Current Results

On this page, we list some key papers that address different research problems in cell-free massive MIMO. This list might serve as an accessible entry-point for those who want to work on this field.

If you want your paper to be listed here, please contact Dr Hien Ngo (hien.ngo@qub.ac.uk) directly.

Fundamentals of Cell-Free Massive MIMO

• H. Q. Ngo, "Cell-Free Massive MIMO," in Encyclopedia of Wireless Networks, Springer, 2020.
• G. Interdonato, E. Björnson, H. Q. Ngo, P. Frenger, and E. G. Larsson, “Ubiquitous cell-free massive MIMO communications,” EURASIP J. Wireless Commun. Netw., Aug. 2019.
• H. Q. Ngo, A. Ashikhmin, H. Yang, E. G. Larsson, and T. L. Marzetta, "Cell-free massive MIMO versus small cells," IEEE Trans. Wireless Commun., Jan. 2017, vol. 16, no.3,  pp. 1834 – 1850, March 2017.
• 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. Wireless Commun., vol. 16, no. 7, pp. 4445–4459, Jul. 2017.
• 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, Mar. 2018.
• J. Zhang, S. Chen, Y. Lin, J. Zheng, B. Ai, and L. Hanzo, "Cell-freemassive MIMO: A new next-generation paradigm," IEEE Access, vol. 7, pp. 99 878–99 888, 2019.
• Z. Chen and E. Björnson, "Channel hardening and favorable propagationin cell-free Massive MIMO with stochastic geometry," IEEE Trans. Commun., vol. 66, no. 11, pp. 5205–5219, Nov. 2018.
• G. Interdonato, P. Frenger, and E. G. Larsson, "Scalability Aspects of Cell-Free Massive MIMO," in Proc. IEEE International Conference on Communications (ICC), May 2019.
• E. Björnson  and L. Sanguinetti, "Scalable cell-free massive MIMO systems," IEEE Trans. Commun., vol. 68, no. 7, July 2020.
• E. Björnson, L. Sanguinetti, "Making cell-free massive MIMO competitive with MMSE processing and centralized implementation," IEEE Trans. Commun., Jan 2020.
• Emil Björnson, Jakob Hoydis,  Luca Sanguinetti, “Massive MIMO Networks: Spectral, Energy, and Hardware Efficiency,” Foundations and Trends® in Signal Processing: vol. 11, no. 3-4, pp. 154–655, 2017. (Section 7.4.3 and several other section discuss the fundamentals and its relation to Massive MIMO). 
• M. Matthaiou, O. Yurduseven, H. Q. Ngo, D. Morales-Jimenez, S. L. Cotton, and V. F. Fusco, “The road to 6G: Ten physical layer challenges for communications engineers,” IEEE Communications Magazine, vol. 59, no. 1, Jan. 2021

Performance Analysis 

• Ö. Özdogan, E. Björnson, and J. Zhang, “Performance of Cell-Free Massive MIMO with Rician Fading and Phase Shifts,” IEEE Trans. Wireless Commun., Nov. 2019.
• P. Liu, K. Luo, D. Chen, and T. Jiang, “Spectral efficiency analysis of cell-free massive MIMO systems with zero-forcing detector,” IEEE Trans. Wireless Commun., Feb 2020. 
• Manijeh Bashar, Hien Quoc Ngo, Kanapathippillai Cumanan, Alister G. Burr, Pei Xiao, Emil Björnson, and Erik G. Larsson, “Uplink Spectral and Energy Efficiency of Cell-Free Massive MIMO with Optimal Uniform Quantization,” IEEE Trans. Commun., vol. 69, no. 1, Jan. 2021.
• M. Mohammadali, H. Q. Ngo, and M. Matthaiou, “When cell-free massive MIMO meets OTFS modulation: The downlink case,” in Proc. IEEE International Conference on Communications (ICC), May 2022.

