Merge branch 'i149-iqgen-snr-control' of https://github.com/valeri-atamaniouk/peregrine into i115-glonass-acq

Author: Pasi Miettinen

peregrine/include/glo_ca_code.py

@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+#!/usr/bin/env python
+
+# Copyright (C) 2016 Swift Navigation Inc.
+#
+# Contact: Pasi Miettinen <pasi.miettinen@exafore.com>
+# This source is subject to the license found in the file 'LICENSE' which must
+# be be distributed together with this source. All other rights reserved.
+#
+# THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND,
+# EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
+
+import types
+import sys
+import numpy as np
+
+
+def generate_glo_ca_code():
+  """
+  Function generates PRN sequence for Glonass.
+  All GLONASS satellites use the same C/A-code,
+  generated by a 9-bit shift register.
+  """
+  code = '111111111'
+  output = np.zeros(511, np.int8)
+  for i in xrange(len(output)):
+    if '0' == code[6]:
+      output[i] = 1
+    else:
+      output[i] = -1
+    if int(code[4]) ^ int(code[8]):
+      code = '1' + code[:8]
+    else:
+      code = '0' + code[:8]
+  return output
+
+
+def readonly(value):
+  return property(lambda self: value)
+
+
+class glo_ca_code(types.ModuleType):
+  """
+  Implement module level variable as readonly by imitating module with
+  this class.
+  """
+
+  value = readonly(generate_glo_ca_code())
+
+  def __dir__(self):
+    return ['__doc__', '__name__', 'value']
+
+tmp = glo_ca_code(__name__)
+tmp.__doc__ = """
+  PR ranging code is a sequence of maximum length of shift register with a
+  period 1 millisecond and bit rate 511 kbps. PR ranging code is sampled at
+  the output of 7th stage of the 9-stage shift register. The initialization
+  vector to generate this sequence is (111111111). The first character of the
+  PR ranging code is the first character in the group 111111100, and it is
+  repeated every 1 millisecond. The generating polynomial, which corresponds
+  to the 9-stage shift register is G(X) = 1 + X^5 + X^9
+
+  Function outputs the bitstream as str and time advances from left to right
+  output[0] ... output[510]
+  0ms ----------> 1ms
+
+  In the sequence '0' is represented as '1', 1 as -1
+  """
+sys.modules[__name__] = tmp

peregrine/iqgen/bits/amplitude_base.py

@@ -14,19 +14,130 @@
 
 """
 
+import numpy
+
+
+class NoiseParameters(object):
+  '''
+  Container class for holding noise generation parameters.
+  '''
+
+  def __init__(self, samplingFreqHz, noiseSigma):
+    '''
+    Parameters
+    ----------
+    samplingFreqHz : float or long
+      Sampling frequency in Hz
+    noiseSigma : float
+      Noise Sigma value
+    '''
+    super(NoiseParameters, self).__init__()
+    self.samplingFreqHz = samplingFreqHz
+    self.noiseSigma = noiseSigma
+
+    # Compute coefficient for 1ms integration
+    self.signalK = noiseSigma * 2. * \
+        numpy.sqrt(1000000. / float(samplingFreqHz))
+
+    self.freqTimeTau = 1e-6 * float(samplingFreqHz)
+
+  def getSamplingFreqHz(self):
+    '''
+    Get sampling frequency.
+
+    Returns
+    -------
+    float or long
+      Sampling frequency in Hz
+    '''
+    return self.samplingFreqHz
+
+  def getNoiseSigma(self):
+    '''
+    Get noise Sigma.
+
+    Returns
+    -------
+    float
+      Noise sigma value
+    '''
+    return self.noiseSigma
+
+  def getFreqTimesTau(self):
+    '''
+    Get sampling integration parameter.
+
+    Returns
+    -------
+    float
+      Integration parameter of the sampling frequency times integration time.
+    '''
+    return self.freqTimeTau
+
+  def getSignalK(self):
+    '''
+    Get amplification coefficient for SNR at 0 dB.
+
+    Returns
+    -------
+    float
+      Signal amplification coefficient for SNR at 0 dB.
+    '''
+    return self.signalK
+
 
 class AmplitudeBase(object):
   '''
   Amplitude control for a signal source.
+
+  Attributes
+  ----------
+  UNITS_AMPLITUDE : string
+    Type of object for measuring signal in amplitude. SNR is dependent on
+    amplitude square.
+  UNITS_POWER : string
+    Type of object for measuring signal in power. SNR is linearly dependent on
+    power.
+  UNITS_SNR : string
+    Type of object for measuring signal in SNR.
+  UNITS_SNR_DB : string
+    Type of object for measuring signal in SNR dB.
+
   '''
 
-  def __init__(self):
+  UNITS_AMPLITUDE = 'AMP'
+  UNITS_POWER = 'PWR'
+  UNITS_SNR = 'SNR'
+  UNITS_SNR_DB = 'SNR_DB'
+
+  def __init__(self, units):
     '''
     Constructs base object for amplitude control.
+
+    Parameters
+    ----------
+    units : string
+      Object units. Can be one of the supported values:
+      - AmplitudeBase::UNITS_AMPLITUDE -- Amplitude units
+      - AmplitudeBase::UNITS_SNR_DB -- SNR in dB
+      - AmplitudeBase::UNITS_SNR -- SNR
+      - AmplitudeBase::UNITS_POWER -- Power units
     '''
     super(AmplitudeBase, self).__init__()
+    self.units = units
+
+  def getUnits(self):
+    '''
+    Provides access to units.
+
+    Returns
+    -------
+    string
+      Amplitude units
+    '''
+    return self.units
 
-  def applyAmplitude(self, signal, userTimeAll_s):
+  def applyAmplitude(self, signal, userTimeAll_s, noiseParams=None):
     '''
     Applies amplitude modulation to signal.
 
