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Harvest-Then-Cooperate: Wireless-Powered Cooperative Communications (1404.4120v2)

Published 16 Apr 2014 in cs.IT and math.IT

Abstract: In this paper, we consider a wireless-powered cooperative communication network consisting of one hybrid access-point (AP), one source, and one relay. In contrast to conventional cooperative networks, the source and relay in the considered network have no embedded energy supply. They need to rely on the energy harvested from the signals broadcasted by the AP for their cooperative information transmission. Based on this three-node reference model, we propose a harvest-then-cooperate (HTC) protocol, in which the source and relay harvest energy from the AP in the downlink and work cooperatively in the uplink for the source's information transmission. Considering a delay-limited transmission mode, the approximate closed-form expression for the average throughput of the proposed protocol is derived over Rayleigh fading channels. Subsequently, this analysis is extended to the multi-relay scenario, where the approximate throughput of the HTC protocol with two popular relay selection schemes is derived. The asymptotic analyses for the throughput performance of the considered schemes at high signal-to-noise radio are also provided. All theoretical results are validated by numerical simulations. The impacts of the system parameters, such as time allocation, relay number, and relay position, on the throughput performance are extensively investigated.

Citations (400)

Summary

  • The paper presents the HTC protocol, enabling source and relay nodes to harvest energy from an access point and cooperatively transmit data.
  • It derives a closed-form expression for average throughput over Rayleigh fading channels, validated through numerical simulations.
  • The study evaluates relay selection schemes, offering practical insights on optimizing energy harvesting time and network reliability.

Evaluation of Wireless-Powered Cooperative Communications through the Harvest-Then-Cooperate Protocol

This paper introduces a novel approach within the field of wireless communications, specifically addressing Wireless-Powered Cooperative Communication Networks (WPCCNs). The authors propose a protocol termed "Harvest-Then-Cooperate" (HTC), which leverages wireless energy transfer (WET) for energy-constrained networks and facilitates cooperative information transmission through energy harvesting techniques. The HTC protocol explores the cooperative dynamics between a hybrid access point (AP), a source node, and a relay node, aiming to maximize average throughput even in the absence of traditional energy supplies for the source and relay.

Key Contributions

  1. HTC Protocol Design: The paper designs an HTC protocol wherein the source and relay extract energy from the AP during the downlink (DL) phase and cooperate to transmit information during the uplink (UL) phase. This cooperation is crucial in scenarios where the source-relay channel conditions are favorable compared to direct source-AP communication, thereby enhancing overall network reliability and efficiency.
  2. Mathematical Modeling: The team derives an approximate closed-form expression for the HTC protocol's average throughput over Rayleigh fading channels. The analysis reveals the benefits of incorporating relay nodes, demonstrating that their cooperation can significantly enhance the system's throughput capacity.
  3. Relay Selection Schemes: To optimize performance, the paper evaluates two relay selection schemes: Opportunistic Relaying (OR) and Partial Relay Selection (PRS). OR considers the joint impact of source-to-relay and relay-to-AP links, while PRS focuses on a subset, reducing computational demands and complexity. The authors extend their analysis to scenarios involving multiple relay nodes, offering insights into selection strategies under different conditions.
  4. Performance Analysis and Validation: Theoretical results are validated through numerical simulations. The work provides a comprehensive examination of the effects of various system parameters, such as time allocation for energy harvesting, the number of relays, and relay positioning on throughput performance.

Numerical and Analytical Insights

The paper presents strong numerical evidence supporting the efficacy of the HTC protocol over traditional "harvest-then-transmit" systems. The introduction of relay nodes and their strategic employment prospective increases in throughput, especially highlighted in scenarios with adverse direct link conditions but beneficial source-relay link conditions. The analytical results, compared with simulation outcomes, demonstrate tightly aligned predictions for medium to high SNR conditions, ensuring the proposed model's validity and robustness under practical settings.

Further, it is evident that optimal parameter settings, such as the duration dedicated to energy harvesting, are critical. The analysis showcases how decreasing AP power requirements can enhance efficiency by allowing more time for data transmission while maintaining adequate energy harvesting.

Practical and Theoretical Implications

The work paves the way for efficient design and deployment of WPCCNs in environments where energy efficiency and sustainability are prioritized. Utilizing ambient and dedicated RF signals as energy sources could reduce network dependency on conventional power infrastructures. The proposed protocol is adaptable to various network topologies and can potentially enhance the feasibility of green communication networks by prolonging battery life and reducing the necessity for frequent charging.

Future Prospects

The paper outlines open areas for future exploration, such as incorporating energy accumulation strategies at the relay nodes and considering spatial randomness in node deployment, which could capture more realistic network behaviors. Additionally, examining dynamic relay scheduling schemes that incorporate historical energy consumption patterns may further enhance network performance.

Ultimately, this paper contributes to advancing wireless communications by suggesting robust frameworks for integrating energy harvesting with cooperative communication protocols, broadening the possibilities for sustainable network solutions.