On the Trade-off between Physical Layer Security and Energy Efficiency of Massive MIMO with Small Cells

The primary design goal in cellular technology is to provide high data rate services to its customers while still maintaining energy-efficient transmission over the network. The road to move forward is through deployment of highly densified network topologies. The emergence of these network topologies has also opened up research opportunities on how to exploit their physical layer (PHY) characteristics in order to improve the overall security. In this paper, we analyze the performance of a heterogeneous network that combines massive MIMO technology and small cell networks via spatial soft-cell scheme. An optimization model is formulated that minimizes the total power consumption of the network while satisfying certain degree of Quality-of-Service (QoS) and PHY security. Furthermore, we extend the optimization model to consider uncertainty in the eavesdroppers' channel state information (CSI). Potential tradeoff between PHY security and energy efficiency was investigated. We provide promising results showing that employing massive MIMO at the base station and placing multiple operator-deployed small cell nodes can significantly improve energy efficiency and capacity of the cellular network while providing adequate level of security, even with imperfect knowledge of eavesdropper CSI.