PAPR reduction in underwater acoustic sensor networks: A discrete cosine transform matrix precoding based MIMO-OFDM system

Underwater acoustic sensor networks (UASNs) have got significant importance because of its wide applications, such as ocean observation for scientific and commercial exploration, coastline protection and target detection in military events. UASN air interface adopts orthogonal frequency division multiplexing (OFDM) with multiple input multiple output (MIMO) techniques to improve the multipath performance and data rate. MIMO-OFDM systems have inherent problem of high peak-to-average power ratio (PAPR) which leads to nonlinear distortion of the high-power-amplifier (HPA) and results in inter-carrier-interference (ICI) plus out-of-band radiation. In this paper we present a discrete-cosine transform matrix (DCTM) precoding based space-time-block-coded (STBC) MIMO-OFDM system for PAPR reduction in UASNs. PAPR of the proposed system is analyzed with the root-raised-cosine (RRC) pulse shaping to keep out-of-band (OOB) radiation low and to meet the transmission spectrum mask requirement. Simulation results show that, the proposed system has low PAPR than the walsh-hadamard transform (WHT) precoded OFDM systems and the conventional OFDM systems. The good improvement in PAPR offered by the proposed system significantly reduces the cost and the complexity of the transmitter.