@@ -37,6 +148,8 @@ def applyAmplitude(self, signal, userTimeAll_s):
       [-1; +1]. This vector is modified in place.
     userTimeAll_s : numpy.ndarray
       Sample time vector. Each element defines sample time in seconds.
+    noiseParams : NoiseParameters
+      Noise parameters to adjust signal amplitude level.
 
     Returns
     -------
@@ -45,13 +158,88 @@ def applyAmplitude(self, signal, userTimeAll_s):
     '''
     raise NotImplementedError()
 
-  def computeMeanPower(self):
+  def computeSNR(self, noiseParams):
     '''
-    Computes mean signal power.
+    Computes signal to noise ratio in dB.
+
+    Parameters
+    ----------
+    noiseParams : NoiseParameters
+      Noise parameter container
 
     Returns
     -------
     float
-      Mean signal power for the configured amplitude
+      SNR in dB
     '''
     raise NotImplementedError()
+
+  @staticmethod
+  def convertUnits2SNR(value, units, noiseParams):
+    '''
+    Converts signal units to SNR in dB
+
+    Parameters
+    ----------
+    noiseParams : NoiseParameters
+      Noise parameter container
+
+    Returns
+    -------
+    float
+      SNR in dB
+    '''
+
+    noiseSigma = noiseParams.getNoiseSigma()
+    freqTimesTau = noiseParams.getFreqTimesTau()
+
+    if units == AmplitudeBase.UNITS_AMPLITUDE:
+      power = numpy.square(value)
+      snr = freqTimesTau * power / (4. * noiseSigma * noiseSigma)
+      snrDb = 10 * numpy.log10(snr)
+    elif units == AmplitudeBase.UNITS_POWER:
+      power = value
+      snr = freqTimesTau * power / (4. * noiseSigma * noiseSigma)
+      snrDb = 10 * numpy.log10(snr)
+    elif units == AmplitudeBase.UNITS_SNR:
+      snr = value
+      snrDb = 10 * numpy.log10(snr)
+    elif units == AmplitudeBase.UNITS_SNR_DB:
+      snrDb = value
+    else:
+      assert False
+    return snrDb
+
+  @staticmethod
+  def convertUnits2Amp(value, units, noiseParams):
+    '''
+    Converts signal units to amplitude
+
+    Parameters
+    ----------
+    noiseParams : NoiseParameters
+      Noise parameter container
+
+    Returns
+    -------
+    float
+      SNR in dB
+    '''
+
+    noiseSigma = noiseParams.getNoiseSigma()
+    freqTimesTau = noiseParams.getFreqTimesTau()
+
+    if units == AmplitudeBase.UNITS_AMPLITUDE:
+      amp = value
+    elif units == AmplitudeBase.UNITS_POWER:
+      amp = numpy.sqrt(value)
+    elif units == AmplitudeBase.UNITS_SNR:
+      snr = value
+      amp = numpy.sqrt(4. * snr / freqTimesTau) * noiseSigma
+    elif units == AmplitudeBase.UNITS_SNR_DB:
+      snrDb = value
+      snr = 10. ** (0.1 * snrDb)
+      amp = numpy.sqrt(4. * snr / freqTimesTau) * noiseSigma
+    else:
+      assert False
+    return amp

peregrine/iqgen/bits/amplitude_factory.py

@@ -45,24 +45,29 @@ def fromMapForm(self, data):
       raise ValueError("Invalid object type")
 
   def __PolyAmplitude_ToMap(self, obj):
-    data = {'type': 'PolyAmplitude', 'coeffs': obj.coeffs}
+    data = {'type': 'PolyAmplitude',
+            'coeffs': obj.coeffs,
+            'units': obj.units}
     return data
 
   def __SineAmplitude_ToMap(self, obj):
     data = {'type': 'SineAmplitude',
             'initial': obj.initial,
             'amplitude': obj.amplitude,
-            'period': obj.period_s}
+            'period': obj.period_s,
+            'units': obj.units}
     return data
 
   def __MapTo_PolyAmplitude(self, data):
     coeffs = data['coeffs']
-    return PolyAmplitude(coeffs)
+    units = data['units']
+    return PolyAmplitude(units, coeffs)
 
   def __MapTo_SineAmplitude(self, data):
     initial = data['initial']
     amplitude = data['amplitude']
     period = data['period']
-    return SineAmplitude(initial, amplitude, period)
+    units = data['units']
+    return SineAmplitude(units, initial, amplitude, period)
 
 factoryObject = ObjectFactory()