AUT Journal of Electrical Engineering

AUT Journal of Electrical Engineering

Performance Analysis of Local Processors-Assisted Cell-Free massive Multiple Input Multiple Output Systems

Document Type : Research Article

Authors
Reza Roshanghias 1
Reza Saadat 1
Saeed Gazor 2
1 Department of Electrical Engineering, Yazd University, Yazd, Iran
2 Department of Electrical and Computer Engineering, Queen’s University, Kingston, Canada.
10.22060/eej.2025.23871.5640
Abstract
This paper proposes a local processors-assisted structure (LPs-AS) for cell-free massive multiple-input multiple-output (CF-mMIMO) systems, consisting of a central processor (CP), several access points (APs), and some local processors (LPs). Each LP is connected to the CP and a subset of APs and is used as a precoding unit in downlink (DL). This proposed LPs-AS enables us to implement DL precoders with a semi-distributed approach. In our proposed semi-distributed implementation (SDI), we design precoders at the LPs. This approach differs from centralized implementation (CI) where the precoders are implemented at the CP and distributed implementation (DI) where the precoders are designed at the APs. We evaluate LPs-AS in terms of spectral efficiency (SE) and analytically derive its achievable SE. Furthermore, we propose a power control algorithm to maximize its sum SE, compute the computational complexity (CC) of its minimum mean square error (MMSE) precoders, and compare this CC with its counterpart in CI and DI. Numerical results demonstrate that employing an optimal number of LPs (between 2 and 4) in our proposed LPs-AS, not only enables us to design DL precoders with significantly low CC but also results in an efficient SDI that effectively addresses the problem of low SE in DI.
Keywords
Local Processors-Assisted Structure
Semi-Distributed Implementation
Local Processor
Computational Complexity
Spectral Efficiency
Subjects
[1] E. Björnson, R. Zakhour, D. Gesbert, B. Ottersten, Cooperative multicell precoding: Rate region characterization and distributed strategies with instantaneous and statistical CSI, IEEE Transactions on Signal Processing, 58(8) (2010) 4298-4310.
[2] E. Nayebi, A. Ashikhmin, T.L. Marzetta, H. Yang, B.D. Rao, Precoding and power optimization in cell-free massive MIMO systems, IEEE Transactions on Wireless Communications, 16(7) (2017) 4445-4459.
[3] H.Q. Ngo, A. Ashikhmin, H. Yang, E.G. Larsson, T.L. Marzetta, Cell-free massive MIMO versus small cells, IEEE Transactions on Wireless Communications, 16(3) (2017) 1834-1850.
[4] J. Zhang, E. Björnson, M. Matthaiou, D.W.K. Ng, H. Yang, D.J. Love, Prospective multiple antenna technologies for beyond 5G, IEEE Journal on Selected Areas in Communications, 38(8) (2020) 1637-1660.
[5] C. Beldi, E. Gourar, D. Le Ruyet, H. Shaiek, F. Abdelkefi, Cell-Free Massive MIMO with Imperfect Channel State Information and Hardware Impairments, in:  2024 19th International Symposium on Wireless Communication Systems (ISWCS), IEEE, 2024, pp. 1-6.
[6] F. Riera-Palou, G. Femenias, D. López-Pérez, N. Piovesan, A. de Domenico, Cell-free Processing for 5G Massive MIMO Deployments: Sleep Modes and User Stream Management, IEEE Transactions on Vehicular Technology,  (2024).
[7] M. Joham, W. Utschick, J.A. Nossek, Linear transmit processing in MIMO communications systems, IEEE Transactions on signal Processing, 53(8) (2005) 2700-2712.
[8] Ö.T. Demir, E. Björnson, L. Sanguinetti, Foundations of user-centric cell-free massive MIMO, Foundations and Trends® in Signal Processing, 14(3-4) (2021) 162-472.
[9] D. Wang, M. Tao, X. Zeng, J. Liang, Federated learning for precoding design in cell-free massive mimo systems, IEEE Open Journal of the Communications Society,  (2023).
[10] S.S. Christensen, R. Agarwal, E. De Carvalho, J.M. Cioffi, Weighted sum-rate maximization using weighted MMSE for MIMO-BC beamforming design, IEEE Transactions on Wireless Communications, 7(12) (2008) 4792-4799.
[11] E. Mostafapour, C. Ghobadi, J. Nourinia, N. Ezzati, The one‐bit diffusion for distributed beamforming over cell free wireless networks, IET Communications, 17(19) (2023) 2210-2218.
[12] X. Qiao, Y. Zhang, H. Zhao, L. Yang, H. Zhu, Two-Layer Large Scale Fading Precoding for Cell-Free Massive MIMO: Performance Analysis and Optimization, IEEE Transactions on Vehicular Technology,  (2023).