Beamforming/Combining Techniques

• G. Interdonato, H. Q. Ngo, E. G. Larsson, and P. Frenger, "On the performance of Cell-Free Massive MIMO with short-term power constraints," IEEE International Workshop on Computer Aided Modelling and Design of Communication Links and Networks (CAMAD) 2016.
• 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. Wireless Commun., vol. 16, no. 7, pp. 4445–4459, Jul. 2017.
• M. Attarifar, A. Abbasfar, and A. Lozano, ‘‘Modified conjugate beamforming for cell-free massive MIMO,’’ IEEE Wireless Commun. Lett., vol. 8, no. 2, pp. 616–619, Apr. 2019.
• G. Interdonato, M. Karlsson, E. Björnson, and E. G. Larsson, "Local partial zero-forcing precoding for cell-free massive MIMO", IEEE Trans. Wireless Commun., April 2020. 
• E. Nayebi, A. Ashikhmin, T. L. Marzetta, and B. D. Rao, “Performance of cell-free massive MIMO systems with MMSE and LSFD receivers,” in Asilomar Conference on Signals, Systems and Computers, 2016, pp. 203–207.
• L. Du, L. Li, H. Q. Ngo, T. C. Mai, and M. Matthaiou, “Cell-free massive MIMO: Joint maximum-ratio and zero-forcing precoder with power control,” IEEE Trans. Commun., vol. 69, no. 6, pp. 3741 - 3756, June 2021.
• Giovanni Interdonato, Hien Quoc Ngo, and Erik G. Larsson, “Enhanced Normalized Conjugate Beamforming for Cell-Free Massive MIMO,” IEEE Trans. Commun., vol. 69, no. 5, pp. 2863 - 2877, May 2021.
• Zhe Wang, Jiayi Zhang, Hien Quoc Ngo, Bo Ai, and Merouane Debbah, “Iteratively Weighted MMSE Uplink Precoding for Cell-Free Massive MIMO Systems,” in Proc. IEEE International Conference on Communications (ICC), May 2022.

Transmission Protocol

• S. Buzzi and C. D’Andrea, “Cell-free massive MIMO: User-centric approach,” IEEE Wireless Commun. Lett., vol. 6, no. 6, pp. 706–709, Dec. 2017.
• S. Kim, J. W. Choi, B. Shim, "Downlink Pilot Precoding and Compressed Channel Feedback for FDD-Based Cell-Free Systems," IEEE Trans. Wireless Commun., Sept 2019, submitted.
• T. T. Vu, D. T. Ngo, H. Q. Ngo, and T. Le-Ngoc, “Full-duplex cell-free massive MIMO,” in Proc. IEEE Inter. Conf. Commun. (ICC), May 2019, pp. 1–6.
• A. A. I. Ibrahim, A. Ashikhmin, T. L. Marzetta and D. J. Love, "Cell-free massive MIMO systems utilizing multi-antenna accesspoints," 51st Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, 2017, pp. 1517-1521. 
• M. Karlsson, E. Björnson, E. G. Larsson, “Techniques for System Information Broadcast in Cell-Free Massive MIMO,” IEEE Trans. Commun., vol. 67, no. 1, pp. 244-257, Jan 2019.
• Juwendo Denis, Mohamad Assaad, "Improving Cell-Free massive MIMO Networks Performance: a Users Scheduling Approach," EEE Transactions on Wireless Communications, 2021.
• M. Mohammadali, T. T. Vu, B. N. Beni, H. Q. Ngo, and M. Matthaiou, “Virtually full-duplex cell-free massive MIMO with access point mode assignment,” in Proc. IEEE International Conference on Signal Processing Advances in Wireless Communications (SPAWC), July 2022.

