Greg Davis Scott Hambleton Jon Holton Chris Johnson Chris Monfredo 12/10/13Rochester Institute of Technology1 P14251 Underwater Acoustic Communication

12/10/13Rochester Institute of Technology2 Agenda  Design Updates/Proof of Concept  Software Components  Drawings (EE)  BOM (EE)  Drawings (ME)  BOM (ME)  Final Cost Analysis  Final Risk Analysis  Test Plans  MSD II Schedules

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology3 Frequency Shift Keying:  Produces four different frequencies corresponding to 00, 01, 10, 11  SD Simple modulation and demodulation schemes and circuitry  Quick and efficient set up and delivery times Schedules

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology4 Frequency Shift Keying: Modulation: Theory-produce four different frequencies that each represent a different two bit symbol. These frequencies will be gray coded such that only a maximum of one bit error can occur per demodulation error. After compression and redundancy, we need to send 9768 kbps to meet our 15 kbps customer requirement. This indicates that the lowest possible frequency that can be used is 14.4 kHz. 29 kHz = kHz = kHz = kHz = 10

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology5 Frequency Shift Keying: Modulation: To produce the four needed frequencies, properties of a square wave can be exploited. The main property being used is that in frequency, a square wave, is sync function. A sync function has a large amplitude at the center frequency and multiple harmonics that theoretically occur every 3*fc Using a sharp band pass filter will allow us to keep the large portion of the signal that occurs at the center frequency while removing all of the other harmonics To generate the needed frequency response, an LC band pass filter will be used

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology6 Frequency Shift Keying: Modulation: The LC band pass filter has a center frequency at 1/sqrt(LC), and a bandwidth of 1/(C*R L ). Since the output of our filter will be fed into an amplifier with theoretical infinite input resistance, our bandwidth will be very small; which is desirable. By adjusting the input resistance, we can also adjust the sharpness of each filter Each filter will be fed by a clock pin coming from the RPi, that will provided the square wave at each of the four desired frequencies The output of the four band pass filters will be fed into a 4:1 mux whose output will be controlled via an enable and two addressing pins

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology7 Frequency Shift Keying: Modulation:

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology8 Frequency Shift Keying: Demodulation: To demodulate we are looking to decipher the four different frequencies in order to obtain the original binary message This will be done by taking the incoming signal from the hydrophone, band passing around our frequency range, and then passing the analog signal through an analog to digital converter. The output of the ADC will then be fed back to a pin on the RPi. The DFT will then be performed on the incoming signal in order to determine the largest frequency component. Based on the frequency and the amplitude at this frequency, the incoming message will be decoded. The DFT will be performed using the FFTW C programming package developed by MIT

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology9 Frequency Shift Keying: Demodulation: The FFTW package allows the user to do one or multiple dimension FFT’s with a very simple to use library This package is also optimized for multithreading and also gives the capability to determine the most optimum way in which to take the FFT of the current signal. #include { fftw_complex *in, *out; fftw_plan p;... in = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N); out = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N); p = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);... fftw_execute(p); /* repeat as needed */... fftw_destroy_plan(p); fftw_free(in); fftw_free(out); }

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology10 Frequency Shift Keying: Demodulation: periods: 3 FS: 2.25 MHz

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology11 Dish Concept: Use parabolic collector around hydrophone. Center hydrophone at focal point. Increase gain from transmitter. Parabolic Antenna Concept Radartutorial.eu

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology12 Initial Dish Design: Mounts on top of housing Made from plastic or metal 12” Diameter to increase gain

11/26/13Rochester Institute of Technology13 P14251 Underwater Acoustic Communication CE Overview -Software Architecture -Control unit flowchart and pseudo-code -Error Detection/Correction -Framing Information -Data Rate Analysis

11/26/13Rochester Institute of Technology14 P14251 Underwater Acoustic Communication Software Architecture

11/26/13Rochester Institute of Technology15 P14251 Underwater Acoustic Communication Control Unit Pseudo-Code

11/26/13Rochester Institute of Technology16 P14251 Underwater Acoustic Communication Control Unit Pseudo-Code

11/26/13Rochester Institute of Technology17 P14251 Underwater Acoustic Communication Control Unit Pseudo-Code

11/26/13Rochester Institute of Technology18 P14251 Underwater Acoustic Communication Error Detection and Correction -Hybrid Scheme: ECC and ARQ -EEC Implementation: BCH vs. Reed Solomon -BCH is easier to implement, but requires a much larger amount of redundancy -Reed-Solomon is more complex, but overall much better and requires only 20% redundancy (to correct 10% of errors)

