Spatial Diversity and Multiuser Diversity in Wireless Communications

1. Spatial Diversity and Multiuser Diversity in Wireless Communications Bengt Holter Dept. of Electronics and TelecommunicationsNTNU IKT-2010 seminar, Lillestrøm, Sept. 20/21, 2004

2. Outline • Introduction • Spatial diversity • B. Holter and G. E. Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. • B. Holter and G. E. Øien, ”Performance Analysis of a Rate-Adaptive Dual-Branch Switched Diversity System,” in preparation for submission to IEEE Transactions on Wireless Communications. • Multiuser diversity • B. Holter, M. –S. Alouini, G. E. Øien, and H. –C. Yang, ”Multiuser Switched Diversity Transmission,” accepted for publication in IEEE Vehicular Technology Conference, Los Angeles, USA, September 2004.

3. Introduction • Fading Signal fluctuations caused by multipath propagation and shadowing effects. • Diversity Receiving the same information bearing signal over 2 or more fading channels.

4. Introduction (cont’d) • Space Transmission using multiple transmit/receive antennas. • Frequency Transmission using multiple frequency channels separated by at least the coherence bandwidth. • Time Transmission using multiple time slots separated by at least the coherence time.

5. Spatial diversity • Single-input, single-output (SISO) channel No spatial diversity • Single-input, multiple-output (SIMO) channel Receive diversity • Multiple-input, single-output (MISO) channel Transmit diversity • Multiple-input, multiple-output (MIMO) channel Combined transmit and receive diversity

6. h1* h1  y x h2 h2* Spatial diversity (cont’d) • Maximum ratio combining (MRC)

7. Selectbranch MonitorSNR h1 y x h2 Spatial diversity (cont’d) • Selection combining (SC)

8. switchingthreshold Channelestimator Comparator h1 x h2 Spatial diversity (cont’d) • Switched diversity • Switch-and-stay combining (SSC) • Switch-and-examine combining (SEC)

9. B. Holter and G. E- Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. Introduction • Improvements related to a reduced fading level are commonly quantified by average error rate curves. • The average error rate may in some cases be difficult to evaluate analytically. Motivation • Quantify the severity of fading by using a measure directly related to the fading distribution.

10. 1 1 nT nR B. Holter and G. E- Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. • Amount of fading • [Charash,79]:

11. B. Holter and G. E- Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. Related work • [Win,99] Square root of the AF applied to the combiner output in a hybrid selection/MRC scheme in Rayleigh fading. • [Alouini,02] Closed-form expressions for the AF for dual-branch MRC, SC, and SSC in log-normal fading.

12. B. Holter and G. E- Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. Results • Identically distributed Nakagami-m fading channels • Identically distributed Rayleigh fading channels

13. B. Holter and G. E- Øien, ”On the Amount of Fading in MIMO Diversity Systems,” accepted for publication in IEEE Transactions on Wireless Communications. Results (cont’d) At high SNR [Wang,03]

14. SSC combiner, coherent detection and adaptive decoding Adaptive coded modulator channel state information B. Holter and G. E. Øien, ”Performance Analysis of a Rate-Adaptive Dual-Branch Switched Diversity System,” in preparation for submission to IEEE Transactions on Wireless Communications. Introduction Motivation • The performance of a switched diversity receiver is inferior compared to using an MRC or an SC receiver, but it represents an attractive choice in practice due to its low complexity.

15. B. Holter and G. E. Øien, ”Performance Analysis of a Rate-Adaptive Dual-Branch Switched Diversity System,” in preparation for submission to IEEE Transactions on Wireless Communications. Results with respect to AF Amount of fading as function of switching threshold and spatial power correlation Amount of fading as a function of switching threshold and temporal power correlation

16. B. Holter and G. E. Øien, ”Performance Analysis of a Rate-Adaptive Dual-Branch Switched Diversity System,” in preparation for submission to IEEE Transactions on Wireless Communications. Results (cont’d) Average spectral efficiency (ASE) using optimal switching thresholds. Optimal switching thresholds maximizing the ASE

17. User 1 User 2 User K Multiuser diversity 1 SC SEC 2 Spatial diversity K • Multiuser diversity • Combiner = Base station • Antennas = Individual users

18. B. Holter, M. –S. Alouini, G. E. Øien, and H. –C. Yang, ”Multiuser Switched Diversity Transmission,” accepted for publication in IEEE Vehicular Technology Conference, Los Angeles, USA, September 2004. Introduction • Always searching for the best user results in a high and determinstic feedback load. Motivation • Utilize switched diversity algorithms reported in the literature as multiuser access schemes to reduce the average feedback load. • The base station probes the users in a sequential manner, looking not for the best user but for an acceptable user.

19. User 1 User 2 User K B. Holter, M. –S. Alouini, G. E. Øien, and H. –C. Yang, ”Multiuser Switched Diversity Transmission,” accepted for publication in IEEE Vehicular Technology Conference, Los Angeles, USA, September 2004. Proposed multiuser access schemes • Switch-and-examine transmission (SET) • SET witch post-selection (SETps) • Scan-and-wait transmission (SWT)

20. B. Holter, M. –S. Alouini, G. E. Øien, and H. –C. Yang, ”Multiuser Switched Diversity Transmission,” accepted for publication in IEEE Vehicular Technology Conference, Los Angeles, USA, September 2004. Results Average spectral efficiency (ASE) using optimal switching thresholds. Average feedback load for the switching thresholds which maximizes the ASE.

21. References • [Charash,79] U. Charash, ”Reception through Nakagami fading multipath channels with random delays,” IEEE Transactions on Communications, vol. 27, pp. 657-670, April 1979. • [Win,99] M. Z. Win and J. H. Winters, ”Analysis of hybrid selection/maximal-ratio combining in Rayleigh fading,” IEEE Transactions on Communications, vol. 47, no. 12, pp. 1773-1776, December 1999. • [Alouini,02] M. –S. Alouini and M. K. Simon, ”Dual diversity over log-normal fading channels,” IEEE Transactions on Communications, vol. 50, no. 12, pp. 1946-1959, December 2002. • [Wang,03] Z. Wang and G. B. Giannakis, ”A simple and general parameterization quantifying performance in fading channels,” IEEE Transactions on Communications, vol. 51, no. 8, pp. 1389-1398, August 2003.

22. Additional publications / work in progress by Bengt Holter during the BEATS project • B. Holter, ”On the capacity of the MIMO channel : A tutorial introduction,” in Proc. of IEEE Norwegian Symposium on Signal Processing, pp.167-172, Trondheim, Norway, October 2001. • B. Holter and G. E. Øien, ”The optimal weights of a maximum ratio combiner using an eigenfilter approach,” in Proc. 5th IEEE Nordic Signal Processing Symposium (NORSIG-2002), Hurtigruten, Norway, October 2002. • B. Holter, G. E. Øien, K. J. Hole, and H. Holm, “Limitations in spectral efficiency of a rate adaptive MIMO system utilizing pilot-aided channel prediction,” in Proc. IEEE Vehicular Technology Conference, Jeju, Korea, April 2003. • B. Holter, M. –S. Alouini, G. E. Øien, and H. –C. Yang, ”Multiuser Switched Diversity Transmission,” in preparation for submission to IEEE Transactions on Wireless Communications. • B. Holter and G. E. Øien, ”Performance Analysis of a Rate-Adaptive Dual Diversity System on Correlated Rayleigh Fading Channels,” in preparation.