在近幾年來，無線接取技術的快速成長成了在現今擁擠的無線頻譜中的一大負擔，隨著逐漸增加的基地台(BS)數量，根據光纖的系統架構來提供控制台(CO)與基地台的寬頻接取技術是必須的。這導致結合了光纖與無線技術的產生，這項將無線訊號(RF)調變在光纖上被認知為光載無線系統(RoF)。而光分碼多工系統(OCDMA)被認為是在光載無線系統中較佳的調變方法，這是因為它可以有效提供多重使用者在網路中可非同步傳輸且不用排序。
在這篇論文中，我們提出了一項新穎的光載無線系統，它結合了波長重用技術並利用寬頻光源(BLS)來傳送相位鍵移訊號(BPSK)。為了降低系統的複雜度，我們將來自控制台的下載訊號一部分波長給基地台重新使用來當作上傳訊號，藉著這樣的做法，在基地台架設額外的光源是可以避免的。此外，我們在系統中還採用了效能控制架構來支持在提出的光載無線系統中的差異性服務。為了檢查提出的系統可行度，我們在理論和模擬中分析系統的熱雜訊和相位引發強度雜訊(PIIN)，下載和上傳訊號的位元錯誤率我們也加以驗證。多項的結果顯示出藉著效能控制架構下，我們可以為個別的使用者提供不同錯誤率這項具有區別性的差異性服務。

In recent years, the rapid growth of wireless access technology places a heavy burden on the already congested wireless spectrum. With the throughput of base station (BS) increases gradually, the construction based on optical fiber is required to provide broadband interconnections between the RBSs and central office (CO). This leads to the integration of the optical and wireless broadband infrastructures. The technique of modulating radio frequency (RF) signals onto an optical carrier is known as radio on fiber (RoF). And optical code-division multiple-access (OCDMA) is one of the multiplexing methods for RoF because it provide multiple users to access the network asynchronously without scheduling.
In this study, we propose a novel RoF system consisting of the wavelength reuse technique [7] with a broadband light source (BLS) to convey binary phase shift keying (BPSK) signals. To reduce system complexity, a part of wavelengths for downstream signals from CO is reused by BSs for upstream ones, so that the requirement for a high-quality optical source at BS is avoided. Besides, a simple power control scheme is adopted to support differentiated service in the proposed RoF system. To investigate the feasibility of the proposed system, we analyze the effects of thermal noise and phase-induced intensity noise (PIIN) through theory and simulation. BER performance of downlink and uplink are both demonstrated. The results prove that the differentiated BER achieved by the proposed power control scheme provides distinguish differentiated service provision for individual users.

[1] S. Komaki, K. Tsukamoto, M. Okada, and H. Harada, “Proposal of radio highway networks for future multimedia-personal wireless communications,” in Proc. ICPWC’94, pp. 204–208, Aug. 1994.
[2] T. S. Chu and M. G. Gans, “Fiber optic microcellular radio," IEEE Trans. Veh. Technol., vol. 40, pp. 599–606, 1991.
[3] C. Lim, A. Nirmalathas, M. Bakaul, P. Gamage, K.-L. Lee, Y. Yang, D. Novak, and R. Waterhouse, “Fiber-wireless networks and subsystem technologies,” J. Lightwav Technol., vol. 28, no. 4, pp. 390–405, Feb. 2010.
[4] A. Nirmalathas, D. Novak, and C. Lim, “Wavelength reuse in the WDM optical interface of a millimeter-wave fiber-wireless antennabase station,” IEEE Trans. Microw. Theory Tech., vol. 49, no. 10, pp. 2006–2012, Oct. 2001.
[5] L. Chen, Y. Shao, X. Lei, H. Wen, and S. Wen, "A Novel Radio-Over-Fiber System With Wavelength Reuse for Upstream Data Connection," IEEE Photon. Technol. Lett, vol. 19, no. 6, pp.387-389, Mar. 2007.
[6] A. Nirmalathas, D. Novak, and C. Lim, "Wavelength reuse in the WDM optical interface of a millimeter-wave fiber-wireless antenna base station," IEEE Trans. Microw. Theory Tech., vol. 49, no. 10, pp. 2006–2012, Oct. 2001.
[7] Z. Jia, J. Yu, and G.-K. Chang, “A full-duplex radio-over-fiber system based on optical carrier suppression and reuse,” IEEE Photon. Technol. Lett., vol. 18, no. 16, pp. 1726–1728, Aug. 15, 2006.
[8] J. Yu, Z. Jia, T. Wang, and G.-K. Chang, “A novel radio-over-fiber configuration using optical phase modulator to generate an optical mmwave and centralized lightwave for uplink connection,” IEEE Photon. Technol. Lett., vol. 19, no. 3, pp. 140–142, Feb. 1, 2007.
[9] P.T. Shih, C.T. Lin, W.J. Jiang, Y.H. Chen, J. Chen, and S. Chi, “Full duplex 60-GHz RoF link employing tandem single sideband modulation scheme and high spectral efficiency modulation format,” Opt. Express, vol. 17, no. 22, pp. 19501–19508, 2009.
[10] X. Yu, T. B. Gibbon, and I. T. Monroy, “Bidirectional radio-over-fiber system with phase-modulation downlink and RF oscillator-free uplink using a reflective SOA,” IEEE Photon. Technol. Lett., vol. 20, no. 24, pp. 2180–2182, Dec. 15, 2008.
