[1]	R. Chataut and R. Akl, “Massive MIMO systems for 5G and beyond networks—overview, recent trends, challenges, and future research direction,” Sensors, vol. 20, no. 10, p. 2753, 2020.
[2]	F. B. Saghezchi et al., “Drivers for 5G: The ‘Pervasive Connected World,’” Fundam. 5G Mob. Networks, pp. 1–27, 2015.
[3]	T. Chen, M. Matinmikko, X. Chen, X. Zhou, and P. Ahokangas, “Software defined mobile networks: concept, survey, and research directions,” IEEE Commun. Mag., vol. 53, no. 11, pp. 126–133, 2015.
[4]	S. A. Busari, K. M. S. Huq, S. Mumtaz, L. Dai, and J. Rodriguez, “Millimeter-wave massive MIMO communication for future wireless systems: A survey,” IEEE Commun. Surv. Tutorials, vol. 20, no. 2, pp. 836–869, 2017.
[5]	D. Wu, J. Wang, Y. Cai, and M. Guizani, “Millimeter-wave multimedia communications: challenges, methodology, and applications,” IEEE Commun. Mag., vol. 53, no. 1, pp. 232–238, 2015.
[6]	X. Wang et al., “Millimeter wave communication: A comprehensive survey,” IEEE Commun. Surv. Tutorials, vol. 20, no. 3, pp. 1616–1653, 2018.
[7]	R. CHAKRABORTY, N. KUMARI, M. MOUSAM, and A. MUKHERJEE, “The future of 5G and millimeter waves,” in 2018 Second International Conference on Electronics, Communication and Aerospace Technology (ICECA), 2018, pp. 1679–1683.
[8]	S. Rangan, T. S. Rappaport, and E. Erkip, “Millimeter-wave cellular wireless networks: Potentials and challenges,” Proc. IEEE, vol. 102, no. 3, pp. 366–385, 2014.
[9]	T. L. Marzetta, “Noncooperative cellular wireless with unlimited numbers of base station antennas,” IEEE Trans. Wirel. Commun., vol. 9, no. 11, pp. 3590–3600, 2010.
[10]	F. Rusek et al., “Scaling up MIMO: Opportunities and challenges with very large arrays,” arXiv Prepr. arXiv1201.3210, 2012.
[11]	E. G. Larsson, O. Edfors, F. Tufvesson, and T. L. Marzetta, “Massive MIMO for next generation wireless systems,” IEEE Commun. Mag., vol. 52, no. 2, pp. 186–195, 2014.
[12]	T. L. Marzetta, “Massive MIMO: an introduction,” Bell Labs Tech. J., vol. 20, pp. 11–22, 2015.
[13]	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, 2014.
[14]	M. Kamel, W. Hamouda, and A. Youssef, “Ultra-dense networks: A survey,” IEEE Commun. Surv. Tutorials, vol. 18, no. 4, pp. 2522–2545, 2016.
[15]	D. López-Pérez, M. Ding, H. Claussen, and A. H. Jafari, “Towards 1 Gbps/UE in cellular systems: Understanding ultra-dense small cell deployments,” IEEE Commun. Surv. Tutorials, vol. 17, no. 4, pp. 2078–2101, 2015.
[16]	Nokia, “Ultra Dense Network (UDN),” Nokia, p. 27, 2016, [Online]. Available: https://onestore.nokia.com/asset/200295/Nokia_Ultra_Dense_Network_White_Paper_EN.pdf.
[17]	L. Lu, G. Y. Li, A. L. Swindlehurst, A. Ashikhmin, and R. Zhang, “An overview of massive MIMO: Benefits and challenges,” IEEE J. Sel. Top. Signal Process., vol. 8, no. 5, pp. 742–758, 2014.
[18]	M. A. Albreem, M. Juntti, and S. Shahabuddin, “Massive MIMO Detection Techniques: A Survey,” IEEE Commun. Surv. Tutorials, 2019.
[19]	H. Q. Ngo, E. G. Larsson, and T. L. Marzetta, “Energy and spectral efficiency of very large multiuser MIMO systems,” IEEE Trans. Commun., vol. 61, no. 4, pp. 1436–1449, 2013.