CSI Acquisition

• Y. Jin, J. Zhang, S. Jin, B. Ai, "Channel Estimation for Cell-Free mmWave Massive MIMO Through Deep Learning," IEEE Trans. Vehicular Technol., Vol. PP, no. 99, pp. 1-1, 2019.
• G. Interdonato, H. Q. Ngo, P. Frenger, and E. G. Larsson, "Downlink training in cell-free massive MIMO: A blessing in disguise," IEEE Trans. Wireless Commun., July 2019, accepted.
• M. Attarifar, A. Abbasfar, and A. Lozano, "Random vs structured pilot assignment in cell-free massive MIMO wireless networks," IEEE Int’l Conf. Commun. Workshops (ICCW), May 2018.
• H. Liu, J. Zhang, X. Zhang, A. Kurniawan, T. Juhana, and B. Ai, "Tabu-Search Based Pilot Assignment for Cell-Free Massive MIMO Systems," IEEE Trans. Vehicular Technol., Nov. 2019 (Early Access).
• H. Liu, J. Zhang, X. Zhang, A. Kurniawan, T. Juhana, and B. Ai, “Tabu-Search Based Pilot Assignment for Cell-Free Massive MIMO Systems,” IEEE Trans. Veh. Techno., vol. 69, no. 2, pp. 2286-2290, Feb. 2020.
• Giovanni Interdonato, Hien Quoc Ngo, and Erik G. Larsson, “Enhanced Normalized Conjugate Beamforming for Cell-Free Massive MIMO,” IEEE Transactions on Communications, May 2021.
• Heng Liu, Jiayi Zhang, Shi Jin, and Bo Ai, “Graph Coloring Based Pilot Assignment for Cell-Free Massive MIMO Systems,” IEEE Transactions on Vehicular Technology, vol. 69, no. 8, pp. 9180-9184, Aug. 2020.
• Tien Hoa Nguyen, Trinh Van Chien, Hien Quoc Ngo, Xuan Nam Tran, and Emil Björnson, "Pilot Assignment for Joint Uplink-Downlink Spectral Efficiency Enhancement in Massive MIMO Systems with Spatial Correlation," IEEE Trans. Veh. Techno., vol. 70, no. 8, pp. 8292 - 8297, Aug. 2021.
•  W. Zeng, Y. He, B. Li, and S. Wang, “Pilot assignment for cellfree massive MIMO systems using a weighted graphic framework,” IEEE Trans. Veh. Technol., early access, Apr. 2021.
• N. Garg and T. Ratnarajah, “Generalized Superimposed Training Scheme in Cell-free Massive MIMO Systems,” IEEE Trans. Wireless Commun., March 2022, accepted.

Resource Allocations

• L. D. Nguyen, T. Q. Duong, H. Q. Ngo, and K. Tourki, “Energy efficiency in cell-free massive MIMO with zero-forcing precoding design,” IEEE Commun. Lett.,  vol. 21, no. 8, pp. 1871-1874, Aug. 2017.
• M. Bashar, K. Cumanan, A. G. Burr, H. Q. Ngo, and H. V. Poor, "Mixed Quality of Service in Cell-Free Massive MIMO,"  IEEE Commun. Lett.,  vol. 22, no. 7, pp. 1494-1497, July 2018.
•  M. Bashar, K. Cumanan, A. G. Burr, M. Debbah, and H. Q. Ngo,“On the uplink max–min SINR of cell-free massive MIMO systems,” IEEE Trans. Wireless Commun., vol. 18, no. 4, pp. 2021–2036, Apr. 2019.
• M. Bashar, K. Cumanan, A. G. Burr, H. Q. Ngo, E. G. Larsson, and P. Xiao, “Energy efficiency of the cell-free massive MIMO uplink with optimal uniform quantization,” IEEE Trans. Green Commun. Netw., pp. 1–1, 2019.
• T. C. Mai, H. Q. Ngo, M. Egan, and T. Q. Duong, ‘‘Pilot power control for cell-free massive MIMO,’’ IEEE Trans. Veh. Technol., vol. 67, no. 11, pp. 11264–11268, Nov. 2018.
• M. Alonzo, S. Buzzi, A. Zappone, and C. D’Elia, “Energy efficient power control in cell-free and user-centric massive MIMO at millimeter wave,” IEEE Trans. Green Commun. Netw., Mar. 2019.
• G. Interdonato, P. Frenger, E. G. Larsson, "Utility-based downlink pilot assignment in cell-free massive MIMO," International ITG Workshop on Smart Antennas (WSA), 2018.
• Emil Björnson, Eduard Jorswieck, “Optimal Resource Allocation in Coordinated Multi-Cell Systems,” Foundations and Trends in Communications and Information Theory, vol. 9, no. 2-3, pp. 113-381, 2013.
• Muhammad Farooq, Hien Quoc Ngo, Een-Kee Hong, Le-Nam Tran, “Utility Maximization for Large-Scale Cell-Free Massive MIMO Downlink,” IEEE Trans. Commun., vol. 69, no. 10, pp. 7050 - 7062, Oct. 2021.
• Filipe Conceicao , Carlos Henggeler Antunes, Marco Gomes, Vitor Silva , and Rui Dinis, "Max-Min Fairness Optimization in Uplink Cell-Free Massive MIMO using Meta-Heuristics," IEEE Trans. Commun., Mar 2022.
• T. C. Mai, H. Q. Ngo, L.-N. Tran, “Energy Efficiency Maximization in Large-Scale Cell-Free Massive MIMO: A Projected Gradient Approach,” IEEE Trans. Wireless Commun., Feb 2022.
• Tung T. Vu, Duy T. Ngo, Nguyen H. Tran, Hien Quoc Ngo, Minh N. Dao, and Richard H. Middleton, "Joint Resource Allocation to Minimize Execution Time of Federated Learning in Cell-Free Massive MIMO", IEEE Internets of Things Journal, June 2022, accepted.

