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5G RAN Architcture

5G RAN Architecture

hemraj3k
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5G RAN Architcture

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  1. Prepared: Hemraj Kumar Senior 5G Technology Consultant 5G Overview

  2. LTE RAN Architecture eNodeB BBU = L1+L2+L3 EPC HSS E-UTRAN RRC S6a PDCP MME X2 S1-MME BBU PCRF RLC S11 Uu MAC S1-U Gx eNodeB PHY P-GW S-GW S5 / S8 Fronthaul CPRI SGi RRU RF PDN BBU: Baseband unit. Manages the whole base station, including operating/maintenance and signaling processing. It decides the “CAPACITY” of the system. RRU: Remote Radio unit interfaces with an antenna on one end and BBU on the other. It connects to BBU through CPRI interface and converts RF signal into data signal and vice versa. Further, it does filtering and amplification of RF signal. In fact, it decides the “COVERAGE” of the system” 2

  3. 4G RAN Architecture

  4. NG-RAN Overall Architecture 4

  5. ArchitectureEvolutionfrom4G to 5G Main change is that the original BBU function is split into three parts § RRU (Remote Radio Unit), DU (Distributed Unit), CU (Central Unit) § Allows for decreased fronthaul line rates while meeting latency demands Parts of UP are moved to EPC to CU and DU Non-real-time (NRT) function from BBU to CU Real-time (RT) function from BBU to DU Two new created interfaces are referred to as the high layer split point (Fronthaul II) and the low layer split point (Fronthaul I) 출처: ITU-T GSTR-TN5G Technical Report – Transport Network Support of 5G (2018.2) 5

  6. Disaggregation of gNB The disaggregated RAN breaks up the integrated network system into several functional components(CU,DU&RU) that can then be individually re-located as needed without hindering their ability to work together to provide a holistic network service. The connection between the CU and DU is known as the Midhaul The connection between the Radio Access Unit and Radio Unit is known as the Fronthaul. The Fronthaul has more demanding transport requirements in terms of bandwidth and latency when compared to the Midhaul and Backhaul. The Fronthaul is not an interface standardized by 3GPP. Instead, it is typical to use the Common Public Radio Interface (CPRI) or enhanced CPRI (eCPRI) specifications for the Fronthaul's and eCPRI have been developed by a consortium of companies and are intended to complement the work of 3GPP. Digital Samples Physical layer Processing & coordination Higher Layer processing RF Layer 5G Core Network HLS LLS Backhaul Midhaul Split 2 Latency = 1-2 ms Capacity = C Fronthaul Split 7.2 CU CU 5GC 5GC DU DU RU RU Latency<< 1.0 ms Capacity = C gNB DU (Distributed Unit) gNB RU (Radio Unit) gNB CU (Central Unit) gNB-CU-CP Control Plane gNB-CU-UP User Plane Latency = 50 -200 µs Capacity = C☓6 /10 Compressed = C ☓2 6

  7. CU-DU Split of gNB Contrary to the 4G RAN, the 5G NR logical node, the gNB, is split between Central Units (CUs) and DUs. The benefits for such an architecture are: § Flexible hardware implementation § Coordination of performance features, load management and real time performance optimization § adaptation to various use cases RRC SDAP PDCP gNB-CU F1 F1 F1 RLC gNB gNB-DU gNB-DU MAC PHY The split of the NR functions between CU and DUs is shown in above Figure The choice of a split between Packet Data Convergence Protocol (PDCP) and Radio link control (RLC) was driven by the reason that the split between MN and SN in DC configuration is the same. 7

  8. CUPS(Control & User Plane Separation) The gNB-CU is split into CP and UP for flexible dimensioning and topology. It allows mobile service providers to bring the service closer to the user & reduced the user plane latency. 5G services based around massive Machine Type Communications (mMTC), Ultra Reliable and Low Latency Communications (URLLC), Fixed Wireless Access (FWA), and new industry verticals will generate unique traffic patterns compared to typical mobile data service. The Conventional CUs with fixed Control and User Plane (CU/UP) resources are not suitable to support NR traffic pattern. In fact, for the majority of the most exciting 5G, CUPS is required—virtual reality gaming, emergency response services— because they latency. gNB-CU-UP E1 E1 E1 gNB-CU-CP gNB-CU-UP F1-C applications of gNB-CU-UP F1-C smart cities, F1-U F1-U F1-U F1-U can’t tolerate F1-U F1-U gNB-DU gNB-DU 8

  9. CUPS(Control & User Plane Separation) Single gNB-CU-CP in charge of controlling several gNB-CU-UPs and gNB-DUs. In a live network deployment a single gNB-CU-CP will control hundreds of gNB-DUs and maybe several gNB-CU-UPs. This is why it is misleading to compare the connectivity of a gNB-CU-CP with that of a LTE eNB. Rather it could be compared with a UTRAN RNC controlling a similar number of 3G base stations. F1AP is used for communication between gNB-CU CP and its gNB-DUs while the E1AP is the protocol that connects the gNB-CU-CP with surrounding gNB-CU-UPs. Call-related control plane procedures of F1AP and E1AP are very similar to what is known from NGAP. There is a UE context established between the gNB-CU CP and the gNB-DU. On F1-U a GTP tunnel is established for user plane transport. At the same time an E1 Bearer Context in gNB-CU-CP and gNB-CU-UP keeps track of the most relevant user plane transport parameters. The connectivity between a gNB-CU-UP and a gNB-DU is established by the gNB-CU- CP using Bearer Context Management functions. The gNB-CU-CP selects the appropriate gNB-CU-UP(s) for the requested services for the UE. Data forwarding between gNB-CU-UPs during intra-gNB-CU-CP handover within a gNB may be supported by Xn-U. 9

  10. 5G RAN High Level Architecture CU-CP : gNB-CU-control plane CU-UP : gNB-CU-user Plane DU : Open RAN Distributed unit RU : Open RAN Radio unit AMF UPF 5GC N2 to AMF RRC SDAP RRC SDAP Xn-C PDCP RLC MAC PHY gNB PDCP RLC MAC PHY gNB F1-C Xn-U RRC PDCP-C CU-CP N3 to UPF E1 PDCP- U PHY- High PHY- Low D/A & RFE SDAP RLC MAC F1-U RU DU CU-UP 5G UE Fronthaul CPRI/eCPRI 10

  11. 5G RAN Split Architecture The core of the whole thing is the gNB-Central Unit for the Control Plane (gNB-CU-CP). This function communicates directly with the UE using the NR RRC protocol. It also "talks" to the 5G Core Network represented by the AMF using the NGAP, a protocol very similar to the S1AP known from E-UTRAN. Neighboring 5G base stations are contacted using the XnAP, neighboring eNBs can be reached by using X2AP. The other virtual functions of the gNB are the Central Units for User Plane (gNB-CU - UP) and the Distributed Units (gNB-DU). While the gNB-CU-UP is responsible for handling the transport of payload the gNB-DUs deal with all the allocation of radio resources, especially the scheduling. As a result the lower layer radio interface protocols, especially RLC and MAC terminate in the gNB-DUs. 11

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