Secrecy Wireless Information and Power Transfer with MISO Beamforming (1307.6110v5)

Abstract: The dual use of radio signals for simultaneous wireless information and power transfer (SWIPT) has recently drawn significant attention. To meet the practical requirement that energy receivers (ERs) operate with significantly higher received power as compared to information receivers (IRs), ERs need to be deployed in more proximity to the transmitter than IRs. However, due to the broadcast nature of wireless channels, one critical issue arises that the messages sent to IRs can be eavesdropped by ERs, which possess better channels from the transmitter. In this paper, we address this new secrecy communication problem in a multiuser multiple-input single-output (MISO) SWIPT system where one multi-antenna transmitter sends information and energy simultaneously to an IR and multiple ERs, each with one single antenna. To optimally design transmit beamforming vectors and their power allocation, two problems are investigated with different aims: the first problem maximizes the secrecy rate for IR subject to individual harvested energy constraints of ERs, while the second problem maximizes the weighted sum-energy transferred to ERs subject to a secrecy rate constraint for IR. We solve these two non-convex problems optimally by reformulating each of them into a two-stage problem. First, by fixing the signal-to-interference-plus-noise ratio (SINR) target for ERs (for the first problem) or IR (for the second problem), we obtain the optimal beamforming and power allocation solution by applying the technique of semidefinite relaxation (SDR). Then, the original problems are solved by a one-dimension search over the optimal SINR target for ERs or IR. Furthermore, for each of the two studied problems, suboptimal solutions of lower complexity are also proposed in which the information and energy beamforming vectors are separately designed with their power allocation.

• The paper formulates and solves two non-convex optimization problems to maximize secrecy rate and harvested energy using semidefinite relaxation.
• Simulation results show that the SDR-based approach achieves optimality without relaxation losses, improving both security and energy efficiency.
• The study also introduces suboptimal beamforming strategies with artificial noise to further enhance security while satisfying energy harvesting constraints.

An Analysis of Joint Secrecy Beamforming and Energy Harvesting in MISO SWIPT Systems

This paper contributes to the field of simultaneous wireless information and power transfer (SWIPT) systems by exploring the potential for combining these functionalities in the presence of security constraints. The primary focus is on a multiple-input single-output (MISO) downlink system facilitating both information and energy transmission to a single information receiver (IR) and multiple energy receivers (ERs). This paper addresses two core optimization problems that balance the trade-off between secrecy and energy efficiency.

Overview of Core Problems and Solutions

The paper develops two problems pertinent to SWIPT with security constraints:

1. Problem 1 (P1): The goal is to maximize the secrecy rate for the IR while ensuring energy harvesting constraints are met for each ER.
2. Problem 2 (P2): This aims at maximizing the weighted sum of harvested energy at ERs, while maintaining a predetermined secrecy rate for the IR.

Both problems are inherently non-convex due to the conflicting relationships between information leakage and energy transfer goals. However, the authors employ semidefinite relaxation (SDR) techniques, which provide globally optimal solutions despite the problems' non-convex nature.

The paper establishes that solving these problems involves a two-stage method. In the initial stage, the signal-to-interference-plus-noise ratio (SINR) target is fixed at the receivers, allowing for beamforming and power allocation optimization using the SDR approach. The subsequent stage involves a one-dimensional search for the optimal SINR target.

Numerical Results and Algorithmic Strategies

Simulation results highlight the effectiveness of the proposed SDR-based method. Notably, the SDR achieves optimality without relaxation losses, underlining its applicability in complex SWIPT scenarios. For cases requiring lower computational complexity, two suboptimal beamforming strategies are introduced, both notably aligning with the null space of receiver channels to optimize joint performance.

Results demonstrate the utility of deploying artificial noise (AN) carried by energy beams in improving security, as these energy beams not only assist in power transfer but also act as AN to degrade any potential information leakage to ERs.

Implications and Theoretical Insights

The findings in this paper are significant for SWIPT systems where maintaining information secrecy is vital. By effectively leveraging the dual purpose of interference (both as an energy signal and a security measure), this approach provides a framework for advancing not only SWIPT capabilities but also for integrating security layers into power-harvesting networks.

In terms of practical impact, optimized beamforming solutions demonstrate realizable improvements in secure and efficient power transfer across such hybrid networks. The applied methodology could advance appliances such as wireless charging and secure communication in environments with strict energy harvesting and security constraints.

Future Directions

This research opens avenues for extending similar methodologies to complex systems involving multi-IR, multi-ER setups, or full-duplex configurations, allowing for simultaneous bi-directional communication and power exchange. Furthermore, exploring physical channel impairments or communication under imperfect channel state information (CSI) conditions could lead to practical adaptations of the proposed solutions in real-world deployments. The paper also lays foundational work for exploring combined cryptographic and physical-layer security approaches for enhanced confidentiality in wireless networks.

In conclusion, this paper offers a comprehensive exploration of integrating secure information transmission with power harvesting, leveraging the inherent characteristics of MISO configurations to present robust solutions that satisfy both practical and security requirements of modern communication networks.