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Proceedings Paper

Performance of the 2-D asynchronous OCDMA system with ASE light sources
Author(s): Bin Ni; James S. Lehnert
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Paper Abstract

The wavelength-hopping/time-spreading scheme for optical code-division multiple-access (OCDMA), also known as the 2-D scheme, has been studied by many researchers for more than a decade. In all of previous analyses, the light sources were modeled as perfectly incoherent, which requires infinite bandwidth, and chip-synchrony was assumed for mathematical simplicity. Therefore, it is important to study how the system actually performs with true asynchrony and practical light sources. The amplified spontaneous emission (ASE) source is a desirable source for the incoherent OCDMA system because of its broad bandwidth, large power, and low cost. In this paper, each chip generated by the transmitter is a rectangular ASE pulse with a Gaussian-distributed electrical field. The coherence time is much smaller than the chip duration, but non-zero. Because of this partial coherence of the light source, beat noise will occur when multiple pulses are combined. In addition, interfering pulses may only partially overlap with the pulses from the desired user due to the asynchrony, which introduces more randomness into the decision statistic. Both factors are taken into account when the distribution of the decision statistic is derived mathematically. Simulations of the bit-error rate (BER) are performed, and the results show that the coherence time may be the major limiting factor on the system performance. For example, when the coherence time is only 1/100 of the chip duration, the BER is 1-4 orders of magnitude worse than that of the ideal case.

Paper Details

Date Published: 10 September 2005
PDF: 10 pages
Proc. SPIE 5908, Optical Information Systems III, 59080W (10 September 2005); doi: 10.1117/12.617491
Show Author Affiliations
Bin Ni, Purdue Univ. (United States)
James S. Lehnert, Purdue Univ. (United States)


Published in SPIE Proceedings Vol. 5908:
Optical Information Systems III
Bahram Javidi; Demetri Psaltis, Editor(s)

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