眾所皆知，正交多重接取包含了分頻多工接取(FDMA)、分時多工接取(TDMA)與分碼多工接取(CDMA)，而其中的正交分頻多工接取(OFDMA)是目前行動通訊系統主要採用的多工技術，然而，隨著行動網路的快速發展推動了數據流量的巨量增長，因此，頻譜效率成為了處理爆炸性數據流量的關鍵挑戰之一，近幾年來，非正交多重接取(NOMA)被認為是一個具有前景的技術並且可能會被下一代的多重接取技術採用，但是在NOMA中為了區分不同的用戶，用戶之間必須維持著特定的功率比，這個條件可能在某些通道條件下難以達到，例如在5G毫米波的小型基地台中由一個遠端無線電站(RRH)服務的用戶會具有不同的通道條件，這將會導致用戶間無法達到接收端需求的功率比，因此，我們提出了使用索引調變(Index-modulation, IM)整合NOMA的版本(NOMA-IM)，相較於NOMA，利用索引調變特性的NOMA-IM可以提供更多具有彈性的功率比。
在這篇論文中，一個新穎的NOMA-IM系統在有著光載射頻前傳的毫米波多用戶無線電接取系統中進行實驗展示，並在接收端中使用連續干擾消除法(SIC)用於區分不同用戶，實驗結果顯示了以適合功率域多工的功率比範圍而言， NOMA-IM可以比傳統的NOMA提供更多的彈性以及增加頻譜效益，此外，NOMA-IM還可以透過調整索引調變的參數來減輕用戶之間的干擾。

It is well known that Orthogonal multiple access (OMA) include frequency-division multiple access (FDMA), time-division multiple access (TDMA), code-division multiple access (CDMA) and orthogonal frequency division multiple access (OFDMA) has been the major multiple access technology adopted by the current system of mobile communication. However, the fast growth of mobile internet has propelled data traffic massive increase, hence, the spectral efficiency becomes one of the key challenges to handle such explosive data traffic. In recent years, non-orthogonal multiple access (NOMA) has been considered as a promising technique and it may be adopted by next generation multiple access technique, but in order to distinguish different users in NOMA, a certain power ratio between users need to be maintained, this condition may be difficult to achieve in some channel condition, for example, users served by one remote radio unit (RRU) in a 5G millimeter wave small cell can have different channel conditions and it will cause user could not achieve the power ratio which receiver require, thus, We propose to use the index modulation combine non-orthogonal multiple access (NOMA-IM) scheme, compare to NOMA, NOMA-IM can provide more flexible power ratio which take advantage of the characteristics of index modulation.
In this paper, a novel NOMA-IM system is experimentally demonstrated in a multi-users millimeter wave radio access system with radio-over-fiber (RoF) fronthaul, and successive interference cancellation (SIC) is implemented in receiver to separate different user. Experimental results show that in terms of appropriate power ratio range for power domain multiple access, NOMA-IM can provide more flexibility and enhance spectral efficiency than conventional NOMA, furthermore, NOMA-IM has the ability to mitigate the interference between users by adjust index-modulation parameters.

