# Energy-Throughput Tradeoff in Sustainable Cloud-RAN with Energy Harvesting

## TL;DR

This paper explores the energy-throughput tradeoff in sustainable Cloud-RAN systems with renewable energy sources, proposing an optimal joint beamforming strategy and an efficient online algorithm, validated through extensive simulations.

## Contribution

It introduces a convex relaxation approach for joint beamforming optimization in energy-harvesting Cloud-RAN, proving tightness and providing a practical online solution.

## Key findings

- Proposed a convex relaxation for the non-convex optimization problem.
- Proved the tightness of the relaxation with rank-one optimal solutions.
- Demonstrated the superiority of the proposed beamforming strategy through simulations.

## Abstract

In this paper, we investigate joint beamforming for energy-throughput tradeoff in a sustainable cloud radio access network system, where multiple base stations (BSs) powered by independent renewable energy sources will collaboratively transmit wireless information and energy to the data receiver and the energy receiver simultaneously. In order to obtain the optimal joint beamforming design over a finite time horizon, we formulate an optimization problem to maximize the throughput of the data receiver while guaranteeing sufficient RF charged energy of the energy receiver. Although such problem is non-convex, it can be relaxed into a convex form and upper bounded by the optimal value of the relaxed problem. We further prove tightness of the upper bound by showing the optimal solution to the relaxed problem is rank one. Motivated by the optimal solution, an efficient online algorithm is also proposed for practical implementation. Finally, extensive simulations are performed to verify the superiority of the proposed joint beamforming strategy to other beamforming designs.