Spatial Diversity and Multiuser Diversity in Wireless Communications

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Spatial Diversity and Multiuser Diversity in
Wireless Communications

• Bengt Holter
• Dept. of Electronics and TelecommunicationsNTNU

IKT-2010 seminar, Lillestrøm, Sept. 20/21, 2004
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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.

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Introduction

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

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Introduction (contd)

• 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.

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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

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Spatial diversity (contd)

• Maximum ratio combining (MRC)

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Spatial diversity (contd)

• Selection combining (SC)

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Spatial diversity (contd)

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

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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.

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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

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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.

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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

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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 (contd)
At high SNR Wang,03
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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.

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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
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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 (contd)

Average spectral efficiency (ASE) using optimal
switching thresholds.
Optimal switching thresholds maximizing the ASE
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Multiuser diversity
1
SC SEC
2
Spatial diversity
K

• Multiuser diversity
• Combiner Base station
• Antennas Individual users

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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.

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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.
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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.

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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.