MULTIPLE%20INPUT%20MULTIPLE%20OUTPUT%20SYSTEMS%20(MIMO)

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MULTIPLE INPUT MULTIPLE OUTPUT SYSTEMS (MIMO)

• By MOHAMMED BERHEA

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1. Introduction

• MIMO Systems
• use multiple inputs and multiple outputs from a
  single channel
• are defined by Spatial Diversity and Spatial
  Multiplexing

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Spatial Diversity and Spatial Multiplexing

• Spatial Diversity
• Signal copies are transferred from multiple
  antennas or received at more than one antenna
• redundancy is provided by employing an array of
  antennas, with a minimum separation of ?/2
  between neighbouring antennas
• Spatial Multiplexing
• the system is able to carry more than one data
  stream over one frequency, simultaneously

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Why MIMO?

• There is always a need for increase in
  performance in wireless systems
• Significant increase in spectral efficiency and
  data rates
• High Quality of Service (QoS)
• Wide coverage, etc.
• Wireless channel that we are using is very
  unfriendly
• Suffers from Cochannel interference and signal
  level fading
• It provides a limited bandwidth
• power falls off with distance

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MIMO System solutions

• By using Multiple Output Multiple Input (MIMO)
  systems
• Diversity gain mitigates the fading and increases
  coverage and improves QoS
• Multiplexing gain increases capacity and spectral
  efficiency with no additional power or bandwidth
  expenditure
• Array gain results in an increase in average
  receive SNR.
• Spatial Diversity and Spatial Multiplexing can
  be conflicting goals

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Spatial Multiplexing

• MIMO channels can be decomposed into a number of
  R parallel independent channels ? Multiplexing
  Gain
• Principle Transmit independent data signals from
  different antennas to increase the throughput,
  capacity.

Source An Overview of MIMO Systems in Wireless
Communications www.iet.ntnu.no/projects/beats/Docu
ments/mimo.pdf
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MEMO capacity on fading channels

• The capacity increase can be seen by comparing
  MEMO systems with SISO, SIMO, and MISO systems
• SISOcapacity is given by Shannons classical
  formula
• Where B is the BW and h is the fading gain
• SIMO (with M transmitting antennas), the capacity
  is given by 2
• MISO (with M transmitting antennas), the capacity
  is given by 2

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MEMO capacity on fading channels

• The capacity for MIMO systems can have the
  following forms (Assuming Tx antennas Rx
  antennas N)
• A) If the channel is not known at the
  transmitter
• Where Es is the total power, s2 is noise level of
  AWGN
• Hence the power is equally shared by each channel
• The capacity grows linearly with the number of
  antennas
• B) If the channel is known at the transmitter

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MEMO capacity on fading channels

• With the channel known at the transmitter, the
  total power allocation the each channel will be
  based on watterfilling.
• Watterfilling Strong Sub-channel, with low noise
  power level will be assigned with a higher signal
  power.
• Where sN2 s2 / hn2

Illustrating Watterfilling
Source MIMO Systems and Transmit Diversity,
www.comm.utoronto.ca/rsadve/Notes/DiversityTransm
it.pdf
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Average capacity of a MIMO Rayleigh fading
channel
Source Space-time Diversity Codes for Fading
Channels, 3
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Spatial Diversity

• Improves the signal quality and achieves a higher
  SNR at the receiver-side
• Principle of diversity relies on the transmission
  of structured redundancy

yi
xi
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MIMO Diversity and Reliability

• The performance improvement in SNR and error
  probability for MIMO can be compared with SISO,
  SIMO, and MISO
• The detailed calculation for SNR and Pe is shown
  in 1
• SISO
• Receive Diversity (SIMO)

and
and
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MIMO Diversity and Reliability

• The values for SNR and Pe for
• Transmit Diversity (MISO)
• Transmit/Receive Diversity (MIMO)
• The received signal at antenna i will be
• H is the channel fading matrix

and
and
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Conclusion

• The capacity of Receive or Transmit Diversity
  grows logarithmically with the number of antennas
• Capacity of MEMO increases linearly with the
  number of antennas
• Using Spatial Diversity
• The SNR increases and Pe decreases when using
  MIMO
• Spatial Multiplexing and Spatial Diversity are
  conflicting objectives

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References

• 1 MIMO Architecture for Wireless Communication
  Intel Technology Journal, vol. 10, Issue 02, May
  2006
• 2 MIMO Systems and Transmit Diversity,
• www.comm.utoronto.ca/rsadve/Notes/DiversityTrans
  mit.pdf
• 3 R.A. Carrasco, Space-time Diversity Codes for
  fading Channel,
• Staffordshire University
• 4 D. Gesbert, M.Shafi, D. Shiu, P. Smith, and
  A. Naguib, From Theory to Practice An Overview
  of MIMO SpaceTime Coded Wireless Systems
• IEEE JOURNAL ON SELECTED AREAS IN
  COMMUNICATIONS, VOL. 21, NO. 3, APRIL 2003
• 5 Introduction to MIMO Systems Application
  Note 1MA102, Rohde schwarz