Add a method to compute specular component in Rician fading channel.

[1] Lee M. Garth, Peter J. Smith, Mansoor Shafi, "Exact Symbol Error Probabilities for SVD Transmission
        of BPSK Data over Fading Channels", IEEE 2005.

Author: akou97

commpy/channels.py

@@ -1,4 +1,4 @@
-# Authors: Veeresh Taranalli < veeresht @ gmail.com > & Bastien Trotobas < bastien.trotobas @ gmail.com >
+# Authors: Veeresh Taranalli <veeresht@gmail.com> & Bastien Trotobas <bastien.trotobas@gmail.com>
 # License: BSD 3-Clause
 
 """
@@ -19,7 +19,8 @@
 
 from __future__ import division, print_function  # Python 2 compatibility
 
-from numpy import complex, abs, sqrt, sum, zeros, identity, hstack, einsum, trace, kron, absolute, fromiter, array, exp
+from numpy import complex, abs, sqrt, sum, zeros, identity, hstack, einsum, trace, kron, absolute, fromiter, array, exp, \
+    pi, cos
 from numpy.random import randn, random, standard_normal
 from scipy.linalg import sqrtm
 
@@ -416,6 +417,47 @@ def _update_corr_KBSM(self, betat, betar):
         # updating of correlation matrices
         self.fading_param = self.fading_param[0], alpha * self.fading_param[1] * Et, self.fading_param[2] * Er
 
+
+    def specularH(self, thetar, dr, thetat, dt):
+
+        """
+        Calculate the specular components of H the channel gain as in [1].
+        ref: [1] Lee M. Garth, Peter J. Smith, Mansoor Shafi, "Exact Symbol Error Probabilities for SVD Transmission
+        of BPSK Data over Fading Channels", IEEE 2005.
+
+        Parameters
+        ----------
+        thetat : float
+                the angle of departure.
+
+        dt : postive float
+                the antenna spacing in wavelenghts of departure.
+
+        thetar : float
+                the angle of arrival.
+
+        dr : positie float
+                the antenna spacing in wavelenghts of arrival.
+
+        Returns
+        -------
+        H      : 2D ndarray of shape (nb_rx, nb_tx)
+                 the specular components of channel gains to be use as mean in Rician fading.
+
+        Raises
+        ------
+        ValueError
+                    If dt or dr are negative.
+
+        """
+        if dr < 0 or dt < 0 :
+            raise ValueError("the distance must be positive ")
+        H = zeros((self.nb_rx,self.nb_tx),dtype=complex)
+        for n in range(self.nb_rx):
+            for m in range(self.nb_tx):
+                H[n,m] = exp(1j*2*pi*(n*dr*cos(thetar)-m*dt*cos(thetat)))
+        return H
+
     @property
     def fading_param(self):
         """ Parameters of the fading (see class attribute for details). """

commpy/tests/test_channels.py

@@ -406,6 +406,15 @@ def check_correlation(chan, Rt, Rr):
             assert_allclose(chan.k_factor, 5,
                             err_msg='Wrong k-factor with correlated rician fading')
 
+            # Test specularH
+            with assert_raises(ValueError):
+                chan.specularH(0,-1,0,1)
+
+            mean = chan.specularH(0,0.1,0.5,1)
+            chan.expo_corr_rician_fading(mean, 5, exp(-0.1j*pi), exp(-0.2j*pi), 3, 2)
+            check_chan_gain(mod, chan)
+            assert_allclose(chan.k_factor, 5,
+                            err_msg='Wrong k-factor with correlated rician fading')
 
 
 @dec.slow