Hardware Impairments

• J. Zhang, Y. Wei, E. Bjornson, Y. Han, and S. Jin, “Performance analysis and power control of cell-free massive MIMO systems with hardware impairments,” IEEE Access, vol. 6, pp. 55302–55314, 2018.
• X. Zhang, D. Guo, K. An, and B. Zhang, “Secure Communications Over Cell-Free Massive MIMO Networks With Hardware Impairments,” IEEE Syst. J., 2019.
• X. Hu, C. Zhong, X. Chen, W. Xu, H. Lin, and Z. Zhang, ‘‘Cell-freemassive MIMO systems with low resolution ADCs,’’ IEEE Trans. Wireless Commun., vol. 67 , no.10, Oct. 2019. 
• Y. Zhang, M. Zhou, H. Cao, L. Yang, and H. Zhu, "On the Performance of Cell-Free Massive MIMO with Mixed-ADC under Rician Fading Channels," IEEE Wireless Commun. Lett., Oct. 2019.
• H. Masoumi and M. J. Emadi, ‘‘Performance analysis of cell-free massive MIMO system with limited fronthaul capacity and hardware impairments,’’ IEEE Trans. Wireless Commun., Nov. 2019 (Early Access).
• J. Mo. Palacios, O. Raeesi, A. Gokceoglu, and M. Valkama, "Impact of channel non-reciprocity in cell-free massive MIMO," IEEE Wireless Commun. Lett., Dec. 2019.
• J. Zheng, J. Zhang, L. Zhang, X. Zhang and B. Ai, “Efficient Receiver Design for Uplink Cell-Free Massive MIMO With Hardware Impairments,” IEEE Trans. Veh. Techno., Feb 2020. 
• J. A. C. Sutton, H. Q. Ngo, and M. Matthaiou, “Cell-free massive MIMO with multiple-antenna users under I/Q imbalance,” in Proc. European Signal Processing Conference (EUSIPCO), August 2021.
• V. Tentu, E. Sharma, D. N. Amudala and R. Budhiraja, UAV-Enabled Hardware-Impaired Spatially Correlated Cell-Free Massive MIMO Systems: Analysis And Energy Efficiency Optimization, IEEE Trans. Commun., vol. 70, pp 2722 - 2741, Apr. 2022.

