---
# System prepended metadata

title: 'Principle of Diversity : Combat Fading'

---

#  Principle of Diversity : Combat Fading 
![image](https://hackmd.io/_uploads/rJWh6OIg0.png)
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.

![image](https://hackmd.io/_uploads/HkGNlKLeA.png)
For Diveristy,
* Multiple links between TX,RX
* Alternative Path for communication.

![image](https://hackmd.io/_uploads/B1OfukPlA.png)
Diversity is used in serval 3G/4G systems such as,
* 3G
    * WCDMA
    * HSDPA
* 4G
    * HSDPA
    * WiMAX

![image](https://hackmd.io/_uploads/BkWx3yPgR.png)
* With increasing # of anntenas L, Prob. of deep fade decreases.
* This leads to a significant decrease on BER.

### P.22
![Lecture 18_ Intuition for Deep Fade in Multi-Antenna System 7-3 screenshot](https://hackmd.io/_uploads/B1dt1gDlR.png)
* **For system to be in DeepFade, all links have to be in DeepFade.**

![Lecture 19_ Definition of Diversity Order 1-32 screenshot](https://hackmd.io/_uploads/BJIV7ePe0.png)
### Diversity Order : To characterize Diversity of  a system

# CDMA : Code Division Multiple Access
![Lecture 26_ Introduction to Code Division Multiple Access (CDMA) 1-58 screenshot](https://hackmd.io/_uploads/S1roTQuxC.png)

* CDMA : Is a multiple access Technology

* ### TDMA
    ![Lecture 26_ Introduction to Code Division Multiple Access (CDMA) 8-23 screenshot](https://hackmd.io/_uploads/rJ0RAmOxC.png)

* ### FDMA
    ![Lecture 26_ Introduction to Code Division Multiple Access (CDMA) 10-57 screenshot](https://hackmd.io/_uploads/B1Sr14uxA.png)

* CDMA : 
    * **Different users are allocated Different codes.**
    * use Codes for Multiple Access

# MIMO

![image](https://hackmd.io/_uploads/Sk7FL_5eA.png)

![image](https://hackmd.io/_uploads/BkCFIOqlC.png)
* Possible by **Transmitting several info. streams in parallel.**

## Spatial Multiplexing
![image](https://hackmd.io/_uploads/rJPAIuqxA.png)
* 用空間去增加bit rate,而不是fc,time,etc.

![image](https://hackmd.io/_uploads/Hk1vPOce0.png)

![image](https://hackmd.io/_uploads/r1uy__ceA.png)

![image](https://hackmd.io/_uploads/rJ1MQKqx0.png)

![image](https://hackmd.io/_uploads/rkqsmK9x0.png)






