LabVIEW Multicore Real-Time Multi-Input Muli-Output Discrete Multitone Transceiver Testbed

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LabVIEW Multicore Real-Time Multi-Input
Muli-Output Discrete Multitone Transceiver Testbed

• Yousof Mortazavi,
• Aditya Chopra, and Prof. Brian L. Evans
• Wireless Networking and Communications Group
• The University of Texas at Austin

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Introduction
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Discrete Multitone Modulation

• DMT modulation is used in wireline communication
  systems (e.g. DSL)
• Divide frequency selective channel into many
  narrowband subchannels
• Transmit data over each frequency flat subchannel
• Modulate/demodulate multicarrier signal using
  Fast Fourier Transform

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MIMO DMT Testbed

• Design Goal Create a 2x2 DMT hardware testbed
• Enable rapid prototyping/testing of new designs
• Provide user with complete control over system
  parameters
• Connect to different cables
• Visualize channel state and communication
  performance
• Benefits of Hardware Testbed
• Configure system parameters and signal processing
  blocks
• Evaluate communication performance vs.
  computational complexity tradeoffs
• Support many different cables
• Design Challenges
• Real-time constraints on transmitter and receiver
  system
• Analog front-ends for signal conditioning

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Modem Implementation- Hardware
PXI Backplane - PXI-1045
TX0
TX1
RX0
RX1
Embedded PC PXI-8106
TCP Link
PXI-5421 A/D
PXI-5122 D/A
LPF
LPF
LPF
LPF
H
H
H
H
LPF Low Pass Filter H Hybrid
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Modem Implementation- Software

• Real-Time Target
• LabVIEW Real-Time Vis
• Accesses hardware
• Calls DLL functions
• C Dynamic Link Library (DLL)
• Digital discrete-time baseband processing
• Generates/processes samples sent/received to/from
  hardware
• Real-time operating system
• Runs on target to guarantee real-time performance
• Desktop PC
• TCP/IP link to real-time target
• Asynchronous visualization and control using
  LabVIEW

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Evolution of the Testbed
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Bit Allocation

• Fixed amount of energy available to transmit per
  DMT symbol
• DMT allows different number of bits transmitted
  on each tone
• Adapt bit allocation to maximize throughput or
  SNR margin on each tone
• Hughes Hartog bit allocation algorithm 1987
  implemented

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Far-End Crosstalk Cancellation

• Far End Crosstalk provides significant
  deterioration in bit rate
• Using vectored DMT Ginis Cioffi, 2002 multiple
  receivers operate together to cancel crosstalk
• Other crosstalk cancellation methods
• Linear zero-forcing equalizer
• Non-linear successive interference cancellation

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Vectored DMT

• Uses channel estimate and both received signals
  to effectively cancel crosstalk

Estimate channel matrix H
Training (per-tone)?
For each tone, H, Q and R are 2x2 matrices
H Q R
Symbol decoding (per-tone)?
Q
R
y0
Successive Interference Cancellation
Slicer
QHY
y1
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Experimental Results

• System Parameters
• 256 tones per DMT symbol
• Maximum Transmitted Voltage 5.0V
• Receiver noise floor -60dB
• 1000ft CAT-5 cable
• Inter-twisted pairs for maximum far-end
  crosstalk
• Far-end crosstalk limits SNR to 10dB

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Experimental Results
SIC Successive Interference Cancellation
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Target CPU Utilization
Target CPU Utilization
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References

• D. Hughes-Hartog, Ensemble modem structure for
  imperfect transmission media. U.S. Patents Nos.
  4,679,227 (July 1987), 4,731,816 (March 1988),
  and 4,833,706 (May 1989)
• G. Ginis and J. Cioffi, Vectored transmission
  for digital subscriber line systems, IEEE J.
  Select. Areas Commun., vol. 20, no. 5, pp.
  1085-1104, Jun. 2002

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Backup
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Analog Front-End

• Hybrid circuits from Texas Instruments
• Line Driver / 2-wire to 4-wire Interface
• Custom passive analog filters from TTE
• Serve as anti-aliasing filters for TX and RX