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COST 289 Etienne Auger, Carlo Mutti, Marc Kuhn and Armin Wittneben
Interference Cancellation in MIMO-OFDM System with Outdated Channel State Information COST 289 Etienne Auger, Carlo Mutti, Marc Kuhn and Armin Wittneben © ETH Zürich | WCG
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Content Introduction System model Signal detection
Multi-stream interference precoder Outdated channel state information Signal detection Interference cancellation Conclusion
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Introduction Multiple-input multiple-output (MIMO) systems are facing multi-stream interferences (MSI) In a downlink scenario, no/little data exchange is assumed between users MSI suppression can be performed at the transmitter side if channel state information (CSI) is available [Auger-2005] If only partial CSI is available: interferences not fully suppressed
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System model MIMO-OFDM system
Precoder for multi-stream interference in time domain with instant. power constraint Synchronous transmission Detection based on maximum a posteriori criterium
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Channel model Channel matrix H in time domain
L taps subchannel: Hi,j[n] entries ~ i.i.d. CN(0,1/L) Perfect CSI at the receiver, outdated CSI at the transmitter
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Outdated channel state information [Goeckel]
Delay in perfect feedback link due to dedicated feedback channel or TDD perfect: no error occurs during feedback precoder matches an outdated channel E[ Hi,j[n] . i,j[n] ] = c (0≤c≤1/L) receiver knows H and
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Equivalent channel time domain frequency domain perfect CSIT
outdated CSIT with frequency domain
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Interference energy equivalent channel matrix
energy in signal subchannel energy in interference subchannel (0≤ρ≤1)
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Interference cancellation
received vector in frequency domain transmitted vector in frequency domain detection of s[k] when is known s1,s2 from 4-QAM constellation AWGN noise
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Vector detection with single observation
joint MAP detection look for and equiprobable inputs: maximize and 2 pairs candidates: at receiver 1 at receiver 2 choose element with largest estimated SINR (minimal estimated noise and interf. realization) implies information exchange between receivers
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User detection with single obervation
no information exchange between receivers single user MAP detection minimize (ln is concave)
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Interference cancellation
step 1 : parallel successive cancellation
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ZF vs. MSI for imperfect CSI
ZF based on no IC, just detection ρ≠1: MSI more robust than ZF user detection
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Detection step (joint vs. user detection)
same results with y2 user detection performs badly when low correlation joint detection on interf. terms for low correlation joint detection on signal terms best
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Interference cancellation
user detection with several iterations does not improve much SER joint detection remains best for any # iterations
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Conclusion MSI precoder performance with outdated CSIT and perfect CSIR signal detection with single observation joint or for each user interference cancellation SINR based iterative joint detection achieves better user SER
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Thank you !! Questions
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Simulation results for user detection
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Results for joint detection
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Joint vs. User detection
From 2 iterations, joint and user detection have similar performance
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Conclusion MIMO-OFDM with MSI precoder perfect CSIR and outdated CSIT
IC required optimal user and joint detection multistage IC for both detections
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Multistage parallel: successive: same scheme as for multistage detection for user
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