แนวคิดหลัก
The core message of this article is to investigate the performance of an active reconfigurable intelligent surface (RIS)-aided uplink massive multiple-input multiple-output (MIMO) system in the presence of imperfect channel state information (CSI) and phase noise at the active RIS. The authors derive a closed-form expression for a lower bound of the achievable rate and analyze the power scaling laws of the considered system.
บทคัดย่อ
The article focuses on an active RIS-aided uplink massive MIMO wireless communication system, considering the phase noise at the active RIS and the direct links between the users and the base station (BS).
Key highlights:
- The authors employ a two-timescale scheme, where the beamforming at the BS is adjusted based on the instantaneous aggregated CSI, and the statistical CSI serves as the basis for designing the phase shifts at the active RIS, to reduce the feedback overhead and computational complexity.
- The authors derive the analytical closed-form expression of a lower bound of the achievable rate based on the estimated aggregated channel using the linear minimum mean square error (LMMSE) technique.
- The power scaling laws of the active RIS-aided system are investigated, and the authors find that the thermal noise will cause the lower bound of the achievable rate to approach zero as the number of BS antennas or reflecting elements increases to infinity.
- An optimization approach based on genetic algorithms is introduced to tackle the phase shift optimization problem, aiming to maximize the minimum user rate and ensure fairness among multiple users.
- Numerical results reveal that the active RIS can greatly enhance the performance of the considered system under various settings.
สถิติ
The total power consumption of the uplink active RIS-aided system is given by Ptotal = ∑K
k=1 p + Pcir + ξ−1PA, where Pcir = N (PSC + PDC) is the circuit power, and ξ is the power amplifier efficiency.
The large-scale fading coefficients for the user-RIS channel, RIS-BS channel, and user-BS channel are modeled as αk = 10−3r−2
UR, β = 10−3d−2.8
RB, and γk = 10−3dUB
k
−4.2, respectively.
คำพูด
"Owing to its capability to amplify the incident signals, active RIS can mitigate the multiplicative fading effect inherent in the passive RIS-aided system."
"We find that the thermal noise will cause the lower bound of the achievable rate to approach zero as the number of M or N increases to infinity."