Current generation Flash devices experience significant read-channel
degradation from damage to the oxide layer during program and erase operations.
Information about the read-channel degradation drives advanced signal
processing methods in Flash to mitigate its effect. In this context, channel
estimation must be ongoing since channel degradation evolves over time and as a
function of the number of program/erase (P/E) cycles. This paper proposes a
framework for ongoing model-based channel estimation using limited channel
measurements (reads). This paper uses a channel model characterizing
degradation resulting from retention time and the amount of charge programmed
and erased. For channel histogram measurements, bin selection to achieve
approximately equal-probability bins yields a good approximation to the
original distribution using only ten bins (i.e. nine reads). With the channel
model and binning strategy in place, this paper explores candidate numerical
least squares algorithms and ultimately demonstrates the effectiveness of the
Levenberg-Marquardt algorithm which provides both speed and accuracy.Comment: 6 pages, 8 figures, Submitted to the IEEE International
Communications Conference (ICC) 201