ofdm-mimo implementation in line of sight microwave for logtel
TRANSCRIPT
OFDM-MIMO implementation in Line Of Sight microwave/millimeter wave link
Baruch [email protected]
Introduction
• Implementation of OFDM-MIMO in line of sight microwave link
• Description of hardware prototype of mm wave PTP microwave that employs OFDM-MIMO.
• Important Implementation issues in microwave link that employs OFDM-MIMO
The MIMO Spatial multiplexing implementation
• The MIMO spatial implementation exploits random independent and identical distributed (iid) channel.
• The orthogonality of the channel is usually achieved by existing of reach scattering.
• Spatial multiplexing suffer degradation in its performance if significant direct path (LOS) exists in the Rician channel.
• LOS microwave link cannot implement MIMO since it relies mainly on strong LOS component
The Spatial Multiplexing principles in LOS link
• The receiver antenna array is located in the near field zone of the transmitter antenna array.
• The spherical wave front from each transmitter antenna causes phase difference at the receiver antennas.
• LOS Spatial Multiplexing exploits this phase difference to grant orthogonality to the link channel for implementation of spatial multiplexing.
The Near Field multiplexing
• The receiving array is located in the near field of the transmitting array.
• Since the wave front is not planar there is phase gradient upon the receiving array.
• If the phase gradient is set to certain predetermined value the link channel becomes orthogonal.
Geometry orthogonalization
‘R
R
Linear antenna array requirement full rank condition
d‘R
R
d‘R
R
Phase difference between R and R’:360º/(2*n) in optimal orthogonal condition
n antennas
1 42opt
nRd
n
RnR
ndopt
412
n
R
Basic Block diagram - dual antenna arrays
V21
V12
V22
V11 U11
U21
U12
U22
x1’
x2’
y1’
y2’
H11
H22
H21
H12
x1
x2y2
y1
Tx Beam former
Diversity Gain
Rx Beam former
SeparationChannel
Singular Value Decomposition
y’
1
2
3
1
2
3
z’
zUxVyU
zxVUy
zHxy
domainfrequncy
tztxthty
domaintime
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)()(*)()(
X’
The de-multiplexing process
3
2
1
3
2
1
3
2
1
3
2
1
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z
z
z
x
x
x
y
y
y
Noise statistics has not changed (unitary rotation)Singular values represent virtual gain
TeraWave gallery
Test site in France