Robust Secrecy Beamforming for MIMO SWIPT with Probabilistic Constraints

This paper unifies integrated sensing and communication (ISAC) and simultaneous wireless information and power transfer (SWIPT), by investigating a new multi-functional multiple-input multiple-output (MIMO) system that integrates wireless sensing, communication, and powering. In this system, a multi-antenna hybrid access point (H-AP) transmits wireless signals to communicate with a multi-antenna information decoding (ID) receiver, wirelessly charges a multi-antenna energy harvesting (EH) receiver, and performs radar target sensing based on the echo signal concurrently. Under this setup, we aim to reveal the fundamental performance tradeoff limits among sensing, communication, and powering, in terms of the estimation Cramér-Rao bound (CRB), achievable communication rate, and harvested energy, respectively. In particular, we consider two different target models for radar sensing, namely the point and extended targets, for which we are interested in estimating the target angle and the complete target response matrix, respectively. For both models, we define the achievable CRB-rate-energy (C-R-E) region and characterize its Pareto boundary by maximizing the achievable rate at the ID receiver, subject to the estimation CRB requirement for target sensing, the minimum harvested energy requirement at the EH receiver, and the maximum transmit power constraint at the H-AP. We obtain partitionable optimal transmit covariance matrix solutions to the two formulated problems by applying advanced convex optimization techniques. The numerical results demonstrate the optimal C-R-E region boundary achieved by our proposed design, as compared to the benchmark schemes based on time division and eigenmode transmission (EMT).

In this letter, we consider a multiple-input-multiple-output (MIMO) downlink system with simultaneous wireless information and power transfer (SWIPT), where the information sent to the desired receiver (DR) may be wiretapped by the malicious energy harvesting (EH) receivers (potential eavesdroppers). Assuming the channel state information (CSI) of the EH receivers is not perfectly known at the transmitter, we aim to maximize the worst-case secrecy rate by jointly designing the precoding matrix, AN covariance matrix and power splitting ratio, under the constraints of total transmit power and harvested energy at receivers. The formulated problem is non-convex and semi-infinite, which is hard to tackle. To solve it, we first deal with the non-convexity caused by CSI errors with the aid of the S-Procedure, and then employ the Taylor series approximation techniques to transfer the nonconvex problem into a convex optimization problem. Based on that, we propose an iterative algorithm with proved convergence to solve the original problem. Simulation results are finally provided to show the effectiveness of our proposed robust transmit design.

In this paper, we provide a comprehensive literature survey on simultaneous wireless information and power transfer (SWIPT) in multi-antenna systems. We first review recent contributions on the theory analysis of SWIPT from information theoretic standpoint and introduce the tradeoff between information transfer and power transfer under various settings. Then, we focus on the utilization of multi-antenna techniques to solve existing problems of SWIPT. Contributions on the implementation aspects of multi-antenna SWIPT are summarized. The performance of SWIPT is evaluated by different metrics, therefore, we review the works on dynamic SWIPT optimization based on objective function using multi-antenna techniques. In addition, the implementation of SWIPT brings up secure issue. Thus, we summarize recent works on secure SWIPT. Finally, we present researches combining SWIPT with state-of-the-art techniques due to potential application in different scenarios.

In this paper, we investigate the simultaneous wireless information and power transfer (SWIPT) in a multiple-input multiple-output (MIMO) amplify-and-forward relay communication system, where the relay is an energy harvesting (EH) node and harvests the energy the signals transmitted from the source. The harvested energy is partially used to forward signals from the source to the destination, and the remaining energy is stored for other usages. The SWIPT in relay-assisted communication is interesting as long as the relay stores energy from the source and the destination receives successfully the data from the source. In this context, we propose to investigate the source and relay precoders that characterize the relationship between the achievable stored energy at the relay and the achievable source-to-destination rate, namely, the rate-stored energy (R-E) tradeoff region. First, we consider the ideal scheme, where there is the simultaneous operation of the EH and information decoding (ID) receivers at the relay. Then, we consider practical schemes, such as the power splitting and the time switching that separate the operation of EH and ID receivers over power domain or time domain, respectively. Moreover, we study the case of imperfect channel state information at the relay and the destination, and characterize its impact on the achievable R-E region. Through the simulation results, we show the effect of the position of the relay and the channel uncertainty on the achievable R-E regions of all the schemes when the used energy at the relay is constant or variable. We also show that, although it provides an outer bound on the achievable rate-energy region in one-hop MIMO systems, the ideal scheme provides only an upper bound on the maximum achievable end-to-end rate and not an outer bound on the R-E region.

