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Paper details
Number 3 - September 2025
Volume 35 - 2025
Doppler shift determination methods dedicated to MBFSK modulation
Agnieszka Czapiewska, Andrzej Łuksza, Jan H. Schmidt, Ryszard Studański, Łukasz Wojewódka, Andrzej Żak
Abstract
The progressive development of AUVs (Autonomous Underwater Vehicles) is creating demand for wireless underwater
communications. The most commonly used transmission medium in water is acoustic wave. Unfortunately, the underwater
hydroacoustic channel is characterized by strong multipath, especially in shallow reservoirs and in combination with hydrotechnical infrastructure. In addition, there is a Doppler effect in the case of reciprocal movement of the transmitting
and receiving parts. This effect in a hydroacoustic channel causes a significant frequency shift due to the relatively low
propagation speed of the acoustic wave. Knowledge of the frequency of the received signal is crucial in the reception
process. The authors of the current publication have found through a number of studies that the MBFSK (Multiple Binary
Frequency Shift Keying) modulation provides relatively high transmission bit rates in a multipath channel. In the current
publication, two Doppler factor estimation methods dedicated to this modulation are presented: the double DFT and the
correlation method. These methods were tested with utilization of signals recorded in real environment under conditions
of strong multipath in motion. Research was conducted at the speeds of 0.5, 1 and 1.5 m/s between the transmitter and
receiver. The results show that the proposed methods have comparable Doppler shift estimation quality to the well-known
pilot method, without decreasing the bandwidth allocated for data transmission.
Keywords
underwater communication, multipath channels, Doppler shift, Doppler measurement, MBFSK