Adaptive Soft Detection for Flash Memory.

To provide reliability of flash memory, error-correcting codes are usually used which can be further enhanced by moving on from hard-decision to soft-decision decoders. This requires multiple readings to obtain a reliability measure of the stored data, which is complicated by the fact that a posteriori probability distributions change as the memory ages through retention and wear-out. The existing methods for reading a flash memory either assume knowledge of these distributions or require a large number of readings for accurate estimation. In this letter, we propose a low-complexity algorithm that tracks the soft-decision boundaries and estimates the corresponding log-likelihood ratios (LLRs). It does not require any additional readings and only involves simple calculations using already available variables. The efficacy is verified through the simulations and is shown to provide near-optimal performance. [ABSTRACT FROM AUTHOR]