1. An operating method of a memory system including a nonvolatile memory device, the operating method comprising: reading data from a plurality of memory cells connected to a selected word line through a plurality of read operations using different read voltages to configure read data symbols, the read data symbols comprising a first read data symbol in correspondence to an observation cell and a second read data symbol in correspondence to an interference cell; identifying the interference cell of the observation memory cell of the plurality of memory cells using permutation information; and determining a logical value of the observation memory cell by referring to the first read data symbol and the second read data symbol of the interference cell.