A New RIS Architecture With a Single Power Amplifier: Energy Efficiency and Error Performance Analysis

Abstract

Reconfigurable intelligent surface (RIS)-assisted communication has recently attracted the community's attention as a potential candidate for next generation wireless communication networks. Various studies have been carried out on this technology, which allows the control of the signal propagation environment by network operators. However, when an RIS is used in its inherently passive structure, it appears to be only a supportive technology for communications, while suffering from a multiplicative path loss. Therefore, researchers have lately begun to focus on RIS hardware designs with minimal active elements to further boost the benefits of this technology. In this paper, we present a simple hardware architecture for RISs including a single and variable gain amplifier for reflection amplification to confront the multiplicative path loss. The end-to-end signal model for communication systems assisted with the proposed amplifying RIS design is presented, together with an analysis focusing on the capacity maximization and theoretical bit error probability performance, which is verified by computer simulations. In addition, the advantages of the proposed amplifying RIS design compared to its passive counterpart are discussed. It is shown that the proposed RIS-based system significantly eliminates the double fading problem appearing in conventional passive RIS-assisted systems and improves the energy efficiency.INDEX TERMS Reconfigurable intelligent surface (RIS), active RIS, amplifying RIS, energy efficiency, performance analysis.

Reconfigurable Intelligent Surface Enabled Over-the-Air Uplink Non-orthogonal Multiple Access

“…By combining passive and active RIS technologies, hybrid systems may be constructed to enhance communication system performances and novel solutions [22], [24]. Albeit its numerous benefits, active RIS designs also have drawbacks such as increased hardware complexity, increased power consumption and costs [17]. Hence, hybrid designs considering passive and active architectures are more promising.…”

“…Additionally, considering α is the same for all elements, the gain α can also be expressed in terms of the system parameters as α = P RIS t /M P t C h , where C h is the average channel power of the users. It is important to note that for practicality, α is limited to a minimum of 0 dB and a maximum of 30 dB [17]. However, for the sake of better visualization explanations, Fig.…”

“…An RIS is a large array with many cost-effective elements that can reflect, adjust, absorb and even amplify impinging signals with an adjustable reflecting coefficient [8]. By doing so, RISs may artificially enhance existing wireless communication by suppressing interference [9]- [11], increasing capacity [12], [13], extending coverage [14]- [16], and providing energy efficiency [17]- [19], all without the need for additional RF chains. RISs may also be used in applications such as localization, Wi-Fi, etc.…”

“…RISs typically work best in scenarios where direct links do not exist or are substantially weak [5], [20], [21]. Furthermore, a major challenge in RIS technology is the multiplicative path loss of the transmitter-RIS-receiver link, hence, making significant gains very difficult for passive RIS designs [5], [17], [22], [23].…”

Pervasive Machine Learning for Smart Radio Environments Enabled by Reconfigurable Intelligent Surfaces

“…The authors in [89] considered the application of RISs to assist the uplink transmission from multiple UEs to a multi-antenna BS, and devised an optimization framework for jointly designing the transmit covariance matrices and the RIS phase profile with partial Channel State Information (CSI). In [90], [91], active RISs were considered, which can adapt the phase and amplify the magnitude of the reflected incident signal simultaneously with the support of an additional power source. A joint optimization of the RIS phase profile and the BS beamforming vector was presented in [90] with the objective to minimize the BS transmit power.…”