Abstract
In this paper, we present a novel multirate, differentiated
quality of service (QoS) optical CDMA (OCDMA) system using multilevel signaling
technique. The emphasis is on OCDMA systems employing multi-length variable-weight
optical orthogonal codes (MLVW-OOC) as signature sequence. We begin by presenting
a two-class variable-weight OCDMA system in which all users have the same
energy level in one bit duration. As a consequence, high weight users transmit
their corresponding optical pulses at a lower power while low weight users
transmit their corresponding optical pulses at a higher power level. We show
that using this multilevel signaling technique, while employing the well known
optical AND logic gate receiver structure, we achieve a considerable improvement
in the performance of low-weight (high-power) users while the performance
of high-weight (low-power) users not altered in comparison to one-level system.
In the next step, we indicate that by using the recently introduced multistage
receiver structure, which employs advanced optical logic gate elements, interferences
at different power levels are distinguishable so that the performance of both
high-weight and low-weight users are improved. Furthermore, we employ multilevel
signaling technique in OCDMA system based on MLVW-OOC (multirate, differentiated
QoS system). We show that using multilevel signaling technique in such a system
results to the performance improvement. To analyze the performance of the
system we obtain a closed-form relation expressing an upper bound on the probability
of error of the system. Finally, to validate the upper bound, the analytical
results are compared to the results of system simulation. The numerical closeness
between the analytical and system simulation reveals the tightness of the
obtained upper bound, hence making them quite useful in evaluating the above
system's performance.
© 2009 IEEE
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