1. Transmit Diversity in 3G CDMA System 指導老師：黃文傑 博士 學生：吳濟廷 2003.9.24

2. OUTLINE  Introduction  Transmit diversity basics  Open loop TD in 3G  Close loop TD in 3G  Comparison of TD methods  Conclusion

3. Introduction  Improvement of system capacity  Downlink intensive in 3G system  Effective and practical aspect

4. Transmit Diversity Basics  The channel  Delay diversity  Frequency diversity

5. TD Basics ~ channel  Combat fading  Coherence bandwidth Single-path two-path

6. TD Basics ~ delay diversity  Add two independent fading signals together to aid in demodulation  Two antennas have unique pilot symbol

7. TD Basics ~ frequency diversity  Separate in sufficient large freq. to ensure independent fading  Hard to implement in band-limited system

8. Open loop TD in 3G  Advantage Signaling overhead is not required MS receiver complexity is low  Disadvantage Channel information not used

9. Orthogonal TD,where and are complementary OTD transmitter

10. Space-time TD This transform maximize the diversity gain antenna time

11. Close loop TD in 3G  Advantage Adaptive in nature Using feedback to get optimal weight  Disadvantage Waste of channel bandwidth

12. Transmit adaptive array Transmit adaptive array method Spreading sequence

13. Issues and solutions(1/3)  Precision Issue  Limited feedback available capacity Solutions  Quantize the complex feedback coefficient  Only feedback the phase information

14. Issues and solutions(2/3)  Feedback error Issue  Not protected by FEC Solutions  Hypothesis testing  decision-directed method ~ create a replica of the error frame

15. Issues and solutions(3/3)  Feedback delay Issue  Delay causes the Tx weights outdated Solutions  AR ( auto-regressive ) process

16. Comparison of TD methods Performance of TD methods

17. Conclusion  Open loop TD has good performance in high velocity  Close loop TD has good performance in low velocity  How to mixture the OL and CL diversity ??