UNDERWATER OPTICAL COMMUNICATION SYSTEM

• US 20140212142A1
• Filed: 07/10/2013
• Published: 07/31/2014
• Est. Priority Date: 07/12/2012
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Rus, Daniela, Doniec, Marek W.
• Granted Patent: US 9,031,413 B2
• Time in Patent Office: Days
• US Class Current: 398/104
• CPC Class Codes: H04B 10/80 Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
• CPC Class Codes: H04B 13/02 Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
• CPC Class Codes: H04L 7/0075 with photonic or optical means

Abstract

A method of optical underwater communications comprises applying a Fountain code to a plurality of data blocks. A sequence of optical data packets is transmitted through an underwater communications channel. Each optical data packet comprises one of the plurality of data blocks preceded by a preamble. The sequence of optical data packets transmitted through the underwater communication channel is received to generate a sequence of received data packets. The sequence of received data packets is sampled with the sampling clock to recover the plurality of data blocks.

Claims

1. A method of optical underwater communication comprising:

applying a Fountain code to a plurality of data blocks;

transmitting a sequence of optical data packets through an underwater communication channel, each optical data packet comprising one of the plurality of data blocks preceded by a preamble;

receiving the sequence of optical data packets transmitted through the underwater communication channel to generate a sequence of received data packets;

synchronizing a sample rate of a sampling clock to a data rate of at least one preamble in the sequence of received data packets; and

sampling the sequence of received data packets with the sampling clock to recover the plurality of data blocks.

2. The method of claim 1 further comprising generating a video image from a number of received data packets, the number being less than a total number of optical data packets in the transmitted sequence of optical data packets, and wherein each of the number of received data packets represents different temporal portions of a video frame.

3. The method of claim 2 wherein at least two of the temporal portions of the video frame are not sequential in time.

4. The method of claim 1 wherein the Fountain code is a Luby Transform.

5. The method of claim 1 wherein each optical data packet further comprises a Read-Solomon code and a Cyclical Redundancy Code (CRC).

6. The method of claim 5 wherein at least one of the Read-Solomon code and the CRC cause erasure of the received data packet upon detection of an unrecoverable error.

7. The method of claim 1 wherein each of a plurality of bits in each of the plurality of data blocks is encoded with a Manchester Encoding.

8. The method of claim 1 wherein the preamble includes a Barker code.

9. The method of claim 1 further comprising activating, for each of the plurality of data blocks, a number of light emitting diodes (LEDs) in an array of LEDs in an underwater transmitter, the number of LEDs determined by a multi-bit value in each of the data blocks.

10. The method of claim 1 further comprising controlling an intensity, for each of the plurality of data blocks, a number of light emitting diodes (LEDs) in an array of LEDs in an underwater transmitter, the number of LEDs determined by a multi-bit value in each of the data blocks.

11. A method of data muling comprising:

determining a position of a transmit optical modem relative to a receive optical modem based on an intensity of an optical data packet transmitted by the transmit optical modem through an underwater communication channel and received by the receive optical modem;

modifying the position until the intensity exceeds a threshold;

transmitting a sequence of optical data packets through an underwater communication channel, each optical data packet comprising one of a plurality of data blocks preceded by a preamble, wherein the plurality of data blocks has a Fountain code applied thereto;

receiving the sequence of optical data packets transmitted through the underwater communication channel to generate a sequence of received data packets;

synchronizing a sample rate of a sample clock to a data rate of at least one preamble in the sequence of received data packets; and

sampling the sequence of received data packets with the sample clock to recover the plurality of data blocks.

12. The method of claim 11 further comprising determining the intensity of the optical data packet based on the preamble in the received data packet.

13. The method of claim 12 wherein the position is determined by an Optical Stochastic Gradient Descent algorithm.

14. The method of claim 11 further comprising determining a general location of the transmit optical modem before determining the position, the general location determined by receiving an acoustic beacon transmitted by the transmit optical modem, the general location positioning the receive optical modem sufficiently close to the receive optical modem to enable determining the intensity of the optical data packet.

15. The method of claim 14 wherein the general location is determined by an Acoustic Stochastic Gradient Descent algorithm.

16. The method of claim 11 wherein the position is maintained by maximizing the intensity.

17. The method of claim 11 wherein the receive optical modem is repositioned to a predicted location of a next transmit optical modem after the receive optical modem has received a number of received data packets.

18. The method of claim 11 further comprising transmitting, from the receive optical modem to the transmit optical modem, a quality metric based on a quality of a received data packet, and the transmit optical modem adjusting a transmit characteristic of the transmit optical modem to improve the quality of the received data packet.

19. The method of claim 11 wherein adjusting the transmit characteristic includes modifying a length of each of the plurality of data blocks.

20. An apparatus for optical underwater data transmission comprising:

a controller configured to receive a video image from a device interface, the controller configured to partition the video image into a plurality of transmit data blocks by applying a Fountain code and the controller configured to store the transmit data blocks in a transmit buffer;

a Manchester encoder in electrical communication with the transmit buffer, the Manchester encoder configured to encode a bit stream of the transmit data block with a Manchester code;

a preamble encoder in electrical communication with the Manchester encoder, the preamble encoder configured to prepend a Barker code to the transmit data block to form a transmit data packet; and

a light emitting diode (LED) driver in electrical communication with at least one LED, the LED driver activating at least one LED based on a plurality of logic levels in the transmit data packet.