Interference Avoidance Using Uneven Intensity Spreading Scheme for OCDMA

Shoichiro MATSUMOTO  Koji KAMAKURA  

Publication
IEICE TRANSACTIONS on Communications   Vol.E95-B   No.11   pp.3445-3455
Publication Date: 2012/11/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E95.B.3445
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Optical Fiber for Communications
Keyword: 
optical CDMA,  collision avoidance,  multiple access interference (MAI),  optical fiber communication,  optical orthogonal code,  

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Summary: 
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 OCDMA with on-off keying (OOK), the proposed architecture creates an uneven-intensity pulse sequence where one of the pulses has higher intensity than the others. The high-intensity pulse allows source nodes to use increased sensing threshold for channel sensing, which leads to an increase in the number of chip offsets available for collision-free transmission. Our receiver with a hard limiter (HL) allows destination nodes to receive the transmission without false positives. Interference avoidance performance is examined by deriving the collision probability and comparing it with the conventional interference avoidance with equal-intensity spreading. Our numerical results show that our architecture has lower collision probability, shorter time required for channel sensing, higher throughput, higher bit rate, and supports more nodes than the conventional one for a fixed collision probability.