Multi-User Detection for the Optical Code Division Multiple Access (OCDMA): Optical Parallel Interference Cancellation (OPIC)

Optical Code Division Multiple Access (OCDMA) has recently been proposed as an
alternative to frequency and time based multiple access methods for the next generation
high-speed optical fiber networks. This is because such system offers a large bandwidth.
Based on the vast amount of bandwidth available in optical line, OCDMA system has
received much attention in fiber optic Local Area Network (LAN) where the traffic is
typically bursty. However, Multiple Access Interference (MAl), which is originated from
other simultaneous users, severely limits the capacity of the system. In addition, the need
for dynamic threshold in the Conventional Correlation Receiver (CCR) is a very
demanding requirement particularly in the high speed LANs.
To overcome the stated problems, Optical Parallel Interference Cancellation is used
throughout this thesis. Optical Hard Limiter (OHL) has been placed at the front of the
OPIC receiver to reduce the effect of MAl and fixed threshold is used to overcome the
problem of dynamic threshold. The study carried out using theoretical and simulation.
The results reveal that, OPJC system is attractive technology for next generation optical
networks. The drawback of OPIC is the increases in the demand for hardware in each
receiver. As a result, it requires more complex hardware, higher processing time and cost.
To overcome these difficulties, an efficient method is proposed called, One Stage Optical
Parallel Interference Cancellation (OS-OPIC) which is based mainly on the OPIC.
Performance analysis of the proposed design is done using Optical Orthogonal Code
(OOC) as a signature sequence and a new expression for error probability is
demonstrated. It is shown that, the proposed method is effective to reduce the hardware
complexity, processing time and cost while maintaining the same BER at the cost of
increasing threshold value.