A decoder was developed that decodes a serial concatenated pulse position modulation (SCPPM) encoded information sequence. The decoder takes as input a sequence of four bit loglikelihood ratios (LLR) for each PPM slot in a codeword via a XAUI 10-Gb/s quad optical fiber interface. If the decoder is unavailable, it passes the LLRs on to the next decoder via a XAUI 10-Gb/s quad optical fiber interface. Otherwise, it decodes the sequence and outputs information bits through a 1- GB/s Ethernet UDP/IP (User Datagram Protocol/Internet Protocol) interface.

The throughput for a single decoder unit is 150-Mb/s at an average of four decoding iterations; by connecting a number of decoder units in series, a decoding rate equal to that of the aggregate rate is achieved. The unit is controlled through a 1-GB/s Ethernet UDP/IP interface.

This ground station decoder was developed to demonstrate a deep space optical communication link capability, and is unique in the scalable design to achieve real-time SCPPM decoding at the aggregate data rate.

This work was done by Kevin J. Quirk, Jonathan W. Gin, Danh H. Nguyen, Huy Nguyen, Michael A. Nakashima, and Bruce E. Moision of Caltech for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-47729

NASA Tech Briefs Magazine

This article first appeared in the November, 2012 issue of NASA Tech Briefs Magazine.

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