9 research outputs found
Intelligent Reflecting Surface Aided Wireless Power Transfer With a DC-Combining Based Energy Receiver and Practical Waveforms
This paper studies intelligent reflecting surface (IRS) aided wireless power transfer (WPT) to batteryless Internet of Everything (IoE) devices. A practical energy receiver (ER) with multiple antennas is investigated. Multiple RF energy flows gleaned by all the receive antennas are input multiple energy harvesters, which are further rectified to direct-current (DC) energy. The resultant multiple DC energy flows are then combined in the DC domain for energy storage. Three classic waveforms, namely deterministic waveform, M-QAM waveform, and Gaussian waveform, are considered for WPT. We maximize the output DC power by jointly designing the active transmit beamformer of the transmitter and the passive reflecting beamformer of the IRS with the above-mentioned waveforms, respectively, subject to the transmit power constraint at the transmitter and to the limited resolution constraints on the phase-shifters of the IRS. A low complexity alternating optimization (AO) algorithm is proposed, which converges to a Karush-Kuhn-Tucker (KKT) point and thus results in a locally optimal solution. The numerical results demonstrate that the Gaussian waveform has the best energy performance with a low input RF power to the energy harvesters. By contrast, the deterministic waveform becomes superior with a high input RF power to the energy harvesters
Joint Transceiving and Reflecting Design for Intelligent Reflecting Surface Aided Wireless Power Transfer
In an intelligent reflecting surface (IRS) aided wireless power transfer (WPT) system, a practical architecture of an energy receiver (ER) is proposed, which includes multiple receive antennas, an analog energy combiner, a power splitter and multiple energy harvesters. In order to maximise the output direct-current (DC) power, the transmit beamformer of the transmitter, the passive beamformer of the IRS, the energy combiner, and the power splitter of the ER are jointly optimised. The optimisation problem is equivalently divided into two sub-problems, which independently maximises the input RF power and the output DC power of the energy harvesters, respectively. A successive linear approximation (SLA) based algorithm with a low complexity is proposed to maximise the input RF power to the energy harvesters, which converges to a Karush-Kuhn-Tucker (KKT) point. We also propose an improved greedy randomized adaptive search procedure (I-GRASP) based algorithm having better performance to maximise the input RF power. Furthermore, the optimal power splitter for maximising the output DC power of the energy harvesters is derived in closed-form. The numerical results are provided to verify the performance advantage of the IRS-aided WPT and to demonstrate that conceiving the optimised energy combiner achieves better WPT performance than the deterministic counterpart
Robust Sum-Rate Maximization in Transmissive RMS Transceiver-Enabled SWIPT Networks
In this paper, we propose a state-of-the-art downlink communication
transceiver design for transmissive reconfigurable metasurface (RMS)-enabled
simultaneous wireless information and power transfer (SWIPT) networks.
Specifically, a feed antenna is deployed in the transmissive RMS-based
transceiver, which can be used to implement beamforming. According to the
relationship between wavelength and propagation distance, the spatial
propagation models of plane and spherical waves are built. Then, in the case of
imperfect channel state information (CSI), we formulate a robust system
sum-rate maximization problem that jointly optimizes RMS transmissive
coefficient, transmit power allocation, and power splitting ratio design while
taking account of the non-linear energy harvesting model and outage probability
criterion. Since the coupling of optimization variables, the whole optimization
problem is non-convex and cannot be solved directly. Therefore, the alternating
optimization (AO) framework is implemented to decompose the non-convex original
problem. In detail, the whole problem is divided into three sub-problems to
solve. For the non-convexity of the objective function, successive convex
approximation (SCA) is used to transform it, and penalty function method and
difference-of-convex (DC) programming are applied to deal with the non-convex
constraints. Finally, we alternately solve the three sub-problems until the
entire optimization problem converges. Numerical results show that our proposed
algorithm has convergence and better performance than other benchmark
algorithms
Energy-Efficient Hybrid Beamforming for Multi-Layer RIS-Assisted Secure Integrated Terrestrial-Aerial Networks
The integration of aerial platforms to provide ubiquitous coverage and connectivity for densely deployed terrestrial networks is expected to be a reality in the emerging sixth-generation networks. Energy-effificient and secure transmission designs are two important components for integrated terrestrial-aerial networks (ITAN). Inlight of the potential of reconfigurable intelligent surface (RIS) for significantly reducing the system power consumption and boosting information security, this paper proposes a multi-layer RIS-assisted secure ITAN architecture to defend against simultaneous jamming and eavesdropping attacks, and investigates energy-efficient hybrid beamforming for it. Specifically, with the availability of imperfect angular channel state information (CSI), we propose a block coordinate descent (BCD) framework for the joint optimization of the user’s received decoder, the terrestrial and aerial digital precoder, and the multi-layer RIS analog precoder to maximize the system energy efficiency (EE) performance. For the design of the received decoder, a heuristic beamforming scheme is proposed to convert the worst-case design problem into a min-max one and facilitate the developing a closed-form solution. For the design of the digital precoder, we propose an iterative sequential convex approximation approach via capitalizing the auxiliary variables and first-order Taylor series expansion. Finally, a monotonic vertex-update algorithm with a penalty convex-concave procedure (P-CCP) is proposed to obtain the analog precoder with satisfactory performance. Numerical results show the superiority and effectiveness of the proposed optimization framework and architecture over various benchmark schemes
1 Energy-Efficient Hybrid Beamforming for Multi-Layer RIS-Assisted Secure Integrated Terrestrial-Aerial Network
The integration of aerial platforms to provide ubiq-
uitous coverage and connectivity for densely deployed terrestrial
networks is expected to be a reality in emerging sixth-generation
networks. Energy-effificient design and secure transmission are
two crucial issues for integrated terrestrial-aerial networks.
With this focus, due to the potential of RIS in substantially
saving power consumption and boosting the security of private
information by enabling a smart radio environment, this paper
investigates the energy-efficient hybrid beamforming for multi-
layer reconfigurable intelligent surface (RIS)-assisted secure in-
tegrated terrestrial-aerial network for defending against simul-
taneous jamming and eavesdropping attacks. Specifically, with
the available of angular information based imperfect channel
state information (CSI), we propose a framework for the joint
optimization of user’s received precoder, terrestrial BS’s and
HAP’s digital precoder, and multi-layer RIS analog precoder
to maximize the system energy efficiency (EE) performance. For
the design of received precoder, a heuristic beamforming scheme
is proposed to convert the worst-case problem into a min-max
one such that a closed-form solution is derived. For the design
of digital precoder, we propose an iterative sequential convex
approximation approach via capitalizing the auxiliary variables
and first-order Taylor series expansion. Finally, a monotonic
vertex-update algorithm with penalty convex concave procedure
is proposed to obtain analog precoder with low computational
complexity. Numerical results show the superiority and effective-
ness of proposed optimization framework and architectur