Massachusetts Institute of Technology

Nortel Networks Corporation

Marvin Scheinbart

Richard L Angle

Geoffrey B Ladwig

Scott A Hamilton

Hemonth G Rao

Andrew Fletcher

Nicholas Hardy

A multi-rate, burst-mode, photon-counting receiver can communicate at data rates up to 10.416 Mb/s over a 30-foot water channel. With added attenuation, the maximum link loss is 97.1 dB at &#x3bb;=517 nm. In clear ocean water, this equates to link distances up to 148 meters. For &#x3bb;=470 nm, the achievable link distance in clear ocean water is 450 meters. The receiver incorporates soft-decision forward error correction (FEC) that supports multiple code rates to achieve error-free performance. A burst-mode receiver architecture provides robust performance with respect to unpredictable channel obstructions. The receiver can detect the data rate on-the-fly and adapts to changing levels of signal and background light. The receiver updates its phase alignment and channel estimates every frame, allowing for rapid changes in water quality as well as motion between transmitter and receiver.

Methods and apparatus for free-space undersea communications

A memory management technique for maintaining packet order in a packet processing system involves maintaining a START indicator and a VALID indicator for each memory block in a packet memory. Packets are written in a number of successive memory blocks, and the START indicator corresponding to the first memory block of the number of successive memory blocks is set to indicate that the packet is available for processing. The packets are processed by a packet processor. When the packet processor completes the processing of a particular packet, the VALID indicator corresponding to the first memory block associated with that packet is set to indicate that the packet is ready to be forwarded. The packet may become ready to be forwarded out of order. However, the packets are forwarded in first-in-first-out order by processing the packets in first-in-first-out order and only forwarding a particular packet if the VALID indicator corresponding to the first memory block associated with that packet is set to indicate that the packet is ready to be forwarded. Thus, a packet is not forwarded unless and until all previous packets have been forwarded, even if the packet is ready to be forwarded before one or more previous packets.

Memory management technique for maintaining packet order in a packet processing system

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Chelmsford, MA, United States of America

Marvin Scheinbart