A Novel Optical Code-Division-Multiple-Access Network Architecture with Spectral / Spatial Coding Scheme Using Partial Modified Prime Codes
Date Issued
2005
Date
2005
Author(s)
Niu, Chun-Tao
DOI
zh-TW
Abstract
Code-division-multiple-access ( CDMA ) plays an important role in communications technologies nowadays. Almost all the modern communications techniques apply the concept of CDMA. The CDMA technology in mobile communications field has already been well-developed. CDMA has advantages such as multiple access, anti-jamming, high-level security, asynchronous transmission, multi-path resistance, and multi-rate transmission. Nevertheless, the interference between users so-called the multiple-user interference ( MUI ) degenerates the system performance. The MUI increases when the number of simultaneous users grows. The influence of the MUI can be suppressed if the cross-correlations between users are low, and if the auto-correlation of each user is large. Thus, it is a significant issue to develop optical codes with these good properties.
The optical signal power is always non-negative. Therefore, there is more challenge to develop optical codes than electrical codes. Due to non-negative optical power, the cross-correlations between optical codewords are large compared with electrical codes. As a consequence, the MUI is more severe in optical CDMA ( OCDMA ) systems. In order to increase the maximum number of users under a specific performance, the cross-correlations between users have to be lowered. Therefore, the two-dimensional ( 2-D ) coding schemes attract a lot of attention. In recent years, two two-dimensional coding OCDMA schemes are developed to increase the maximum number of users: time / frequency and spectral / spatial coding scheme. A novel spectral-amplitude coding optical CDMA ( SAC-OCDMA ) network architecture using spectral / spatial coding scheme is proposed in this paper.
Multi-fiber OCDMA networks are attractive because fibers are cheap nowadays. The phase-induced intensity noise ( PIIN ) limits the performance of SAC-OCDMA systems. The influence of the PIIN does not disappear by simply increasing the power of optical signal when the power is large enough. Therefore, it is a main issue how to suppress the PIIN. It is known that the PIIN increases with the beating probability of the codewords of the OCDMA system. A new scheme which further suppresses the PIIN is proposed in this paper, and the system performance is thus increased. The beating probability of the optical codes is decreased due to the properties of the partial modified prime codes which is used in the system. Therefore, the PIIN is further suppressed in the proposed system. Because of the new optical network architecture and the suppressed PIIN, the power demand of the proposed system is low compared with other OCDMA systems. The proposed system operates well when the optical signal power is -10 dBm while other OCDMA systems operate well only when the power is above 0 dBm.
Subjects
光分碼多工
二維編碼
質數碼
OCDMA
coding
prime codes
Type
thesis
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