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

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

doi:10.1109/wcnc51071.2022.9771760

Cited by 7 publications

(2 citation statements)

References 8 publications

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“…We develop an SRS pilot sequence assignment based on mutually orthogonal Latin squares [9] aiming to reduce outliers, and propose the R-PCA algorithm from [10] at the RUs for subspace estimation of their associated users. While we have assumed perfect subspace knowledge in [5], [11], we show in this paper that the proposed schemes lead to accurate subspace estimates being able to closely approach the system performance assuming perfect subspace knowledge and ideal partial channel state information (CSI), respectively.…”

Section: Introductionmentioning

confidence: 97%

Robust PCA for Subspace Estimation in User-Centric Cell-Free Wireless Networks

Göttsch

Osawa

Ohseki

et al. 2022

2022 IEEE 23rd International Workshop on Signal Processing Advances in Wireless Communication (SPAWC)

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We consider a scalable user-centric cell-free massive MIMO network with distributed remote radio units (RUs), enabling macrodiversity and joint processing. Due to the limited uplink (UL) pilot dimension, multiuser interference in the UL pilot transmission phase makes channel estimation a non-trivial problem. We make use of two types of UL pilot signals, sounding reference signal (SRS) and demodulation reference signal (DMRS) pilots, for the estimation of the channel subspace and its instantaneous realization, respectively. The SRS pilots are transmitted over multiple time slots and resource blocks according to a Latin squares based hopping scheme, which aims at averaging out the interference of different SRS co-pilot users. We propose a robust principle component analysis approach for channel subspace estimation from the SRS signal samples, employed at the RUs for each associated user. The estimated subspace is further used at the RUs for DMRS pilot decontamination and instantaneous channel estimation. We provide numerical simulations to compare the system performance using our subspace and channel estimation scheme with the cases of ideal partial subspace/channel knowledge and pilot matching channel estimation. The results show that a system with a properly designed SRS pilot hopping scheme can closely approximate the performance of a genie-aided system.

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Section: Introductionmentioning

confidence: 97%

Robust PCA for Subspace Estimation in User-Centric Cell-Free Wireless Networks

Göttsch

Osawa

Ohseki

et al. 2022

2022 IEEE 23rd International Workshop on Signal Processing Advances in Wireless Communication (SPAWC)

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“…As one of the pilot decontamination methods, in [3], [4], we have investigated a subspace projection (SP) based channel estimation, which uses receiver side discrete Fourier transform (DFT) processing. In this paper, channel subspace means the space on dominant signals of the MIMO channel covariance matrix which is observed by applying principal component analysis (PCA).…”

Section: Introductionmentioning

confidence: 99%

Effective Overloaded Pilot Assignment with Pilot Decontamination for Cell-Free Systems

Osawa¹,

Göttsch²,

Ohseki³

et al. 2022

Preprint

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The pilot contamination in cell-free massive multipleinput-multiple-output (CF-mMIMO) must be addressed for accommodating a large number of users. We have investigated a decontamination method called subspace projection (SP). The SP separates interference from co-pilot users by using the orthogonality of subspaces of each users' principal components. The SP based decontamination has a potential to further improve spectral efficiency (SE), which is limited by a non-overloaded pilot assignment (PA) rule where each radio unit (RU) does not assign the same pilot to different users. Motivated by this limitation, this paper introduces semi-overloaded and overloaded PA methods adjusted for the decontamination in order to improve the sum SE of CF systems. Numerical simulations show that the overloaded and semi-overloaded PA give higher SE than that of non-overloaded PA at a high user density scenario.

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QoS-Aware Downlink Beamforming for Joint Transmission in Multi-Cell Networks

Lin,

Liu

2023

2023 Asia Pacific Signal and Information Processing Association Annual Summit and Conference (APSIPA ASC)

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

Cited by 7 publications

References 8 publications

Robust PCA for Subspace Estimation in User-Centric Cell-Free Wireless Networks

Robust PCA for Subspace Estimation in User-Centric Cell-Free Wireless Networks

Effective Overloaded Pilot Assignment with Pilot Decontamination for Cell-Free Systems

QoS-Aware Downlink Beamforming for Joint Transmission in Multi-Cell Networks

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