[20]	J. Hoydis, S. Ten Brink, and M. Debbah, “Massive MIMO in the UL/DL of cellular networks: How many antennas do we need?,” IEEE J. Sel. Areas Commun., vol. 31, no. 2, pp. 160–171, 2013.
[21]	L. Liu, Y. Chi, C. Yuen, Y. L. Guan, and Y. Li, “Capacity-achieving MIMO-NOMA: iterative LMMSE detection,” IEEE Trans. Signal Process., vol. 67, no. 7, pp. 1758–1773, 2019.
[22]	H. Q. Ngo, E. G. Larsson, and T. L. Marzetta, “The multicell multiuser MIMO uplink with very large antenna arrays and a finite-dimensional channel,” IEEE Trans. Commun., vol. 61, no. 6, pp. 2350–2361, 2013.
[23]	D. Chizhik, G. J. Foschini, M. J. Gans, and R. A. Valenzuela, “Keyholes, correlations, and capacities of multielement transmit and receive antennas,” IEEE Trans. Wirel. Commun., vol. 1, no. 2, pp. 361–368, 2002.
[24]	A. G. Burr, “Capacity bounds and estimates for the finite scatterers MIMO wireless channel,” IEEE J. Sel. Areas Commun., pp. 812–818, 2003.
[25]	T. L. Marzetta, Fundamentals of massive MIMO. Cambridge University Press, 2016.
[26]	A. Chockalingam and B. S. Rajan, Large MIMO systems. Cambridge University Press, 2014.
[27]	A.-S. Bana et al., “Massive MIMO for internet of things (IoT) connectivity,” Phys. Commun., vol. 37, p. 100859, 2019.
[28]	L. You et al., “Network massive MIMO transmission over millimeter-wave and terahertz bands: Mobility enhancement and blockage mitigation,” IEEE J. Sel. Areas Commun., vol. 38, no. 12, pp. 2946–2960, 2020.
[29]	H. Q. Ngo, A. Ashikhmin, H. Yang, E. G. Larsson, and T. L. Marzetta, “Cell-free massive MIMO versus small cells,” IEEE Trans. Wirel. Commun., vol. 16, no. 3, pp. 1834–1850, 2017.
[30]	E. Nayebi, A. Ashikhmin, T. L. Marzetta, and B. D. Rao, “Performance of cell-free massive MIMO systems with MMSE and LSFD receivers,” in 2016 50th Asilomar Conference on Signals, Systems and Computers, 2016, pp. 203–207.
[31]	E. Nayebi, A. Ashikhmin, T. L. Marzetta, H. Yang, and B. D. Rao, “Precoding and power optimization in cell-free massive MIMO systems,” IEEE Trans. Wirel. Commun., vol. 16, no. 7, pp. 4445–4459, 2017.
[32]	A. A. I. Ibrahim, A. Ashikhmin, T. L. Marzetta, and D. J. Love, “Cell-free massive MIMO systems utilizing multi-antenna access points,” in 2017 51st Asilomar Conference on Signals, Systems, and Computers, 2017, pp. 1517–1521.
[33]	H. Q. Ngo, L.-N. Tran, T. Q. Duong, M. Matthaiou, and E. G. Larsson, “On the total energy efficiency of cell-free massive MIMO,” IEEE Trans. Green Commun. Netw., vol. 2, no. 1, pp. 25–39, 2017.
[34]	S. Elhoushy and W. Hamouda, “Downlink Performance of Limited-Fronthaul Cell-Free Massive MIMO,” in ICC 2021-IEEE International Conference on Communications, 2021, pp. 1–6.
[35]	G. Interdonato, E. Björnson, H. Q. Ngo, P. Frenger, and E. G. Larsson, “Ubiquitous cell-free massive MIMO communications,” EURASIP J. Wirel. Commun. Netw., vol. 2019, no. 1, p. 197, 2019.
[36]	H. Q. Ngo, E. G. Larsson, and T. L. Marzetta, “Aspects of favorable propagation in massive MIMO,” in 2014 22nd European Signal Processing Conference (EUSIPCO), 2014, pp. 76–80.
