 wiring between the CU/DU and the RUs. An ISC deployment can lever- age existing networking infrastructure with higher latency and lower bandwidth but comes at challenges for supporting advanced algorithms (centralized processing/CoMP) as shown in Fig. 1 -31. - Given cost being a prime consideration, we assume RF spectrum utilization being the key and hence a drive for centralized processing. As a side benefit, we note that CU/DU/RU Chapter 1 Open radio access network overview 39 IP/router + core hub IP Backhaul FIGURE 1-31 Integrated small cell deployment architecture. CU/DU + CU/DU + core hub core hub IP Backhaul IP Backhaul FIGURE 1-32 CU/DU/RU deployment architecture. processing architecture allows for more choices for COTS hardware platforms and associated (somewhat) reduced time-to-market. In this CU/DU/RU deployment, the centralized unit implements the MAC/upper layer stacks and physical layer functions in addition to the core network components. By implica- tion, the bandwidth between centralized unit and DU is higher than for the ISC. A potential bandwidth/cabling overhead mitigation is the use of a "fronthaul gateway" which can reduce cabling overhead (star VS hub topologies) but can also support advanced functions such as CoMP. The deployment is shown in Fig. 1-32. To dimension the system to the next level of detail, we consider RF aspects and fronthaul bandwidths/wiring associated with the CU/DU/RU architecture. Let's assume that maxi- mum/peak over-the-air bandwidth is < 100 MHz and we can have two to four antennas at each RU. Calculating the bandwidth associated with two to four antennas at 100 MHz RF (per Chapter 3), we see that when using IQ compression, a 10 Gbps Ethernet link (which can be supported by both electrical and optical links) supports this bandwidth. Let's assume fronthaul gateway (GW in Fig. 1-32 on the right-hand side) aggregating RU traffic from V 8 RUs into a single 25 Gbps Ethernet link using downlink joint transmission and uplink joint 40 Open Radio Access Network (O-RAN) System