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Satellite RF Links In The Disadvantaged Marine Environment John Borden Dr. Jeffrey N. Shaumeyer Wavix, Incorporated Offshore Communications 2002 October.

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Presentation on theme: "Satellite RF Links In The Disadvantaged Marine Environment John Borden Dr. Jeffrey N. Shaumeyer Wavix, Incorporated Offshore Communications 2002 October."— Presentation transcript:

1 Satellite RF Links In The Disadvantaged Marine Environment John Borden Dr. Jeffrey N. Shaumeyer Wavix, Incorporated Offshore Communications 2002 October 2, 2002 Houston, TX

2 Page 2October 3, 2002Offshore Communications 2002 Topics Wavix Background Disadvantaged Marine Applications Marine Environment Characteristics Common Protocol Solutions Wavix Solution Project Synergies

3 Page 3October 3, 2002Offshore Communications 2002 Wavix Background Concept development work started in 1995 –Initial funding via NASA/GSFC SBIR teamed with Woods Hole Oceanographic Institution –Additional funding from Navy, NSF, NASA/SSC Incorporated Wavix in January 1999 Original idea was to commercialize oceanographic data collection from buoys Developed WavSat in response to lack of affordable, high-throughput communications Received financing for satellite system from Linsang Partners in Nov 2000

4 Page 4October 3, 2002Offshore Communications 2002 Wavix Satellite System Store-and-forward satellite communication service – in underserved areas Humanitarian workers in developing countries Crewmen onboard merchant ships at sea Recreational use of the oceans –Data transmission Oceanography/Meteorology Oil and gas exploration and production Shipping Stasia 906 Satellite Groundstation –Custom-designed in-house for our applications

5 Page 5October 3, 2002Offshore Communications 2002 Current Projects Ocean Data Telemetry Microsat Link –Phase 1 SBIR with Office of Naval Research –Conceptual design of a satellite system to support oceanography –Leading to ONR-funded design, construction and launch of a satellite Robust Ultra High Frequency (UHF) Satellite Communications Protocol for UUVs –Phase 1 SBIR with Naval Undersea Warfare Center –Advanced satellite-communication protocol for use in harsh marine environments –Leading to use on Navy’s next-generation military satellite communication system

6 Page 6October 3, 2002Offshore Communications 2002 Disadvantaged Marine Applications Applications where the antenna is close to the water surface Data Collection Buoys –Moored buoys for oceanography, meteorology –Drifters and profilers UUVs/AUVs –Military systems for reconnaissance –Research applications

7 Page 7October 3, 2002Offshore Communications 2002 Typical Applications

8 Page 8October 3, 2002Offshore Communications 2002

9 Page 9October 3, 2002Offshore Communications 2002 Marine Environment Characteristics Marine channels are prone to large scale errors Burst errors and signal fading are the major contibutors –Wash over of the near-surface antenna causing signal fading from ground-plane disruptions and possible transients in conductance will contribute burst errors. –Wave motions rocking the UUV may contribute to signal fading –Shadowing by waves will contribute to signal fading –High seas may contribute to fading and burst errors by coating the antenna with sea water or altering local RF propagation characteristics

10 Page 10October 3, 2002Offshore Communications 2002 Marine Environment Characteristics –Surface waves create reflections with dynamic multipath contributions to signal interference –Along the path of propagation, changeable atmospheric conditions contribute to signal fading and burst errors –The open-air RF channel is noisy with Additive White Gaussian Noise that contributes to Bit-Error Rates If the noise environment is predominantly bursty in nature, describing a channel as having a high BER can obscure the fact that the Gaussian noise itself is actually rather small –Contention for available channel space and interference from datagram collisions Bit-error rates (BER) or worse –compared to achieved by many terrestrial systems

11 Page 11October 3, 2002Offshore Communications 2002 Common Protocol Solutions Modify existing protocols at the Network or Transport layers of the OSI Model. TCP/IP has considerable inefficiencies due to the long round-trip time –Slow start and congestion avoidance slows link speed –Window size limits throughput –Requirement for positive acks slows link speed The Space Communications Protocol Standard is an improvement on the TCP/IP suite of protocols –Scaled windows and time stamps –Fast retransmit and recovery –Selective acknowledgment Assumes error-free or very low bit-error link Adds overhead - using more of the limited throughput

12 Page 12October 3, 2002Offshore Communications 2002 Illustration courtesy Catherine Werst

13 Page 13October 3, 2002Offshore Communications 2002 Wavix Protocol Solution Needs to be attacked at the lowest levels –Physical layer the physical characteristics of the RF signaling –Data-Link layer reliable data delivery across the physical layer Diverse array of noise-mitigation techniques –Metaframing –Time-Division, Multiple-Access Operation –Data Backcapture –Bit Interleaving –DC Balance & Scrambling –Forward Error Correction (FEC)

14 Page 14October 3, 2002Offshore Communications 2002 Wavix Protocol Solution (cont.) Metaframing –imposes structure on the bitstream –structure adds information to mitigate synchronization problems –allows multiple, simultaneous user channels on the RF link Time-Division, Multiple-Access (TDMA) Operation –metaframes are issued by the satellite node at fixed time intervals –user synchronizes its timing to uplink in the allotted channel Data Backcapture –receiver maintains a buffer of recently received bits –receiver can locate previously received frames in the already- received bitstream by counting backwards –frame synchronization appears to be nearly instantaneous

15 Page 15October 3, 2002Offshore Communications 2002 Wavix Protocol Solution (cont.) Bit Interleaving –Frames are written sequentially into a buffer –When the buffer is full, bits are transmitted by column –As bits are received they are written into columns –Frames are read out by rows. DC Balance & Scrambling –avoid low-frequency components in the RF signal Forward Error Correction (FEC) –number of bit errors that can be corrected determines the size of the FEC code –FEC mechanisms are best implemented in the frame

16 Page 16October 3, 2002Offshore Communications 2002 Protocol Advantages Metaframing creates a DC-balanced, hierarchical structure that makes synchronization more robust Metaframing and TDMA allows multiple, simultaneous user channels on the RF link Individual channels can operate with independent transmission protocols Metaframing with Data Backcapture can increase data- transmission efficiency Priority allocation of channels fits easily into the metaframe structure Additional techniques to increase error immunity in the bitstream, such as Interleaving, Data Scrambling, and FEC, are easily accommodated

17 Page 17October 3, 2002Offshore Communications 2002 Project Synergies Oceanography –Argo profilers Navy UUVs –Mine detection Oil exploration –Current monitoring Delay-Tolerant Networking –Interplanetary Internet


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