Communication device for performing differential phase shift keying based on a plurality of previous signals and operating method thereof

A method of determining a symbol corresponding to an input signal, the method comprising:

• generating a first phase difference between a first input signal and a previous signal, wherein the first input signal is input in a previous sequence prior to a target sequence, and wherein the previous signal is received prior to the previous sequence;
• generating a second phase difference between a second input signal and the previous signal, wherein the second input signal is input in the target sequence;
• and
• determining an expected phase difference between the second input signal and the first input signal based on the first phase difference and the second phase difference.

A communication device comprising:

• a first phase difference calculator configured to calculate a first phase difference between a phase of a first previous signal and a phase of a second previous signal, wherein the first previous signal is received prior to a target signal, and wherein the second previous signal is received prior to the first previous signal;
• a second phase difference calculator configured to calculate a second phase difference between a phase of the target signal and the phase of the second previous signal;
• a target likelihood generator configured to generate target likelihoods that a phase difference between the target signal and the previous first previous signal corresponds to each of a plurality of symbols based on the first phase difference and the second phase difference;
• and
• an expected value determiner configured to determine, based on the target likelihoods, an expected symbol for the target signal or an expected phase difference between the target signal and the first previous signal.