Anthony D. Weathers

An efficient on-the-fly encoding algorithm for binary and finite field LDPC codes

We present a general framework on prototype structures for efficiently encoding low density parity check codes on-the-fly. The encoding algorithm is applicable to finite field based codes and can handle a wide range of high code rates and large block lengths. This structure can be used particularly in data storage and multimedia applications with increased code rate and throughput requirements. We also establish the necessary and sufficient conditions for the existence of such encoders.

Read Level Profiling Algorithms for NAND Based SSD Flash

In a NAND flash memory, optimal read levels for minimizing bit error rate (BER) can be determined as offsets from a default read level. In general, memory would be allocated to store all the offset values for each of the 128 word-lines in a block using three or more different read levels per word-line. Fluctuations occur in optimal read levels from word-line to word- line but nevertheless demonstrate a behavior that allows a compression of the number of read level offsets to be stored. It is desirable to reduce the memory required to store the offsets and to smooth the noisy estimates. We present three read level profiling algorithms with two optimization criteria to reduce the number of read level offsets that needs to be stored while minimizing the degradation in BER. The read level profiling algorithms cluster the word-lines into groups in which the word-lines belonging to the same group have the same read level offset value. These algorithms are tested on lab data and it has been shown that with a moderate number of groups, no significant BER degradation occurs that would increase decoding errors.