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Approved for public release; distribution is unlimited. / Direct-Sequence Spread-Spectrum (DS-SS) is among the preferred modulation techniques for military applications. DS-SS offers three greatly desired characteristics. It allows for the development of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI) systems and has a very good performance in fading channels. This thesis investigates the performance of the "Cross-Product RV (CRV) decomposition" as the basis of blind-equalization algorithms. The CRV is a rank-revealing decomposition alternative to the Eigenvalue Decomposition (EVD) that can provide a recursively updated estimate of the signal and noise subspace at a reduced computational cost. The CRV updating algorithm is implemented in MATLAB and evaluated in a previously proposed communication scheme intended for use in an underwater acoustic network called Seaweb. The underwater channel is modeled with the Monterey-Miami Parabolic Equation Model (MMPE) for various multipath perturbations. The receiver performance is examined using Monte Carlo simulation. Bit-error rates versus signal-to-noise ratio are presented for various, noise assumptions, and receiver synchronization assumptions. / Lieutenant, Hellenic Navy

Approved for public release; distribution is unlimited / Establishing a full-duplex underwater network, researching and applying a CDMA protocol to this network, providing a recommendation for a full-duplex underwater network and providing recommendations for using CDMA to increase the efficiency of this network are the general scope of this thesis. A connection that allows traffic in both directions simultaneously underwater is the example of fullduplex communication. Compared to a half duplex configuration, the full duplex network underwater may provide a better networking environment. Currently, most Underwater Acoustic Networks (UANs) still utilize half-duplex network communication. CDMA is the third kind of channel partitioning protocol. Most of the wireless communication devices utilize different kinds of CDMA protocol as a reliable and faster communication. The research conducted in establishing a full-duplex UAN using CDMA may provide reliable and faster communication compared to half-duplex. / Lieutenant Junior Grade, Turkish Navy

This research concerns the continuing development of Seaweb underwater networking. In this type of wireless network the radio channel is replaced by an underwater acoustic channel which is strongly dependent on the physical properties of the ocean medium and its boundaries, the link geometry and the ambient noise. Traditional acoustic communications have involved a priori matching of the signaling parameters (e.g., frequency band, source level, modulation type, coding pulse length) to the expected characteristics of the channel. To achieve more robust communications among the nodes of the acoustic network, as well as high quality of service, it is necessary to develop a type of adaptive modulation in the acoustic network. Part of this process involves estimating the channel scattering function in terms of impulse response, the Doppler effects, and the link margin. That is possible with the use of a known probe signal for analyzing the response of the channel. The estimated channel scattering function can indicate the optimum signaling parameters for the link (adaptive modulation). This approach is also effective for time varying channels, including links between mobile nodes, since the channel characteristics can be updated each time we send a probe signal.

Upper layer temperature in the western Philippine Sea near Taiwan was sampled using a coastal monitoring buoy with fifteen themistors attached from July 28-August 7, 2005. Internal waves and internal solitons were identifed during the empirical orthogonal function analysis. Without the IW and IS, the power spectra, structure functions, and singular measures (respresenting the intemittency) of the temprature field satisfy the power law with multi-scale characteristics at all depths. The IW does not change the basic characteristics of the multifractal structure. However, the IS changes the power exponent of the power spectra drastically, especially in the low wave number domain. It breaks down the power law of the structure function and increases the intermittency parameter. The physical mechanisms causing these different effects need to be explored futher. The Comprehansive Acoustic Simulation System was applied to determine how the IS affect the mines detection by computing the transmission loss (TL) and the ray traces of rand-dependent and range independent cases during the IS period. The maximum TL difference is 20 dB. As a result, the mine detection probability will dramatically be reduced to 1% of the original detection probability.

Approved for public release, distribution unlimited / Underwater Acoustic Networks (UAN) have two immutable obstacles to overcome; the hostile environment in which it must operate; and the combination of the propagation speed of sound in water, and the latency in communication that this produces, and the dynamic nature of the water column with respect to its attenuation of the sound signal. These combined issues make it very costly and time consuming to setup a UAN just to test new protocols that may or may not be able to mitigate the limitations of this environment. There exists, then, a need for an ability to test a new protocol without the overhead of creating a physical UAN. The goal of this thesis is to provide a more hospitable, adaptable, flexible, and easily useable tool with which to test new protocols for UANs, as well as providing the ability for the Physics field to test new physical layer encodings. This simulation environment will provide the glue, or bridge, between the two disciplines by working as a common tool for both.

The U.S. Navy is developing through-water acoustic communications capability for undersea, distributed systems. These wireless communication links form a wide-area network of fixed nodes consistent with future autonomous sensors on the seafloor. Mobile nodes may operate in the domain of the grid using the fixed nodes as both navigation reference points and communication access points. This thesis evaluates the experimental performance of such networked communications between an undersea vehicle and a ship. Physical-layer considerations include refraction, wind-induced ambient noise, and vehicle aspect angle.

Approved for public release, distribution is unlimited / This thesis is an analysis of the link-layer and network-layer performance of an experimental Seaweb undersea acoustic network. The objective is to statistically determine RTS/CTS handshaking and ARQ retransmission performance during the Fleet Battle Experiment-India, executed in June 2001. Many factors constrain or impair undersea acoustic communications. Analysis of a sample portion of the data reveals insights about the overall throughput, latency, and reliability of the Seaweb network. / Lieutenant, United States Navy

Approved for public release, distribution unlimited / This study sought to experimentally quantify the sonar performance of omni-directional receivers as a means to passively detect vocalizing Odontocetes. To accomplish this objective, controlled experiments using a calibrated mid-frequency sound source were conducted on the San Clemente Island Underwater Range (SCIUR) in July 2002. Six Odontocete signals were selected for transmission: 2 orca and 2 pilot whale whistles, and sperm whale and Risso's dolphin clicks. Several hundred iterations of each signal were broadcast at stations 300 m to 12,000 m from the range's moored, three-element array. Statistical analyses were performed on the output of an energy and matched filter detector to quantify detection probability (P(D)) and range limits as a function of false alarm rate (P(FA)), signal type, and signal to noise ratio (SNR). The matched filter was generally the superior performer, detecting the orca2 and pilot1 whistles beyond 5000 m with a 90% P(D), 1% P(FA), and source level (SL) of 140 dB re 1 æPa. For the same conditions, the orca1 and sperm whale calls were detected at 1500 m, but the pilot2 and Risso's dolphin signals were not detected at the peak realized SNR of (-2) dB. The energy detector had no detections with a 90% P(D) and 1% P(FA) at this (-2) dB SNR, but all signals except one orca whistle were detectable beyond 1000 m with a 50% P(D) and 1% P(FA). The sperm whale was the exceptional energy detector performer, with detection ranges exceeding 7 km (140 dB re 1 æPa SL) at the 50% P(D) and 1% P(FA) / Lieutenant Commander, United States Navy