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and sent to the demodulator for accurate symbol timing. — Figure 50 and sent to the demodulator for accurate symbol timing.

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Table 2.1: 2009 Sensor Deployment around Moorea The present state of sensing systems in Moorea is primitive; ecological re- recently set aside large tracts of reefs around Moorea as protected areas. search could be significantly enhanced with appropriate technology. Currently, cover of coral and abundance of reef fishes are high, and the Territorial Government

2.1 describes the types, quantity, cost, and sampling regimes of these sensors. The ability to perform real-time, adaptive ecological experiments would

Figure 2.2 depicts an autonomous drifter swarm. The potential applications of this new technology are far-reaching and

would provide an inexpensive and reliable option for real-time telemetry Figure 2.3: Southern California Coastal Ocean Observing System

Figure 3.1: Electromagnetic Spectrum existing underwater systems that make use of RF waves. of conductivity, wavelength, and air/water interface on RF waves and describes Pure water is an insulator, but as found in its natural state, water contains

Figure 3.2: RF Attenuation vs. Frequency in Fresh and Sea Water 3.1.2 Wavelength

underwater communications. Figure 3.3: RF Wavelength vs. Frequency in Sea Water, Fresh Water, and Air

Figure 3.4: Air to Water Refraction Loss as a Function of Frequency and fresh water. As frequency increases refraction loss decreases. Where f is the frequency in Hz, and o is the conductivity in S/m.

from a transmitter into a body of seawater and picked up by a distant receiver. metal transmitting and receiving aerials are surrounded by waterproof electrically The first commercial underwater radio-frequency (RF) modem in the world, 2006. It can communicate over several tens of meters at a rate of 100bps. Wireless

Table 3.1: Rates, Ranges, and Uses of Wireless Fibre Systems RF Modems Uptical Waves are electromagnetic waves Naving wavelengths between ZUUTIN blue light) and 700nm (red light). Due to their very short wavelength, high fre- yuency, and high speed (light in the ocean travels at a velocity equal to the velocity f light in a vacuum divided by the index of refraction (n), which is typically n = .33 [41]), optical waves offer the possibility for very high speed communication inderwater (up to 1Gbps). However, optical waves used as wireless communica- ion carriers are generally limited to very short distances because of severe water \bsorption at the optical frequency band and strong backscatter from suspended varticles [42]. The section discusses the basic physics of optical waves underwater nd existing underwater systems that make use of optical waves.

light spectrum. The scattering process of optical waves and the wavelength dependence of is valid for all possible ratios of particle diameter to wavelength [47]. Scattering in

The Spectral transmittance over the upper 10m of water for Jerlov water types I: extremely pure ocean water; II: turbid tropical-subtropical water; for particles with diameter x; and p(x) is the probability distribution function of III: mid-latitude water; 1-9: coastal waters of increasing turbidity [44, 48 where x is the particle diameter, C..a(x) is the scattering cross section

far. Figure 3.8: Acoustic Absorption as a function of temperature, pressure, and ny [59] attenuated within a short distance while low frequency acoustic waves can trave

Figure 3.12: Ray Trace for a 40kHz source with a 15 degree beam angle placed at 10 meters depth in a body of water 11 meters deep with a constant sound speed of 1500 m/s and the theory of normal modes provide the basis for such propagation modeling mechanisms is based on the theory and models of sound propagation. Ray theory Bellhop is a commonly used, highly efficient ray tracing model. The un-

Figure 6.2: Class A Amplifier Input/Output Characteristic ficiency). A typical Class A input / output characterisitic is shown in Figure 6.2 Unlike a Class A amplifier, a Class B amplifier consists of two complimen-

Figure 6.4: Class AB Amplifier Input/Output Characteristic for one transistor

Figure 6.5: Block diagram of a basic switching or PWM (Class-D) amplifier

Figure 6.6: Block diagram of the power amplifier design making use of a class AB and class D amplifier to achieve linearity and efficiency

Each of the relay outputs are connected to one another but none are open unless The number of windings (N), voltage output, and transciever power con

Table 6.1: Power Management Characteristics 3.3 Impedance Matching Circuit Impedance matching is the practice of setting the input impedance of ar

The transducer’s impedance varies across frequencies as it is an active el-

Figure 6.12: Electrical Equiavalent Circuit Model for a Transducer

With the circuit shown in Figure 6.16, Figures 6.17, 6.18, and 6.19 shov As the transducer is mostly capacitive, the impedance matching circuit

Figure 6.20: Estimated Power Coupled into the Transducer Although the power coupled into the transducer cannot directly be mea-

