The Impact of Baseband Functional Splits on Resource Allocation in 5G Radio Access Networks

We study physical-layer (PHY) baseband functional split policies in 5G Centralized Radio-Access-Network (C-RAN) architectures that include a central location, the baseband unit (BBU) with some BBU servers, and a set of Base Stations (BSs), the remote radio heads (RRHs), each with a RRH server. Each RRH is connected to the BBU location through a fronthaul link. We consider a scenario with many frame streams at the BBU location, where each stream needs to be processed by a BBU server before being sent to a remote radio-head (RRH). For each stream, a functional split needs to be selected, which provides a way of partitioning the computational load of the baseband processing chain for stream frames between the BBU and RRH servers. For streams that are served by the same BBU server, a scheduling policy is also needed. We formulate and solve the joint resource allocation problem of functional split selection, BBU server allocation and server scheduling, with the goal to minimize total average end-to-end delay or to minimize maximum average delay over RRH streams. The total average end-to-end delay is the sum of (i) scheduling (queueing) and processing delay at the BBU servers, (ii) data transport delay at the fronthaul link, and (iii) processing delay at the RRH server. Numerical results show the resulting delay improvements, if we incorporate functional split selection in resource allocation.