https://blog.wongcw.com/2021/03/15/%e7%88%ad%e5%a5%aa5g-mid-band%e9%a0%bb%e8%ad%9c%ef%bc%9a%e7%be%8e%e5%9c%8b%e9%81%8b%e7%87%9f%e5%95%86%e8%b1%aa%e6%93%b2%e6%95%b8%e7%99%be%e5%84%84%e7%be%8e%e5%85%83%e8%b3%bc%e8%b2%b7/