[37]	Z. Chen and E. Björnson, “Channel hardening and favorable propagation in cell-free massive MIMO with stochastic geometry,” IEEE Trans. Commun., vol. 66, no. 11, pp. 5205–5219, 2018.
[38]	M. Bashar, K. Cumanan, A. G. Burr, H. Q. Ngo, and M. Debbah, “Cell-free massive MIMO with limited backhaul,” in 2018 IEEE International Conference on Communications (ICC), 2018, pp. 1–7.
[39]	Q. Zhang, S. Jin, K.-K. Wong, H. Zhu, and M. Matthaiou, “Power scaling of uplink massive MIMO systems with arbitrary-rank channel means,” IEEE J. Sel. Top. Signal Process., vol. 8, no. 5, pp. 966–981, 2014.
[40]	T. L. Marzetta, “How much training is required for multiuser MIMO?,” in 2006 fortieth asilomar conference on signals, systems and computers, 2006, pp. 359–363.
[41]	J. Jose, A. Ashikhmin, T. L. Marzetta, and S. Vishwanath, “Pilot contamination and precoding in multi-cell TDD systems,” IEEE Trans. Wirel. Commun., vol. 10, no. 8, pp. 2640–2651, 2011.
[42]	S. M. Shahabi, M. Ardebilipour, and Y. Omid, “Low-complexity fairness-driven pilot decontamination schemes for multi-cell massive MIMO systems,” Phys. Commun., vol. 36, p. 100803, 2019.
[43]	Y. Wang, C. Li, Y. Huang, D. Wang, T. Ban, and L. Yang, “Energy-efficient optimization for downlink massive MIMO FDD systems with transmit-side channel correlation,” Ieee Trans. Veh. Technol., vol. 65, no. 9, pp. 7228–7243, 2015.
[44]	O. Saatlou, M. O. Ahmad, and M. N. S. Swamy, “Spectral efficiency maximization of a single cell massive MU-MIMO down-link TDD system by appropriate resource allocation,” IEEE Access, vol. 7, pp. 182758–182771, 2019.
[45]	H. Yang and T. L. Marzetta, “Performance of conjugate and zero-forcing beamforming in large-scale antenna systems,” IEEE J. Sel. Areas Commun., vol. 31, no. 2, pp. 172–179, 2013.
[46]	H. Q. Ngo and E. G. Larsson, “Blind estimation of effective downlink channel gains in massive MIMO,” in 2015 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2015, pp. 2919–2923.
[47]	M. Wang and D. Wang, “Sum-rate of multi-user MIMO systems with multi-cell pilot contamination in correlated Rayleigh fading channel,” Entropy, vol. 21, no. 6, p. 573, 2019.
[48]	F. A. Pereira de Figueiredo, D. A. Mendes Lemes, C. Ferreira Dias, and G. Fraidenraich, “Massive MIMO channel estimation considering pilot contamination and spatially correlated channels,” Electron. Lett., vol. 56, no. 8, pp. 410–413, 2020.
[49]	R. R. Muller, “A random matrix model of communication via antenna arrays,” IEEE Trans. Inf. theory, vol. 48, no. 9, pp. 2495–2506, 2002.
[50]	M. Miriestahbanati and M. R. Soleymani, “Spectral Efficiency Maximization of Multiuser Massive MIMO with a Finite Dimensional Channel,” in ICC 2019-2019 IEEE International Conference on Communications (ICC), 2019, pp. 1–7.
[51]	O. Saatlou, M. O. Ahmad, and M. N. S. Swamy, “Spectral efficiency maximization of multiuser massive MIMO systems with finite-dimensional channel via control of users’ power,” IEEE Trans. Circuits Syst. II Express Briefs, vol. 65, no. 7, pp. 883–887, 2017.
[52]	H. Q. Ngo, M. Matthaiou, and E. G. Larsson, “Massive MIMO with optimal power and training duration allocation,” IEEE Wirel. Commun. Lett., vol. 3, no. 6, pp. 605–608, 2014.
[53]	A. Khansefid and H. Minn, “Asymptotically optimal power allocation for massive MIMO uplink,” in 2014 IEEE Global Conference on Signal and Information Processing (GlobalSIP), 2014, pp. 627–631.