[1] B. Anass, "An overview of non-orthogonal multiple access", ZTE Commun., vol. 15, no. s1, pp. 1-30, Jun. 2017.”
[2] S. Shen, Y. Chen, Q. Zhou and G. Chang, "Demonstration of Pattern Division Multiple Access with Message Passing Algorithm in MMW-RoF Systems," 2020 Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA, 2020, pp. 1-3.
[3] Y. Tian, K. Lee, C. Lim and A. Nirmalathas, "Demonstration of Non-Orthogonal Multiple Access Scheme using Multilevel Coding without Successive Interference Cancellation with 60 GHz Radio-over-Fiber Fronthaul," 2018 Optical Fiber Communications Conference and Exposition (OFC), San Diego, CA, 2018, pp. 1-3.
[4] C. Lim, Y. Tian, A. Nirmalathas and K. Lee, "Advanced Techniques for 60 GHz Fronthaul Links," 2019 Asia Communications and Photonics Conference (ACP), Chengdu, China, 2019, pp. 1-3.
[5] Y. Chen et al., "Toward the Standardization of Non-Orthogonal Multiple Access for Next Generation Wireless Networks," in IEEE Communications Magazine, vol. 56, no. 3, pp. 19-27, March 2018, doi: 10.1109/MCOM.2018.1700845.
[6] Javier Campos, "Understanding the 5G NR Physical Layer", Keysight Technologies release, November 2017.
[7] K. Higuchi and A. Benjebbour, “Non-orthogonal multiple access (NOMA) with successive interference cancellation for future radio access,” IEICE Trans. Commun., vol. E98-B, no. 3, pp. 403–414, Mar. 2015.
[8] J. Zyren and W. McCoy. Overview of the 3GPP Long Term Evolution Physical Layer, Online available, July 2007.
[9] T. Tang, X. Zou, P. Li, W. Pan, B. Luo and L. Yan, "Proposal and Demonstration of Subcarrier Index Modulation OFDM for RoF System With Enhanced Spectral Efficiency," in Journal of Lightwave Technology, vol. 36, no. 19, pp. 4501-4506, Oct.1, 2018, doi: 10.1109/JLT.2018.2829746.
[10] E. Basar, "Index modulation techniques for 5G wireless networks," in IEEE Communications Magazine, vol. 54, no. 7, pp. 168-175, July 2016, doi: 10.1109/MCOM.2016.7509396.

[11] E. Basar, M. Wen, R. Mesleh, M. Di Renzo, Y. Xiao and H. Haas, "Index Modulation Techniques for Next-Generation Wireless Networks," in IEEE Access, vol. 5, pp. 16693-16746, 2017, doi: 10.1109/ACCESS.2017.2737528.
[12] E. Başar, Ü. Aygölü, E. Panayırcı and H. V. Poor, "Orthogonal Frequency Division Multiplexing With Index Modulation," in IEEE Transactions on Signal Processing, vol. 61, no. 22, pp. 5536-5549, Nov.15, 2013, doi: 10.1109/TSP.2013.2279771.
[13] Defense Innovation Board, "The 5G Ecosystem: Risks & Opportunities for DoD", April 2019.
[14] C. Lim, A. Nirmalathas, Yizhuo Yang, D. Novak and R. Waterhouse, "Radio-over-fiber systems," 2009 Asia Communications and Photonics conference and Exhibition (ACP), Shanghai, 2009, pp. 1-10.
[15] C. Lim et al., "Fiber-Wireless Networks and Subsystem Technologies," in Journal of Lightwave Technology, vol. 28, no. 4, pp. 390-405, Feb.15, 2010, doi: 10.1109/JLT.2009.2031423.
[16] A. J. J. O. E. Lowery, "Amplified-spontaneous noise limit of optical OFDM lightwave systems," vol. 16, no. 2, pp. 860-865, 2008.
[17] S. Coleri, M. Ergen, A. Puri and A. Bahai, "Channel estimation techniques based on pilot arrangement in OFDM systems," in IEEE Transactions on Broadcasting, vol. 48, no. 3, pp. 223-229, Sept. 2002, doi: 10.1109/TBC.2002.804034.
[18] C. Lim, Y. Yang, and A. Nirmalathas, "Transport schemes for fiber-wireless technology: Transmission performance and energy efficiency," in Photonics, 2014, vol. 1, no. 2, pp. 67-82: Multidisciplinary Digital Publishing Institute.
[19] B. Anass, "IMT-2020 Radio Interface Standardization Trends in ITU-R", NTT DOCOMO Technical Journal., vol. 19, no. 3, pp. 55-63, Jan. 2018.”
[20] Dahmen-Lhuissier, S. (n.d.). Mobile Technologies - 5g, 5g Specs: Future Technology. Retrieved from https://www.etsi.org/technologies/5g
[21] 3GPP TSG RAN WG1, R1-1804576, Sanya, China, April 16th – 20th, 2018