Performance Analysis of Receiver for Underwater Acoustic Communications Using Acquisition Data in Shallow Water

This paper describes an acoustic communication receiver structure, which is designed for QPSK (Quadrature Phase Shift Keying) signal with 25 kHz carrier frequency and 5 kHz symbol rate, and takes samples from received signal at 100 kHz sampling rate, Based on the described receiver structure, optimum design parameters, such as number of taps of FF (Feed-lForward) and FB (Feed-Back) filters and forgetting factor of RLS (Recursive Least Square) algorithm, of joint equalizer are determined to minimize the BER (Bit Error Rate) performance of the joint equalizer output symbols when the acquisition data in shallow water using implemented acoustic transducers is decimated at a rate of 21 and then enforced to the input of receiver. The transmission distances are 1,4 km, 2,9 km, and 4.7 km, Analysis results show that the optimum number of taps of FF and FB filters are different according to the distance between source and destination, but the optimum or near optimum value of forgetting factor is 0,997. Therefore, we can reach a conclusion that the proper receiver structure could change the number of taps of FF and FB filters with the fixed forgetting factor 0,997 according to the transmission distance, Another analysis result is that there are an acceptable performance degradation when the 16-tap-length simple filter is used as a low-pass filter of receiver instead of 1.61-tap-length matched. filter,