[1] L. Dai, B. Wang, Y. Yuan, S. Han, I. Chih-Lin, and Z. Wang, “Nonorthogonal multiple access for 5G: solutions, challenges, opportunities, and future research trends,” IEEE Commun. Mag., vol. 53, no. 9, pp. 74–81, September 2015.##
[2] 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 Veh. Technol. Conf. (VTC), Dresden, Germany, pp. 1–5, Jun 2013.##
[3] Z. Ding, H. Dai, and H. V. Poor, “Relay Selection for Cooperative NOMA,” IEEE Wireless Commun. Lett., vol. 5, no. 4, pp. 416–419, Aug. 2016, pp. 1393–1405, 2016.##
[4] S. Timotheou and I. Krikidis, “Fairness for non-orthogonal multiple access in 5G systems,” IEEE Signal Process. Lett., vol. 22, no. 10, pp. 1647–1651, Oct. 2015.##
[5] H.-M. Wang, T.-X. Zheng, J. Yuan, D. Towsley, and M. H. Lee, “Physical layer security in heterogeneous cellular networks,” IEEE Trans. Commun., vol. 64, no. 3, pp. 1204–1219, Mar. 2016.##
[6] Y. Zhang, H.-M. Wang, Q. Yang, and Z. Ding, “Secrecy sum rate maximization in non-orthogonal multiple access,” IEEE Commun. Lett. vol. 20, no. 5, pp. 930–933, May 2016.##
[7] M. Qin, S. Yang, H. Deng, and M. H. Lee, “Enhancing security of primary user in underlay cognitive radio networks with secondary user selection,” IEEE Access, vol. 6, pp. 32624–32636, 2018.##
[8] N. Nandan, S. Majhi, and H. C. Wu, “Secure beamforming for MIMO NOMA based cognitive radio network,” IEEE Commun. Lett., vol. 22, no. 8, pp. 1708–1711, Aug. 2018.##
[9] Z. Yang, J. A. Hussein, P. Xu, Z. Ding, and Y. Wu, “Power allocation study for non-orthogonal multiple access networks with multicastunicast transmission,” IEEE Trans. Wireless Commun., vol. 17, no. 6, pp. 3588–3599, Jun. 2018.##
[10] L. Lv, Z. Ding, Q. Ni, and J. Chen, “Secure MISO-NOMA transmission with artificial noise,” IEEE Trans. Veh. Technol., vol. 67, no. 7, pp. 6700–6705, Jul. 2018.##
[11] Y. Liu, Z. Qin, M. Elkashlan, Y. Gao, and L. Hanzo, “Enhancing the physical layer security of non-orthogonal multiple access in large-scale networks,” IEEE Trans. Wireless Commun., vol. 16, no. 3, pp. 1656– 1672, Mar. 2017.##
[12] X. Chen, Z. Zhang, C. Zhong, D. W. K. Ng, and R. Jia, “Exploiting inter-user interference for secure massive non-orthogonal multiple access,” IEEE J. Sel. Areas Commun., vol. 36, no. 4, pp. 788–801, Apr. 2018.##
[13] M. F. Hanif, Z. Ding, T. Ratnarajah, and G. K. Karagiannidis, “A minorization-maximization method for optimizing sum rate in the downlink of non-orthogonal multiple access systems,” IEEE Trans Signal Process, vol. 64(1), pp. 76-88, 2016.##
[14] Y. Zhang, H.-M. Wang, T.-X. Zheng, and Q. Yang, “Energy-efficient transmission design in non-orthogonal multiple access. IEEE Trans Veh Technol,” vol. 66(3), pp. 2852-2857, 2017.##
[15] Ming Zeng, Man-Phong Nguyen, A. Dobre Octavia, H. Vincent Poor, “Securing Downlink Massive MIMO-NOMA Networks With Artificial Noise,” IEEE Journal of Selected Topics in Signal Processing, vol. 13, Issue 3, June 2019.##
[16] Pooja Singh and Aditya Trivedi, “NOMA and massive MIMO assisted physical layer security using artificial noise precoding,” Physical Communication, vol. 39, April 2020.##
[17] S. M. Riazul Islam, Nurilla Avazov, Octavia A. Dobre, and Kyung-Sup Kwak, “Power-Domain Non-Orthogonal Multiple Access (NOMA) in 5G Systems: Potentials and Challenges,”
IEEE Communications Surveys & Tutorials vol. 19,
Issue 2, 2017.##
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