Spatial Diversity and Multiuser Diversity in Wireless

Communications

Bengt HolterDept. of Electronics and

TelecommunicationsNTNU

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

FadingSignal fluctuations caused by multipath propagation and shadowing effects.

DiversityReceiving the same information bearing signal over 2 or more fading channels.

Introduction (cont’d)

SpaceTransmission using multiple transmit/receive antennas.

FrequencyTransmission 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) channelNo spatial diversity

Single-input, multiple-output (SIMO) channelReceive diversity

Multiple-input, single-output (MISO) channel Transmit diversity

Multiple-input, multiple-output (MIMO) channelCombined transmit and receive diversity

Spatial diversity (cont’d)

•Maximum ratio combining (MRC)

h1

h2

h1*

h2*

yx

Spatial diversity (cont’d)

•Selection combining (SC)

h1

h2

yx

MonitorSNR

Selectbranch

Spatial diversity (cont’d)

Switched diversity Switch-and-stay combining (SSC) Switch-and-examine combining (SEC)

h1

h2

x

ComparatorChannelestimator

switchingthreshold

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

nRnT

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.

Adaptivecoded

modulator

SSC combiner,coherent detectionand 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

SCSEC

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.

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)

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.

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. 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.

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.

Additional publications / work in progress by Bengt Holter during the BEATS project