Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

Abstract: Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile charging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is applied to derive the tradeoffs between the network parameters including p, q, and the BS/PB densities under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product the BS density decreases with increasing p following a power law where the exponent is proportional to the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product between q, the PB density, and the BS density raised to a power proportional to the path-loss exponent has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, a similar result is obtained with the aforementioned product increased by the array gain. Last, similar results are derived for the case of mobiles having small energy storage.

• The paper proposes a hybrid network architecture that integrates power beacons with cellular base stations to deliver continuous wireless power transfer.
• The paper applies stochastic geometry to derive trade-offs between transmission power, power beacon density, and outage constraints, offering key performance insights.
• The paper demonstrates that beamforming in directed microwave power transfer reduces power requirements, paving the way for efficient network deployment.

Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

The paper "Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment" by Kaibin Huang and Vincent K. N. Lau develops a comprehensive framework for integrating wireless power transfer (WPT) into cellular networks to provide continuous power supply to mobile devices. This integration promises to eliminate traditional power cords and chargers, thereby significantly enhancing user convenience.

Detailed Architectural Proposition

The authors propose a hybrid network architecture where power beacons (PBs) are randomly deployed in an existing cellular network to supply power to mobile devices using microwave power transfer (MPT). The integration of PBs into the cellular network introduces the concept of a "hybrid network" that operates under an outage constraint on data links.

Stochastic Geometry-Based Modeling

The deployment and performance of this hybrid network are analyzed based on stochastic-geometry modeling. Here, the single-antenna base stations (BSs) and PBs follow independent homogeneous Poisson point processes (PPPs) with given densities. The mobiles are uniformly distributed in the Voronoi cells generated by the BSs. This sophisticated model allows the authors to derive trade-offs between network parameters including transmission power, PB density, and network architecture under specific constraints.

Key Analytical Results

1. Cellular Network Deployment:
   • Non-zero Noise: The paper establishes that to meet the outage probability constraint, the product of mobile transmission power $p$ and BS density $\lambda_b^{\frac{\alpha}{2}}$ must exceed a certain threshold determined by the path-loss exponent $\alpha$.
   • Interference-Limited Scenario: Outage probability becomes independent of $p$ and $\lambda_b$ under zero-noise conditions.
2. Hybrid Network Deployment:
   • For isotropic MPT with large energy storage at mobiles, the product of PB transmission power $q$, PB density $\lambda_p$, and BS density $\lambda_b^{\frac{\alpha}{2}}$ should be above a threshold to comply with the outage constraint.
   • For directed MPT with large storage, the product $z_m q \lambda_p \lambda_b^{\frac{\alpha}{2}}$ (with $z_m$ representing the array gain) condenses the required threshold, indicating the effectiveness of beamforming in reducing required $q$.
   • For scenarios with small energy storage, additional conditions are imposed to ensure that the instantaneous received power adheres to the threshold with high probability, leading to complex conditions involving path-loss exponents for both data and MPT links.

Theoretical and Practical Implications

The research offers significant theoretical and practical contributions. The derived trade-offs provide valuable guidelines for the efficient deployment of hybrid networks. The insights into the role of PB density and transmission power can facilitate the design of future cellular networks with integrated WPT capabilities.

Future Directions

The paper indicates several avenues for future research. Notably, extending the proposed modeling framework to consider various real-world factors such as:

• Different antenna configurations
• More complex channel models for small-cell environments
• Hotspot traffic scenarios using clustered point processes
• The impact of mobility on WPT efficiency
• Dynamics of energy levels in mobile devices

Conclusion

In summary, the analytical findings of the paper shed light on the intricate requirements for deploying PBs in cellular networks to ensure efficient and reliable WPT. By leveraging stochastic-geometry models, the authors provide a robust framework for understanding the interplay between transmission power, PB density, and network performance under stringent outage constraints. This paper forms a foundational step towards realizing the future vision of perpetually powered mobile devices in seamlessly integrated hybrid networks.