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Turbo equalization for MIMO SC-FDMA underwater acoustic communications

The single-carrier frequency-division multiple access (SC-FDMA) or the discrete Fourier transform (DFT) pre-coded orthogonal frequency-division multiple access (OFDMA) technique has been adopted in the uplink transmission of the long term evolution (LTE) terrestrial communication standard, for its lower peak-to-average power ratio (PAPR) and similar receiver complexity, compared with OFDM. It is, however, rarely investigated in underwater acoustic (UWA) communications. This paper presents an SC-FDMA transceiver scheme for multiple-input, multiple-output (MIMO) UWA communications, and studies the performance of turbo equalization on the receiver side. The signalling of the pilot symbols bypasses the DFT precoding module, so the channel estimation and the carrier frequency offset (CFO) estimation are performed in a similar way as in a conventional OFDM system. A recently proposed high-performance frequency-domain turbo equalization technique is adopted for detecting the data symbols, which suffer inter-symbol interference (ISI) due to the DFT spreading operation. Experimental results clearly show the performance gain attributed to the turbo equalization, especially for high-order modulations.