# -*- coding: utf-8 -*-
import os
import numpy as np
import matplotlib.pyplot as plt
 
# -----------------------------
# Matplotlib キャッシュディレクトリ設定（警告回避）
# -----------------------------
# 書き込み可能なディレクトリを指定
os.environ['MPLCONFIGDIR'] = '/tmp/matplotlib_config'  # Linux/macOS
# Windowsの場合:
# os.environ['MPLCONFIGDIR'] = r'C:\Temp\matplotlib_config'
 
# -----------------------------
# Received power calculation (Free-space)
# -----------------------------
def received_power(distance_m, frequency_hz, tx_power_dbm=20):
    c = 3.0e8  # speed of light [m/s]
    wavelength = c / frequency_hz
    fspl_db = 20 * np.log10(4 * np.pi * distance_m / wavelength)
    rx_power_dbm = tx_power_dbm - fspl_db
    return rx_power_dbm
 
# -----------------------------
# Settings
# -----------------------------
distances = np.linspace(1, 200, 200)  # distance [m]
tx_power_dbm = 20                     # transmit power [dBm]
 
rx_24 = received_power(distances, 2.4e9, tx_power_dbm)
rx_5  = received_power(distances, 5.0e9, tx_power_dbm)
 
# -----------------------------
# Plot
# -----------------------------
plt.figure(figsize=(8,5))
plt.plot(distances, rx_24, label="2.4 GHz", color="green", linewidth=2)
plt.plot(distances, rx_5,  label="5 GHz",  color="blue", linestyle="--", linewidth=2)
 
plt.title("Received Power vs Distance (Free Space)")
plt.xlabel("Distance [m]")
plt.ylabel("Received Power [dBm]")
plt.grid(True, linestyle="--", alpha=0.7)
plt.legend()
plt.tight_layout()
plt.show()
 

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