The Impact of Subspace-Based Pilot Decontamination in User-Centric Scalable Cell-Free Wireless Networks

Göttsch, Fabian; Osawa, Noboru; Ohseki, Takeo; Yamazaki, Kosuke; Caire, Giuseppe

doi:10.1109/spawc51858.2021.9593169

Cited by 13 publications

(27 citation statements)

References 7 publications

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“…However, we allow each RRH to have an M -antennas array, such that the total number of antenna elements M L is generally larger than K. We employ a scalable user-centric architecture based on dynamic cluster formation, as proposed in several recent papers (see [5]), such that every UE is served by a finite-size cluster of RRHs even if the network is arbitrarily large. We extend our previous work [6] by investigating DL precoding and power allocation schemes. UL-DL SINR duality in cell-free wireless networks was studied in [7] and shown to hold in terms of the Signal to Interference plus Noise Ratio (SINR) expression resulting from the so-called use-and-then-forget (UatF) bound, where all necessary terms to compute the "true" UatF bound are assumed to be somehow known to a central processor (CP) devoted to DL power allocation.…”

Section: Introductionmentioning

confidence: 86%

“…with components CN p0, 1 τpSNR q. The second term in (31) contains the remaining pilot contamination from UEs i ‰ k using the same pilot t k (see [6] for details).…”

Section: Ul Channel Estimationmentioning

confidence: 99%

“…We refer the reader to our previous work [6] for a detailed system model description, and provide a summary in the following. We consider a cell-free wireless network in TDD operation mode with L RRHs, each equipped with M antennas, and K single-antenna UEs.…”

Section: System Modelmentioning

confidence: 99%

“…Both RRHs and UEs are distributed on a squared region on the 2-dimensional plane. As a result of the cluster formation scheme in [6] with SNR threshold η, each UE k is connected to a cluster C k Ď rLs " t1, 2, . .…”

Section: System Modelmentioning

confidence: 99%

“…However, it incurs the disadvantage of centralized power allocation computation, requiring OpK 2 q signal coefficients to be collected at a processing unit to compute the duality DL powers. We compare the DL rates achieved with the proposed nominal UL-DL duality to equal power allocation (EPA), using the proposed combining methods in [6]. Further, we compare with two state-of-the-art distributed schemes, local partial zero-forcing from [8] and local zero-forcing adapted to a system with user-centric clusters.…”

Section: Introductionmentioning

confidence: 99%

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Uplink-Downlink Duality and Precoding Strategies with Partial CSI in Cell-Free Wireless Networks

Göttsch¹,

Osawa²,

Ohseki³

et al. 2022

Preprint

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We consider a scalable user-centric wireless network with dynamic cluster formation as defined by Björnsson and Sanguinetti. After having shown the importance of dominant channel subspace information for uplink (UL) pilot decontamination and having examined different UL combining schemes in our previous work, here we investigate precoding strategies for the downlink (DL). Distributed scalable DL precoding and power allocation methods are evaluated for different antenna distributions, user densities and UL pilot dimensions. We compare distributed power allocation methods to a scheme based on a particular form of UL-DL duality which is computable by a central processor based on the available partial channel state information. The new duality method achieves almost symmetric "optimistic ergodic rates" for UL and DL while saving considerable computational complexity since the UL combining vectors are reused as DL precoders.

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Section: Introductionmentioning

confidence: 86%

“…with components CN p0, 1 τpSNR q. The second term in (31) contains the remaining pilot contamination from UEs i ‰ k using the same pilot t k (see [6] for details).…”

Section: Ul Channel Estimationmentioning

confidence: 99%

Section: System Modelmentioning

confidence: 99%

Section: System Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Uplink-Downlink Duality and Precoding Strategies with Partial CSI in Cell-Free Wireless Networks

Göttsch¹,

Osawa²,

Ohseki³

et al. 2022

Preprint

Self Cite

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Dynamic Fronthaul Load Optimization for Uplink Scalable Cell-Free User-Centric Massive MIMO

Li,

Göttsch,

et al. 2024

ICC 2024 - IEEE International Conference on Communications

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Fairness Scheduling in Dense User-Centric Cell-Free Massive MIMO Networks

Göttsch

Osawa

Ohseki

et al. 2022

2022 56th Asilomar Conference on Signals, Systems, and Computers

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We consider fairness scheduling in a user-centric cell-free massive MIMO network, where L remote radio units, each with M antennas, serve K « LM user equipments (UEs). Recent results show that the maximum network sum throughput is achieved where Kact « LM 2 UEs are simultaneously active in any given time-frequency slots. However, the number of users K in the network is usually much larger. This requires that users are scheduled over the time-frequency resource and achieve a certain throughput rate as an average over the slots. We impose throughput fairness among UEs with a scheduling approach aiming to maximize a concave component-wise non-decreasing network utility function of the per-user throughput rates. In cell-free user-centric networks, the pilot and cluster assignment is usually done for a given set of active users. Combined with fairness scheduling, this requires pilot and cluster reassignment at each scheduling slot, involving an enormous overhead of control signaling exchange between network entities. We propose a fixed pilot and cluster assignment scheme (independent of the scheduling decisions), which outperforms the baseline method in terms of UE throughput, while requiring much less control information exchange between network entities.

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The Impact of Subspace-Based Pilot Decontamination in User-Centric Scalable Cell-Free Wireless Networks

Cited by 13 publications

References 7 publications

Uplink-Downlink Duality and Precoding Strategies with Partial CSI in Cell-Free Wireless Networks

Uplink-Downlink Duality and Precoding Strategies with Partial CSI in Cell-Free Wireless Networks

Dynamic Fronthaul Load Optimization for Uplink Scalable Cell-Free User-Centric Massive MIMO

Fairness Scheduling in Dense User-Centric Cell-Free Massive MIMO Networks

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