> For the complete documentation index, see [llms.txt](https://jen-hsuan-hsieh.gitbook.io/protocol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jen-hsuan-hsieh.gitbook.io/protocol/chapter5-wireless-network/54lte/547fdd-tdd-half-duplex-fdd.md).

# 5.4.7.FDD, TDD, Half Duplex FDD

* FDD

  * 分頻多工(Frequency-Division Duplexing, FDD)
  * 在頻率軸上以成對的方式進行分頻使用, 一頻帶用於下行頻寬(DL Bandwidth), 另一頻帶用於上行頻寬(UL Bandwidth)
  * 在相同頻寬配置下, FDD則為相同頻寬的上下行配置, 上下行各占用一半的資源比例, 此比例為固定

  ![](https://3840825399-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4M0G8PXRnA3yHgZCAL%2F-M4M0Gn8DmjJ2aT88bjY%2F-M4M0Hz7mj_sRo6IvxuN%2F%E8%9E%A2%E5%B9%95%E5%BF%AB%E7%85%A7%202017-06-13%20%E4%B8%8B%E5%8D%887.24.19.png?generation=1586302893508439\&alt=media)
* TDD

  * 分時多工(Time Division Duplexing, TDD)
  * 頻譜為上下行所共用, 上下行的配置是以時間進行分時配置, 一部分時間安排下行傳送, 另一部分則安排上行傳送. 在下行轉上行時, 會有一段保護時間(Guard Period, GP)用於接收與傳送間進行轉換

  ![](https://3840825399-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4M0G8PXRnA3yHgZCAL%2F-M4M0Gn8DmjJ2aT88bjY%2F-M4M0HzAr5fJnDPiJioq%2F%E8%9E%A2%E5%B9%95%E5%BF%AB%E7%85%A7%202017-06-13%20%E4%B8%8B%E5%8D%887.24.25.png?generation=1586302893379529\&alt=media)
* FDD v.s. TDD
  * 1.FDD模式為成對的頻譜配置, 而TDD為單一的頻譜配置
* Half Duplex FDD
  * 1.Cost < FDD