Spectral Efficiency Analysis of Hybrid Relay-Reflecting Intelligent Surface-Assisted Cell-Free Massive MIMO Systems

Nguyen, Nhan T.; Nguyen, Van‐Dinh; Nguyen, Hieu V.; Ngo, Hien Quoc; Chatzinotas, Symeon; Juntti, Markku

doi:10.1109/twc.2022.3217828

Cited by 28 publications

(11 citation statements)

References 68 publications

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“…Motivated by this, the works [13] and [14] investigated the key benefits of active RIS-assisted networks in terms of secrecy improvement and throughput maximization. In addition, the authors of [15] proposed another RIS architecture enabling simultaneous signal reflection and amplification, termed hybrid relay-RIS (HR-RIS). Different from the active RIS that enables signal amplification by embedding negative resistance components into each element, HR-RIS requires expensive and powerhungry RF chains to amplify signals.…”

Section: A Related Workmentioning

confidence: 99%

Intelligent Reflecting Surface-Aided Full-Duplex Covert Communications: Information Freshness Optimization

Wang

Zheng

et al. 2023

IEEE Trans. Wireless Commun.

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Although reconfigurable intelligent surfaces (RISs) can improve the performance of wireless networks by smartly reconfiguring the radio environment, existing passive RISs face two key challenges, i.e., double-fading attenuation and dependence on grid/battery. To address these challenges, this paper proposes a new RIS architecture, called multi-functional RIS (MF-RIS). Different from conventional reflecting-only RIS, the proposed MF-RIS is capable of supporting multiple functions with one surface, including signal reflection, amplification, and energy harvesting. As such, our MF-RIS is able to overcome the double-fading attenuation by harvesting energy from incident signals. Through theoretical analysis, we derive the achievable capacity of an MF-RIS-aided communication network. Compared to the capacity achieved by the existing self-sustainable RIS, we derive the number of reflective elements required for MF-RIS to outperform self-sustainable RIS. To realize a self-sustainable communication system, we investigate the use of MF-RIS in improving the sum-rate of multi-user wireless networks. Specifically, we solve a non-convex optimization problem by jointly designing the transmit beamforming and MF-RIS coefficients. As an extension, we investigate a resource allocation problem in a practical scenario with imperfect channel state information. By approximating the semi-infinite constraints with the Sprocedure and the general sign-definiteness, we propose a robust beamforming scheme to combat the inevitable channel estimation errors. Finally, numerical results show that: 1) compared to the self-sustainable RIS, MF-RIS can strike a better balance between energy self-sustainability and throughput improvement; and 2) unlike reflecting-only RIS which can be deployed near the transmitter or receiver, MF-RIS should be deployed closer to the transmitter for higher spectrum efficiency.

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Section: A Related Workmentioning

confidence: 99%

Intelligent Reflecting Surface-Aided Full-Duplex Covert Communications: Information Freshness Optimization

Wang

Zheng

et al. 2023

IEEE Trans. Wireless Commun.

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“…Simulations revealed that the proposed algorithm outperforms the benchmark algorithms that optimize one or two types of these parameters. In [18], Nguyen et al designed a hybrid Relay-RIS architecture in which a small number of passive elements are substituted with active processing units and pointed out that the proposed hybrid Relay-RIS architecture achieves a significant improvement in the SE performance over the pure passive RIS architecture at the cost of increased power consumption. Note that [15]- [18] all used the DE scheme, which minimizes the pilot overhead but degrades the accuracy of the channel estimation.…”

Section: A Related Workmentioning

confidence: 99%

“…In [18], Nguyen et al designed a hybrid Relay-RIS architecture in which a small number of passive elements are substituted with active processing units and pointed out that the proposed hybrid Relay-RIS architecture achieves a significant improvement in the SE performance over the pure passive RIS architecture at the cost of increased power consumption. Note that [15]- [18] all used the DE scheme, which minimizes the pilot overhead but degrades the accuracy of the channel estimation. Bashar et al [19] designed an ON/OFF estimation (OE) scheme that estimated the indirect RIS-assisted channel sequentially and proposed an efficient max-min SE optimization algorithm with respect to the RIS phase shifts under zero-forcing receivers.…”

Section: A Related Workmentioning

confidence: 99%

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Performance Analysis of RIS-Assisted Cell-Free Massive MIMO Systems With Transceiver Hardware Impairments

Zhang,

Xia,

Zhao

et al. 2023

IEEE Trans. Commun.

