Implementation of Underwater Channel Emulator (1804) Aaron DeMaio, - - PowerPoint PPT Presentation

Implementation of Underwater Channel Emulator (1804)

Aaron DeMaio, Michael Stratton, and Nicholas Gorbenko Advisor: Dr. Peter WIllett Sponsor: The MITRE Corporation

Overview

• Introduction

○ The MITRE Corporation ○ Underwater ACOMMS

• Background

○ Current Technology ○ Drawbacks of current methods

• Channel Emulation

○ What is modeled ○ Main problems

• Design Plan

○ Basic plan ○ Future plans

• Timeline
• Conclusion

Introduction

• The MITRE Corporation

○ Manages Federally funded research and development centers ○ Based in Bedford, Massachusetts

• Underwater acoustic communications (ACOMMS)

○ 71 percent of the earth is covered in water ■ 95 percent unexplored ○ Underwater communication systems have great importance Figure 1: Current Underwater nodal system

Background

• Current Technology

○ Radio wave communication ■ Seawater absorbs radio waves ○ Light communication ■ Attenuation in water is great and the signals are easily lost in underwater channels with poor clarity ○ Cables ■ Impractical ■ Easy to disrupt ○ Acoustic Figure 2: Global underwater fiber optic cable network

Drawbacks of Current Methods

• Testing on site

○ Costly ○ Environment and channel need to be static

• RF Emulators

○ Do not work well underwater

• Pure Software Simulation

○ Cannot test hardware

Channel Emulation

• Software Defined Radio System

○ Models time-varying underwater channel and effects in software and hardware ○ Design Platform ■ Based in C++ ■ Uses 3 USRP X310 Software Defined Radios ○ Benefits ■ Cheaper ■ More reliable ■ More closely models underwater channels ■ Modular Figure 3: USRP X310 Software Defined Radio

Main Underwater Effects

• Four main problems with underwater channel modeling

○ Path losses due to spreading and absorption ○ Ambient noise ○ Reverberation due to multipath ○ Doppler spreading Figure 4: Multipath reverberation

Basic Plan

• Data modulated by BPSK from a laptop and given to the first USRP X310 for

transmission

• Transmitter USRP sends a signal with a bandwidth of 4kHz carrying the data
• Second USRP as a transceiver connected to another laptop via. Ethernet

○ Receives data wirelessly from transmitter ○ Transmits data wirelessly to receiver

• Laptop will process the received signals and add channel effects
• Final USRP will receive signal and its attached laptop will demodulate the signal

and obtain the data

Static Channel Response - SNR = -10

The Setup

*CE = Channel emulator

Basic Plan (cont.)

• Creating the channel

○ Code in C++ to model the channel effects ■ Ambient noise modeled with Gaussian Curve ■ Path Losses modeled with spherical spreading ■ Reverberation due to multipath modeled with time-varying response ■ Doppler spreading modeled by adding frequency variations

Time Varying Channel Response

• Autoregressive Function can be used to

partially model a time varying system

• Dictates that the current output is linearly

dependent on the previous outputs with a coefficient

Checking Data Accuracy

• How can the validity of the channel simulation be established?

○ Test USRPs in a tub of water, hydrophone used to receive signal ○ Send the same message as above using our channel emulator instead of the tub of water and compare the results ○ Check data efficacy using a pool as well to gather data with increased length of channel ○ Compare the second data set with results of channel emulator

Fall Timeline

Spring Timeline

Budget

• There is nothing necessary for this project that is not provided

○ USRPs provided by MITRE ○ Hydrophones provided by MITRE ○ Laptops borrowed from UConn ○ Ethernet cables brought from home

Questions?