RS-Enhanced TCM for Multilevel Flash Memories

• Published in: IEEE transactions on communications Vol. 61; no. 5; pp. 1674 - 1683
• Main Authors: Jieun Oh, Jeongseok Ha, Jaekyun Moon, Ungerboeck, G.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.05.2013; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Ash; Coding, codes; Convolution; Convolutional codes; Decoders; Decoding; Encoding; Error correction; Errors; Exact sciences and technology; flash memory; Flash memory (computers); Information, signal and communications theory; Maximum likelihood decoding; Modulation; multi-level coded-modulation; Multilevel; Permissible error; Probability density function; Reed-Solomon codes; Signal and communications theory; Studies; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Teletraffic; Transmission and modulation (techniques and equipments); Trellis-coded modulation; Reed Solomon code; Performance evaluation; Multistage method; Error estimation; Trellis-coded modulation; multi-level coded-modulation; Flow rate regulation; Control system; Error rate; Teletraffic; flash memory; Decoding; Mixed method; Reed-Solomon codes; Concatenation; Simulation; Traffic management; Trellis coded modulation; Analytical method; Traffic control; Multilevel system; Signal to noise ratio
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2013.022713.120333

Multilevel flash memories store more than one bit per storage cell and are further characterized by large word (page) sizes and very low target error rates. In this paper, a high-rate error control scheme is presented that uses inner trellis-coded modulation (TCM) for storing two bits per cell with five possible charge levels. The coded subset-label bits and the uncoded signal-label bits of TCM are independently protected by separate outer Reed-Solomon (RS) codes. The resulting scheme permits multistage decoding. Errors made by the TCM decoder in the subset-label bits occur in bursts and are corrected by the associated first RS decoder prior to determining signal-label bits and correcting errors in those bits by the associated second RS decoder. The multi-stage decoding avoids the significant spread of errors from subset-label bits into the generally larger number of signal-label bits which is typical for conventional serial RS-TCM concatenation when the inner TCM system operates at relatively low SNR. The error performance of the proposed scheme is evaluated at low error rates by a mixed simulation-analytic method. It is shown that the proposed scheme exhibits highly favorable performance vs. complexity tradeoffs compared to the other schemes.