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

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.

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

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.

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

Spatial diversity (cont’d) Maximum ratio combining (MRC) h1h1 h2h2 h1*h1* h2*h2*  y x

Spatial diversity (cont’d) Selection combining (SC) h1h1 h2h2 y x Monitor SNR Select branch

Spatial diversity (cont’d) Switched diversity Switch-and-stay combining (SSC) Switch-and-examine combining (SEC) h1h1 h2h2 x Comparator Channel estimator switching threshold

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.

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]: 1 nRnR nTnT 1

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.

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

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]

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. Adaptive coded modulator SSC combiner, coherent detection and adaptive decoding channel state information 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.

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

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

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

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 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.

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 Proposed multiuser access schemes Switch-and-examine transmission (SET) SET witch post-selection (SETps) Scan-and-wait transmission (SWT) 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 Results Average spectral efficiency (ASE) using optimal switching thresholds. Average feedback load for the switching thresholds which maximizes the ASE.

References [Charash,79] U. Charash, ”Reception through Nakagami fading multipath channels with random delays,” IEEE Transactions on Communications, vol. 27, pp , April [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 , December [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 , December [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 , August 2003.

B. Holter, ”On the capacity of the MIMO channel : A tutorial introduction,” in Proc. of IEEE Norwegian Symposium on Signal Processing, pp , Trondheim, Norway, October 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 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 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. Additional publications / work in progress by Bengt Holter during the BEATS project