은밀 수중음향통신을 위한 PN 코드 설계

Abstract

In recent years, underwater acoustic communication have received much attention as their applications, have begun to shift from military toward commercial. The growing interest in underwater acoustic communications come as a response to the rapidly growing needs for wireless underwater communications, brought in part by the broadening of applications, such as military and commercial ones.

Covert underwater acoustic communications are conducted at a low received SNR(signal-to-noise ratio) to deter eavesdroppers to sense the presence of the transmitted signal. Successful detection at intended receiver heavily relies on the processing gain achieved by employing the DS-SS(direct-sequence spread-spectrum) technique. For scenarios that lack a sufficiently low SNR to maintain LPD(low probability of detection), another metric, referred to as LPI(low probability of interception), is of interest to protect the privacy of the transmitted information. If covert underwater communications take place in underwater environments, then additional challenges are present. The time-varying nature of the underwater acoustic channel prevents the employment of a long spreading waveform. Furthermore, underwater acoustic environments are frequency selective channels with long memory, which imposes challenges to the design of the PN(pseudo noise) code.

In this thesis, a covert underwater communication system that adopts the DS-SS technique and PN code. Emphasis is placed on the design of a PN code that not only accounts for the transceiver structure and frequency-selective nature of the underwater channel, but also possesses a superior LPI. The proposed techniques are evaluated using both simulation and lake trial.