Limiting Doppler Shift Effect on Cell-Free Massive MIMO Systems: A Stochastic Geometry Approach

Elhoushy, Salah; Hamouda, Walaa

doi:10.1109/twc.2021.3069141

Cited by 10 publications

(3 citation statements)

References 30 publications

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“…System performance analysis of cell-free massive MIMO has been thoroughly studied [5], [32], [33] in the literature. [5] studied the downlink transmission and analyzed the average user rate (i.e., the achievable ergodic rate averaged over AP and user positions) with both maximum ratio transmission (MRT) and zero-forcing beamforming (ZFBF).…”

Section: Related Workmentioning

confidence: 99%

“…[5] studied the downlink transmission and analyzed the average user rate (i.e., the achievable ergodic rate averaged over AP and user positions) with both maximum ratio transmission (MRT) and zero-forcing beamforming (ZFBF). [32] assumed that APs are Poisson point process (PPP) distributed and formulated a lower-bound of the downlink average spectral efficiency based on stochastic geometry. With both APs and users randomly distributed, approximate expressions of the average uplink rate were derived in [33].…”

Section: Related Workmentioning

confidence: 99%

“…Proof: See Appendix C. ■ By taking the first derivative of (30) with respect to λ, we have (32), shown at the bottom of this page. According to Theorem 1, one can obtain from (32) that…”

Section: B Optimal Ap-selection Ratio λ *mentioning

confidence: 99%

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Energy-Efficient Clustered Cell-Free Networking With Access Point Selection

Zhou,

Wang,

Liu

et al. 2024

IEEE Open J. Commun. Soc.

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Ultra-densely deploying access points (APs) to support the increasing data traffic would significantly escalate the cell-edge problem resulting from traditional cellular networks. By removing the cell boundaries and coordinating all APs for joint transmission, the cell-edge problem can be alleviated, which in turn leads to unaffordable system complexity and channel measurement overhead. A new scalable clustered cell-free network architecture has been proposed recently, under which the large-scale network is flexibly partitioned into a set of independent subnetworks operating parallelly. In this paper, we study the energy-efficient clustered cell-free networking problem with AP selection. Specifically, we propose a user-centric ratio-fixed AP-selection based clustering (UCR-ApSel) algorithm to form subnetworks dynamically. Following this, we analyze the average energy efficiency achieved with the proposed UCR-ApSel scheme theoretically and derive an effective closed-form upper-bound. Based on the analytical upper-bound expression, the optimal AP-selection ratio that maximizes the average energy efficiency is further derived as a simple explicit function of the total number of APs and the number of subnetworks. Simulation results demonstrate the effectiveness of the derived optimal AP-selection ratio and show that the proposed UCR-ApSel algorithm with the optimal AP-selection ratio achieves around 40% higher energy efficiency than the baselines. The analysis provides important insights to the design and optimization of future ultra-dense wireless communication systems.INDEX TERMS Clustered cell-free networking, subnetwork, clustering, energy efficiency analysis, access point selection I. IntroductionTraditional cellular network partitions the wireless network into a set of cells, and one base-station (BS) is located at the cell center to serve users within its coverage. Since users are randomly distributed, there might be users located in the cell boundary areas, leading to the well-known celledge problem, that is, the cell-edge users experience poor network services due to low received signal power and strong inter-cell interference. To support the extremely high data rate and low traffic delay of numerous intelligent devices and services, such as autonomous vehicles, smart homes, digital twins and holographic communications, BSs would be ultra-densely deployed in the sixth-generation (6G) mobile communication systems [2], which in turn exacerbates the cell-edge problem. Therefore, the cellular network architecture might not be suitable for future ultra-dense wireless communication systems.To avoid the cell-edge problem, coordinating all the geographically distributed access points (APs), which are equivalent to BSs, to jointly serve all users on the same

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