This letter characterizes the performance of maximum ratio transmission (MRT) in ad hoc networks with simultaneous wireless information and power transfer (SWIPT). We assume that the transmitters are equipped with multiple antennas and use MRT, while the typical receiver is equipped with a single antenna and an energy harvesting receiver using time switching (TS) or power splitting (PS) receiver architectures. First, using stochastic geometry and considering the signal-to-interference plus noise ratio, we derive the exact outage probability at the reference receiver in closed-form. Simulation results confirm the accuracy of the derived analytical expressions. Then, we use the delay-tolerant throughput and delay-limited throughput, which are related to the outage probability, as metrics to study the system performance. The results show that for the delay-limited throughput, PS outperforms TS at low rate or at high energy harvesting ratio, respectively. For delay-tolerant throughput, PS always outperforms TS for any energy harvesting ratio.

The main challenges of sensing in harsh industrial and biological environments are the limited energy of sensor nodes and the difficulty of charging sensor nodes. Simultaneous wireless information and power transfer (SWIPT) is a non-invasive option to replenish energy. SWIPT harvests energy and decodes information from the same RF signal, which is influencing the design of a wireless sensor network. In multi-hop multi-flow wireless sensor networks, interference generally exists, and the interference has a different influence on SWIPT. Route, interference and SWIPT are dependent. However, existing works consider SWIPT link resource allocation with a given route or only select path for one flow without interference. Therefore, this paper firstly analyzes the influence of interference on SWIPT, and select the SWIPT routing with interference. We design an interference-based information and energy allocation model to maximize the link capacity with SWIPT. Then, we design an interference-aware route metric, formulate SWIPT routing problem, and design an interference-aware SWIPT routing algorithm. The simulation results show that as the number of flows increases, there is more likely to obtain performance gains from interference and SWIPT.

We consider Multiple-input multiple-output (MIMO) wiretap channel with one transmitter, one receiver, one cooperative jammer, and one eavesdropper, where each node equips with multiple antennas. Eigenbeam-space division multiplexing (E-SDM) and cooperative jamming are known as the techniques improving secrecy rate. E-SDM enables the transmitter and the legitimate receiver to communicate with each other in parallel using channel state information (CSI) known to them to maximize the legitimate receiver's mutual information. On the other hand, cooperative jamming is to jam only the eavesdropper to degrade eavesdropper's mutual information. However, co-channel interference and residual interference from the cooperative jammer are caused by channel estimation error, which degrades legitimate receiver's mutual information. How these interference influence on the secrecy rate has not been clarified. In this paper, we derive lower and upper bounds on secrecy rate using legitimate receiver's mutual information in the presence of channel estimation error and eavesdropper's mutual information who uses minimum mean square error (MMSE) receiver. We analyze the effect of co-channel interference and residual interference from the cooperative jammer on the secrecy rate.

Energy supply is a key factor affecting the normal operation of energy-constrained networks. Simultaneous wireless information and power transfer (SWIPT) technology can be used to obtain a stable and continuous energy source. But SWIPT need to take into account data transmission rate and energy harvesting performance, it is necessary to design a complex physical layer method to improve the energy efficiency of SWIPT system. The paper studies a multiple input multiple output (MIMO) SWIPT system based on space-time coding, the transmitter sends the information using the space-time encoder through multi-antenna transmission, the receiver uses the space-time decoder to decode the information and collect the energy. The expressions of channel capacity and energy harvesting under MIMO are given respectively. The energy harvesting optimization target equation under coding conditions is established. The simulation results show that the using of space-time coding can reduce the data transmission error rate of MIMO SWIPT system and improve the energy harvesting performance of the user terminals.

This paper studies the robust beamforming design for simultaneous wireless information and power transfer (SWIPT)-enabled networks, where the rate-splitting (RS) scheme and the power-splitting (PS) energy harvesting (EH) receiver are adopted for secure information transfer and EH, respectively. In order to explore the worst-case energy efficiency (EE) performance limit of the system, an EE maximization problem is formulated with the elliptically bounded channel state information error model under the constraints of the quality of service (QoS) requirements of information decoding users, the EH requirements of EH users and the power budget at the transmitter. To tackle the formulated non-convex problem, a sequential minimal optimization-based algorithm is first proposed to construct a mapping table and the optimal PS ratios of the PS EH receiver are found by searching the table. Then, a dual-layer iterative algorithm is designed to obtain the maximal EE based on the Dinkelbach’s method in the inner loop and the successive convex approximation method in the outer loop. To accelerate the convergence of the outer loop, an efficient initialization algorithm is also designed. Simulation results show that the RS scheme contributes to the EE enhancement, and the PS EH receiver enlarges the rate-energy region restricted by the non-linear EH circuit. Moreover, traditional sum-rate maximization design and power minimization design may induce a notable worst-case EE performance loss at the high-power region and the low-QoS requirement region, respectively.

