constellations.
---
gr-digital/python/qam.py | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
(limited to 'gr-digital/python/qam.py')
diff --git a/gr-digital/python/qam.py b/gr-digital/python/qam.py
index 5b1f7683b8..0635fda75e 100644
--- a/gr-digital/python/qam.py
+++ b/gr-digital/python/qam.py
@@ -157,14 +157,20 @@ def qam_constellation(constellation_points=_def_constellation_points,
else:
raise ValueError("Mod code is not implemented for QAM")
if differential:
- points = make_differential_constellation(constellation_points, gray_coded)
+ points = make_differential_constellation(constellation_points, gray_coded=False)
else:
points = make_non_differential_constellation(constellation_points, gray_coded)
side = int(sqrt(constellation_points))
width = 2.0/(side-1)
- # No pre-diff code
- # Should add one so that we can gray-code the quadrant bits too.
- pre_diff_code = []
+ # For differential and gray-coded then gray-code the first two
+ # bits with a pre_diff_code.
+ # FIXME: It would be good to have a test to make sure that gray-coded constellations
+ # are really gray-coded. Perhaps by checking on the correlation between bit-errors.
+ if differential and gray_coded:
+ m = constellation_points
+ pre_diff_code = range(0, m/2) + range(3*m/4, m) + range(m/2, 3*m/4)
+ else:
+ pre_diff_code = []
constellation = digital_swig.constellation_rect(points, pre_diff_code, 4,
side, side, width, width)
return constellation
--
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