import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import butter, lfilter

def gfsk_cpm_modulation(data, symbol_rate, bit_rate, modulation_index):
    time = np.arange(0, len(data) / bit_rate, 1 / symbol_rate)
    modulated_signal = np.zeros_like(time)

    phi = 0
    for i in range(len(data)):
        phi += 2 * np.pi * (bit_rate / symbol_rate) * modulation_index * (data[i] - 0.5)
        modulated_signal[i] = np.cos(phi)

    return time, modulated_signal

def apply_gaussian_filter(signal, filter_order, cutoff_frequency):
    # Design a digital Butterworth low-pass filter
    nyquist = 0.5
    normal_cutoff = cutoff_frequency / nyquist
    b, a = butter(filter_order, normal_cutoff, btype='low', analog=False, output='ba')
    
    # Apply the digital filter
    filtered_signal = lfilter(b, a, signal)
    return filtered_signal

def main():
    # Modulation Parameters
    symbol_rate = 1000   # Symbol rate in symbols per second
    bit_rate = 1000      # Bit rate in bits per second
    modulation_index = 0.5

    # Generate random binary data
    np.random.seed(42)   # For reproducibility
    data = np.random.randint(0, 2, size=100)

    # Digital filter parameters
    filter_order = 8          # Adjust as needed
    cutoff_frequency = 0.1     # Adjust as needed (normalized cutoff frequency)

    # GFSK-CPM Modulation without Digital filter
    time, modulated_signal_before_filter = gfsk_cpm_modulation(data, symbol_rate, bit_rate, modulation_index)

    # Apply Digital filter
    modulated_signal_after_filter = apply_gaussian_filter(modulated_signal_before_filter, filter_order, cutoff_frequency)

    # Plot the GFSK-CPM modulated signals
    plt.plot(time, modulated_signal_before_filter, color='blue', label='Before Filter')
    plt.plot(time, modulated_signal_after_filter, color='red', label='After Filter (Digital)')
    
    plt.title('GFSK-CPM Modulation with Digital Filter')
    plt.xlabel('Time (s)')
    plt.ylabel('Amplitude')
    plt.legend()
    plt.show()

if __name__ == "__main__":
    main()