Energy Efficient Robust F-RAN Downlink Design for Hard and Soft Fronthauling

Multicasting popular contents (e.g. HD video streaming) with high data rates is a typical scenario in the future 5G system. In this paper, we investigate the downlink design of multicast Fog Radio Access Network (F-RAN), where each Remote Radio Head (RRH) is equipped with a cache module and has some limited signal processing functionalities. Caching some popular contents at the off-peak hours might not only greatly decrease the service delay, but also, as we are going to show, reduce the energy consumption of the network. Hence, the minimization of network energy consumption is considered within this work. In particular, information compression based (soft) fronthauling and information sharing based (hard) fronthauling are discussed. Based on only imperfect CSI, we propose algorithms for robust network design, where RRH deactivation, power and fronthauling traffic control, beamformer and precoder construction, etc., are jointly optimized for soft and hard fronthauling, respectively.