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Asia Communications and Photonics Conference

A Novel Quasi-synchronous Coherent Time-Spreading Optical CDMA System

Jianhua Ji, Fangping Gong

Published Jan 1, 2009• 1 citation
Publisher

Abstract

We propose a novel quasi-synchronous coherent time-spreading optical CDMA, where the synchronization among users can be controlled within permissible time delay. Relationship between the system performance and code parameters is analyzed. Within permissible time delay, the mean intensity of aperiodic cross-correlation equals zero, and the beat noise can be removed.

DOI
10.1364/acp.2009.wl70

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We propose a novel quasi-synchronous coherent time-spreading optical CDMA, where the synchronization among users can be controlled within permissible time delay. Relationship between the system performance and code parameters is analyzed. Within permissible time delay, the mean intensity of aperiodic cross-correlation equals zero, and the beat noise can be removed.
We propose a novel quasi-synchronous coherent time-spreading optical CDMA (TS-OCDMA) system, where the synchronization among users can be controlled within permissible time delay. Relationship between the system performance and code parameters is analyzed. In quasi-synchronous coherent TS-OCDMA system, beat noise (BN) and multiple-access interference (MAI) are depend- ent on the mean intensity of aperiodic cross-correlation within permissible time delay. LA sequence is employed in this network, and code performance is analyzed. Within permissible time delay, the mean intensity of aperiodic cross-correlation equals zero, and hence the BN and MAI can be eliminated in quasi-synchronous coherent TS- OCDMA system. When the time delay is out of zero correlation zone, crosstalk value of LA sequence is less than that of Gold sequence. Therefore, quasi-synchronous coherent TS-OCDMA using LA sequence is beneficial in a low-user-load OCDMA network.
The performance of WDM-based coherent time-spreading OCDMA system is studied. Upper bound and lower bound of normalized throughput are obtained with 8 wavelength channels and 127 length and 511 length Gold codes. It is shown that when all simultaneous users are equally allocated to different wavelength channels, WDM+ TS OCDMA has much better performance. However, if there is no central control to allocate wavelength channels equally, WDM+ TS OCDMA system has the in-between performance of normalized throughput.
The performance of coherent time-spreading (TS) and asynchronous TS phase coding optical code division multiple access (OCDMA) systems is investigated and analyzed. Particular consideration is given however to both beat noise (BN) and multiple-access interference (MAI) effects, and the impact of decision threshold on the bit-error-rate (BER) performance is evaluated. Improvement of the BER performance can be obtained by use of optimum threshold detection, and the improvement is more apparent in the asynchronous TS OCDMA scheme for a low number of simultaneous users with long code length.