Flexible functional split for cost-efficient C-RAN

Abstract In this paper, we study a multi-tier C-RAN architecture and propose flexible heterogeneous functional split schemes for it based on the concept of virtual remote radio heads (V-RRHs), aiming at optimizing the resource utilization and reducing the overall cost of BBU pool. A V-RRH consists of a digital unit (DU) borrowed from the macro base stations (BSs) to host a few baseband (BB) processing functionalities and a radio unit (RU) with RF functionality. Specifically, three types of V-RRHs differing in their numbers of BB processing function slices are considered in three functional split options. We aim at finding the optimal functional split option for each task and thus allocate the appropriate function slice block (FSB) of BBU pool for it. The issue of optimally allocating FSBs to tasks is normalized to a zero–one (0-1) packing problem which is NP-complete and solved by an integer non-linear programming model. To solve the 0-1 packing problem, we divide it into three stages and propose a heuristic algorithm. Numerical results show the proposed flexible functional split strategies outperform the existing C-RAN and D-RAN schemes in various aspects.