A novel method for increasing the spectral efficiency of optical CDMA

Chang

et al. 2013

J. Lightwave Technol.

中華民國一百零一年七月 I II 致謝來到中興大學電機所碩士班兩年，很高興完成這份碩士論文，首先非常感謝指導教授楊谷章博士的諄諄教誨，不管是在專業領域以及論文撰寫方面都給予相當豐富的指導。讓我在通訊領域以及其他相關方面的知識得以有重大的進步，也跟楊老師學習到更有效率的研究方法和精神，老師對於研究的專注和執著深深讓我感受到想要有所作為，就應該付出這樣的態度。其次感林茂昭教授、趙啟超教授和張敏寬教授對於論文初稿上的建議和指導和口試時所提供寶貴的意見，可以使得本論文的內容和結構上更加的完善最後我想感謝這兩年碩士班所認識的同學和朋友們，使我個人不管是在專業領域或是心智方面甚至是解決問題的能力都有非常卓越的成長，在此感謝實驗室的學長呈源、同學彥峰、峻丞、孝鑫、還有很多的好朋友、學弟妹以及在背後支持我的父母親友們，讓我可以順利的從研究所畢業取得碩士學位。 III 摘要在最新提出的光纖多樣性分碼多工系統，為以達到更好的傳送品質，每一個使用者的每個訊號都傳送多次相同的拷貝，且每個碼在傳送前使用不同的平移，以達到每個拷貝之間的獨立性。但是由於在短碼長且位元同步的情況下，難以僅使用不同位移而達到獨立性，故在這篇論文，我們將結合位元非同步和拷貝之間的獨立性這種更接近現實生活中的情況去分析光纖多樣性分碼多工系統並且推導出一個廣義的公式，更精準的模型。最後，我們將介紹不同的位移顆粒度，用以改善傳送品質與拷貝之間的相關系。 IV AbstractIn our recently proposed diversity O-CDMA scheme, every simultaneous user transmitted multiple copies of an optical code per data bit of one in order to achieve good code performance. To maintain performance, our analysis showed that copy independency wasessential, which was achieved by time-shifting these copies to different chip (or time-slot) positions per bit duration. However, complete copy independency is hard to achieve under the conventional chip-synchronous assumption, especially in short code length. In this paper, we combine the realistic effects of chip asynchronism and copy dependency in the analysis of such diversity O-CDMA systems and formulate a new, generalized, and more accurate performance model.

Section: Introductionmentioning

confidence: 99%

Design and Analysis of Generalized Diversity Optical CDMA Systems

Chang

et al. 2013

J. Lightwave Technol.

“…Furthermore, as practical incoherent O-CDMA systems should be operated in a MAI-limited (i.e., best case) scenario [28], the effects of physical noises and beat noise are neglected in this section in order to have a true performance comparison with and without the proposed code-shifting technique. Thus, there is no decision error in receiving a data bit 1 in the OOK incoherent O-CDMA system because an autocorrelation peak exists on top of MAI.…”

Section: New Performance Analytical Modelmentioning

confidence: 99%

“…On the other hand, "incoherent" O-CDMA systems use "asynchronous" "unipolar" optical codes with nonzero "periodic" cross-correlation value of one or two in order to minimize the MAI [7], [10], [17]- [25]. In general, coherent O-CDMA supports higher spectral efficiency but is more sensitive to beat noise and physical impairments than incoherent O-CDMA [6], [14], [26]- [28]. As there exist rich collections of asynchronous unipolar optical codes, incoherent O-CDMA is more flexible in the choices of optical codes and code parameters, and potentially supports a variety of applications, such as optical-wireless, avionics communications, and multirate, multi-QoS, multimedia services [5], [10]- [12], [19], [22], [28]- [32].…”

mentioning

confidence: 99%

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

Lin

Chang

et al. 2015

IEEE Trans. Commun.

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.

“…No perfect decoding, code independency, the specific kind of all-optical thresholders in use, or physical-layer modeling is assumed. Functioning in a different principle from SPE-OCDMA, incoherent O-CDMA is best to operate in a MAI-limited environment [24]. Thus, this paper focus on the effect of fiber temperature fluctuations to the code properties.…”

mentioning

confidence: 99%

Pulse-Power-Detection Analysis of Incoherent O-CDMA Systems Under the Influence of Fiber Temperature Fluctuations

Tsai

Lin

et al. 2017

J. Lightwave Technol.

In this paper, a pulse-shift technique, which divides every time slot (or chip) into equal-width sub-chips, is used to model the effect of fiber temperature fluctuations in incoherent (asynchronous) optical code-division multiple-access (O-CDMA) systems. With the advances in all-optical thresholding technology, power detection of ultrashort optical pulses is possible. This paper also formulates a new pulse-power-detection model for incoherent O-CDMA and applies it to the analysis of the pulseshift technique. Numerical studies and computer simulations are presented to validate the new analytical model. Our study shows that the pulse-power model results in better performance than the conventional pulse-energy model in incoherent O-CDMA. Index Terms-optical code division multiple access, optical fiber communications, temperature fluctuation, time skew I. INTRODUCTION O PTICAL code-division multiple access (O-CDMA) has recently attracted interests in high-speed fiber-optic systems and networks because it carries desirable characteristics, such as dynamic bandwidth assignment, efficient in bursty traffic, soft limit in the number of subscribers, and gradual performance degradation as a function of the number of simultaneous users [1]-[9]. With the advances in technology, multiuser experimental testbeds operating at 10 Gbit/s have been demonstrated [10]-[12]. The choice of suitable optical codes is important in the design of incoherent (or directdetection) O-CDMA systems because the codes affect spectral efficiency, capacity, and the amount of multiple-access interference (MAI), which, in turn, determines system performance.