Abstract
A fertile technique, for increasing single-user throughput while keeping
a constraint on the light pulsewidth, is proposed for spectral-amplitude-coding
optical code-division multiple-access (SAC-OCDMA) systems. In this technique,
two-level M-ary
overlapping pulse-position modulation (M-OPPM) scheme is adopted and each user is
assigned two orthogonal code sequences to represent these two levels. The
code sequences are selected from a minimum cross-correlation code set. The
bit error rate (BER) of the proposed system is derived, taking into account
the effects of phase-induced intensity noise, shot noise, and thermal noise
in addition to the multiple-access interference. The BER performance of this
system is compared to other systems adopting M-PPM and OOK schemes under same pulsewidth
constraints. Our results reveal that, while keeping the BER well below a prescribed
threshold, the proposed M-OPPM SAC-OCDMA system achieves higher transmission rate as compared
to both M-PPM
and OOK SAC-OCDMA systems under same constraints. Specifically the transmission
rate of a single user of the proposed system can be increased by about 34.44%
as compared to traditional systems.
© 2013 IEEE
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