OFDM inter-carrier interference reduction using pulse shaping function for underwater acoustic communications systems

Due to multipath propagation and frequency selective fading, there are many obstacles for reliable and high data rate underwater acoustic (UWA) communication. The effective use of OFDM in underwater channel also suffers from its high sensitivity to carrier frequency offset, which distorts the orthogonality between subcarriers due to Inter-Carrier Interference (ICI). Bandwidth limited systems often employ pulse shaping techniques for the reduction of ICI, and minimize the likelihood of errors at the receiver. Such reduction can be achieved by minimizing the side lobes as much as possible. Since the side lobes contribute to the ICI power, which also results in the decrease of Signal to Interference Ratio (SIR). In this paper, the ICI and SIR performance under pulse shaping technique is studied for underwater acoustic channel. Performance comparison of OFDM Discrete Fourier Transform (DFT)-based pulses and Discrete Cosine Transform (DCT)-based pulses is conducted. Simulation results show that, the modified raised cosine pulse shape technique can achieve better performance of ICI power reduction, SIR and BER performances for underwater acoustic channel in comparison to several other commonly used pulses. The IDCT-OFDM is strongly resistant to inter-carrier interference in underwater acoustic channel. The resultant system can also demonstrate reasonably good bit error rate performance. A system scheme is then proposed based on the identified signal pulse.