I. Introduction
The telecom industry has been witnessing a traffic explosion in recent years and has reached a broad consensus on the strong continuation of this trend for the next decade. To meet the ever-demanding expectations of mobile broadband users in fifth generation (5G), network densification and cloud radio access network (C-RAN) are recognized as two key enabling technologies [1]. By centralizing the baseband processing resources of all base stations (BSs) into a super resource pool at a central unit (CU) and incorporating coordinated multipoint (CoMP) transmission techniques, C-RAN can significantly improve the system performance with affordable cost [2].