Performance of Spread Spectrum Based Multi-Carrier System in Underwater Communication Using Transmitter Pre-Processing

Abstract

In this paper, we evaluate the bit-error-rate (BER) performance of a turbo-coded, transmitter pre-processing-assisted spread spectrum technology-based multi-carrier (MC) system for the acoustic information transmission in underwater communication. Our primary goal is to improve the power efficiency of the system in terms of signal-to-noise ratio (SNR) while obtaining achievable BER in underwater communication. In underwater communication, inter-symbol-interference and acoustic interference are the two most important issues, which affect the system performance. We use spread spectrum technique to mitigate the effects of unwanted information in the presence of ambient noise. Multi-user transmitter pre-processing (MUTP) is the digital processing method, which is carried out at the transmitter side to offer the low complexity of the receiver. We formulate the singular value decomposition-based pre-processing matrix using noisy feedback of vector quantized (VQ) estimated channel information (CI). We consider the MC communication to mitigate the effects of multi-path propagations. We realize iterative style of decoding algorithm at the receiver to retrieve the acoustic information from the ambient noise contaminated acoustic signals. In particular, we evaluate the error-rate analysis of MC system for realistic channel model based on shallow water channel model, which consists of 11 tap delay. Simulation results emanating from this paper bring to surface the considered coded MC system with MUTP offering a better BER performance with power efficiency regarding SNR while retaining the low complexity of the receiver. Furthermore, we observe that there is an improvement in the system performance when perfect CI is utilized to frame the pre-processing matrix compared with noise contaminated VQ-CI.