Figure 7.1: Block diagram of classic matched filter FSK demodulator minimum theoretical bandwith for a binary FSK scheme is 2X the bit rate (in Hz). Phase Shift Keying: In M-ary phase shift keying (PSK), the data are = bo id So PN transmitted by shifting the phase of a continuous carrier to one of M discrete phases. PSK signals require less transmitted power for a given probability of error than FSK systems (as shown in Figure 7.2) and require less bandwidth (the mini- mum theoretical bandwith for a PSK scheme is bit rate (in Hz)) , but require more coherent detection, either by regenerating a local carrier in the receiver (as shown in Figure 7.3, or by using differential detection in which the previous bit is used as the phase reference for the current bit [124]. Although coherent detection could be used with FSK, the complexity required in the receiver for carrier regeneration jus- tifies the better bit error rate (BER) performance of PSK. To combat intersymbol interference caused by multipath and frequency spreading, channel equalization transmitted by shifting the phase of a continuous carrier to one of M discrete

Figure 7.2: Bit Error Rate of MFSK and MPSK for a given probability of error 1el clearing, higher bit rates may be achieved at the expense of a more complex meet channel conditions. As coherent modulation does not have to wait for chan-

Figure 7.3: Block diagram of a coherant PSK receiver phase-shift-keying (PSK) is used to map information bits to symbols before spread-

Table 7.1: Digital Transceiver Parameters raw bit rate for low-data rate sensor networking applications. 7.3.1 Modulator In a digital transceiver, the modulator is responsible for translating a bit

space frequencies. Figure 7.5: Block Diagram of FSK Modulator offsets that were different enough to distinguish between the desired mark and 7.3.2 Digital Down Converter consuming portion of the modulator is the cosine look up table. To save resources,

design program from Carnegie Mellon well known for creating compact filters. The low-pass filter is a small 20-tap FIR filter designed using Spiral [144], a filter 7.3.3 Symbol Synchronizer

Figure 7.7: Process of Symbol Synchronization value and the synchronization point is located (Figure 7.7).

threshold to synchronize on the next incoming packet. 7.3.4 Demodulator A demodulator converts the analog waveform it receives back into the digi-

Figure 7.14: (a) Clock Division, (b) Added Flip Flop between clock domain to avoid metastability to avoid random problems caused by metastability.

local bus (PLB), based on the IBM standard 64-bit PLB architecture specification. faces to the digital modem through two fast simplex links (FSLs), point-to-point,

transceiver through sending a command signal through the FSL bus signaling the digital transceiver to turn on. When the digital transceiver is ready to begin re- ceiving signals, it sends an interrupt back to MicroBlaze to indicate initialization is complete. The digital transceiver then begins the down conversion and synchro- nization process, processing the signal received from the ADC and looking for a peak above the threshold to indicate a packet has been received. If the digital transceiver finds a peak above the threshold, it finds the synchronization point, and demodulates the packet. The demodulated bits are stored in the FSL FIFO. and demodulates the packet. The demodulated bits are stored in the FSL FIFO. When the full packet has been demodulated, the digital transceiver sends is complete. The digital transceiver then begins the down conversion and synchro-

Table 7.2: Digital Design Resource Usage that can fit the design.

Table 7.4: Digital Transceiver Design Comparison DSSS) and are implemented on various hardware platforms.

Table 7.3: FPGA Power Consumption From Table 7.3 we observe that the quiescent power contributes significantly

Mission Bay Test Set Up. (a) Transmitter on dock, (b) Receiver on boat boat this distance and hence could just be detected above the converter’s noise. This

in the subsections below. 8.2.1 Hard Wired Tests For digital testing, we purchased a prototype test platform, the DINI DMEG-

with ModelSim. For our initial in-water tests of the digital hardware, we sent a packet con-

dB. The test was repeated with different data bits 10 times all producing 0% error. Figure 8.7: Snapshot of hardware simulation result for 12” bucket test

modem to improve the performance of the modem in high multipath environments. Figure 8.9: Multipath Amplitude Delay Profile at 50m in the Canyon View Pool

Table 9.1: Data amounts for major sensors and sensor packages on the CHARM

Table 9.2: UCSDModem Power Characteristics Figure 9.2 and Table 9.3 show the routing, energy and cost results respec- consumption through multiple transmissions over shorter distances. tively of the linear programming model for minimizing battery energy and cost

its data directly to the surface node.

Table 9.3: Minimum Energy and Cost Requirements for a 6 month deployment of the CHARM mooring Figure 9.2 also shows the routing results of the linear programming model for maximizing the network lifetime, giving each node only 140kJ of energy. The

Table A.1: Underwater Modem Bill of Materials