Abstract
This paper proposes an underwater communication receive model based on the spread spectrum technique in order to provide the characteristic of a low probability of interception. To do this, turbo equalization techniques employing Bahl-Cocke-Jelinek-Raviv (BCJR) decoding to improve performance through repetition are applied to offer excellent performance even at a low signal to noise ratio (SNR) of transmitted signals due to the spread spectrum technique. A turbo equalization model based on RAKE which increase signal power by summing the received signal through the multipath is proposed to compensate distorted data due to multipath channel and the performance improvements were proven by applying the threshold and weighted coefficient in the RAKE receiver model. The model was applied to covert underwater communication in a multi-sensor environment, and the efficiency of the proposed method was proven through underwater experiments.
Highlights
Various studies have been actively underway on underwater acoustic communication with a low probability of interception (LPI) to promote reliable communication [1,2,3]
Previous studies on covert underwater communication have focused only on improving the transmission rate at the time varying underwater channel or increasing the transmission and receiver distance, and few studies have been conducted on transmission performance in an environment in which covertness must be emphasized
The RAKE receive structure was applied to the iterative decoding-based turbo equalization model to propose an efficient decoding mode, and performance was improved by applying the threshold value and weighted coefficient
Summary
Various studies have been actively underway on underwater acoustic communication with a low probability of interception (LPI) to promote reliable communication [1,2,3]. The covert underwater acoustic communication system satisfies both the LPI characteristic, in which the transmitted signal is not intercepted by receivers other than the intended receiver, and the low probability of detection (LPD). A direct sequence spread spectrum that ensures covertness is applied by multiplying the pseudo noise (PN) code sequence that has P chips by the transmission signals to be transmitted. The spread spectrum technique can obtain diffusion gain in the multi-sensor communication and a frequency diversity effect in underwater acoustic communication, where selective frequency fading occurs even when data transmission efficiency is sacrificed [6]
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