Adaptive signal processing

This research proposes a cluster-based target tracking strategy for one
moving object using wireless sensor networks. The sensor field is organized in 3
hierarchal levels. 1-bit message is sent when a node detects the target.
Otherwise the node stays silent. Since in wireless sensor network nodes have
limited computational resources, limited storage resources, and limited battery,
the code for predicting the target position should be simple, and fast to execute.
The algorithm proposed in this research is simple, fast, and utilizes all available
detection data for estimating the location of the target while conserving energy.
lbis has the potential of increasing the network life time.
A simulation program is developed to study the impact of the field size
and density on the overall performance of the strategy. Simulation results show
that the strategy saves energy while estimating the location of the target with an
acceptable error margin.

A Motion Compensated (MC) Ultra Short Baseline (USBL) Acoustic Positioning
System (APS) operable in shallow water and port environment has been implemented at
Florida Atlantic University. Multi-tones signal modulation and log-likelihood
maximization enable this APS to operate in volumes of water of less than 10 cubic
meters. Standard deviations of the acoustic source elevation and azimuth estimates were
computed to be 3 degrees in an 8 cubic meters test tank, and reduce to 0.9 degree in a 2
meters deep marina. The motion compensating system estimates the array position and
orientation while merging noisy measurements from a Magnetic, Angular Rate, and
Gravity (MARG) sensor and a Differential Global Positioning System (DGPS) using
Kalman filters. Experiments show 0.67 and 2.67 degrees of error for the array tilt and
heading estimates, and 0.74 meter for the array position estimate.

A methodology to estimate the state of a moving marine vehicle, defined by its position, velocity and heading, from an unmanned surface vehicle (USV), also in motion, using a stereo vision-based system, is presented in this work, in support of following a target vehicle using an USV.

The underwater channel poses numerous challenges for acoustic communication.
Acoustic waves suffer long propagation delay, multipath, fading, and potentially
high spatial and temporal variability. In addition, there is no typical underwater
acoustic channel; every body of water exhibits quantifiably different properties. Underwater
acoustic modems are traditionally operated at low frequencies. However, the
use of broadband, high frequency communication is a good alternative because of the
lower background noise compared to low-frequencies, considerably larger bandwidth
and better source transducer efficiency. One of the biggest problems in the underwater
acoustic communications at high frequencies is time-selective fading, resulting
in the Doppler spread. While many Doppler detection, estimation and compensation
techniques can be found in literature, the applications are limited to systems operating
at low frequencies contained within frequencies ranging from a few hundred Hertz
to around 30 kHz.

Channel assignment in multi-radio networks is a topic of great importance because
the use of multiple channels and multiple radios reduces interference and increases the
network throughput. The goal of our research is to design algorithms that maximize the
use of available resources while providing robustness to primary users that could reclaim
one or more channels. Our algorithms could be used in ad hoc networks, mesh networks,
and sensor networks where nodes are equipped with multiple radios. We design
algorithms for channel assignment which provide robustness to primary users without
assuming an accurate primary user behavior model. We also compute bounds for capacity
in grid networks and discuss how the capacity of a network changes when multiple
channels are available. Since preserving energy is very important in wireless networks,
we focus on algorithms that do not require powerful resources and which use a reduced
number of messages.

High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining.

In wireless orthogonal frequency division multiple-access (OFDMA) standards,
subcarriers are grouped into chunks and a chunk of subcarriers is made as the minimum allocation unit for subcarrier allocation. We investigate the chunk-based resource allocation for OFDMA downlink, where data streams contain packets with diverse bit-errorrate (BER) requirements. Supposing that adaptive transmissions are based on a number of discrete modulation and coding modes, we derive the optimal resource allocation scheme that maximizes the weighted sum of average user rates under the multiple BER and total power constraints. With proper formulation, the relevant optimization problem is cast as an integer linear program (ILP). We can rigorously prove that the zero duality gap holds for the formulated ILP and its dual problem. Furthermore, it is shown that the optimal strategy for this problem can be obtained through Lagrange dual-based gradient iterations with fast convergence and low computational complexity per iteration. Relying on the stochastic optimization tools, we further develop a novel on-line algorithm capable of dynamically learning the underlying channel distribution and asymptotically approaching the optimal strategy without knowledge of intended wireless channels a priori. In addition, we extend the proposed approach to maximizing the a-fair utility functions of average user rates, and show that such a utility maximization can nicely balance the trade-off between the total throughput and fairness among users.

There have been much technological advances and research in Unmanned Surface
Vehicles (USV) as a support and delivery platform for Autonomous/Unmanned
Underwater Vehicles (AUV/UUV). Advantages include extending underwater search and
survey operations time and reach, improving underwater positioning and mission
awareness, in addition to minimizing the costs and risks associated with similar manned
vessel operations. The objective of this thesis is to present the design and development a
high-level fuzzy logic guidance controller for a WAM-V 14 USV in order to
autonomously launch and recover a REMUS 100 AUV. The approach to meeting this objective is to develop ability for the USV to intercept and rendezvous with an AUV that is in transit in order to maximize the probability of a final mobile docking maneuver. Specifically, a fuzzy logic Rendezvous Docking controller has been developed that generates Waypoint-Heading goals for the USV to minimize the cross-track errors between the USV and AUV. A subsequent fuzzy
logic Waypoint-Heading controller has been developed to provide the desired heading
and speed commands to the low-level controller given the Waypoint-Heading goals.
High-level mission control has been extensively simulated using Matlab and partially
characterized in real-time during testing. Detailed simulation, experimental results and
findings will be reported in this paper.

The overall objective of this work is to evaluate the ability of homing and docking an unmanned underwater vehicle (Hydroid REMUS 100 UUV) to a moving unmanned surface vehicle (Wave-Adaptive Modular Surface Vehicle USV) using a Hydroid Digital Ultra-Short Baseline (DUSBL) acoustic positioning system (APS), as a primary navigation source. An understanding of how the UUV can rendezvous with a stationary USV first is presented, then followed by a moving USV. Inherently, the DUSBL-APS is susceptible to error due to the physical phenomena of the underwater acoustic channel (e.g. ambient noise, attenuation and ray refraction). The development of an APS model has allowed the authors to forecast the UUV’s position and the estimated track line of the USV as determined by the DUSBL acoustic sensor. In this model, focus is placed on three main elements: 1) the acoustic channel and sound ray refraction when propagating in an in-homogeneous medium; 2) the detection component of an ideal DUSBL-APS using the Neyman-Pearson criterion; 3) the signal-to-noise ratio (SNR) and receiver directivity impact on position estimation. The simulation tool is compared against actual open water homing results in terms of the estimated source position between the simulated and the actual USBL range and bearing information.

The measurement of the Scattering function of time-variant fading channels is of strong interest in the field of underwater acoustic communications, as it indicates the limitations of the channel capacity. It also helps reducing the development time of acoustic communication systems and the need for on-site tests using so-called "fading simulators". The Scattering function is interpreted as the expected power received at a given time-delay and frequency shift for a given signal transmitted through the acoustic channel. It has been estimated using a fourth-moment method developed by Kailath from 18 to 30 kHz, 8-ms broad-band chirps and 20--28 kHz, 28-ms pseudo noise sequences. These signals were transmitted periodically in the shallow coastal waters of South Florida from a static source, and recorded from a 64-channel receiver array located at a distance of 1000 meters. Spatial beamforming has been applied to study the spatial sensitivity of the scattering function.