Advantages of pulse-shaping applied to OFDM systems over underwater acoustic channels

Orthogonal frequency division multiplexing (OFDM) systems combat inter-symbol interferences (ISI) using cyclic prefix (CP) or the equivalent guard interval (GI) in case of zero-padded (ZP) OFDM. Nevertheless, inter-carrier interferences (ICI) due to the synchronization mismatches for instance, remain a strong disadvantage. Pulse-shaping is one of the solutions introduced in narrow band context. In this paper, we explored the use of this technique in wideband environments such underwater acoustic (UWA) channel. For this purpose, we developed an appropriate pulse-shaped CP-OFDM scheme. In addition to ICI reduction over channels with Doppler shift and spread, the proposed system, compared to the conventional CP-OFDM, achieves at equal transmit power important E_b/N_o savings: the longer the CP, the greater the saving. Unlike existing pulse-shaped OFDM designs, we propose to share out pulse-shaping between transmission and reception modules. Results from simulations are corroborated by sea trials.