DESIGN AND IMPLEMENTATION OF AN ADAPTIVE MODULATION SCHEME FOR UNDERWATER ACOUSTIC COMMUNICATION SYSTEMS

Underwater acoustic communication systems have become increasingly important due to their wide range of applications, including oceanography, underwater exploration, and military operations. However, underwater communication systems face significant challenges, such as severe attenuation, multipath interference, and Doppler spread, which significantly affect the performance of the communication system. Adaptive modulation schemes have emerged as a promising solution to address these challenges by adjusting the modulation scheme based on the current channel conditions. This paper presents the design and implementation of an adaptive modulation scheme for underwater acoustic communication systems. The proposed scheme is based on the concept of the system (AMC) technique, which has been widely used in terrestrial wireless communication systems. The proposed scheme consists of three main components: a channel estimator, a modulation selector, and a rate selector. In the proposed scheme, the CSI is estimated using a pilot signal that is transmitted periodically. The pilot signal is designed to have a known structure, which enables the receiver to estimate the CSI with high accuracy. The modulation selector is responsible for selecting the appropriate modulation scheme based on the estimated CSI. The proposed scheme uses a set of predefined modulation schemes, including binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and 16- quadrature amplitude modulation (16-QAM). The modulation scheme is selected based on the channel quality indicator (CQI), which is derived from the estimated CSI. The rate selector is responsible for selecting the appropriate data rate based on the selected modulation scheme and the estimated CSI. The proposed scheme uses a set of predefined data rates, including 1, 2, 4, and 8 bits per symbol. The data rate is selected based on the modulation scheme and the CQI