The difficulty of implementing RAN functionality in a cloud-platform
lies in the tight constraints caused by the 3GPP LTE protocol
stack. This implies that individual tasks need to finish within a
predefined time window. Figure 3 shows relevant parts of the
3GPP LTE protocol stack and two exemplary functional splits that
correspond to options (C) and (D) in Figure 1. In the following, we
discuss the benefits and challenges of a cloud implementation of
three representative parts of the signal processing chain.