rface within the radio network for splitting the functionality between a distributed RF site and the centralized edge cloud site. Radio cloud implementation enables network scalability, for example, when adding a large number of IoT-connected devices. Figure 3.26 illustrates the main functionality split options and the related transport requirements. The rightmost figure shows the distributed option where all radio functions are close to the antenna. That option is used in most LTE networks and is also typical in 5G networks. The leftmost figure shows another option that has been used in LTE networks. It is baseband hoteling, where all the baseband processing is located in a centralized place. The Common Public Radio Interface (CPRI) interface can be used between the baseband and RF. CPRI requires very low latency, and the CPRI data rate requirement increases as a function of the bandwidth and the number of antennas. If we have a 100 MHz 5G carrier with 64TRX massive MIMO with 16 streams, the CPRI data rate requirement is close to 1 Tbps without CPRI compression, which makes it difficult to use the CPRI interface in 5G. Therefore, two other functionality split options with a more relaxed transport requirement are considered. Low-layer and higher-layer split options have the delay critical functions located close to the RF and the less delay critical functions at the edge cloud site. That allows the transport requirements to be minimized. If the transport network can provide low latency (<1 ms), then just part of Layer 1 (Fast Fourier Transform [FFT] and channel coding) is located close to the Typical network architecture Large number Very few Future architecture Radio Edge cloud processing processing Core Figure 3.25 Network architecture evolution. Reference eCPRI High layer split Classical Baseband hotel Low layer split distributed Edge cloud Layer 3 Layer 3 Layer 3 Layer 2 Layer 2 Layer 2 high 10 Gbps Layer 1 high Layer 1 high >5 ms 10 Gbps Layer 1 low >1 ms Layer 3 10-100 Gbps <1 ms Layer 2 high 1 Tbps <0.1 ms