Hybrid Active-Passive RIS Transmitter Enabled Energy-Efficient Multi-User Communications

A novel hybrid active-passive reconfigurable intelligent surface (RIS) transmitter enabled downlink multi-user communication system is investigated. Specifically, RISs are exploited to serve as transmitter antennas, where each element can flexibly switch between active and passive modes to deliver i...

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Veröffentlicht in:IEEE transactions on wireless communications Jg. 23; H. 9; S. 10653 - 10666
Hauptverfasser: Huang, Ao, Mu, Xidong, Guo, Li, Zhu, Guangyu
Format: Journal Article
Sprache:Englisch
Veröffentlicht: New York IEEE 01.09.2024
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Schlagworte:
Algorithms
Antennas
Array signal processing
Beamforming
Communications systems
Complexity
Downlink
Energy efficiency
energy-efficient design
hybrid reconfigurable intelligent surface
Mixed integer
mixed-integer nonlinear programming
Multi-user communication
Nonlinear programming
Optimization
Radio transmitters
Reconfigurable intelligent surfaces
Resource management
RIS element scheduling
Transmitters
Transmitting antennas
Wireless communication
ISSN:1536-1276, 1558-2248
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Zusammenfassung:A novel hybrid active-passive reconfigurable intelligent surface (RIS) transmitter enabled downlink multi-user communication system is investigated. Specifically, RISs are exploited to serve as transmitter antennas, where each element can flexibly switch between active and passive modes to deliver information to multiple users. The system energy efficiency (EE) maximization problem is formulated by jointly optimizing the RIS element scheduling and beamforming coefficients, as well as the power allocation coefficients, subject to the user's individual rate requirement and the maximum RIS amplification power constraint. Using the Dinkelbach relaxation, the original mixed-integer nonlinear programming problem is transformed into a nonfractional optimization problem with a two-layer structure, which is solved by the alternating optimization approach. In particular, an exhaustive search method is proposed to determine the optimal operating mode for each RIS element. Then, the RIS beamforming and power allocation coefficients are properly designed in an alternating manner. To overcome the potentially high complexity caused by exhaustive searching, we further develop a joint RIS element mode and beamforming optimization scheme by exploiting the Big-M formulation technique. Numerical results validate that: 1) The proposed hybrid RIS scheme yields higher EE than the baseline multi-antenna schemes employing fully active/passive RIS or conventional radio frequency chains; 2) Both proposed algorithms are effective in improving the system performance, especially the latter can achieve precise design of RIS elements with low complexity; and 3) For a fixed-size hybrid RIS, maximum EE can be reaped by setting only a minority of elements to operate in the active mode.
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ISSN:1536-1276
1558-2248
DOI:10.1109/TWC.2024.3373900