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Proceedings Paper

Coherent optical pulse CDMA systems based on I-Q noncoherent demodulation of M-ary orthogonal signals
Author(s): Wei Huang; Ivan Andonovic
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Paper Abstract

Coherent optical pulse CDMA systems based on noncoherent demodulation of M-ary orthogonal signals are proposed. Each of the J information bits is encoded and transmitted as a M (equals2J) symbol word of a family of Hadamard-Walsh orthogonal sequences. A pulsed laser is employed at the transmitter, modulated by the symbol sequence and encoded by an optical tapped delay-line encoder to generate a unique optical pseudo-random sequence (bipolar code). At the receiver, a pulsed local oscillator followed by a tapped delay-line encoder is employed to produce the optical code sequence of the intended user. Correlation between the received signal and the local code is executed through a coherent optical correlator comprising a 3 dB coupler and balanced detector. Noncoherent demodulation of the M-ary orthogonal signals based on the maximum-likelihood criterion is used to recover the information bits. After a description of the network implementation, the performance of the system is theoretically analyzed and its numerical evaluation given. It is shown that the ratio of the number of available users to the practical code gain at a BER equals 10-9 is approximately 3.7% - 5%. Although a fewer number of users can be supported compared to full coherent reception (10%), the system no longer requires phase locking whilst keeping the advantages of the coherent approach. Hence the linewidth requirement of the laser sources is relaxed. The performance and the implementation of the system are still significantly better than conventional incoherent optical pulse CDMA systems utilizing unipolar codes.

Paper Details

Date Published: 7 October 1998
PDF: 12 pages
Proc. SPIE 3531, All-Optical Networking: Architecture, Control, and Management Issues, (7 October 1998); doi: 10.1117/12.327088
Show Author Affiliations
Wei Huang, Univ. of Strathclyde (United Kingdom)
Ivan Andonovic, Univ. of Strathclyde (United Kingdom)

Published in SPIE Proceedings Vol. 3531:
All-Optical Networking: Architecture, Control, and Management Issues
John M. Senior; Chunming Qiao, Editor(s)

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