Design and Analysis of Asynchronous Incoherent Optical-CDMA Systems Using a New Code-Shifting Technique

Abstract

In this paper, a novel code-shifting technique, which can be added atop asynchronous incoherent optical code-division multiple-access systems without complex modifications, is proposed and studied. The new technique divides the time-slot (or chips), in which the optical pulses of codewords are located, into g equal-width sub-chips; every pulse is randomly and independently shifted to start at one of the g sub-chips of its own chip, where g > 1 is a positive integer. The effects of this random g-shift to the cross-correlation property and performance of asynchronous optical codes (of periodic crosscorrelation functions of at most one) are formulated. Although it is found that the periodic cross-correlation functions are worsened to 3 − 2/g, our theoretical and computer-simulation results show an unconventional finding that code performance improves as g increases.

New Tree-Structured Optical Codes for Incoherent Optical-CDMA Applications

“…Beyond the scope of this paper, it is important to point out that impairments in optical fiber, such as chromatic dispersion and temperature fluctuation, can cause deleterious effects to optical codes [29]- [31]. As studied by Osadola, et al [30], the temperature fluctuation in optical fiber causes time skew and width narrowing in the pulses of the codewords and then reduces the autocorrelation peaks.…”

“…Thus, an in-depth study of the effect of chromatic-dispersion to 2-D optical codes should be conducted. For example, it was found in [31] that optical codes could have improved performance, under the effect of random time skew to the pulses of the codewords (e.g., caused by temperature fluctuation [30]), when there existed a feedback mechanism at the decoder tracking the autocorrelation peaks. Because temperature fluctuation and chromatic dispersion have the similar effect of causing time skew in optical pulses, the finding in [31] may give an insight and be helpful in developing a mitigation approach toward the effect of chromatic dispersion to 2-D optical codes after further research.…”

Performance Enhancement of Optical PPM-CDMA Using Successive Interference Cancellation Scheme

“…Optical CDMA system has attracted much attention during the last decade and it is considered as the most promising candidate for the high-speed optical networks, the next generation of PON access networks [1]- [3]; optical CDMA has been implemented and examined in the asynchronous and communications [4]- [5].…”

Analysis and Design of Adaptive OCDMA Passive Optical Networks

“…OCDMA has some advantages over other multi-access methods such as simple and asynchronous operation, high resource utilization and capability of providing differentiated classes of Quality of Service (QoS) for different users. The performance of OCDMA networks is mainly limited by Multi-Access Interference (MAI) from other users [1]- [5]. There are research results that have combined the concepts of Orthogonal Frequency Division Multiple-Access (OFDMA) and OCDMA (known as Multi-Carrier OCDMA) [3], [6] or Wavelength Division Mohammad Hadi is a PhD student at department of Electrical Engineering, Sharif University of Technology, e-mail: mhadi@ee.sharif.edu.…”