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Integrating reconfigurable intelligent surface (RIS) into cell-free massive multiple-input multiple-output (MIMO) is a promising approach to enhance the coverage quality, spectral efficiency (SE), and energy efficiency. In this paper, an RISassisted cell-free massive MIMO downlink system suffering from the transceiver hardware impairments (T-HWIs) is investigated. To improve the accuracy of the direct estimation (DE) scheme, a modified ON/OFF estimation (MOE) with moderate pilot overhead is proposed. Relying on the knowledge of imperfect channel state information, we derive closed-form expressions of the lower-bound achievable SE with T-HWIs under both DE and MOE schemes. The closed-form results facilitate the investigation of how RIS improves the downlink SE under various system settings and allow us to explore the trade-off strategies between using more hardware-impaired APs and low-cost RISs in terms of the downlink SE and power consumption. Numerical results validate the theoretical analysis and show that the proposed MOE scheme outperforms the DE scheme in terms of the downlink SE. Moreover, the benefits of introducing RIS into hardwareimpaired cell-free massive MIMO systems are also illustrated.Index Terms-Cell-free massive multiple-input multiple-output (MIMO), reconfigurable intelligent surface (RIS), transceiver hardware impairments (T-HWIs), channel estimation, performance analysis. I. INTRODUCTIONAs a potential candidate technology for future sixthgeneration (6G) communications, cell-free massive multipleinput multiple-output (MIMO) is attracting growing interest

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“…In a UC CF-mMIMO system, each AP serves only a predefined number of UEs rather than all. Recently, in [28], authors proposed the hybrid relay-reflecting intelligent surface-assisted CF-mMIMO system where the SE for the uplink and downlink of the proposed system was analyzed. Most of the papers mentioned above derived and analyzed SE using the popular use-and-then-forget (UaTF) bound.…”

mentioning

confidence: 99%

Outage Probability Analysis of Uplink Cell-Free Massive MIMO Network With and Without Pilot Contamination

Shekhar,

Srinivasan,

Kalyani

et al. 2024

IEEE Open J. Commun. Soc.

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This paper derives approximate outage probability (OP) expressions for uplink cell-free massive multiple-input-multiple-output (CF-mMIMO) systems with and without pilot contamination. The system's access points (APs) are considered to have imperfect channel state information (CSI). The signalto-interference-plus-noise ratio (SINR) of the CF-mMIMO system is approximated via a Log-normal distribution using a two-step moment matching method. OP and ergodic rate expressions are derived with the help of the approximated Log-normal distribution. For the no-pilot contamination scenario, an exact expression is first derived using conditional expectations in terms of a multi-fold integral. Then, a novel dimension reduction method is used to approximate it by the sum of single-variable integrations. Both the approximations derived for the CF-mMIMO systems are also useful for single-cell collocated massive MIMO (mMIMO) systems and lead to closed-form expression. The derived expressions closely match the simulated numerical values for OP and ergodic rate. INDEX TERMS Cell-free massive MIMO, outage probability, univariate dimension reduction I. INTRODUCTIONC ELL-free massive multiple-input multiple-output (CF-mMIMO) system is envisioned as a key enabler for sixth-generation (6G) communication systems. [1]-[4]. CF-mMIMO system contains many access points (APs) that are connected to a central processing unit (CPU) and jointly serve all the user equipment (UE) by coherent joint transmission and reception [5], [6]. The name cell-free comes from the fact that there are no boundaries, and each AP serves all the UEs. This differs from a conventional small-cell system where each AP serves only a particular set of UEs. Early works in [7], [8] compare the CF-mMIMO system with a conventional small-cell system and show a multifold improvement in 95%-likely throughput can be expected from CF-mMIMO.

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Spectral Efficiency Analysis of Hybrid Relay-Reflecting Intelligent Surface-Assisted Cell-Free Massive MIMO Systems

Cited by 28 publications

References 68 publications

Intelligent Reflecting Surface-Aided Full-Duplex Covert Communications: Information Freshness Optimization

Intelligent Reflecting Surface-Aided Full-Duplex Covert Communications: Information Freshness Optimization

Performance Analysis of RIS-Assisted Cell-Free Massive MIMO Systems With Transceiver Hardware Impairments

Outage Probability Analysis of Uplink Cell-Free Massive MIMO Network With and Without Pilot Contamination

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