Principle of Diversity : Combat Fading

For Single Link,

• If the single link is in a deep fade, it disrupts communication.
• There is No ALTERNATIVE.
• If single link is in deepfade, performance is BAD.

For Diveristy,

• Multiple links between TX,RX
• Alternative Path for communication.

Diversity is used in serval 3G/4G systems such as,

• 3G
  • WCDMA
  • HSDPA
• 4G
  • HSDPA
  • WiMAX

• With increasing # of anntenas L, Prob. of deep fade decreases.
• This leads to a significant decrease on BER.

P.22

• For system to be in DeepFade, all links have to be in DeepFade.

Diversity Order : To characterize Diversity of a system

CDMA : Code Division Multiple Access

• CDMA : Is a multiple access Technology

• TDMA

• FDMA

• CDMA :

  • Different users are allocated Different codes.
  • use Codes for Multiple Access

MIMO

• Possible by Transmitting several info. streams in parallel.

Spatial Multiplexing

• 用空間去增加bit rate,而不是fc,time,etc.