Interference Avoidance Using Uneven Intensity Spreading Scheme for OCDMA

We propose an interference avoidance architecture using uneven spreading as a media access mechanism for optical code division multiple access (OCDMA). While an equal-intensity pulse sequence encoded with the spreading sequence assigned to each node is transmitted for a "1\´\´ bit in conventional OCDMAs with on-off keying (OOK), in our proposed architecture an uneven-intensity pulse sequence is done where one of the pulses has higher intensity than the others. The high-intensity pulse allows source nodes to sense the channel more precisely before their transmissions to schedule their transmissions to avoid interference. Our receiver with a hard limiter (HL) allows destination nodes to receive the transmission without bit collision. Interference avoidance performance is examined by deriving the bit collision probability and comparing it with the one of the conventional OCDMA with interference avoidance. Our numerical results show that our architecture has lower bit collision probability than the conventional architecture with equal-intensity spreading, and that it offers higher throughput, higher bit rate, and more nodes than the conventional one for a fixed bit collision probability.