基于非均匀感知策略的MLC闪存系统

MLC Flash Memory Based on Non-Uniform Sensing Strategy

面向多级单元(Multi-Level Cell,MLC)的LDPC码的最小和(Min-Sum,MS)译码算法译码性能取决于码字中每个比特对应的对数似然比(Log-Likelihood Ratio,LLR)的准确度,然而基于均匀感知策略的MLC电压读取方法需要提高感知精度才能获取精度高的LLR值,这将增加MLC闪存单元的读取时间.针对这种情况,本文提出一种基于非均匀感知策略的MLC闪存MS译码算法,该算法对MLC闪存阈值电压的感知采用非均匀的感知策略.在相同的感知精度下,相比于均匀感知策略,非均匀感知策略能够提高LLR的准确度,获得更低的原始比特错误率.仿真结果表明,在MLC闪存信道条件下,该算法既可保证MLC闪存单元可靠性,而且保持较快的读取速度,从而实现了译码速度和译码性能间的良好折衷.

The performance of min-sum（MS） decoding algorithm depends on each bit corresponding to the accuracy of log-likelihood ratio（LLR） for multi-level cell（MLC）. However, uniform sensing strategy needs to increase the sensing precision in order to obtain high accuracy of LLR, which increases the reading latency of MLC. In this study, an MS decoding algorithm is proposed for MLC flash memory, which uses non-uniform sensing strategy for the threshold voltage of MLC. In the same sensing precision, compared to the uniform sensing strategy, the non-uniform sensing strategy can improve the accuracy of LLR and lower the raw bit error rate. The simulation results show that the proposed method can not only guarantee the reliability of the MLC flash memory, but also keep the fast reading speed for MLC flash memory, thus achieving a better tradeoff between complexity and decoding performance.