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Analysis and Improvement of Media Access Control in Optical CDMA Networks

Khazraei Sholayfar, Simin | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45871 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Pakravan, Mohammad Reza
  7. Abstract:
  8. The increasing demand for high speed communications has made the optical fiber a favorite choice for different networks ranging from Local Area Networks (LANs) to Wide Area Networks (WANs). In this research we focus on the analysis and design of improved optical communication techniques with a focus on LAN applications.Noting the advantages of Optical Code Division Multiple Access (OCDMA), we have selected this method as the base of data transmission. Different modulation schemes can be implemented in an OCDMA system. Among these, Pulse Position Modulation (PPM) schemes can improve the system performance. We have evaluated Overlapping PPM (OPPM) in an OCDMA system employing Generalized Optical Orthogonal Codes (GOOC), taking into account thermal noise and APD2 effect. We demonstrated that considering all these noise sources, generalized codes can support more users and provide higher spectral efficiency compared to strict optical orthogonal codes. Using the results, we derived a procedure for proper selection of system parameters in a system design process. Differential Pulse Position Modulation (DPPM) is a modulation scheme that can be used in an OCDMA system. Using analytical techniques and simulation procedures, we show that employing DPPM and GOOC can reduce the error probability and increase the throughput in comparison to OCDMA-PPM systems.In a multiple access systems where users randomly generate traffic, more intelligence can be used to increase the system performance. In an OCDMA system that uses intensity modulation and direct detection (IM/DD), Multiple Access Interference (MAI) is the main factor that causes reception errors. When a packet is received with un-recoverable error, it should be retransmitted and that can lead to an increase in network traffic, more interference and more errors for packets. We have considered the case of an OCDMA system that is using a slotted ALOHA mechanism to control the re-transmission of packets. We analyzed the key network performance indicators, including its throughput, delay and stability. The results show that using GOOC accompanied with OPPM improves system transient and stable characteristics. We have also considered the case of ALOHA where the time is not slotted and users transmit variable length packets at desired time. We have evaluated the system performance and introduced an algorithm which controls when users can access the channel. This algorithm considerably improves the system throughput and increases its stability
  9. Keywords:
  10. Optical Local Area Network (OLAN) ; Stability ; Optical Code Division Multiple Access (OCDMA) ; ALOHA Network ; Overlapping Pulse Position Modulation (OPPM) ; Unslotted Network ; Differential Pulse Position Modulation ; Slotted Network

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