ASK変調のスペクトル(3)

import matplotlib.pyplot as plt
import numpy as np

# よく使う変数
pi=np.pi
deg2rad=pi/180.0
twopi=2*pi

# シンボル列を引き延ばす
def extend_symbol_to_simulation_sampling_rate(symbols,t_symbol,t_simulation_sampling):
    # シンボル数
    size_of_symbols=symbols.size
    # 最後のシンボルが終わる時間
    end_time=size_of_symbols*t_symbol
    # 計算タイミング
    t=np.arange(0,end_time,t_simulation_sampling)
    # 各シンボルの開始（終了）時間
    t_periods_of_symbols=np.append(0,np.arange(1,size_of_symbols,1)*t_symbol)
    # 結果データ領域確保
    ex_symbols=np.zeros_like(t)
    # 先頭データは入れておく
    ex_symbols[0]=symbols[0]
    # 各シンボルについて、その期間のインデックスを取得し、データを入れ込む
    for i in range(0,size_of_symbols):
        ex_symbols[np.where(t>t_periods_of_symbols[i])]=symbols[i]
    return ex_symbols,end_time
        
def generate_ask(f_carrier,f_sym,f_samp_generation,phase_carrier_initial,symbols_in_base):
    t_sym=1/f_sym
    t_samp_generation=1/f_samp_generation
    omega_carrier=twopi*f_carrier
    # シンボルを計算用に拡張
    [symbols,t_end]=extend_symbol_to_simulation_sampling_rate(symbols_in_base,t_sym,t_samp_generation)
    # 計算するタイミング
    t=np.arange(0,t_end,t_samp_generation)
    # 波形生成
    amp_t=np.exp(1j*omega_carrier*t+phase_carrier_initial)*symbols
    return t,symbols,amp_t

def main():
    # 設定
    f_carrier=433.92e6            # 搬送波周波数 in Hz
    f_sym=2e6                 # シンボルレート in Hz
    f_samp_generation=1e10     # 計算のサンプリングレート in Hz
    t_samp_generation=1/f_samp_generation
    phase_initial=0*deg2rad  # 搬送波の初期位相(何でもいい) in rad
    #symbols_in_base=np.array([1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0])
    symbols_in_base=np.array([1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0])
    t,baseband_t,amp_t=generate_ask(f_carrier,f_sym,f_samp_generation,phase_initial,symbols_in_base)
    #今回の計算は実部だけでやったので
    amp_t=np.real(amp_t)

    number_of_samples=t.size
    # fftする
    amp_f=np.fft.fft(amp_t)/(number_of_samples/2)
    amp_f=np.abs(amp_f)
    freq=np.fft.fftfreq(number_of_samples,t_samp_generation)

    # プロット
    fig=plt.figure()
    fig.add_subplot(3,1,1)
    plt.plot(t,baseband_t)
    fig.add_subplot(3,1,2)
    plt.plot(t,amp_t)
    fig.add_subplot(3,1,3)
    plt.plot(freq[0:int(number_of_samples/2)],amp_f[0:int(number_of_samples/2)])
    plt.xlim(f_carrier-10e6,f_carrier+10e6)
    plt.show()

    amp_f=20*np.log10(amp_f)
    fig=plt.figure()
    plt.plot(freq[0:int(number_of_samples/2)],amp_f[0:int(number_of_samples/2)])
    plt.xlim(f_carrier-10e6,f_carrier+10e6)
    plt.ylim(-50,0)
    plt.show()

main()