1. An operating method of a memory system including a nonvolatile memory device, the operating method comprising: reading a 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 a read data symbol, the read data symbol configured to comprise a first read data symbol in correspondence to an observation cell and a second read data symbol in correspondence to interference cells; identifying the interference cells of the observation memory cell from the plurality of memory cells using permutation information; and determining the logical value of the observation memory cell referring to the first read data symbol and the second read data symbol of the interference cells.