With the exponential growth of data traffic in modern mobile networks and the emergence of variety of connected devices, congestion mitigation in cellular networks has become a major concern. Therefore, in this paper, we propose and extensively describe a new drone-based mechanism allowing to relay traffic and improve network performances. Scenarios related to the appearance, disappearance and mobility of the traffic hotspot are thoroughly specified and developed. The proposed solution is efficient in terms of capacity improvement with a good reactivity to the appearance of traffic hotspots. Moreover, the deployed drones are very energy-efficient in the way they operate in the proposed mechanism. This encourages more and more operators to deploy such solutions leveraging their investments