OFDM-MIMO implementation in Line Of Sight microwave/millimeter wave link

Baruch Cyzsbaruch_cyzs@hotmail.com

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

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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

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Basic Block diagram - dual antenna arrays

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Tx Beam former

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Rx Beam former

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Singular Value Decomposition

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The de-multiplexing process

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Test site in France