Architectures of MIMO Channel Sounder Jun-ichi TAKADA Tokyo - - PowerPoint PPT Presentation

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Architectures of MIMO Channel Sounder

Jun-ichi TAKADA Tokyo Institute of Technology

ICT 2010 Special Session “ICT for WiMedia UWB” August 24, 2010 - KMITL, Thailand

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Ultra Wideband (UWB) Systems

• FCC’s policy

– Underlay: Level below unintentional emission

• Short range

– No frequency allocation

• Plenty of bandwidth

– Potential broadband

• Location awareness

– High resolution in delay domain

3 4 5 6 7 8 9 10 11

• 90
• 80
• 70
• 60
• 50
• 40

EU Japan USA indoor Frequency [GHz] PSD e.i.r.p. [dBm/MHz]

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Ultra Wideband (UWB) Systems

• Example applications

– WiMedia : High speed PAN – IEEE 802.15.4a : low speed, location aware – IEEE 802.15.6 : body area

• Issues

– Strong objections from victim systems – Too much emphasis on high speed PAN

• Strong competitors: 802.15.3c and 802.11n
• Large power consumption due to OFDM

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Ultra Wideband (UWB) Systems

• Advantages of impulse radio

– Low power consumption – High resolution in time domain

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UWB Channel Characterization

• Two aspects of channel

– Impulse response between Tx and Rx ports – Interference from other systems

• System evaluation via channel model

– Mathematical model based on measurements – To be standardized for comparison

• Channel sounding

– Measurement of channel impulse response

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Radio Channel

Rx Rx Tx

Antennas and Propagation shall be separated in the model

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Why shall Antennas and Propagation be separated in the model?

• Antennas

– Manmade device – Designed and controlled

• Propagation

– Natural phenomenon – Given as condition Quite different factors

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Propagation Path Modeling

Rx Rx Tx

• Delay time (DT)
• Doppler frequency (DF)
• Directions of departure and arrival (DoD/DoA)
• Magnitude (polarimetric)

Note: Just approximation

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Channel Sounding

Measurement of channel property

• Delay time – Wideband signal
• Doppler frequency – Dynamic measurement
• Directions – Array antennas
• Magnitude – Sufficient power

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Channel Sounder Architecture (1)

 VNA + synthetic array antenna (SAA)

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Channel Sounder Architecture (2)

Tx Rx storage

AO CG LO AO: Atomic Oscillator, CG: Clock Generator, LO: Local Oscillator AO CG LO

• Time division multiplexing (TDM)

– Available as commercial sounder

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Channel Sounder Architecture (3)

Tx Rx Tx Rx Tx Rx Tx Rx AO CG LO AO CG LO AO: Atomic Oscillator, CG: Clock Generator, LO: Local Oscillator

• Full MIMO

– Implemented by software radio platform

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Comparison among MIMO Sounder Architectures

# of Tx & Max delay MUX response Spatial scan Speed # of Tx/Rx # of MUXs Arbitrary # of array elements Very high High Low HW Complexity Fast Slow Impossible Doppler Full MIMO TDM SAA

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Comparison among MIMO Sounder Architectures

B-B for all RF pairs, array B-B, array Back-to- back Calibration Small Large Very small RF power Full MIMO TDM SAA

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TDM and Full MIMO Sounders

• Measurement time only dominated by # of

Rx

– TDM and other Tx multiplexing need same time length for separation

• Cost proportional to # of RF/BB chain

– More expensive for high power

• Hardware sharing for full MIMO

– Extra storage needed for sounding

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Static Double Directional Channel

Rx Rx Tx

    

  

 





   

L l l ,l ,l l

f f a f H

1 Rx Rx Tx Tx Rx Tx Multipath

2 j exp , ,     Ω Ω Ω Ω Ω Ω

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Static SISO Channel

Rx Rx Tx

   

   

 

Channel TxAntenna Tx RxAntenna Rx 1

, , exp j2

L l ,l ,l l l

H f a f H f H f f  



 



Ω Ω

Similar to Friis’ formula

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Summary

• Different MIMO channel sounder

architectures – pros and cons

• Issues skipped due to time constraint

– Sounding signal design – Parameter estimation – Power handling – Measurement results

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Synchronization between Tx and Rx

Need of absolution synchronization

• Clock timing

– Absolute delay – Synchronization of multiplexer

• Carrier frequency / phase

– Coherence in TDM; array & Doppler – Separation of Tx signals in full MIMO

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Synchronization between Tx and Rx

• VNA (short range only)
• Cable connection (short range only)
• Atomic oscillator
• GPS (outdoor only)

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