In this letter, we propose a novel simultaneous wireless information and power transfer (SWIPT) scheme, namely the frequency-splitting (FS) SWIPT, which separates the power and data signals in the frequency domain. The proposed FS SWIPT scheme is advantageous in that it can maximize the efficiency of the high power amplifier (HPA) in the transmitter and reduce the harmonic distortion caused by the nonlinearity of the HPA. We design a receiver circuit for the FS SWIPT by using a circulator and filters. We analyze the FS and conventional power-splitting (PS) SWIPT schemes in consideration of the nonlinearity of the HPA. We show that the proposed FS SWIPT greatly outperforms the PS SWIPT in terms of the harvested power and signal-to-noise ratio (SNR).

Simultaneous wireless information and power transfer (SWIPT) formed by the mixture of communication technology and power transmission is one of the research focuses in the field of wireless communication. This paper introduces the architecture of the SWIPT system, analyzes the key technologies, presents a 2.45GHz microwave rectifier circuit at low input power for energy harvesting. Finally, with the use of Ultra-Narrow Band (UNB) as the modulation scheme, the practical SWIPT receiver system is modeled and simulated. The results provide that using UNB signal as the modulation scheme is a new feasible way for SWIPT.

Chapter 10 - Transmit beamforming for simultaneous wireless information and power transfer

Simultaneous wireless information and power transfer (SWIPT) has emerged as a viable technique to energize and connect low-power autonomous devices and enable future Internet of Things (IoT). A major challenge of SWIPT is the energy consumption of the receiver of such low-power devices. An attractive low-power solution consists of an integrated information decoder (ID) and energy harvester (EH) architecture for SWIPT receiver (IntRx) where the received radiofrequency (RF) signal is first rectified before being used for information decoding. Such architecture eliminates the need for energy-consuming RF components, such as local oscillators and mixers. This article proposes a novel modulation and demodulation method for the IntRx SWIPT architecture based on pulse position modulation (PPM) where information is encoded in the position of the pulse. The new method transmits high amplitude pulses to increase the peak-to-average power ratio (PAPR) of the transmit signal and exploits the EH's nonlinearity so as to boost the harvested dc power. Simultaneously, the information can be decoded from the rectifier signal by simply finding the position of the pulse in a certain symbol duration. We have analyzed both the information and the power transfer performance of the newly proposed PPM for IntRx SWIPT theoretically, numerically, and experimentally. To that end, we have established a SWIPT system testbed in an indoor environment by prototyping a base station to transfer information-power signal and the IntRx SWIPT receiver, including ID and EH blocks. The performance evaluation of the PPM was carried out in various conditions, and the results have been compared and contrasted to conventional signals. Theoretical, numerical, and experimental results highlight the significant benefits of the proposed PPM scheme to enhance the power transfer performance and operate information decoding with low-power consumption.

Unmanned aerial vehicles (UAVs) equipped with reconfigurable intelligent surfaces (RIS) provide several perquisites in inaccessible regions, yet the limited battery life of the UAV is a concern that needs to be addressed. This study suggests a new scheme that combines the nearest neighbor search (NNS) method for UAV trajectories and a simultaneous wireless information and power transfer (SWIPT) model that splits the passive reflecting elements of the RIS in the geometric space to forward information and harvest energy concurrently. Nonetheless, users' mobility and ever-changing channel conditions pose a challenge in achieving an optimal wireless system. To tackle these issues, this study employs a twin delayed deep deterministic policy gradient (TD3)-based algorithm to enhance the proposed SWIPT model while ensuring the QoS. Simulation results illustrate the efficiency of the proposed robust TD3-based SWIPT model with UAV-RIS assistance implemented in MIMO communication. The proposed model has demonstrated superior performance in comparison to existing solutions. The results show that the model achieves a 70% energy efficiency and improves the system's capacity by up to 56.3%.

In this paper, we investigate a new approach for simultaneous wireless information and power transfer (SWIPT) in point-to-point multiple-input multiple-output (MIMO) system with spatial switching (SS) reception. The new approach is based on the generalized triangular decomposition (GTD). The approach takes advantage of the GTD structure to allow the transmitter to use the strongest subchannel jointly for energy harvesting and information exchange while these transmissions can be separated at the receiver to comply with the SS system requirements. An optimal solution is developed in the paper for SWIPT based on GTD that jointly obtains the optimal subchannels assignment and maximizes the total data rate while meeting the minimum requirement of the harvested energy with limited total transmitted power. The theoretical and numerical results presented in this paper show that the proposed approach significantly outperforms the state of the art spatial domain SWIPT systems based on the singular value decomposition (SVD).