1. An operating method of a memory system including a nonvolatile memory device, the operating method comprising: reading an observation memory cell at least one time with different read voltages to configure a first read data symbol; reading a plurality of interference memory cells adjacent to the observation memory cell at least one time with different read voltages to configure second read data symbols; and determining a logical value of the observation memory cell, based on the first read data symbol and the second read data symbols.