RRH Clustering in Cloud Radio Access Networks with Re-association Consideration

Cloud Radio Access Network (C-RAN) is an evolution in the base station architecture, mainly composed of two elements: The Base Band Unit (BBU) and the Remote Radio Head (RRH). This new architecture separates the two elements (the BBUs from RRHs), to group all the BBUs into one cloud, while RRHs are distributed across many sites. Unlike in conventional architecture, many RRHs can be associated to one BBU when traffic load is low, allowing better exploitation of radio resources. A dynamic re-association between BBUs and RRHs is crucial, since coping with traffic load can enable reduction in power consumption and enhancement in energy efficiency. However, re-associations between BBUs and RRHs would cost frequent handovers for users connected to re-associated RRHs. Unlike the existing studies, the aim of this paper is to solve the dynamic aspect of the BBU-RRH association. To that end, we introduce a tunable biobjective optimization problem formulated as a Set Partitioning Problem (SPP). The purpose is to jointly minimize the power consumption and the re-association rate of users experiencing a BBU change, subject to a minimum guarantee of Quality of Service (QoS). A heuristic approach is also introduced and provides close performance to the optimal solution.