Robust Resource Allocation for STAR-RIS Assisted SWIPT Systems
IEEE Transactions on Wireless Communications(2024)
Abstract
A simultaneously transmitting and reflecting reconfigurable intelligent
surface (STAR-RIS) assisted simultaneous wireless information and power
transfer (SWIPT) system is proposed. More particularly, an STAR-RIS is deployed
to assist in the information/power transfer from a multi-antenna access point
(AP) to multiple single-antenna information users (IUs) and energy users (EUs),
where two practical STAR-RIS operating protocols, namely energy splitting (ES)
and time switching (TS), are employed. Under the imperfect channel state
information (CSI) condition, a multi-objective optimization problem (MOOP)
framework, that simultaneously maximizes the minimum data rate and minimum
harvested power, is employed to investigate the fundamental rate-energy
trade-off between IUs and EUs. To obtain the optimal robust resource allocation
strategy, the MOOP is first transformed into a single-objective optimization
problem (SOOP) via the ϵ-constraint method, which is then reformulated
by approximating semi-infinite inequality constraints with the S-procedure. For
ES, an alternating optimization (AO)-based algorithm is proposed to jointly
design AP active beamforming and STAR-RIS passive beamforming, where a penalty
method is leveraged in STAR-RIS beamforming design. Furthermore, the developed
algorithm is extended to optimize the time allocation policy and beamforming
vectors in a two-layer iterative manner for TS. Numerical results reveal that:
1) deploying STAR-RISs achieves a significant performance gain over
conventional RISs, especially in terms of harvested power for EUs; 2) the ES
protocol obtains a better user fairness performance when focusing only on IUs
or EUs, while the TS protocol yields a better balance between IUs and EUs; 3)
the imperfect CSI affects IUs more significantly than EUs, whereas TS can
confer a more robust design to attenuate these effects.
MoreTranslated text
Key words
Reconfigurable intelligent surfaces,simultaneous transmission and reflection,simultaneous wireless information and power transfer,resource allocation,imperfect CSI
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