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

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. Introduction. Discrete Multitone Modulation.

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

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  1. LabVIEW Multicore Real-Time Multi-Input Muli-Output Discrete MultitoneTransceiver Testbed YousofMortazavi, Aditya Chopra, and Prof. Brian L. Evans Wireless Networking and Communications Group The University of Texas at Austin

  2. Introduction

  3. 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

  4. 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

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

  6. 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

  7. Evolution of the Testbed

  8. 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

  9. 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

  10. 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 QHY Slicer y1

  11. 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

  12. Experimental Results SIC – Successive Interference Cancellation

  13. Target CPU Utilization Target CPU Utilization

  14. 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

  15. Backup

  16. 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

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