diff options
| -rw-r--r-- | gr-digital/lib/digital_costas_loop_cc.cc | 39 | ||||
| -rw-r--r-- | gr-digital/lib/digital_costas_loop_cc.h | 2 |
2 files changed, 24 insertions, 17 deletions
diff --git a/gr-digital/lib/digital_costas_loop_cc.cc b/gr-digital/lib/digital_costas_loop_cc.cc index d7f98e142..b18b83aeb 100644 --- a/gr-digital/lib/digital_costas_loop_cc.cc +++ b/gr-digital/lib/digital_costas_loop_cc.cc @@ -28,7 +28,7 @@ #include <gr_io_signature.h> #include <gr_expj.h> #include <gr_sincos.h> -#include <math.h> +#include <gr_math.h> #define M_TWOPI (2*M_PI) @@ -49,9 +49,9 @@ digital_costas_loop_cc::digital_costas_loop_cc (float damping, float nat_freq, gr_make_io_signature (1, 1, sizeof (gr_complex)), 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) + d_max_freq(1.0), d_min_freq(-1.0), d_phase(0.0), d_freq(0.0), + d_damping(damping), d_nat_freq(nat_freq), d_order(order), + d_phase_detector(NULL) { // initialize gains from the natural freq and damping factors update_gains(); @@ -78,8 +78,21 @@ digital_costas_loop_cc::digital_costas_loop_cc (float damping, float nat_freq, 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())) { + /* This technique splits the 8PSK constellation into 2 squashed + QPSK constellations, one when I is larger than Q and one where + Q is larger than I. The error is then calculated proportionally + to these squashed constellations by the const K = sqrt(2)-1. + + The signal magnitude must be > 1 or K will incorrectly bias + the error value. + + Ref: Z. Huang, Z. Yi, M. Zhang, K. Wang, "8PSK demodulation for + new generation DVB-S2", IEEE Proc. Int. Conf. Communications, + Circuits and Systems, Vol. 2, pp. 1447 - 1450, 2004. + */ + + float K = (sqrt(2.0) - 1); + if(fabsf(sample.real()) >= fabsf(sample.imag())) { return ((sample.real()>0 ? 1.0 : -1.0) * sample.imag() - (sample.imag()>0 ? 1.0 : -1.0) * sample.real() * K); } @@ -145,10 +158,7 @@ digital_costas_loop_cc::work (int noutput_items, optr[i] = iptr[i] * nco_out; error = (*this.*d_phase_detector)(optr[i]); - if (error > 1) - error = 1; - else if (error < -1) - error = -1; + error = gr_branchless_clip(error, 1.0); d_freq = d_freq + d_beta * error; d_phase = d_phase + d_freq + d_alpha * error; @@ -171,10 +181,7 @@ digital_costas_loop_cc::work (int noutput_items, optr[i] = iptr[i] * nco_out; error = (*this.*d_phase_detector)(optr[i]); - if (error > 1) - error = 1; - else if (error < -1) - error = -1; + error = gr_branchless_clip(error, 1.0); d_freq = d_freq + d_beta * error; d_phase = d_phase + d_freq + d_alpha * error; @@ -185,9 +192,9 @@ digital_costas_loop_cc::work (int noutput_items, 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; } } diff --git a/gr-digital/lib/digital_costas_loop_cc.h b/gr-digital/lib/digital_costas_loop_cc.h index 9c112d328..2c4c38e8b 100644 --- a/gr-digital/lib/digital_costas_loop_cc.h +++ b/gr-digital/lib/digital_costas_loop_cc.h @@ -81,7 +81,7 @@ class digital_costas_loop_cc : public gr_sync_block ) 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; + float d_damping, d_nat_freq; int d_order; digital_costas_loop_cc (float damping, float nat_freq, |