在本論文中，我們針對包含一個基地台和兩個使用者的非正交多重接取下行系統 (NOMA)，提出適用於非完美通道估測情境具有低複雜度的功率分配方法；在給定通道估測值以及相應的均方誤差情況下，我們先利用現有的通道容量下界表示式決定系統的中斷機率上界；接著，分別針對單輸入單輸出 (SISO) 和多輸入多輸出 (MIMO) 情境，在總功率限制條件下，推導出可最小化系統中斷機率上界的功率分配封閉解 (closed-form solutions)。這些封閉解都僅需簡單的數學運算，因此具有低實現複雜度；另外，電腦模擬結果顯示，在非完美通道估測情境下，所提出的SISO-NOMA和MIMO-NOMA功率分配方法在兩個使用者間最差的位元錯誤率效能 (worst bit-error-rate performance) 表現上，優於傳統的固定式功率分配方法以及未考量通道估測均方誤差的類似功率分配方法。

In this thesis, we propose low-complexity power allocation methods for a downlink non-orthogonal multiple access (NOMA) system with a base station and two users under imperfect channel estimation. Given channel estimates and the corresponding mean-squared error (MSE) information, existing capacity lower bounds are used to determine an upper bound of the system outage probability based on the minimum rate requirements of both users. Subsequently, we derive closed-form power allocation solutions for the two users for both single-input single-output (SISO) and multiple-input multiple-output (MIMO) scenarios such that the outage probability’s upper bound is minimized under a total power constraint. Each solution requires only numerical operations to calculate the power allocation factor, and the computational complexity is low for practical applications. As shown by computer simulation results for downlink SISO-NOMA and MIMO-NOMA systems with imperfect channel estimation, the proposed methods have better worst bit-error-rate performance for the two users than the conventional approach with a fixed power allocation factor and similar schemes that do not consider channel MSEs for power allocation.

[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] Y. Saito, Y. Kishiyama, A. Benjebbour, T. Nakamura, A. Li, and K. Higuchi, “Non-orthogonal multiple access (NOMA) for cellular future radio access,” in Proc. IEEE 77th Veh. Technol. Conf. (VTC-Spring), Dresden, Germany, Jun. 2013.
[5] 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. Int. Symp. Intell. Signal Process. Commun. Syst. (ISPACS), Okinawa, Japan, Nov. 2013, pp. 770–774.
[6] 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.
[7] T. M. Cover and J. A. Thomas, Elements of Information Theory. Hoboken, NY, USA: Wiley, 1991.
[8] 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.
[9] S. Timotheou, and I. Krikidis, “Fairness for non-orthogonal multiple access in 5G systems,” IEEE Wireless Commun Lett., vol. 22, no. 10, pp. 1647–1651, Oct. 2015.
[10] 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.
[11] M. Medard, “The effect upon channel capacity in wireless communications of perfect and imperfect knowledge of the channel,” IEEE Trans. Inf. Theory, vol. 46, no. 3, pp. 993–946, May 2000
[12] T. Yoo, and A. Goldsmith, “Capacity and power allocation for MIMO channels with channel estimation error,” IEEE Trans. Inf. Theory, vol. 52, no. 5, pp. 2203–2214, May 2006
[13] S. Han, S. Ahn, E. Oh, and D. Hong, “Effect of channel-estimation error on BER performance in cooperative transmission,” IEEE Trans. Veh. Technol., vol. 58, no. 4, pp. 2083–2088, May 2009.
[14] W. Cai, C. Chen, L. Bai, Y. Jin, and J. Choi, “User selection and power allocation schemes for downlink NOMA systems with imperfect CSI,” in Proc. IEEE 84th Veh. Technol. Conf. (VTC-Fall), Montreal, Canada, Sep. 2016, pp. 1–5.
[15] H. Wang, Z. Zhang, and X. Chen, “Energy-efficient power allocation for non-orthogonal multiple access with imperfect successive interference cancellation,” in Proc. IEEE Int. Conf. Wireless Commun. Signal Process. (WCSP), Nanjing, China, Oct. 2017, pp. 1–6.
[16] K. Senel and S. Tekinay, “Optimal power allocation in NOMA systems with imperfect channel estimation,” in Proc. IEEE Global Commun. Conf. (GLOBECOM), Singapore, Dec. 2017, pp. 1–5.
[17] J. Cui, Z. Ding, and P. Fan, “Outage probability constrained MIMO-NOMA designs under imperfect CSI,” IEEE Trans Wireless Commun., vol. 17, no. 12, pp. 8239–8255, Dec. 2018.
[18] B.-Y. Huang, “Power allocation based on imperfect channel state information for downlink non-orthogoanl multiple access systems,” M.S. thesis, Inst. Commun. Eng., National Tsing Hua Univ., Hsinchu, Taiwan, Aug. 2018.
[19] Y.-C. Wang, “Investigation of power allocation based on SINR balancing for NOMA systems with imperfect channel estimation,” M.S. dissertation, Dept. Electron. Eng., Univ. Surrey, Gulidford, Surrey, U.K., Apr. 2019.
[20] C.-L. Wang, Y.-C. Wang, and P. Xiao, "Power allocation based on SINR balancing for NOMA systems with imperfect channel estimation," in Proc. 13th Int. Conf. Signal Process. Commun. Syst. (ICSPCS), Gold Coast, Australia, Dec. 2019.
[21] D. Tse and P. Viswanath, Fundamentals of Wireless Communication. Cambridge, U.K.: Cambridge Univ. Press, 2005.