1 files changed, 84 insertions, 4 deletions

diff --git a/gr-digital/include/digital_impl_mpsk_snr_est.h b/gr-digital/include/digital_impl_mpsk_snr_est.h
index a96f3e9c1..e530782bc 100644
--- a/gr-digital/include/digital_impl_mpsk_snr_est.h
+++ b/gr-digital/include/digital_impl_mpsk_snr_est.h
@@ -29,7 +29,7 @@ enum snr_est_type_t {
   SNR_EST_SIMPLE = 0,	// Simple estimator (>= 7 dB)
   SNR_EST_SKEW,	        // Skewness-base est (>= 5 dB)
   SNR_EST_M2M4,         // 2nd & 4th moment est (>= 1 dB)
-  SNR_EST_SVN           // SVN-based est (>= 0dB)
+  SNR_EST_SVR           // SVR-based est (>= 0dB)
 };
 
 /*!
@@ -98,6 +98,21 @@ class DIGITAL_API digital_impl_mpsk_snr_est_m2m4 :
   double d_y1, d_y2;
   
  public:
+  /*! \brief SNR Estimator using 2nd and 4th-order moments.
+   *
+   *  An SNR estimator for M-PSK signals that uses 2nd (M2) and 4th
+   *  (M4) order moments. This estimator uses knowledge of the
+   *  kurtosis of the signal (k_a) and noise (k_w) to make its
+   *  estimation. We use Beaulieu's approximations here to M-PSK
+   *  signals and AWGN channels such that k_a=1 and k_w=2. These
+   *  approximations significantly reduce the complexity of the
+   *  calculations (and computations) required.
+   *
+   *  Reference:
+   *  D. R. Pauluzzi and N. C. Beaulieu, "A comparison of SNR
+   *  estimation techniques for the AWGN channel," IEEE
+   *  Trans. Communications, Vol. 48, No. 10, pp. 1681-1691, 2000.
+   */
   digital_impl_mpsk_snr_est_m2m4(double alpha);
   ~digital_impl_mpsk_snr_est_m2m4() {}
 
@@ -106,16 +121,81 @@ class DIGITAL_API digital_impl_mpsk_snr_est_m2m4 :
   double snr();
 };
 
+class DIGITAL_API digital_impl_snr_est_m2m4 :
+  public digital_impl_mpsk_snr_est
+{
+ private:
+  double d_y1, d_y2;
+  double d_ka, d_kw;
+  
+ public:
+  /*! \brief SNR Estimator using 2nd and 4th-order moments.
+   *
+   *  An SNR estimator for M-PSK signals that uses 2nd (M2) and 4th
+   *  (M4) order moments. This estimator uses knowledge of the
+   *  kurtosis of the signal (k_a) and noise (k_w) to make its
+   *  estimation. In this case, you can set your own estimations for
+   *  k_a and k_w, the kurtosis of the signal and noise, to fit this
+   *  estimation better to your signal and channel conditions.
+   *
+   *  A word of warning: this estimator has not been fully tested or
+   *  proved with any amount of rigor. The estimation for M4 in
+   *  particular might be ignoring effectf of when k_a and k_w are
+   *  different. Use this estimator with caution and a copy of the
+   *  reference on hand.
+   *
+   *  The digital_mpsk_snr_est_m2m4 assumes k_a and k_w to simplify
+   *  the computations for M-PSK and AWGN channels. Use that estimator
+   *  unless you have a way to guess or estimate these values here.
+   *
+   *  Original paper: 
+   *  R. Matzner, "An SNR estimation algorithm for complex baseband
+   *  signal using higher order statistics," Facta Universitatis
+   *  (Nis), no. 6, pp. 41-52, 1993.
+   *
+   *  Reference used in derivation:
+   *  D. R. Pauluzzi and N. C. Beaulieu, "A comparison of SNR
+   *  estimation techniques for the AWGN channel," IEEE
+   *  Trans. Communications, Vol. 48, No. 10, pp. 1681-1691, 2000.
+   */
+  digital_impl_snr_est_m2m4(double alpha, double ka, double kw);
+  ~digital_impl_snr_est_m2m4() {}
+
+  int update(int noutput_items,
+	     gr_vector_const_void_star &input_items);
+  double snr();
+};
+
 
-class DIGITAL_API digital_impl_mpsk_snr_est_svn :
+class DIGITAL_API digital_impl_mpsk_snr_est_svr :
   public digital_impl_mpsk_snr_est
 {
  private:
   double d_y1, d_y2;
   
  public:
-  digital_impl_mpsk_snr_est_svn(double alpha);
-  ~digital_impl_mpsk_snr_est_svn() {}
+  /*! \brief Signal-to-Variation Ratio SNR Estimator.
+   *
+   *  This estimator actually comes from an SNR estimator for M-PSK
+   *  signals in fading channels, but this implementation is
+   *  specifically for AWGN channels. The math was simplified to
+   *  assume a signal and noise kurtosis (k_a and k_w) for M-PSK
+   *  signals in AWGN. These approximations significantly reduce the
+   *  complexity of the calculations (and computations) required.
+   *
+   *  Original paper:
+   *  A. L. Brandao, L. B. Lopes, and D. C. McLernon, "In-service
+   *  monitoring of multipath delay and cochannel interference for
+   *  indoor mobile communication systems," Proc. IEEE
+   *  Int. Conf. Communications, vol. 3, pp. 1458-1462, May 1994.
+   *
+   *  Reference:
+   *  D. R. Pauluzzi and N. C. Beaulieu, "A comparison of SNR
+   *  estimation techniques for the AWGN channel," IEEE
+   *  Trans. Communications, Vol. 48, No. 10, pp. 1681-1691, 2000.
+   */
+  digital_impl_mpsk_snr_est_svr(double alpha);
+  ~digital_impl_mpsk_snr_est_svr() {}
 
   int update(int noutput_items,
 	     gr_vector_const_void_star &input_items);