Media access control for optical CDMA networks through interference avoidance

This work proposes Interference Avoidance, a contention media access control protocol for optical Code Division Multiple Access (CDMA) Local Area Networks (LANs). Optical CDMA is a direct sequence spread spectrum technology for multiplexing transmissions on an optical fiber. When used as the physical layer of a LAN, its throughput tends to zero at high offered load because of multiuser interference. Interference Avoidance prevents this throughput collapse of optical CDMA networks at high offered load.; An optical CDMA LAN exhibits two unique properties: non-mutually destructive interference and correlation of state. Interference Avoidance exploits these properties to reduce packet loss because of interference. It extends the Carrier Sensing mechanism to high speed, shared medium, optical networks. Interference Avoidance consists of state estimation and transmission scheduling. This work proposes algorithms for transmission scheduling and state estimation. The transmission scheduling algorithms stabilize the throughput at around 30% of the maximum at high offered load, under the assumption of perfect state estimation. Under identical conditions, throughput without transmission scheduling tends to zero. The algorithms achieve throughput within 10% of optimal codeword scheduling algorithms. The complexity of the algorithms is linear in codeset length, enabling low complexity hardware implementation. The performance of the state estimation algorithms approaches that of perfect state estimation as the codeset length increases and weight decreases, with a low number (< 100) of estimation samples. The complexity of the algorithms is linear in the number of estimation samples, allowing for low complexity hardware implementation. This work also demonstrates the feasibility of transmission scheduling using a laboratory testbed. Measurements from the testbed show that transmission scheduling reduces the bit error rate in the presence of severe physical layer noise and potentially improves throughput performance as load is increased.