[11] G. Puerto, J. Mora, B. Ortega, and J. Capmany, “Wavelength data rewriter for centralized-source radio-over-fiber access networks,” IEEE Photon. Technol. Lett., vol. 22, no. 15, pp. 1102–1104, Aug. 1, 2010.
[12] H.C. Ji, H. Kim, and Y. C. Chung, “Full-duplex radio-over-fiber system using phase-modulated downlink and intensity-modulated uplink,” IEEE Photon. Technol. Lett., vol. 21, no. 1, pp. 9–11, Jan. 1, 2009.
[13] R. Scholtz, “The spread spectrum concept,” IEEE Transactions on Communications, vol. 25, no. 8, pp. 748-755, August 1977.
[14] J. Y. Hui, “Pattern Code Modulation and Optical Decoding — A Novel Code-Division Multiplexing Technique for Multifiber Network,” IEEE J. Select. Area Commun., vol. SAC-3, no. 6, pp. 916–27, Nov. 1985.
[15] J. A. Salehi, “Code division multiple-access techniques in optical fiber networks—Part II: Systems performance analysis,” IEEE Trans. Commun., vol. 37, no. 8, pp. 834–842, Aug. 1989.
[16] D. Zaccarin and M. Kavehrad, "An optical CDMA system based on spectral encoding of LED," IEEE Photon. Technol. Lett., vol. 5, pp. 479-482, 1993.
[17] X. Zhou, H. M. H. Shalaby, C. Lu, and T. Cheng, “Code for spectral amplitude coding optical CDMA systems,” Electron. Lett., vol. 36, pp. 728–729, Apr. 13, 2000.
[18] S. Kajiya, K. Tsukamoto, and S. Komaki, “Proposal of fiber-optic radio highway networks using CDMA method,” IEICE Trans. Electron., vol. E79-C, no. 1, pp. 111–117, Jan. 1996.
[19] K. Tsukamoto, T. Higashino, T. Nakanishi, and S. Komaki, “Direct optical switching code-division multiple-access system for fiber-optic radio highway networks,” J. Lightwave Technol., vol. 21, no. 12, pp. 3209-3220, Dec. 2003.
[20] B. K. Kim, S. Park, Y. Yeon, and B. W. Kim, “Radio-over-fiber system using fiber-grating-based optical CDMA with modified PN codes,” IEEE Photon. Technol. Letter, vol. 15, no. 10, pp. 1485–1487, Oct. 2003.
[21] C.C. Yang; J.F. Huang; H.H. Chang, and K.S. Chen, "Radio Transmissions over Residue-Stuffed-QC-Coded Optical CDMA Network," IEEE Communications Letters., vol.18, no.2, pp.329-331, February 2014.
[22] L.S. Chen; G.C. Yang; C.Y. Chang, and W.C. Kwong, "Study of Power Control on Double-Weight Codes With an Arbitrary Maximum Cross-Correlation Value in Variable-QoS Optical CDMA," Lightwave Technology, Journal of , vol.29, no.21, pp.3293-3303, Nov.1, 2011.
[23] S. Khaleghi, M.R. Pakravan, and H. Goudarzi, "Providing multiclass of services in optical CDMA packet networks," Internet, 2008. ICI 2008. 4th IEEE/IFIP International Conference on , vol., no., pp.1,6, 23-25 Sept. 2008.
[24] Z. Quanyan and L. Pavel, "Enabling differentiated services using generalized power control model in optical networks," IEEE Trans. Commun., vol. 57, no. 9, pp. 2570-2575, Sep. 2009.
[25] C.C. Yang, J.F Huang, and T.C. Hsu, "Differentiated Service Provision in Optical CDMA Network Using Power Control," IEEE Photon. Technol. Lett., vol.20, no. 20, pp. 1664-1666, Oct. 2008.
[26] K. O. Hill and G. Meltz, “Fiber Bragg grating technology fundamentals and overview,” J. Lightwave Technol., vol. 15, pp. 1263–1276, Aug. 1997.
[27] D. K. W. Lam, and B. K. Garside, “Characterization of single-mode optical fiber filters,” Applied Optics, vol. 20, pp. 440-445, 1981.
[28] E.D.J. Smith, R.J. Blaikie, and D.P. Taylor, “Performance enhancement of spectral-amplitude-coding optical CDMA using pulse-position modulation,” IEEE Transactions on Communications, vol. 46, pp. 1176-1185, Sept. 1998.
[29] Z. Wei, H. M. H. Shalaby, and H. Ghafouri-Shiraz, “Modified quadratic congruence codes for fiber bragg grating based spectral-amplitude-coding optical CDMA systems,” J. Lightwave Technol., vol. 19, no. 9, pp. 1274-1281, September 2001.
[30] W. Huang, M. Nakagawa, Nonlinear effect of direct-sequence CDMA in optical transmission, IEICE Trans. Commun. E78-B (5) (1995) 702–708.
[31] J.F. Huang, C.T. Yen, and T.Y. Li, ‘Nonlinearity effect of electro-optical modulator response in double spread CDMA radio-over-fiber transmissions’, Opt. Fiber Technol., 2008, 14, (3), pp. 247–258.