Analysis and Design of Adaptive OCDMA Passive Optical Networks

Optical code division multiple access (OCDMA) systems can support multiple classes of service by differentiating code parameters, power level, and diversity order. In this paper, we analyze bit error rate (BER) performance of a multiclass 1-D/2-D OCDMA system and propose a new approximation method that can be used to generate accurate estimation of system BER using a simple mathematical form. The proposed approximation provides insight into proper system level analysis, system level design and sensitivity of system performance to the factors such as code parameters, power level, and diversity order. Considering code design, code cardinality, and system performance constraints, two design problems are defined and their optimal solutions are provided. We, then, propose an adaptive OCDMA passive optical networks (OCDMA-PON) that adaptively shares unused resources of inactive users among active ones to improve upstream system performance. Using the approximated BER expression and defined design problems, two adaptive code allocation algorithms for the adaptive OCDMA-PON are presented and their performances are evaluated by simulation. Simulation results show that the adaptive code allocation algorithms can increase average transmission rate or decrease average transmitted optical power of optical network units for dynamic traffic patterns. According to the simulation results, for an adaptive OCDMA-PON with BER value of $10^{-7}$ and user activity probability of 0.5, transmission rate (transmitted optical power) can be increased (decreased) by a factor of 2.53 (0.25) compared to fixed code assignment.