On the Capacity of the Beta-Binomial Channel Model for Multi-Level Cell Flash Memories

TL;DR

This paper investigates the capacity of the beta-binomial channel model for multi-level cell flash memories, finds the original model's capacity to be zero, and proposes a refined model with a higher, empirically supported capacity estimate.

Contribution

It introduces the truncated-support beta-binomial (TS-BBM) model and derives its capacity, providing a more realistic upper bound for flash memory coding rates.

Findings

Original BBM model capacity is zero.

TS-BBM model capacity varies with P/E cycling stress.

Empirical data supports the refined model's capacity estimates.

Abstract

The beta-binomial (BBM) channel model was recently proposed to model the overdispersed statistics of empirically observed bit errors in multi-level cell (MLC) flash memories. In this paper, we study the capacity of the BBM channel model for MLC flash memories. Using the compound channel approach, we first show that the BBM channel model capacity is zero. However, through empirical observation, this appears to be a very pessimistic estimate of the flash memory channel capacity. We propose a refined channel model called the truncated-support beta-binomial (TS-BBM) channel model and derive its capacity. Using empirical error statistics from 1X-nm and 2Y-nm MLC flash memories, we numerically estimate the TS-BBM channel model capacity as a function of the program/erase (P/E) cycling stress. The capacity of the 2-TS-BBM channel model provides an upper bound on the coding rates for the flash memory chip assuming a single binary error correction code is used.