From b30c79326c3eedf5ebf20be62306f0511b98a0e7 Mon Sep 17 00:00:00 2001
From: Tom Rondeau
Date: Tue, 29 Mar 2011 00:48:49 -0400
Subject: gr-digital: restructured Costas loop to be specified in terms of the
damping factor and natural frequency instead of randomly setting the gains.
Much more robust in simulation.
---
gr-digital/lib/digital_costas_loop_cc.cc | 55 +++++++++++++++++++-------------
gr-digital/lib/digital_costas_loop_cc.h | 38 ++++++++++++----------
2 files changed, 53 insertions(+), 40 deletions(-)
(limited to 'gr-digital/lib')
diff --git a/gr-digital/lib/digital_costas_loop_cc.cc b/gr-digital/lib/digital_costas_loop_cc.cc
index 537f54f2d..d7f98e142 100644
--- a/gr-digital/lib/digital_costas_loop_cc.cc
+++ b/gr-digital/lib/digital_costas_loop_cc.cc
@@ -33,28 +33,29 @@
#define M_TWOPI (2*M_PI)
digital_costas_loop_cc_sptr
-digital_make_costas_loop_cc (float alpha, float beta,
- float max_freq, float min_freq,
+digital_make_costas_loop_cc (float damping, float nat_freq,
int order
) throw (std::invalid_argument)
{
- return gnuradio::get_initial_sptr(new digital_costas_loop_cc (alpha, beta,
- max_freq, min_freq,
+ return gnuradio::get_initial_sptr(new digital_costas_loop_cc (damping,
+ nat_freq,
order));
}
-digital_costas_loop_cc::digital_costas_loop_cc (float alpha, float beta,
- float max_freq, float min_freq,
+digital_costas_loop_cc::digital_costas_loop_cc (float damping, float nat_freq,
int order
) throw (std::invalid_argument)
: gr_sync_block ("costas_loop_cc",
gr_make_io_signature (1, 1, sizeof (gr_complex)),
- gr_make_io_signature (1, 2, sizeof (gr_complex))),
- d_alpha(alpha), d_beta(beta),
- d_max_freq(max_freq), d_min_freq(min_freq),
- d_phase(0), d_freq((max_freq+min_freq)/2),
- d_order(order), d_phase_detector(0)
+ gr_make_io_signature2 (1, 2, sizeof (gr_complex), sizeof(float))),
+
+ d_max_freq(1.0), d_min_freq(-1.0), d_freq(0.0),
+ d_damping(damping), d_nat_freq(nat_freq),
+ d_phase(0), d_order(order), d_phase_detector(NULL)
{
+ // initialize gains from the natural freq and damping factors
+ update_gains();
+
switch(d_order) {
case 2:
d_phase_detector = &digital_costas_loop_cc::phase_detector_2;
@@ -78,7 +79,6 @@ float
digital_costas_loop_cc::phase_detector_8(gr_complex sample) const
{
float K = sqrt(2.0) - 1;
-
if(abs(sample.real()) >= abs(sample.imag())) {
return ((sample.real()>0 ? 1.0 : -1.0) * sample.imag() -
(sample.imag()>0 ? 1.0 : -1.0) * sample.real() * K);
@@ -104,15 +104,24 @@ digital_costas_loop_cc::phase_detector_2(gr_complex sample) const
}
void
-digital_costas_loop_cc::set_alpha(float alpha)
+digital_costas_loop_cc::set_natural_freq(float w)
+{
+ d_nat_freq = w;
+ update_gains();
+}
+
+void
+digital_costas_loop_cc::set_damping_factor(float eta)
{
- d_alpha = alpha;
+ d_damping = eta;
+ update_gains();
}
void
-digital_costas_loop_cc::set_beta(float beta)
+digital_costas_loop_cc::update_gains()
{
- d_beta = beta;
+ d_beta = d_nat_freq*d_nat_freq;
+ d_alpha = 2*d_damping*d_nat_freq;
}
int
@@ -122,7 +131,7 @@ digital_costas_loop_cc::work (int noutput_items,
{
const gr_complex *iptr = (gr_complex *) input_items[0];
gr_complex *optr = (gr_complex *) output_items[0];
- gr_complex *foptr = (gr_complex *) output_items[1];
+ float *foptr = (float *) output_items[1];
bool write_foptr = output_items.size() >= 2;
@@ -140,21 +149,21 @@ digital_costas_loop_cc::work (int noutput_items,
error = 1;
else if (error < -1)
error = -1;
-
+
d_freq = d_freq + d_beta * error;
d_phase = d_phase + d_freq + d_alpha * error;
-
+
while(d_phase>M_TWOPI)
d_phase -= M_TWOPI;
while(d_phase<-M_TWOPI)
d_phase += M_TWOPI;
-
+
if (d_freq > d_max_freq)
- d_freq = d_max_freq;
- else if (d_freq < d_min_freq)
d_freq = d_min_freq;
+ else if (d_freq < d_min_freq)
+ d_freq = d_max_freq;
- foptr[i] = gr_complex(error,0);
+ foptr[i] = d_freq;
}
} else {
for (int i = 0; i < noutput_items; i++){
diff --git a/gr-digital/lib/digital_costas_loop_cc.h b/gr-digital/lib/digital_costas_loop_cc.h
index 256423aae..9c112d328 100644
--- a/gr-digital/lib/digital_costas_loop_cc.h
+++ b/gr-digital/lib/digital_costas_loop_cc.h
@@ -58,8 +58,7 @@ typedef boost::shared_ptr<digital_costas_loop_cc> digital_costas_loop_cc_sptr;
digital_costas_loop_cc_sptr
-digital_make_costas_loop_cc (float alpha, float beta,
- float max_freq, float min_freq,
+digital_make_costas_loop_cc (float damping, float nat_freq,
int order
) throw (std::invalid_argument);
@@ -77,18 +76,30 @@ digital_make_costas_loop_cc (float alpha, float beta,
class digital_costas_loop_cc : public gr_sync_block
{
friend digital_costas_loop_cc_sptr
- digital_make_costas_loop_cc (float alpha, float beta,
- float max_freq, float min_freq,
+ digital_make_costas_loop_cc (float damping, float nat_freq,
int order
) throw (std::invalid_argument);
float d_alpha, d_beta, d_max_freq, d_min_freq, d_phase, d_freq;
+ float d_nat_freq, d_damping;
int d_order;
- digital_costas_loop_cc (float alpha, float beta,
- float max_freq, float min_freq,
- int order
- ) throw (std::invalid_argument);
+ digital_costas_loop_cc (float damping, float nat_freq,
+ int order
+ ) throw (std::invalid_argument);
+
+
+ /*! \brief update the system gains from omega and eta
+ *
+ * This function updates the system gains based on the natural
+ * frequency (omega) and damping factor (eta) of the system.
+ * These two factors can be set separately through their own
+ * set functions.
+ *
+ * These equations are summarized nicely in this paper from Berkeley:
+ * http://www.complextoreal.com/chapters/pll.pdf
+ */
+ void update_gains();
/*! \brief the phase detector circuit for 8th-order PSK loops
* \param sample complex sample
@@ -113,21 +124,14 @@ class digital_costas_loop_cc : public gr_sync_block
public:
- /*! \brief set the first order gain
- * \param alpha
- */
- void set_alpha(float alpha);
+ void set_natural_freq(float w);
+ void set_damping_factor(float eta);
/*! \brief get the first order gain
*
*/
float alpha() const { return d_alpha; }
- /*! \brief set the second order gain
- * \param beta
- */
- void set_beta(float beta);
-
/*! \brief get the second order gain
*
*/
--
cgit