The paper examines the version of a multiple frequency-shift keying with a single and double differential phase-shift keying of each subcarrier. Adding the differential phase-shift keying of subcarriers to the multiple frequency-shift keying modulation allowed reducing the data transmission bit error rate with the capability of incoherent detection. A 1-st order differential binary phase-shift keying of subcarriers (MFSK-DBPSK) provides the best considered bit error rate but for small frequency offsets. A double differential binary phase-shift keying of subcarriers (MFSK-DDBPSK) provides the advantage over the MFSK regardless of the frequency offset and the advantage over MFSK-DBPSK with the frequency offset. An additional double difference phase-shift keying makes it possible to reduce the BER and increase the data rate at the same frequency band as the conventional MFSK.

MFSK, double differential phase-shift keying, frequency offset, noncoherent detection.