[54]	Q. Zhang, S. Jin, M. McKay, D. Morales-Jimenez, and H. Zhu, “Power allocation schemes for multicell massive MIMO systems,” IEEE Trans. Wirel. Commun., vol. 14, no. 11, pp. 5941–5955, 2015.
[55]	H. V. Cheng, E. Björnson, and E. G. Larsson, “Uplink pilot and data power control for single cell massive MIMO systems with MRC,” in 2015 International Symposium on Wireless Communication Systems (ISWCS), 2015, pp. 396–400.
[56]	H. V. Cheng, E. Björnson, and E. G. Larsson, “Optimal pilot and payload power control in single-cell massive MIMO systems,” IEEE Trans. Signal Process., vol. 65, no. 9, pp. 2363–2378, 2016.
[57]	L. You, Y. Huang, D. Zhang, Z. Chang, W. Wang, and X. Gao, “Energy Efficiency Optimization for Multi-cell Massive MIMO: Centralized and Distributed Power Allocation Algorithms,” IEEE Trans. Commun., 2021.
[58]	O. Saatlou, M. O. Ahmad, and M. N. S. Swamy, “Joint data and pilot power allocation for massive MU-MIMO downlink TDD systems,” IEEE Trans. Circuits Syst. II Express Briefs, vol. 66, no. 3, pp. 512–516, 2018.
[59]	M. Miriestahbanati, O. Saatlou, and M. R. Soleymani, “Maximizing the spectral efficiency of finite dimensional multiuser massive MIMO,” Phys. Commun., p. 101430, 2021.
[60]	S. Vishwanath, N. Jindal, and A. Goldsmith, “Duality, achievable rates, and sum-rate capacity of Gaussian MIMO broadcast channels,” IEEE Trans. Inf. theory, vol. 49, no. 10, pp. 2658–2668, 2003.
[61]	E. Björnson, E. G. Larsson, and M. Debbah, “Massive MIMO for maximal spectral efficiency: How many users and pilots should be allocated?,” IEEE Trans. Wirel. Commun., vol. 15, no. 2, pp. 1293–1308, 2015.
[62]	T. T. Do, E. Björnson, E. G. Larsson, and S. M. Razavizadeh, “Jamming-resistant receivers for the massive MIMO uplink,” IEEE Trans. Inf. Forensics Secur., vol. 13, no. 1, pp. 210–223, 2017.
[63]	S. Jin, X. Wang, Z. Li, K.-K. Wong, Y. Huang, and X. Tang, “On massive MIMO zero-forcing transceiver using time-shifted pilots,” IEEE Trans. Veh. Technol., vol. 65, no. 1, pp. 59–74, 2015.
[64]	Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, “Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels,” IEEE Trans. signal Process., vol. 52, no. 2, pp. 461–471, 2004.
[65]	C.-B. Chae, D. Mazzarese, N. Jindal, and R. W. Heath, “Coordinated beamforming with limited feedback in the MIMO broadcast channel,” IEEE J. Sel. Areas Commun., vol. 26, no. 8, pp. 1505–1515, 2008.
[66]	K. S. Gomadam, H. C. Papadopoulos, and C.-E. Sundberg, “Techniques for multi-user MIMO with two-way training,” in 2008 IEEE International Conference on Communications, 2008, pp. 3360–3366.
[67]	S. M. Kay, Fundamentals of statistical signal processing. Prentice Hall PTR, 1993.
[68]	S. Boyd and L. Vandenberghe, Convex optimization. Cambridge university press, 2004.
[69]	T. Van Chien, T. N. Canh, E. Björnson, and E. G. Larsson, “Power control in cellular massive MIMO with varying user activity: A deep learning solution,” IEEE Trans. Wirel. Commun., vol. 19, no. 9, pp. 5732–5748, 2020.
[70]	G. Interdonato, H. Q. Ngo, E. G. Larsson, and P. Frenger, “How much do downlink pilots improve cell-free massive MIMO?,” in 2016 IEEE Global Communications Conference (GLOBECOM), 2016, pp. 1–7.
[71]	A. M. Tulino and S. Verdú, “Random matrix theory and wireless communications,” Found. Trends® Commun. Inf. Theory, vol. 1, no. 1, pp. 1–182, 2004.