Characterizing the Relation Between Processing Power and Distance Between BBU and RRH in a Cloud RAN

In cloud radio access networks (C-RANs), base stations are replaced by remote radio heads (RRHs) having their signals processed in a base-band unit (BBU). A BBU is limited to processing the signals of RRHs within a maximum distance, determined according to delay constraints. This delay is affected by three factors: 1) the distance between BBU and RRH; 2) channel conditions; and 3) processing power available. This letter characterizes the relationship between these factors. Our results show that the processing power must be increased significantly for RRHs experiencing low signal-to-noise ratio (SNR) and/or at a longer distance from the BBU. The good news is that RRHs experiencing high SNR can have their processing take place in the cloud, at significant distances, and still meet tight bit error rate and latency constraints. These two observations open the door to the possibility of dynamic load balancing mechanisms that change the locus of processing in a C-RAN according to channel conditions and availability of processing resources.