Equalization Strategies for 10-Gb/s Transmission over Multimode FibreBertram LeestiPh.D. CandidateDepartment of Electrical and Computer Engineering

June 24, 2005

MotivationInterest in using installed multimode fibre at 10 Gb/sProblem: modal dispersion causes severe intersymbol interference (ISI) Requires adaptive equalization!

Feedforward EqualizationCan be implemented in continuous-time or discrete-timeAt multi-Gb/s speeds, continuous-time implementation popular (less power)Problem with FFE: noise enhancement

Decision-Feedback EqualizationLess noise enhancement than FFE alone since decisions are noise-freeError propagation can occurDelay through feedback path limits speed, so look-ahead architecture often used

Max. Likelihood Sequence DetectionProblem with DFE: by canceling ISI, some signal energy is lostMLSD:Uses ISI to determine the most likely sequence of bitsComputes metrics for different sequences, and chooses sequence with minimum metricComplexity grows exponentially with length of channel impulse responseFFE followed by MLSD:FFE equalizes to a simple response (e.g., 1+D)MLSD complexity is minimized

Performance ComparisonFor this example:DFE is 1 dB better than FFEFFE + MLSD is 1.2 dB better than DFEMLSD is 0.7 dB better than FFE + MLSDFuture work:Timing recoveryImplementationFibre impulse responses obtained at http://www.ieee802.org/3/aq/