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In our recently proposed diversity O-CDMA scheme, every user transmitted multiple copies of its optical codeword per data bit of one in order to improve code performance. Our analysis assumed that users were “chip-synchronized” among their transmissions, and the copies of each user's codeword were allocated at different chip (or time-slot) positions, per bit duration, in order to maintain “copy independency” for good code performance. However, copy independency is hard to achieve, especially in short code length. In addition, it is known that code performance can be improved if all simultaneous users are assumed to transmit chip-asynchronously. In this paper, we combine the realistic effects of user asynchronism and copy dependency in the analysis of our diversity O-CDMA scheme and formulate a new, generalized, more accurate performance model. Furthermore, the improvement in copy dependency and code performance due to the use of finer “granularity” in the chip positions allowed for the copies of each user's codeword are studied with the support of computer simulation.
Date of Publication: April15, 2013