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Proceedings Paper

Turbo-decoding of a convolutionally encoded OCDMA system
Author(s): Daniel Efinger; Robert Fritsch
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Paper Abstract

We present a novel multiple access scheme for Passive Optical Networks (PON) based on optical Code Division Multiple Access (OCDMA). Di erent from existing proposals for implementing OCDMA, we replaced the predominating orthogonal or weakly correlated signature codes (e.g. Walsh-Hadamard codes (WHC)) by convolutional codes. Thus CDMA user separation and forward error correction (FEC) are combined. The transmission of the coded bits over the multiple access fiber is carried through optical BPSK. This requires electrical field strength detection rather than direct detection (DD) at the receiver end. Since orthogonality gets lost, we have to employ a multiuser receiver to overcome the inherently strong correlation. Computational complexity of multiuser detection is the major challenge and we show how complexity can be reduced by applying the turbo principle known from soft-decoding of concatenated codes. The convergence behavior of the iterative multiuser receiver is investigated by means of extrinsic information transfer charts (EXIT-chart). Finally, we present simulation results of bit error ratio (BER) vs. signal-to-noise ratio (SNR) including a standard single mode fiber in order to demonstrate the superior performance of the proposed scheme compared to those using orthogonal spreading techniques.

Paper Details

Date Published: 11 February 2005
PDF: 11 pages
Proc. SPIE 5625, Optical Transmission, Switching, and Subsystems II, (11 February 2005); doi: 10.1117/12.576915
Show Author Affiliations
Daniel Efinger, Univ. of Stuttgart (Germany)
Robert Fritsch, Univ. of Stuttgart (Germany)

Published in SPIE Proceedings Vol. 5625:
Optical Transmission, Switching, and Subsystems II
Cedric F. Lam; Wanyi Gu; Norbert Hanik; Kimio Oguchi, Editor(s)

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