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diff --git a/gr-digital/include/digital_impl_mpsk_snr_est.h b/gr-digital/include/digital_impl_mpsk_snr_est.h new file mode 100644 index 000000000..df7dbadec --- /dev/null +++ b/gr-digital/include/digital_impl_mpsk_snr_est.h @@ -0,0 +1,279 @@ +/* -*- c++ -*- */ +/* + * Copyright 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_IMPL_MPSK_SNR_EST_H +#define INCLUDED_DIGITAL_IMPL_MPSK_SNR_EST_H + +#include <digital_api.h> +#include <gr_sync_block.h> + +//! Enum for the type of SNR estimator to select +/*! \ingroup snr_blk + * \anchor ref_snr_est_types + * + * Below are some ROUGH estimates of what values of SNR each of these + * types of estimators is good for. In general, these offer a + * trade-off between accuracy and performance. + * + * \li SNR_EST_SIMPLE: Simple estimator (>= 7 dB) + * \li SNR_EST_SKEW: Skewness-base est (>= 5 dB) + * \li SNR_EST_M2M4: 2nd & 4th moment est (>= 1 dB) + * \li SNR_EST_SVR: SVR-based est (>= 0dB) +*/ +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_SVR // SVR-based est (>= 0dB) +}; + +/*! \brief A parent class for SNR estimators, specifically for M-PSK + * signals in AWGN channels. + * \ingroup snr_blk + */ +class DIGITAL_API digital_impl_mpsk_snr_est +{ + protected: + double d_alpha, d_beta; + + public: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + */ + digital_impl_mpsk_snr_est(double alpha); + virtual ~digital_impl_mpsk_snr_est(); + + //! Get the running-average coefficient + double alpha() const; + + //! Set the running-average coefficient + void set_alpha(double alpha); + + //! Update the current registers + virtual int update(int noutput_items, + const gr_complex *in); + + //! Use the register values to compute a new estimate + virtual double snr(); +}; + + +//! \brief SNR Estimator using simple mean/variance estimates. +/*! \ingroup snr_blk + * + * A very simple SNR estimator that just uses mean and variance + * estimates of an M-PSK constellation. This esimator is quick and + * cheap and accurate for high SNR (above 7 dB or so) but quickly + * starts to overestimate the SNR at low SNR. + */ +class DIGITAL_API digital_impl_mpsk_snr_est_simple : + public digital_impl_mpsk_snr_est +{ + private: + double d_y1, d_y2; + + public: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + */ + digital_impl_mpsk_snr_est_simple(double alpha); + ~digital_impl_mpsk_snr_est_simple() {} + + int update(int noutput_items, + const gr_complex *in); + double snr(); +}; + + +//! \brief SNR Estimator using skewness correction. +/*! \ingroup snr_blk + * + * This is an estimator that came from a discussion between Tom + * Rondeau and fred harris with no known paper reference. The idea is + * that at low SNR, the variance estimations will be affected because + * of fold-over around the decision boundaries, which results in a + * skewness to the samples. We estimate the skewness and use this as + * a correcting term. + */ +class DIGITAL_API digital_impl_mpsk_snr_est_skew : + public digital_impl_mpsk_snr_est +{ + private: + double d_y1, d_y2, d_y3; + + public: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + */ + digital_impl_mpsk_snr_est_skew(double alpha); + ~digital_impl_mpsk_snr_est_skew() {} + + int update(int noutput_items, + const gr_complex *in); + double snr(); +}; + + +//! \brief SNR Estimator using 2nd and 4th-order moments. +/*! \ingroup snr_blk + * + * 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. + */ +class DIGITAL_API digital_impl_mpsk_snr_est_m2m4 : + public digital_impl_mpsk_snr_est +{ + private: + double d_y1, d_y2; + + public: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + */ + digital_impl_mpsk_snr_est_m2m4(double alpha); + ~digital_impl_mpsk_snr_est_m2m4() {} + + int update(int noutput_items, + const gr_complex *in); + double snr(); +}; + + +//! \brief SNR Estimator using 2nd and 4th-order moments. +/*! \ingroup snr_blk + * + * 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. + */ +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: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + * \param ka: estimate of the signal kurtosis (1 for PSK) + * \param kw: estimate of the channel noise kurtosis (2 for AWGN) + */ + digital_impl_snr_est_m2m4(double alpha, double ka, double kw); + ~digital_impl_snr_est_m2m4() {} + + int update(int noutput_items, + const gr_complex *in); + double snr(); +}; + + +//! \brief Signal-to-Variation Ratio SNR Estimator. +/*! \ingroup snr_blk + * + * 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. + */ +class DIGITAL_API digital_impl_mpsk_snr_est_svr : + public digital_impl_mpsk_snr_est +{ + private: + double d_y1, d_y2; + + public: + /*! Constructor + * + * Parameters: + * \param alpha: the update rate of internal running average + * calculations. + */ + digital_impl_mpsk_snr_est_svr(double alpha); + ~digital_impl_mpsk_snr_est_svr() {} + + int update(int noutput_items, + const gr_complex *in); + double snr(); +}; + +#endif /* INCLUDED_DIGITAL_IMPL_MPSK_SNR_EST_H */ |