A Study on a Broadband Beamformer for Underwater Acoustic Communication

Abstract

Beamforming for underwater acoustic communication (UAC) is affected by the broadband feature of UAC signal, which has relatively low center frequency compared with the signal bandwidth. In this paper, we present a baseband equivalent array signal model for phase-coherent underwater acoustic communications and we show computer simulation results for the broadband finite impulse response (FIR) beamformer performance according to the change of FIR filter order and the tap spacing in a QPSK UAC system with center frequency 25KHz and symbol rate 5KHz. The results show that the broadband FIR beamformer achieves practically optimum signal to interference and noise ratio (SINR) and outperforms the conventional narrowband beamformer by 0.5dB of SINR when the inter-tap delay is a quarter of the symbol interval and the order of FIR filter is one. The broadband FIR beamformer performance is degraded when the FIR filter order is increased above the optimum value. The inter-tap delay should be small enough and it is related to the optimum FIR filter order.