 split options. As we will show later in the discussion on ISCs, the fronthaul throughput requirements (and the limitations on available throughput) impose hard limitations to centralization. Centralized processing features: Coordinated Multipoint Processing Cellular networks do not consist of just a single base station talking to multiple clients but have several base stations covering a geographical area-as large as a country or as small as an enterprise or industrial site. This creates the problem of interference: when a client is physically between two base stations, it will receive two signals with similar signal strength. Similarly, this client would transmit a signal to two base stations simultaneously, potentially 26 Open Radio Access Network (O-RAN) Systems Architecture and Design DL From Network UL To Network IP/IPSec/GTP De-tunneling IP/IPSec/GTP Tunneling Option 1/2-2 (CP Only) PDCP re-transmit buffer PDCP Header Compress PDCP Header De-Compress PDCP SN Attach PDCP Re-ordering PDCP Ciphering PDCP De-ciphering PDCP Header Attach PDCP Header Detach Option 2-1 (UP Only) RLC Transmit Buffer Option 3 RLC Segmentation RLC Concatenation RLC Header Attach RLC Re-Ordering Option 4 MAC Multiplexing MAC De-Multiplexing Option 5 MAC HARQ MAC HARQ Data Channel Transfer Data Channel Transfer Option 6 To PHY From PHY FIGURE 1-22 Options 2, 3, 4, 5, and 6 splits. causing interference to another user trying to do the same. This is shown in Fig. 1-24 where the colored bands indicate the frequency used to communicate between the client and the base station for that specific base station/sector. Frequency reuse techniques are commonly used in cellular networks to mitigate this type of interference, but they come at the expense of lower spatial bandwidth efficiency. In a generic frequency reuse scheme, the total available bandwidth is divided into subbands and used by different cells in a way that no two neighboring cells would use the same subband. See Fig. 1-25 for an example dividing up the frequency into three bands a