Improved Space Clustering for Single-Carrier Underwater Acoustic Communications

Beamforming then equalization (BF-EQU) is drawing increased research attentions for underwater acoustic (UWA) communications deploying an array on the receiver side. Compared with conventional multichannel equalization without beam-forming, the BF-EQU scheme enjoys improved performance and/or reduced complexity. In this paper, we propose an im-proved BF-EQU scheme for single-carrier UWA communications. Our contribution lies in three aspects: first, Khatri-Rao (KR) subspace preprocessing is employed in direction-of-arrival (DoA) estimation such that spurious DoAs can be mitigated; second, null-steering (NS) beamforming is used to form directional signals based on DoA estimations; last, a direct adaptive equalizer (DAE) enabled by improved proportionate normalized least mean squares (IPNLMS) algorithm is adopted to recover transmitted symbols from directional signals. The proposed receiver scheme was tested by numerical and experimental data, and the results showed it achieves extra performance gain over existing BF-EQU schemes.