Real-time Video Streaming from Mobile Underwater Sensors

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Seongwon Han (UCLA)Roy Chen (UCLA)Youngtae Noh (Cisco Systems Inc.)Mario Gerla (UCLA)

Real Time Video Streaming

Real-time video streaming between Autonomous Underwater Vehicles (AUVs) and monitoring center (Surface buoy, ship)

Increasing demand for High resolution video streaming

But, traditionally limited due to narrow bandwidth of acoustic channel

Solution -> Optical Communications

But Optical Communications have many drawbacks (Short range,

Line of sight)

We propose a hybrid solution that combines acoustic and optical communications to overcome the obstacles

Underwater Media Review

Cable tether

Impose a constraint on AUV’s mobility

Nearly impossible to wire multiple AUVs (cables will be tangled)

Acoustic wave

Low Data rate, long propagation delay, high error rate, multi-path effect, consumes a lot of energy especially for sending data

Optical LED

Requires alignment for communication (Light emitter & receiver)

Short Communication range: 10 to 100m

Affected by water “purity”

Megabit/s data rates

Related Works

There are many efforts to realize real-time video streaming or at least doing similar thing.

Transferring a low resolution still gray scale image via acoustic links

Problem : it’s far from the real-time monitoring, transferring continuum of images is still a lot of burden for low bandwidth acoustic channel

Image enhancing techniques to get relatively high quality image with low data size

Problem : Still itself cannot achieve our goal

High bandwidth real-time video transfer within short distance (~ 20m)

Problem : communication distance is too short

Solution : Hybrid protocol of Acoustics and Optics

Our goal is to provide real-time video monitoring between AUVs at all timesEven if no optical link is available

Via Acoustics

We focus on image processing technique to produce the image which is at least 90% smaller than low resolution gray scale image

In this way, we can expect at most 3 – 5 frame rate per second (good enough for real-time video monitoring)

Low resolution gray scale image is also transferred via Acoustic channel (either pre-defined interval say every 10 sec or specific image which is requested by user)

Control message is always transmitted via acoustic links

Via Optical links

High definition video is always transmitted via Optical links

Control messages such as ACKs are transmitted via acoustic links

Optical Alignment using Acoustics

1. Send acoustic Invitation

2. Reply to the Invitation

3. Try Optical Connection

Alignment achieved by using acoustic Time-Difference-of-Arrival (TDoA)

Each node advertises its motion to other nodes to enable position prediction

Acoustic Receivers

Scenario : Bottom video exploration

If the node is not within optical range of tree, we can

use acoustic channel to nearest available optical tree

node

Switch to acoustic communications

in murky waters (poor water quality) Buoy

GPS

Acoustic

LinkOptical Link

Create Optical Tree for high quality interactive video

The data and commands in the reverse direction are carried via acoustic

channels

Scenario : a Scouting Expedition

Shallow water inter-submarine video communication

Establish high speed video connections among a team of mini-submarines participating in a scouting

expedition

The acoustic modems are used to position the submarines and to align their lasers The AUVs provide the optical multi hop

mesh

GPS

Video Recording

Example: Image compression

Original image (transferred via Optical link)

full video frame (e.g. 15 fps or higher)

Simplified vector image(transferred via acoustic link short interval)

Full video frame or at least 2-3 fps

Image size is

reduced by

50%

Image size is

reduced by 95%

Gray scale image(transferred via acoustic link large interval)Every 10 - 30 seconds

Video Streaming Example

Surface buoy

1. Low data rate video streaming via Acoustic link

2. High resolution video clip is transferred via Optical link

Surface Buoy

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Frame#

ViaAcoustic

Link

ViaOptical

Link

Examples of compressed images

< Grayscale >35% to the Original Size

< Sobel >29% to the Original

Size

< Original Image>100% to the Original Size

< Gaussian and Sobel >20% to the Original Size

< Our Solution >15% to the Original Size

(Gaussian and Sobel with the adaptive algorithm )

< Canny edge detection >22% to the Original Size

Image Compression Results

< Results of Image Processing on Full-size Images (2592x1944)>

85% reduction

Evaluation: Data RateSet up

We perform data communication between two AquaSeNT acoustic modems

Maximum data rate is 3200 bps according to the specifications

The buffer size is 608bytes

Result

Data rate was monitored as 660 bps (affected by severe multipath fading due to tank wall reflections)

In 640x480 case

- 15 minutes to transmit the unprocessed JPEG file - grayscale: 5mins, Sobel: 3.5 mins, our solution: 2 mins

In 128x96 case- Original: 113 seconds 16 seconds (our solution)

In 64x48 case- 81 seconds 10 seconds

Simulation Results: Latency

QualNet simulator enhanced with an acoustic channel model

Data rate is set to 9600 bps

Packet size is fixed to 512 bytes

Image resolution is 128x96 pixels

250m distance : Original jpg image requires 20 seconds 2.7 seconds (Our solution)

Original

Our Solution

Conclusions

Main contribution: enable reliable real-time video streaming without underwater

optical cables (when the optical channel quits, the acoustic channel takes over)

Acoustic - useful for aligning nodes to initiate optical connection, back up

channel

Optical - useful for transfer of large amounts of data at short range (< 50 m)

Future works - Smooth transition between the acoustic and optical video deliv-

ery mode by using image processing algorithm to compress the video before

transmitting it on the acoustic channel

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