From a5ee5af754abd66a7d7751868e0dcea8c8299264 Mon Sep 17 00:00:00 2001 From: Tom Rondeau Date: Sat, 6 Mar 2010 17:11:58 -0500 Subject: [PATCH] Improved performance of FLL using a more robust error term. --- .../src/lib/general/gr_fll_band_edge_cc.cc | 27 ++++++++++--------- .../src/lib/general/gr_fll_band_edge_cc.h | 8 ++++-- 2 files changed, 21 insertions(+), 14 deletions(-) diff --git a/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.cc b/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.cc index 030e45dd..7f2c468b 100644 --- a/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.cc +++ b/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.cc @@ -53,7 +53,7 @@ gr_fll_band_edge_cc_sptr gr_make_fll_band_edge_cc (float samps_per_sym, float ro } -static int ios[] = {sizeof(gr_complex), sizeof(float), sizeof(float), sizeof(float)}; +static int ios[] = {sizeof(gr_complex), sizeof(float), sizeof(float), sizeof(gr_complex)}; static std::vector iosig(ios, ios+sizeof(ios)/sizeof(int)); gr_fll_band_edge_cc::gr_fll_band_edge_cc (float samps_per_sym, float rolloff, int filter_size, float alpha, float beta) @@ -83,10 +83,11 @@ gr_fll_band_edge_cc::~gr_fll_band_edge_cc () void gr_fll_band_edge_cc::set_alpha(float alpha) { - float eta = sqrt(2.0)/2.0; - float theta = alpha; - d_alpha = (4*eta*theta) / (1.0 + 2.0*eta*theta + theta*theta); - d_beta = (4*theta*theta) / (1.0 + 2.0*eta*theta + theta*theta); + //float eta = sqrt(2.0)/2.0; + //float theta = alpha; + //d_alpha = (4*eta*theta) / (1.0 + 2.0*eta*theta + theta*theta); + //d_beta = (4*theta*theta) / (1.0 + 2.0*eta*theta + theta*theta); + d_alpha = alpha; } void @@ -160,11 +161,12 @@ gr_fll_band_edge_cc::work (int noutput_items, const gr_complex *in = (const gr_complex *) input_items[0]; gr_complex *out = (gr_complex *) output_items[0]; - float *frq, *phs, *err; + float *frq, *phs; + gr_complex *err; if(output_items.size() > 2) { frq = (float *) output_items[1]; phs = (float *) output_items[2]; - err = (float *) output_items[3]; + err = (gr_complex *) output_items[3]; } if (d_updated) { @@ -174,16 +176,17 @@ gr_fll_band_edge_cc::work (int noutput_items, int i; gr_complex nco_out; - float out_upper, out_lower; + gr_complex out_upper, out_lower; float error; + float avg_k = 0.1; for(i = 0; i < noutput_items; i++) { nco_out = gr_expj(d_phase); out[i] = in[i] * nco_out; - out_upper = norm(d_filter_upper->filter(&out[i])); - out_lower = norm(d_filter_lower->filter(&out[i])); - error = out_lower - out_upper; - d_error = 0.01*error + 0.99*d_error; // average error + out_upper = (d_filter_upper->filter(&out[i])); + out_lower = (d_filter_lower->filter(&out[i])); + error = -real((out_upper + out_lower) * conj(out_upper - out_lower)); + d_error = avg_k*error + avg_k*d_error; // average error d_freq = d_freq + d_beta * d_error; d_phase = d_phase + d_freq + d_alpha * d_error; diff --git a/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.h b/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.h index 09baf7fd..178e18f3 100644 --- a/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.h +++ b/gnuradio-core/src/lib/general/gr_fll_band_edge_cc.h @@ -45,8 +45,12 @@ class gri_fft_complex; * (e.g., rolloff factor) of the modulated signal. The placement in frequency of the band-edges * is determined by the oversampling ratio (number of samples per symbol) and the excess bandwidth. * The size of the filters should be fairly large so as to average over a number of symbols. - * The FLL works by calculating the power in both the upper and lower bands and comparing them. The - * difference in power between the filters is proportional to the frequency offset. + * + * The FLL works by filtering the upper and lower band edges into x_u(t) and x_l(t), respectively. + * These are combined to form cc(t) = x_u(t) + x_l(t) and ss(t) = x_u(t) - x_l(t). Combining + * these to form the signal e(t) = Re{cc(t) \times ss(t)^*} (where ^* is the complex conjugate) + * provides an error signal at the DC term that is directly proportional to the carrier frequency. + * We then make a second-order loop using the error signal that is the running average of e(t). * * In theory, the band-edge filter is the derivative of the matched filter in frequency, * (H_be(f) = \frac{H(f)}{df}. In practice, this comes down to a quarter sine wave at the point -- 2.30.2