應用部分變異質數碼波長及空間二維編碼技術之光分碼多工系統

分碼多工在現在的通訊技術中佔有一個很重要的地位。分碼多工技術的好處在於其在同一個頻寬內可以有更多的使用者數、抗干擾能力、保密安全能力、非同步傳輸、以及抗多路徑衰降和多位元服務等等。在光通訊與其他通訊技術最大的不同點在於，光訊號有無負值的特性，而其他通訊領域訊號則是可有正或負值。因此，這個特性就會增加了在光領域做分碼多工的難度。這是因為光訊號無負值的關係，光分碼多工使用者之間的互相關函數就會相對地變大，這樣會增加使用者之間互相的干擾，也就是增加了多使用者干擾對系統的不良影響。但是若是要為了在一定的系統效能下增加使用者數，我們必須讓使用者之間的多工碼的互相關函數盡量降低。所以，光的二維編碼技術應運而生。近年來研發出了同時在波長上與時間上，以及在波長上與空間上展頻的光二維編碼，為的都是要增加使用者數。而本篇論文研究光在波長與空間二維編碼的系統架構。由於現在的光纖價格低廉，使用多條光纖的光分碼多工系統很有其研究價值。而頻率振幅調變之光分碼多工系統其相位引發強度雜訊為限制系統效能最主要的因素。此外，在傳輸能量增加到某一個程度以後，相位引發強度雜訊並不會隨著傳輸能量的增加而對系統的影響減小。所以如何抑制相位引發強度雜訊對系統的影響是研究光頻率振幅調變系統最主要的課題。若每一個使用者之間所使用的多工碼互相撞擊越多，則相位引發強度雜訊就越嚴重。本論文提出了一個新發法及網路結構，充分運用了多條光纖以及在波長上編碼的優點，以及應用了部份變異質數碼的特性，大大地降低了多工碼之間的撞擊機率抑制了相位引發強度雜訊。由於網路結構的不同與相位引發強度雜訊較弱的關係，也使得這個系統的功率需求較其他系統小很多。在光源功率在-15dBm的情況下，唯有我們的系統能夠正常運作；而其他的光發分碼多工系統則需要在0dBm的功率時才能正常運作。除此之外，我們使用的低成本的LED以及FBG的元件，並且傳送機以及接收機結構也較簡單；也就是說我們所提出的新架構有著低成本、高效能的優點。

關鍵字

光分碼多工；二維編碼；質數碼

並列摘要

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.

並列關鍵字

OCDMA ； coding ； prime codes

參考文獻

[1] F. R. K. Chung, J. A. Salehi, and V. K. Wei, “Optical orthogonal codes: design, analysis and applications,” IEEE Trans. Inform. Theory, vol. 35, no. 3, pp.595-604, May 1989.

[2] J. A. Salehi, “Code division multiple-access techniques in optical fiber networks. I. Fundamental principles,” IEEE Trans. Commum., vol. 37, no.8, pp. 824-833, Aug. 1989.

[3] J. A. Salehi, “Code division multiple-access techniques in optical fiber networks. II. System performance analysis,” IEEE Trans. Commun., vol. 37, no8, pp. 834-842, Aug. 1989.

[4] P. R. Prucnal, M. A. Santoro, and T. R. Fan, “Spread spectrum fiber-optic local area network using optical processing,” J. Lightwave Technol., Vol. LT-4, pp. 547-554, May 1986.

[5] W. C. Kwong, P. A. Perrier, and P. R. Prucnal, “Performance comparison of asynchronous and synchronous code-division multiple-access techniques for fiber-optic local area networks,” IEEE Trans. Comm., vol. 39, pp. 1625-1634, Nov. 1991.

國際替代計量

應用部分變異質數碼波長及空間二維編碼技術之光分碼多工系統

全文下載

主題瀏覽