1. Real-time Video Streaming from Mobile Underwater Sensors 1 Seongwon Han (UCLA) Roy Chen (UCLA) Youngtae Noh (Cisco Systems Inc.) Mario Gerla (UCLA)

2. 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

3. 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

4. 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

5. Solution : Hybrid protocol of Acoustics and Optics  Our goal is to provide real-time video monitoring between AUVs at all times Even 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

6. 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

7. 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 Link Optical Link  Create Optical Tree for high quality interactive video  The data and commands in the reverse direction are carried via acoustic channels

8. 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

9. 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

10. 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 12345671234567 Frame# Via Acoustic Link Via Optical Link

11. Examples of compressed images 35% to the Original Size 29% to the Original Size 100% to the Original Size 20% to the Original Size 15% to the Original Size (Gaussian and Sobel with the adaptive algorithm ) 22% to the Original Size

12. Image Compression Results 85% reduction

13. Evaluation: Data Rate Set 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

14. 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

15. 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 delivery mode by using image processing algorithm to compress the video before transmitting it on the acoustic channel 15

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