filterCreationRoutines.py

# -*- coding: utf-8 -*-
"""
Created on Mon Apr 20 14:35:01 2020

@author: Seo
"""

import numpy as np
import scipy.signal as sps
import scipy as sp


def makeSRC4(t, Tb):
    """
    t: array of time values
    Tb: baud period
    """
    X = 2 * t / Tb - 4.0
    with np.errstate(divide="ignore", invalid="ignore"):
        g = np.sinc(X) / (1.0 - X**2)

    # this might not happen if t was not generated exactly at the 0 (due to precision)
    infidx = np.argwhere(g == np.inf).flatten()

    # print('Correcting inf indices..')
    if len(infidx) > 0:
        g[infidx] = 0.5

    return g


def makeSRC4_clipped(t, T, k=1.0):
    """SRC4 pulse shape clipped to only the middle 2 symbols."""
    X = 2 * t / T - 2.0
    g = k * np.sinc(X) / (1.0 - X**2)

    infidx = np.argwhere(g == np.inf).flatten()

    if len(infidx) > 0:
        g[infidx] = k * 0.5

    zeroidx = np.argwhere(t < 0).flatten()
    zero2idx = np.argwhere(t > 2 * T).flatten()

    if len(zeroidx) > 0:
        g[zeroidx] = 0
    if len(zero2idx) > 0:
        g[zero2idx] = 0

    return g


def makeScaledSRC4(up, a=0.5):
    """
    Most use-cases for the pulse-shape require the integral over the pulse to be 0.5;
    for discrete samples this is equivalent to sum(g) = a = 0.5. This function should return
    the pulse at this required scaling factor, but the tuning is supplied as the argument
    'a' if desired.
    """
    t = np.arange(4 * up) / up  # this is in normalized symbol timing ie assume Tb = 1.0

    qa = sp.integrate.quad(makeSRC4, 0, 4, 1.0)

    g = makeSRC4(t, 1.0) / (qa[0] / a) / up

    return g