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+/* -*- c++ -*- */
+/*
+ * Copyright 2006,2011 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+
+#ifndef INCLUDED_DIGITAL_COSTAS_LOOP_CC_H
+#define INCLUDED_DIGITAL_COSTAS_LOOP_CC_H
+
+#include <gr_sync_block.h>
+#include <gri_control_loop.h>
+#include <stdexcept>
+#include <fstream>
+
+
+/*! 
+ * \brief A Costas loop carrier recovery module.
+ * \ingroup sync_blk
+ * \ingroup digital
+ *  
+ *  The Costas loop locks to the center frequency of a signal and
+ *  downconverts it to baseband. The second (order=2) order loop is
+ *  used for BPSK where the real part of the output signal is the
+ *  baseband BPSK signal and the imaginary part is the error
+ *  signal. When order=4, it can be used for quadrature modulations
+ *  where both I and Q (real and imaginary) are outputted.
+ *
+ *  More details can be found online:
+ *
+ *  J. Feigin, "Practical Costas loop design: Designing a simple and
+ *  inexpensive BPSK Costas loop carrier recovery circuit," RF signal
+ *  processing, pp. 20-36, 2002.
+ *
+ *  http://rfdesign.com/images/archive/0102Feigin20.pdf
+ *  
+ * \param alpha the loop gain used for phase adjustment
+ * \param beta the loop gain for frequency adjustments
+ * \param max_freq the maximum frequency deviation (radians/sample) the loop can handle
+ * \param min_freq the minimum frequency deviation (radians/sample) the loop can handle
+ * \param order the loop order, either 2 or 4
+ */
+class digital_costas_loop_cc;
+typedef boost::shared_ptr<digital_costas_loop_cc> digital_costas_loop_cc_sptr;
+
+
+digital_costas_loop_cc_sptr 
+digital_make_costas_loop_cc (float loop_bw, int order
+			     ) throw (std::invalid_argument);
+
+
+/*!
+ * \brief Carrier tracking PLL for QPSK
+ * \ingroup sync_blk
+ * input: complex; output: complex
+ * <br>The Costas loop can have two output streams:
+ *    stream 1 is the baseband I and Q;
+ *    stream 2 is the normalized frequency of the loop
+ *
+ * \p order must be 2 or 4.
+ */
+class digital_costas_loop_cc : public gr_sync_block, public gri_control_loop
+{
+  friend digital_costas_loop_cc_sptr
+  digital_make_costas_loop_cc (float loop_bw, int order
+			       ) throw (std::invalid_argument);
+
+  int d_order;
+
+  digital_costas_loop_cc (float loop_bw, int order
+			  ) throw (std::invalid_argument);
+  
+  /*! \brief the phase detector circuit for 8th-order PSK loops
+   *  \param sample complex sample
+   *  \return the phase error
+   */
+  float phase_detector_8(gr_complex sample) const;    // for 8PSK
+
+  /*! \brief the phase detector circuit for fourth-order loops
+   *  \param sample complex sample
+   *  \return the phase error
+   */
+  float phase_detector_4(gr_complex sample) const;    // for QPSK
+
+  /*! \brief the phase detector circuit for second-order loops
+   *  \param sample a complex sample
+   *  \return the phase error
+   */
+  float phase_detector_2(gr_complex sample) const;    // for BPSK
+
+
+  float (digital_costas_loop_cc::*d_phase_detector)(gr_complex sample) const;
+
+public:
+
+  int work (int noutput_items,
+	    gr_vector_const_void_star &input_items,
+	    gr_vector_void_star &output_items);
+};
+
+#endif