1. Implementation Platform
Multi-Input Multi-Output Discrete Multitone Testbed
Alex Olson, Ian Wong, Aditya Chopra, Yousof Mortazavi and Prof. Brian L. Evans
Embedded Signal Processing Laboratory, The University of Texas at Austin
Goal: Quantify communication performance vs. complexity tradeoffs in a real-time 2x2 MIMO DMT testbed.
System Overview
A real-time hardware testbed for MIMO communication over a wireline transmission medium has been developed.
Discrete-Multitone communication transmits over multiple narrowband frequency flat subchannels or ‘tones’ to achieve high data rates.
Channel Impairments
Implementation Platform
Near end Crosstalk (NEXT) – Portion of the locally transmitted signal that leaks onto the local receiver.
Far end Crosstalk (FEXT) – Portion of the locally transmitted signal that leaks onto the remote receiver.
Time Varying Environment – The physical transmission medium changes as time progresses causing the channel response to be time varying.
Hardware
Software
National Instruments’ embedded computer performs all physical-layer processing.
National Instruments’ hardware generates/receives analog signals
A 1000ft spool of CAT-5e cable provides a realistic medium.
ETS operating system running on an embedded computer provides real-time execution of transceiver.
A desktop PC running LabVIEW 8 is used as an input and visualization tool to display important system parameters.
Conclusions
Solutions
Far end crosstalk in a multi-cable transmission system can severely degrade the bit rate performance.
In the 2x2 MIMO DMT testbed, a bit-rate increase of 99% over a single cable system was achieved using crosstalk cancellation.
Bit loading algorithms can also provide modest bit rate improvements in frequency selective channels.
Bit Allocation
Vectored DMT
Different number of bits are allocated across various tones depending on the SNR on each tone.
Maximizes the data throughput while still ensuring a minimum error margin.
Requires coordination between both transmitters and receivers.
Crosstalk can be removed by linear (Zero-Forcing Equalizer) and non-linear (Successive Interference Cancellation) algorithms at the receiver.