RF-based Energy Harvesting in Decode-and-Forward Relaying Systems: Ergodic and Outage Capacities (1802.03809v1)

Abstract: Radio-frequency energy harvesting constitutes an effective way to prolong the lifetime of wireless networks, wean communication devices off the battery and power line, benefit the energy saving and lower the carbon footprint of wireless communications. In this paper, an interference aided energy harvesting scheme is proposed for cooperative relaying systems, where energy-constrained relays harvest energy from the received information signal and co-channel interference signals, and then use that harvested energy to forward the correctly decoded signal to the destination. The time-switching scheme (TS), in which the receiver switches between decoding information and harvesting energy, as well as the power-splitting scheme (PS), where a portion of the received power is used for energy harvesting and the remaining power is utilized for information processing, are adopted separately. Applying the proposed energy harvesting approach to a decode-and-forward relaying system with the three-terminal model, the analytical expressions of the ergodic capacity and the outage capacity are derived, and the corresponding achievable throughputs are determined. Comparative results are provided and show that PS is superior to TS at high signal-to-noise ratio (SNR) in terms of throughput, while at low SNR, TS outperforms PS. Furthermore, considering different interference power distributions with equal aggregate interference power at the relay, the corresponding system capacity relationship, i.e., the ordering of capacities, is obtained.

• The paper analyzes RF energy harvesting in decode-and-forward relaying systems, examining time-switching and power-splitting protocols for ergodic and outage capacity.
• Performance analysis shows power-splitting outperforms time-switching at high signal-to-noise ratios, while time-switching is better at lower signal-to-noise ratios.
• Using majorization theory, the study finds lowest capacity with equally distributed interference power and highest with a single dominant interferer.

Overview of RF-based Energy Harvesting in Decode-and-Forward Relaying Systems

This paper presents a comprehensive analysis of a radio-frequency (RF) energy harvesting strategy in decode-and-forward (DF) relaying systems. Energy harvesting from ambient RF signals emerges as a solution to prolong the lifetime of wireless networks and eliminate the reliance on traditional power sources like batteries and power lines. The authors propose a cooperative relaying system using interference-aided energy harvesting, where energy-constrained relays harvest energy from both information signals and co-channel interference (CCI) signals. This energy is then used to forward accurately decoded signals to the destination. Two protocols for energy harvesting at the relay—time-switching (TS) and power-splitting (PS)—are examined independently in this paper.

Key Results and Analysis

The paper derives analytical expressions for both the ergodic capacity and the outage capacity of the relaying system, utilizing the TS and PS protocols. The performance analysis reveals that PS outperforms TS at high signal-to-noise ratio (SNR) conditions in terms of throughput. Conversely, at lower SNR conditions, TS achieves higher throughput compared to PS. The findings indicate that while PS benefits from continuous power allocation between signal processing and energy harvesting, TS offers advantages when energy constraints are more severe and circuit simplicity is prioritized.

Furthermore, the paper explores the impact of interference power distributions on system capacity. Using the majorization theory, it is revealed that when the interference power is equally distributed, the system experiences the lowest capacity. Conversely, having a single dominant interferer results in the highest capacity. This insight is valuable for practical applications, especially in the design and deployment of energy harvesting relay networks.

Implications and Future Directions

This paper provides a framework for understanding the complex interplay between energy harvesting and data transmission in wireless relaying networks. The ability to utilize ambient RF signals, including interference, not only enhances energy efficiency but also presents potential to improve system reliability in energy-constrained environments. Future work may extend these results to multi-hop relay systems or investigate adaptive protocols that dynamically switch between TS and PS based on real-time network conditions. There is also potential for exploring the integration of these energy harvesting strategies with contemporary wireless technologies, such as massive MIMO and millimeter-wave communications, to further enhance network efficiency and sustainability.

Conclusion

The proposed RF energy harvesting scheme sets a foundation for sustainable wireless communication systems by leveraging interference, traditionally seen as a hindrance, into a resource for energy replenishment. The results of this paper offer insightful guidelines for designing future wireless communication systems that are not only more energy-efficient but also environmentally friendly. Researchers and engineers can leverage these findings to optimize the deployment of energy-harvesting capable devices, ensuring better utilization of available RF resources.