On Energy Efficiency of Wideband RIS-Aided Cell-Free Network

Siddiqi, Muhammad Zain; MacKenzie, Richard; Hao, Mo; Mir, Talha

doi:10.1109/access.2022.3149095

Cited by 15 publications

(12 citation statements)

References 40 publications

(46 reference statements)

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“…[38]. In addition, to apply in wideband scenario, the same problem is also extended to the OFDM-based system [39] . Particularly, the authors in Ref.…”

Section: Ris-aided Multi-user Transmission Scenariomentioning

confidence: 99%

Reconfigurable intelligent surface-aided wireless communications: An overview

Siddiqi

Mir

2022

Intell. and Converged Netw.

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The reconfigurable intelligent surface (RIS) is an emerging technology, which will hopefully bring a new revolution in wireless communications. The RIS technology can be deployed in an indoor/outdoor environment to dynamically manipulate the propagation environment. The RIS consists of a large number of independently controllable passive elements, and these elements are involved in realizing high passive beamforming gain. Different from the conventional active phased antenna array, there is no dedicated radio-frequency (RF) chain installed at the RIS to perform complex signal processing operations. Therefore, it does not incur additional noise while retransmitting the incident wave, which is substantially a unique feature from the conventional wireless communication systems.Taking advantage of its working principle, RIS has been deployed in various practical scenarios. In this tutorial, at first we will review the latest advances in RIS, including the application scenarios such as the system and channel model, the information theoretic analysis, the physical realization and design, key signal processing techniques such as precoding and channel estimation, and prototyping. Finally, we discuss interesting future research problems for the RIS-aided communications.

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“…[38]. In addition, to apply in wideband scenario, the same problem is also extended to the OFDM-based system [39] . Particularly, the authors in Ref.…”

Section: Ris-aided Multi-user Transmission Scenariomentioning

confidence: 99%

Reconfigurable intelligent surface-aided wireless communications: An overview

Siddiqi

Mir

2022

Intell. and Converged Netw.

Self Cite

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“…The semidefinite relaxation (SDR) technique was applied to solve the passive beamforming problem. In [22], Zhang et al enhanced the EE of cell-free networks by replacing some of the required power-hungry BSs with low-power RISs. A zero-forcing beamforming scheme was implemented to optimise the active beamforming at the BSs, whereas the sequential programming method was adopted to realise passive beamforming at the RISs.…”

Section: Literature Review and Background Workmentioning

confidence: 99%

“…where ‖Q‖ * = ∑ l 𝜇 l (Q) denotes the nuclear norm of Q and 𝜇 l (Q) denotes the l -th largest eigenvalue. Note that Equation (22) indicates that when ‖Q‖ * − 𝜇 1 (Q) → 0, Q has only one non-zero eigenvalue, and then the rank-one constraint (21f) is satisfied. Hence, we transform problem 4 ′ to 5:…”

Section: Passive Beamforming Optimisation With Given W 1 and Wmentioning

confidence: 99%

Energy efficiency of full‐duplex communication system assisted by reconfigurable intelligent surface

Wang

Guan

et al. 2022

IET Communications

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The sixth generation advocates green communications, thus energy efficiency (EE) has become an important metric. In this study, a method to increase the EE of a reconfigurable intelligent surface (RIS) aided point‐to‐point communication system is proposed, where both sources are equipped with multi‐antenna and operate in the full‐duplex (FD) mode. The extra power consumption for self‐interference cancellation in the FD mode is considered and modelled as a linear function of the transmission power. The EE maximisation problem is divided into an active beamforming subproblem for the two multi‐antenna sources and a passive beamforming subproblem for RIS, and an alternative optimisation framework is adopted to solve them iteratively. Dinkelbach's method is used to address the fractional objective function in the active beamforming optimisation problem. The penalty method and successive convex approximation are exploited for passive beamforming design. Simulation results show that the scheme can greatly boost the EE performance compared with the half‐duplex mode and is superior to the sum‐rate‐maximisation scheme in larger transmission power settings. The proposed method can be used to extend the lifetime of communication devices without deteriorating communication performance.

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“…In the relevant literature, to maximize the energy efficiency, Zhang et al [18] proposed a hybrid beamforming (HBF) scheme that decomposed the original optimization problem into two subproblems, i.e., the digital beamforming subproblem and the RIS-based analog beamforming subproblem. Furthermore, the authors of [19] proposed an alternate optimization (AO) algorithm to solve these two beamforming problems alternately by exploiting the zero-forcing (ZF) beamforming scheme and sequential programming (SP) method. An iterative precoding algorithm using Lagrangian transform and fractional programming (FP) was presented in [20] to maximize the energy efficiency of the worst user in a wideband RIS-aided cell-free network.…”

Section: Introductionmentioning

confidence: 99%

Two-Timescale Transmission Design for RIS-Aided Cell-Free Massive MIMO Systems

Dai¹,

Ge²,

Zhi³

et al. 2022

Preprint

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This paper investigates the performance of two-timescale transmission design for uplink reconfigurable intelligent surface (RIS)-aided cell-free massive multiple-input multiple-output (CF-mMIMO) systems. We consider the Rician channel model and design the passive beamforming of RISs based on the long-time statistical channel state information (CSI), while the maximum ratio combining (MRC) technique is utilized to design the active beamforming of base stations (BSs) based on the instantaneous overall channels, which are the superposition of the direct and RIS-reflected channels. Firstly, we derive the closed-form expressions of uplink achievable rate for arbitrary numbers of BS antennas and RIS reflecting elements. Relying on the derived expressions, we theoretically analyze the benefits of RISaided cell-free mMIMO systems and draw explicit insights. Then, based on closed-form expressions under statistical CSI, we maximize the sum user rate and the minimum user rate by optimizing the phase shifts of the RISs based on the genetic algorithm (GA). Finally, the numerical results demonstrate the feasibility and the benefits of deploying large-size RISs into conventional cell-free mMIMO systems.Besides, our results validate the effectiveness of the proposed two-timescale scheme in the RIS-aided cell-free mMIMO systems.

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On Energy Efficiency of Wideband RIS-Aided Cell-Free Network

Cited by 15 publications

References 40 publications

Reconfigurable intelligent surface-aided wireless communications: An overview

Reconfigurable intelligent surface-aided wireless communications: An overview

Energy efficiency of full‐duplex communication system assisted by reconfigurable intelligent surface

Two-Timescale Transmission Design for RIS-Aided Cell-Free Massive MIMO Systems

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