Machine Learning

• T. T. Vu, D. T. Ngo, N. H. Tran, H. Q. Ngo, M. N. Dao, and R. H. Middleton, "Cell-Free Massive MIMO for Wireless Federated Learning", IEEE Trans. Wireless Commun., Oct 2020.
• T. T. Vu , Duy T. Ngo, Nguyen H. Tran, Hien Quoc Ngo, Minh N. Dao, and Richard H. Middleton, "User Selection Approaches to Mitigate Straggler Effect for Federated Learning in Cell-Free Massive MIMO Networks", IEEE Transactions on Wireless Communications, submitted, 2021.
• Yu Jin, Jiayi Zhang, Shi Jin, and Bo Ai, “Channel Estimation for Cell-Free mmWave Massive MIMO Through Deep Learning,” EEE Trans. Veh. Techno., Oct 2019.
• T. T. Vu, Hien Quoc Ngo, Thomas L. Marzetta, and Michail Matthaiou, “How Does Cell-Free Massive MIMO Support Multiple Federated Learning Groups?,” IEEE SPAWC, Italy, Sep. 2021 (Invited Paper).
• T. T. Vu, Duy T. Ngo, Nguyen H. Tran, Hien Quoc Ngo, Minh N. Dao, and Richard H. Middleton, "Joint Resource Allocation to Minimize Execution Time of Federated Learning in Cell-Free Massive MIMO", IEEE Internets of Things Journal, May 2022, accepted.
• L. Luo, J. Zhang, S. Chen, X. Zhang, B. Ai, and D. W. K. Ng, “Downlink power control for cell-free massive MIMO with deep reinforcement learning,” IEEE Transactions on Vehicular Technology, June 2022.
• T. T. Vu, T. V. Chien, C. T. Dinh, H. Q. Ngo, and M. Matthaiou, “Channel estimation in RIS-assisted downlink massive MIMO: A learning-based approach,” in Proc. IEEE International Conference on Signal Processing Advances in Wireless Communications (SPAWC), July 2022. (Invited paper).

Applications of Cell-Free Massive MIMO in Other Systems

• T. X. Doan, H. Q. Ngo, T. Q. Duong, and K. Tourki, "On the performance of multigroup multicast cell-free massive MIMO," IEEE Commun. Lett., vol. 21, no. 12, pp. 2642-2645, Dec. 2017.
• T. M. Hoang, H. Q. Ngo, T. Q. Duong, H. D. Tuan, and A. Marshall, “Cell-free massive MIMO networks: Optimal power control against active eavesdropping,” IEEE Trans. Commun., vol. 66, no. 10, pp. 4724–4737, Oct. 2018.
• Y. Li and G. A. A. Baduge, ‘‘NOMA-aided cell-free massive MIMO systems,’’ IEEE Wireless Commun. Lett., vol. 7, no. 6, pp. 950–953, Dec. 2018.
• S. Dinh, H. Q. Ngo, S. Cotton, “Wireless Powered Wearables using Distributed Massive MIMO,” IEEE Trans. Commun., Dec. 2019.
• F. Rezaei, A. R. Heidarpour, C. Tellambura, and A. Tadaion, "Underlaid spectrum sharing for cell-free massive MIMO-NOMA," IEEE Commun. Lett., Dec. 2019.
• A. A. Nasir, H. D. Tuan, H. Q. Ngo, T. Q. Duong, and H. V. Poor, “Cell-Free Massive MIMO in the Short Blocklength Regime for URLLC,” IEEE Trans. Wireless Commun, vol. 20, no. 9, pp. 5861 - 5871, Sept. 2021.
• T. V. Chien, H. Q. Ngo, S. Chatzinotas, M. D. Renzo, and B. Ottersten, "Reconfigurable Intelligent Surface-Assisted Cell-Free Massive MIMO Systems Over Spatially-Correlated Channels," IEEE Trans. Wireless Commun., Dec. 2021 (Early Access).
• M. Mohammadali, H. Q. Ngo, and M. Matthaiou, “When cell-free massive MIMO meets OTFS modulation: The downlink case,” in Proc. IEEE International Conference on Communications (ICC), May 2022.