#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2015 jaidev <jaidev@newton>
#
# Distributed under terms of the MIT license.

"""
====================================
Spectrum of a Noisy Transient Signal
====================================

This example shows how to generate a noisy transient signal with the following
characteristics:

    * One-sided exponential amplitude modulation (See :ref:`amexpos`)
    * Constant frequency modulation (See :ref:`fmconst`)
    * -5 dB complex gaussian noise (See :ref:`noisecg` and :ref:`sigmerge`)

And how to plot its energy spectrum.

Figure 1.10 of the tutorial.
"""


import numpy as np
import matplotlib.pyplot as plt
from tftb.generators import amexpos, fmconst, sigmerge, noisecg

# Generate a noisy transient signal.
transsig = amexpos(64, kind='unilateral') * fmconst(64)[0]
signal = np.hstack((np.zeros((100,)), transsig, np.zeros((92,))))
signal = sigmerge(signal, noisecg(256), -5)
fig, ax = plt.subplots(2, 1)
ax1, ax2 = ax
ax1.plot(np.real(signal))
ax1.grid()
ax1.set_title('Noisy Transient Signal')
ax1.set_xlabel('Time')
ax1.set_xlim((0, 256))
ax1.set_ylim((np.real(signal).max(), np.real(signal.min())))

# Energy spectrum of the signal
dsp = np.fft.fftshift(np.abs(np.fft.fft(signal)) ** 2)
ax2.plot(np.arange(-128, 128, dtype=float) / 256, dsp)
ax2.set_title('Energy spectrum of noisy transient signal')
ax2.set_xlabel('Normalized frequency')
ax2.grid()
ax2.set_xlim(-0.5, 0.5)

plt.subplots_adjust(hspace=0.5)

plt.show()