2021 IEEE 93rd Vehicular Technology Conference (VTC2021-Spring) 2021
DOI: 10.1109/vtc2021-spring51267.2021.9448802
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Passive RIS vs. Hybrid RIS: A Comparative Study on Channel Estimation

Abstract: The reconfigurable intelligent surface (RIS) plays an important role in maintaining the connectivity in millimeter wave (mmWave) MIMO systems when the direct channel between the transceivers is blocked. However, it is difficult to acquire the channel state information (CSI), which is essential for the design of RIS phase control matrix and beamforming vectors at the transceivers. In this paper, we compare the channel estimation (CE) performance and achieved spectral efficiency (SE) of the purely passive and hy… Show more

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Cited by 49 publications
(41 citation statements)
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“…However, with the proposed HR-RIS architecture, the assumption is less restrictive than with a passive RIS, because the active processing chains can be readily used for channel estimation using their built-in active elements. Specifically, the CSI acquisition for the HR-RIS-aided systems can be conducted by the approaches proposed in [8], [40]. Thereby, our paper focuses on proposing the concept and demonstrates its significant system-level potential.…”
Section: B Motivations and Contributionsmentioning
confidence: 99%
“…However, with the proposed HR-RIS architecture, the assumption is less restrictive than with a passive RIS, because the active processing chains can be readily used for channel estimation using their built-in active elements. Specifically, the CSI acquisition for the HR-RIS-aided systems can be conducted by the approaches proposed in [8], [40]. Thereby, our paper focuses on proposing the concept and demonstrates its significant system-level potential.…”
Section: B Motivations and Contributionsmentioning
confidence: 99%
“…Here the sub-array technique enables the IRS array to be arranged into clusters with each cluster equipped with one RF chain for channel estimation. Similar to [3], in [163], [164], the authors propose a hybrid RIS with a few active elements connected to a RF chain for channel estimation. However, the proposed solutions are hindered by the power budget at the RIS/IRS, as each receive RF chain requires extra power to support the channel estimation operations [6] as well as increased RIS implementation complexity [164].…”
Section: A Ris-aided Rate-splitting Multiple Access (Rsma)mentioning
confidence: 99%
“…In this paper, we develop a new two-stage CE method under the hybrid RIS architecture. Unlike our previous work [16], the proposed CE requires fewer number of active RIS elements and only one-way training (either uplink or downlink). We consider uplink training, where the mobile station (MS) sends pilots to the base station (BS) via the RIS.…”
Section: Introductionmentioning
confidence: 99%
“…In order to ease the CE procedure, Taha et al [14] introduced a few active elements at the RIS with baseband capabilities, which allow the CE at the RIS despite the higher power consumption. Inspired by [14], the hybrid RIS architecture has been further studied in [15], [16], [17], [18]. In [16], we made a comparison in terms of CE between the passive and hybrid architectures for mmWave MIMO systems, which concludes that passive RIS is superior to the hybrid one when CE is done at the RIS.…”
Section: Introductionmentioning
confidence: 99%
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