在本篇論文中，我們對於非正交多重接取下行系統之功率分配與使用者選擇進行探討，此系統中包含一個單一天線的基地台（Base Station）作為訊號源，並有N個單一天線的使用者在其服務範圍之中。在考慮總系統功率、各別使用者的傳輸率需求（Quality-of-Service）以及連續干擾消除（SIC）效能三項限制下，我們針對系統傳送容量最大化之最佳化問題為目標函數，在使用者數量為任意的情形下，得出最佳功率分配之閉合形式解，並透過此功率分配法發展使用者選擇演算法。透過使用者間訊雜比（SNR）的分析，我們提出一個有效降低搜尋複雜度之演算法，同時保障連續干擾消除以及解調訊號的能力，找出每次傳輸單一群組所能支持之最大用戶數量。另外，對於所提出之單天線最佳功率分配及使用者選擇方法，也可透過轉換有效的應用於多天線系統當中。我們將此方法與傳統的正交多重接取系統作比較，模擬結果顯示所提出之功率分配與使用者選擇演算法可以明顯地穩定系統效能，並大幅提升系統的傳輸容量。

In this thesis, we consider power allocation and user selection for a downlink non-orthogonal multiple access (NOMA) system with a base station and N users in the cell. A sum-capacity maximization problem for the single-input, single-output (SISO) case is formulated in terms of power allocation among an arbitrary number of users under a total power constraint and a quality-of-service condition that the minimum rate requirement of each user is satisfied. A closed-form power allocation solution to the problem is derived and then used to develop a user selection method to maximize the number of users in a cluster for NOMA transmission subject to a detection performance requirement with guaranteed successive interference cancellation and a minimum transmit signal-to-noise ratio. Using full search for the optimization of user clustering among N users is complicated, so we sort all users according to their channel gains in descending order and determine the optimal number of NOMA users iteratively to reduce the complexity. At each iteration, all the users are partitioned into several groups and the leading user of each group is clustered for NOMA transmission. The combined user selection and power allocation method for the SISO case can be extended to a multiple-input multiple-output scenario. Computer simulation results demonstrate the effectiveness of the proposed scheme.

Abstract i
Contents ii
List of Figures iii
I. Introduction 1
II. System Model 5
III. Proposed Power Allocation Method 7
A. Problem Formulation 7
B. Proposed Power Allocation 8
IV. Detection-Performance Guaranteed User Selection 11
V. Simulation Results 17
VI. Conclusion 23
Appendix. Proof of the Power Allocation Formulas 24
References 26

[1] Q. C. Li, H. Niu, A. T. Papathanassiou, and G. Wu, “5G network capacity: Key elements and technologies,” IEEE Veh. Technol. Mag., vol. 9, no. 1, pp. 71–78, Mar. 2014.
[2] J. G. Andrews, S. Buzzi, W. Choi, S. V. Hanly, A. Lozano, A. C. K. Soong, and J. C. Zhang, “What will 5G be?,” IEEE J. Sel. Areas Commun., vol. 32, no. 6, pp. 1065–1082, Jun. 2014.
[3] A. Gupta and R. K. Jha, “A survey of 5G network: Architecture and emerging technologies,” IEEE Access, vol. 3, pp. 1206–1232, Jul. 2015.
[4] S. M. R. Islam, N. Avazov, O. A. Dobre, and K. s. Kwak, “Power-domain non-orthogonal multiple access (NOMA) in 5G systems: Potentials and challenges,” IEEE Commun. Surveys Tuts, vol. 19, no. 2, pp. 721–742, 2nd Quart. 2017.
[5] L. Dai, B. Wang, Y. Yuan, S. Han, C.-L. I, and Z. Wang, “Non-orthogonal multiple access for 5G: Solutions, challenges, opportunities, and future research trends,” IEEE Commun. Mag., vol. 53, no. 9, pp. 74–81, Sep. 2015.
[6] Z. Ding Y. Liu, J. Choi, Q. Sun, M. Elkashlan, C.-L. I, and H. V. Poor, “Application of non-orthogonal multiple access in LTE and 5G networks,” IEEE Commun. Mag., vol. 55, no. 2, pp. 185–191, Feb. 2017.
[7] P. Wang, J. Xiao, and L. Ping, “Comparison of orthogonal and non-orthogonal approaches to future wireless cellular systems,” IEEE Veh. Technol. Mag., vol. 1, no. 3, pp. 4–11, Sep. 2006.
[8] Y. Saito, A. Benjebbour, Y. Kishiyama, and T. Nakamura, “System-level performance evaluation of downlink non-orthogonal multiple access (NOMA),” in Proc. IEEE PIMRC, London, U.K., Sep. 2013, pp. 611–615.
[9] Z. Ding, Z. Yang, P. Fan, and H. V. Poor, “On the performance of non-orthogonal multiple access in 5G systems with randomly deployed users,” IEEE Signal Process. Lett., vol. 21, no. 12, pp. 1501–1505, Dec. 2014.
[10] A. Benjebbour, Y. Saito, Y. Kishiyama, A. Li, A. Harada, and T. Nakamura, “Concept and practical considerations of non-orthogonal multiple access (NOMA) for future radio access,” in Proc. IEEE ISPACS, Okinawa, Japan, Nov. 2013, pp. 770–774.
[11] Q. Sun, S. Han, C.-L. I, and Z. Pan, “On the ergodic capacity of MIMO NOMA systems,” IEEE Wireless Commun. Lett., vol. 4, no. 4, pp. 405–408, Aug. 2015.
[12] C.-L. Wang, J.-Y. Chen, and Y.-J. Chen, “Power allocation for a downlink non-orthogonal multiple access system,” IEEE Wireless Commun. Lett., vol. 5, no 5, pp. 532–535, Aug. 2016.
[13] Z. Q. Al-Abbasi, D. K. C. So, and J. Tang, “Energy efficient resource allocation in downlink non-orthogonal multiple access (NOMA) system,” in Proc. IEEE VTC-Spring, Sydney, NSW, Australia, Jun. 2017, pp. 1–5.
[14] Z. Ding, P. Fan, and H. V. Poor, “Impact of user pairing on 5G nonorthogonal multiple-access downlink transmissions,” IEEE Trans. Veh. Technol., vol. 65, no. 8, pp. 6010–6023, Aug. 2016.
[15] L. Shi, B. Li, and H. Chen, “Pairing and power allocation for downlink nonorthogonal multiple access systems,” IEEE Trans. Veh. Technol., vol. 66, no. 11, pp. 10084–10091, Nov. 2017.
[16] M. S. Ali, H. Tabassum, and E. Hossain, “Dynamic user clustering and power allocation for uplink and downlink non-orthogonal multiple access (NOMA) systems,” IEEE Access, vol. 4, pp. 6325–6343, Aug. 2016.
[17] A. Sayed-Ahmed and M. Elsabrouty, “User selection and power allocation for guaranteed SIC detection in downlink beamforming non-orthogonal multiple access,” in Proc. IEEE Wireless Days, Porto, Portugal, Mar. 2017, pp. 188–193.
[18] A. Goldsmith, Wireless Communications. Cambridge, U.K.: Cambridge Univ. Press, 2005.
[19] G. H. Golub and C. F. Van Loan, Matrix Computations, 3rd ed. Baltimore, MD, USA: Johns Hopkins Univ. Press, 1996.