title: Low probability of detection underwater acoustic communications using direct-sequence spread spectrum.
abstract: Direct-sequence spread spectrum is used for underwater acoustic communications between nodes, at least one of which is moving. At-sea data show that the phase change due to source motion is significant: The differential phase between two adjacent symbols is often larger than the phase difference between symbols. This poses a challenge to phase-detection based receiver algorithms when the source or receiver is moving. A pair of energy detectors that are insensitive to the phase fluctuations is proposed, whose outputs are used to determine the relationship between adjacent symbols. Good performance is achieved for a signal-to-noise ratio (SNR) as low as -10 dB based on at-sea data. While the method can be applied to signaling using short code sequences, the focus in this paper is on long code sequences for the purpose of achieving a high processing gain (at the expense of a low data rate), so that communications can be carried out at a low input SNR to minimize the probability of detection (P(D)) by an interceptor. P(D) is calculated for a typical shallow water environment as a function of range for several source levels assuming a broadband energy detector with a known signal bandwidth.
authors.affiliation: Naval Research Laboratory, Washington, DC 20375, USA. yang@wave.nrl.navy.mil
authors.forename: T C
authors.initials: TC
authors.lastname: Yang
authors.forename: Wen-Bin
authors.initials: WB
authors.lastname: Yang
mesh_terms: D000162:Acoustics; D000465:Algorithms; D004301:Doppler Effect; D019015:Geologic Sediments; D015233:Models, Statistical; D009038:Motion; D009792:Oceans and Seas; D011336:Probability; D012372:ROC Curve; D011825:Radar; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013997:Time Factors