[13] E. Björnson, J. Hoydis, L. Sanguinetti, Massive MIMO networks: Spectral, energy, and hardware efficiency, Foundations and Trends® in Signal Processing, 11(3-4) (2017) 154-655.
[14] T.L. Marzetta, E.G. Larsson, H. Yang, H.Q. Ngo, Fundamentals of massive MIMO, Cambridge University Press, 2016.
[15] X. Ma, D. Zhang, M. Xiao, C. Huang, Z. Chen, Cooperative beamforming for RIS-aided cell-free massive MIMO networks, IEEE Transactions on Wireless Communications, 22(11) (2023) 7243-7258.
[16] L. Miretti, E. Björnson, D. Gesbert, Team MMSE precoding with applications to cell-free massive MIMO, IEEE Transactions on Wireless Communications, 21(8) (2022) 6242-6255.
[17] J. Zheng, J. Zhang, B. Ai, Team-Optimal MMSE Combining for Cell-Free Massive MIMO Systems, in:  ICC 2022-IEEE International Conference on Communications, IEEE, 2022, pp. 1306-1311.
[18] I. Atzeni, B. Gouda, A. Tölli, Distributed precoding design via over-the-air signaling for cell-free massive MIMO, IEEE Transactions on Wireless Communications, 20(2) (2020) 1201-1216.
[19] B. Gouda, I. Atzeni, A. Tölli, Distributed precoding design for multi-group multicasting in cell-free massive MIMO, in:  GLOBECOM 2022-2022 IEEE Global Communications Conference, IEEE, 2022, pp. 2388-2393.
[20] B. Gouda, I. Atzeni, A. Tölli, Pilot-aided distributed multi-group multicast precoding design for cell-free massive MIMO, IEEE Transactions on Wireless Communications,  (2024).
[21] S. Saad, A. Almamori, Energy Efficiency Optimization of Cell-Free Massive MIMO with Zero Forcing Precoding, Wireless Personal Communications, 138(1) (2024) 387-408.
[22] J. Kaleva, A. Tölli, M. Juntti, R.A. Berry, M.L. Honig, Decentralized joint precoding with pilot-aided beamformer estimation, IEEE Transactions on Signal Processing, 66(9) (2018) 2330-2341.
[23] N. Fatema, G. Hua, Y. Xiang, D. Peng, I. Natgunanathan, Massive MIMO linear precoding: A survey, IEEE systems journal, 12(4) (2017) 3920-3931.
[24] G. Interdonato, E. Björnson, H. Quoc Ngo, P. Frenger, E.G. Larsson, Ubiquitous cell-free massive MIMO communications, EURASIP Journal on Wireless Communications and Networking, 2019(1) (2019) 1-13.
[25] Y. Shi, J. Zhang, B. O'Donoghue, K.B. Letaief, Large-scale convex optimization for dense wireless cooperative networks, IEEE Transactions on Signal Processing, 63(18) (2015) 4729-4743.
[26] A. Girycki, M.A. Rahman, E. Vinogradov, S. Pollin, Learning-Based Precoding-Aware Radio Resource Scheduling for Cell-Free mMIMO Networks, IEEE Transactions on Wireless Communications, 23(5) (2023) 4876-4888.
[27] Y. Zhang, J. Zhang, Y. Jin, S. Buzzi, B. Ai, Deep learning-based power control for uplink cell-free massive MIMO systems, in:  2021 IEEE global communications conference (GLOBECOM), IEEE, 2021, pp. 1-6.
[28] S. Chakraborty, Ö.T. Demir, E. Björnson, P. Giselsson, Efficient downlink power allocation algorithms for cell-free massive MIMO systems, IEEE Open Journal of the Communications Society, 2 (2020) 168-186.
[29] V.S. Annapureddy, V.V. Veeravalli, Sum capacity of MIMO interference channels in the low interference regime, IEEE Transactions on Information Theory, 57(5) (2011) 2565-2581.
[30] E. Björnson, E. Jorswieck, Optimal resource allocation in coordinated multi-cell systems, Foundations and Trends® in Communications and Information Theory, 9(2–3) (2013) 113-381.
[31] R. Brandt, E. Björnson, M. Bengtsson, Weighted sum rate optimization for multicell MIMO systems with hardware-impaired transceivers, in:  2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE, 2014, pp. 479-483.
[32] Q. Shi, M. Razaviyayn, Z.-Q. Luo, C. He, An iteratively weighted MMSE approach to distributed sum-utility maximization for a MIMO interfering broadcast channel, IEEE Transactions on Signal Processing, 59(9) (2011) 4331-4340.
[33] 3GPP, Feasibility study for further advancements for E‐UTRA (LTE‐advanced), Feasibility study for further advancements for E-UTRA (LTE-Advanced),  (2011).
[34] E. Björnson, L. Sanguinetti, Making cell-free massive MIMO competitive with MMSE processing and centralized implementation, IEEE Transactions on Wireless Communications, 19(1) (2019) 77-90.