11/26/13Rochester Institute of Technology19 P14251 Underwater Acoustic Communication Error Detection and Correction -Reed Solomon encodes k symbols into n codewords -n – k = 2t -Errors are corrected at the symbol level. If a symbol has 4 bits and all of them are wrong, it only counts as one error. -Can vary the code word size with the number of bits per symbol -RS(255, 212) with 4 bits/symbol, RS(1023, 853) with 1 bit/symbol, etc. -For very small frames (i.e. control frames), RS(16, k)

11/26/13Rochester Institute of Technology20 P14251 Underwater Acoustic Communication Error Detection and Correction -Encoding: LFSR based implementation is extremely simple and fast. Will translate well to C

11/26/13Rochester Institute of Technology21 P14251 Underwater Acoustic Communication Error Detection and Correction -Decoding is more complex, but efficient algorithms exist that will help significantly

11/26/13Rochester Institute of Technology22 P14251 Underwater Acoustic Communication Frame Sentinels -Sentinels are a unique pattern of bits that signify the start and end of the frame i.e –data– When preparing the frame for transmission, if the pattern appears anywhere in the data, bit stuffing is used to eliminate it (i.e > ) -Commonly used sentinel which we’ll use is Frame Header -1 bit to signify the type of frame: control or message -1 bit that gets flipped each time a new frame is sent

11/26/13Rochester Institute of Technology23 P14251 Underwater Acoustic Communication Control frame formats -Since it’s especially important to interpret control frames correctly, 4 bits are used to display the unique patterns – Request to Send (RTS) – Clear to Send (CTS) – Acknowledgement (ACK) – Done (Signifies that all frames have been sent) -These 4 bits + the 2 header bits can be encoded with an RS(7, 3) code (2 bits per symbol)

11/26/13Rochester Institute of Technology24 P14251 Underwater Acoustic Communication Frame Sizes - Control Frame: 16 (sentinels) + 14 (data) = 30 bits - Message Frame: 16(sentinels) + X+2 (message) = 18+X bits Propagation delay (20ms for 30m distance) limits the number of frames that can be sent. For 15kb/s, the maximum number of message frames = 9 frames, each containing 1k encoded information bits Increase X to ~1023 bits for Reed-Solomon Encoding

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11/26/13Rochester Institute of Technology26 P14251 Underwater Acoustic Communication Data Rate Analysis – Code Overhead -From SSDR: Compression time is expected to be negligible -Encryption time is a non-factor -Error Encoding time is negligible -FFTW benchmarking info suggests very quick performance times -Error Decoding time may take a bit longer, but millions of clock cycles are available to work with. * We may be able to further lower the number of message frames to eliminate propagation delays. This adds slightly more complexity to error handling.

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Underwater Acoustic Communication 12/10/13Rochester Institute of Technology33 Mechanical Drawings  Assembly  Sheet Metal Housing  Mounting Plate  Front and Back covers

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology34 Assembly Drawing

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology35 Sheet Metal Housing

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology36 Mounting Plate

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology37 Back Cover

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology38 Front Cover

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology39 Mechanical BOM Total Mechanical cost: $113 + Housings and Dishes

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology40 B Spray Test Results: Test Material:Specimen #Initial Mass (grams):Final Mass (grams):Mass Change (grams): 316SS SS SS SS SS ABS Plastic ABS Plastic ABS Plastic ABS Plastic ABS Plastic Naval Brass Naval Brass Naval Brass Naval Brass473 0 Naval Brass Alum Alum Alum Alum Alum Aluminum preformed worst. Naval Brass, ABS Plastic, and 316SS all had no noticeable effects of corrosion 316SS Best choice for cost and machinability.

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology41 Cost Analysis  MSD I Test Cost: $100  Mechanical Component Cost: $113 + Housings  Electrical Component Cost: $ PCBs  Total Budget: $1750  $432 remainder for shipping and emergencies

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology42 Electrical Test Plans  Power Converters <5% Ripple at 1A load for 5V <1% Ripple at 1A load for 3.3V  Power Amplifier Adjustable Gain Find resistance for 10W  AGC 1V Amplitude for any input  LC Filters Adjust values

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology43 Software Test Plans -Unit test all code -Device testing : make sure code actually runs on the Raspberry Pi -Wired device testing : make sure both devices can communicate via wired connection before attempting wireless -Turn functionalities on and off to see that they make a difference

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology44 Mechanical Test Plans

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology45 Risk Analysis

Underwater Acoustic Communication 12/10/13Rochester Institute of Technology46 MSD 2 Schedule