Pattern Code Modulation and Optical Decoding - A Novel Code-Division Multiplexing Technique for Multifiber Networks

Abstract
We consider the use of multiple high-capacity fibers for communications networking. Each user transmits, asynchronously, patterns of optical pulses distributed over the fibers and throughout a time frame. Each receiver has a distinct alphabet of patterns, which are detected by optical correlators. Optical correlation by fiber tapped delay lines provides speedy and easy-to-implement decoders. Thus the individual user obtains a transparent low-speed channel by code multiplexing. The reliability of this low-speed channel can be enhanced by redundantly coding the patterns sent by the user, for which the encoding and decoding processes can be performed electronically. This two-step encoding process is simple to implement, highly reliable at reasonable throughput, and provides asynchronous access with simple protocol. Various components and configurations of this access scheme are described. The information theoretic capacity and the error probability for these configurations are derived. We also demonstrate that hardlimiting and filtering at the receiver reduce error probability significantly.

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