Flexible functional split for cost-efficient C-RAN

Abstract

In this paper, we propose flexible functional split schemes for a multi-tier C-RAN architecture based on the concept of virtual remote radio heads (V-RRHs), aiming at optimizing the resource utilization while reducing the overall cost of BBU pool. A V-RRH consists of a digital unit (DU) that hosts a few baseband (BB) processing functionalities and a radio unit (RU) with RF functionality. Specifically, three types of V-RRHs differing in the number 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 as a zero–one (0–1) packing problem which is NP-complete. To solve the 0–1 packing problem, we divide it into three stages and solve them by a pure integer non-linear programming (PINLP) model. Numerical results show that the proposed flexible functional split strategies comprehensively outperform the existing C-RAN and D-RAN schemes in terms of the overall cost.