From 81e297b48f0ed9abfb3e45b8bc79ef0e40a2458c Mon Sep 17 00:00:00 2001
From: Eric Kooistra <kooistra@astron.nl>
Date: Tue, 7 May 2024 15:08:39 +0200
Subject: [PATCH] Improve comments.
---
applications/lofar2/model/pfb_os/dsp.py | 27 ++++++++++++++-----------
1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/applications/lofar2/model/pfb_os/dsp.py b/applications/lofar2/model/pfb_os/dsp.py
index f3722a2476..02f366ec1b 100644
--- a/applications/lofar2/model/pfb_os/dsp.py
+++ b/applications/lofar2/model/pfb_os/dsp.py
@@ -118,7 +118,7 @@ def impulse_at_zero_crossing(x):
###############################################################################
-# Window design
+# Windowed sinc filter design
###############################################################################
def raised_cosine_response(Ntaps, Tsymbol, beta):
@@ -139,7 +139,7 @@ def raised_cosine_response(Ntaps, Tsymbol, beta):
t = tIndices - tCenter
# sinc term, can use array assignment because sinc(1 / 0) = 1
- hRc = 1 / Tsymbol * np.sinc(t / Tsymbol)
+ hRc = 1 / Tsymbol * np.sinc(t / Tsymbol) # np.sinc(x) = sin(pi x) / (pi x)
# apply cos term, use for loop instead of array assignment, to detect divide by 0
for tI in tIndices:
@@ -150,15 +150,18 @@ def raised_cosine_response(Ntaps, Tsymbol, beta):
def square_root_raised_cosine_response(Ntaps, Tsymbol, beta):
- """Generate a square root raised cosine (RC) FIR filter impulse response.
+ """Generate a square root raised cosine (SRRC) FIR filter impulse response.
+
+ Reference:
+ . [HARRIS section 4.3]
+ . https://en.wikipedia.org/wiki/Root-raised-cosine_filter
- Reference: [HARRIS section 4.3]
Input:
. Ntaps : FIR filter length
. Tsymbol: symbol period in number of samples per symbol
. beta : Roll off factor in [0, 1.0]
Return:
- . hSrrc : impulse response of the square root raised cosine filter.
+ . hSrRc : impulse response of the square root raised cosine filter.
"""
# time axis
tIndices = np.arange(Ntaps)
@@ -166,21 +169,21 @@ def square_root_raised_cosine_response(Ntaps, Tsymbol, beta):
t = tIndices - tCenter
# numerator term, using array assignment
- hSrrc = 1 / Tsymbol * (4 * beta * t / Tsymbol * np.cos(np.pi * (1 + beta) * t / Tsymbol) +
- np.sin(np.pi * (1 - beta) * t / Tsymbol))
+ hSrRc = 1 / Tsymbol * (np.cos(np.pi * (1 + beta) * t / Tsymbol) * 4 * beta * t / Tsymbol +
+ np.sin(np.pi * (1 - beta) * t / Tsymbol))
# apply denumerator term, use for loop instead of array assignment, to detect divide by 0
for tI in tIndices:
t = tI - tCenter
if t == 0.0:
- hSrrc[tI] = 1 / Tsymbol * (1 + beta * (4 / np.pi - 1))
+ hSrRc[tI] = 1 / Tsymbol * (1 + beta * (4 / np.pi - 1))
elif np.abs(t) == Tsymbol / (4 * beta):
- hSrrc[tI] = 1 / Tsymbol * beta / np.sqrt(2) * \
- ((1 + 2 / np.pi) * np.sin(np.pi / (4 * beta)) + \
+ hSrRc[tI] = 1 / Tsymbol * beta / np.sqrt(2) * \
+ ((1 + 2 / np.pi) * np.sin(np.pi / (4 * beta)) +
(1 - 2 / np.pi) * np.cos(np.pi / (4 * beta)))
else:
- hSrrc[tI] /= (1 - (4 * beta * t / Tsymbol)**2) * (np.pi * t / Tsymbol)
- return hSrrc
+ hSrRc[tI] /= (1 - (4 * beta * t / Tsymbol)**2) * (np.pi * t / Tsymbol)
+ return hSrRc
###############################################################################
--
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