# 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)