Wireless Information and Power Transfer: A Dynamic Power Splitting Approach

Abstract: Scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the flat-fading channel, where the receiver replenishes energy via WEH from the signals sent by the transmitter. We consider a SISO (single-input single-output) system where the single-antenna receiver cannot decode information and harvest energy independently from the same signal received. Under this practical constraint, we propose a dynamic power splitting (DPS) scheme, where the received signal is split into two streams with adjustable power levels for information decoding and energy harvesting separately based on the instantaneous channel condition that is assumed to be known at the receiver. We derive the optimal power splitting rule at the receiver to achieve various trade-offs between the maximum ergodic capacity for information transfer and the maximum average harvested energy for power transfer. Moreover, for the case when the channel state information is also known at the transmitter, we investigate the joint optimization of transmitter power control and receiver power splitting. Finally, we extend the result for DPS to the SIMO (single-input multiple-output) system and investigate a low-complexity power splitting scheme termed antenna switching.

• The paper presents an optimal power splitting rule for SISO systems using instantaneous CSI to balance energy harvesting and data decoding.
• The study demonstrates enhanced rate-energy trade-offs with CSIT by jointly optimizing transmitter power control and receiver splitting.
• Extending to SIMO systems, the research introduces a near-optimal antenna switching method that reduces hardware complexity for practical implementations.

Dynamic Power Splitting in Wireless Information and Power Transfer

The paper presents a detailed study on the integration of Wireless Energy Harvesting (WEH) and data communication over a flat-fading channel through a novel approach termed Dynamic Power Splitting (DPS). This study addresses the challenge faced by single-input single-output (SISO) systems—the inability to simultaneously decode information and harvest energy from the same signal.

The authors propose a DPS scheme that allows real-time adjustment of signal power for information decoding and energy harvesting by utilizing instantaneous channel state information (CSI) available at the receiver. The optimization of the power split is central to achieving the trade-offs between maximizing ergodic capacity and harvesting energy, defined as the rate-energy (R-E) region's boundary.

Key Contributions

1. Optimal Power Splitting Rule: For the SISO system, the authors derive the optimal power splitting rule, demonstrating how a fixed amount of power allocated to information decoding can be sustained across varying channel conditions. This rule leverages good channel states for joint benefits in both energy harvesting and information decoding, contrasting with time switching approaches where roles are mutually exclusive.
2. Enhanced R-E Trade-offs with CSIT: The research extends to scenarios where the transmitter also has access to CSI (CSIT). In such cases, joint optimization of power control at the transmitter and power splitting at the receiver is employed. Through this method, notable improvements in the achievable R-E region are observed.
3. Extension to SIMO Systems: The study's scope broadens with the introduction of DPS for single-input multiple-output (SIMO) systems. For this configuration, a uniform power splitting (UPS) strategy across multiple antennas is proven optimal. Additionally, the paper discusses an innovative low-complexity scheme, "antenna switching," which achieves near-optimal R-E trade-offs and is more promising for practical implementations.

Practical Implications

The implementation of DPS can significantly bolster the energy efficiency and operational longevity of wireless devices, particularly in resource-constrained environments such as sensor networks. The antenna switching technique, offering reduced hardware complexity, renders the approach even more applicable.

Numerical Results and Performance

The numerical comparisons reveal significant enhancements in the R-E region using DPS over traditional time-switching methods. Moreover, evidence shows antenna switching approaches the performance of UPS as the number of receiver antennas increases.

Theoretical Significance and Future Work

The findings not only forward practical utility but also enrich theoretical understandings of joint information and power transfer optimization in wireless communication systems. Future research directions could explore the application of DPS in multi-user scenarios and the impact of non-ideal hardware components.

In conclusion, this paper contributes a robust framework for enhancing wireless networks' dual functionality—simultaneous wireless information and power transfer. The proposed strategies open new vistas for research and application in evolving hybrid communication systems.