PDF《4G-5G Interworking》

4G-5G Interworking RAN-level and CN-level Interworking June

2017 1 Contents @2017 Samsung.

All rights reserved. Introduction

2 4G-5G Interworking

2 RAN-level Interworking.2 CN-level Interworking.3 Performance &

Features Comparison.4 Performance Analysis

4 Network Features

11 Deployment Flexibility.12 Migration to a True 5G Network.14 Development at Samsung

15 Conclusion.15 Reference

15 Abbreviations.15

2 4G-5G Interworking @2017 Samsung. All rights reserved. Introduction To provide true 5G service to users, 5G cells will be deployed with full coverage and UE (User Equipment) will be able to connect to 5G network everywhere. However, in the early stage of 5G services, the 5G cells will be partially deployed and there will be 5G coverage holes. The initial 5G commercial service will be launched from early 2019, but the initial investment for 5G service will be limited because of a lack of 5G UE. So, the 5G network needs to be interworked with the existing LTE network. The interworking solution can provide seamless service to users. This white paper introduces the solutions for 4G-5G interworking and compares the solutions in terms of performance, the features and the migration to a true 5G service network. 4G-5G Interworking If 5G cells are not deployed with full coverage, a seamless service can be provided to users by interworking with the existing LTE network, which is already deployed with full coverage. When the network evolved from 3G to LTE, LTE cells were deployed by partial coverage when LTE was first commercialized. In order to overcome coverage shortage, the LTE network also provided seamless service to users by interworking with the 3G network. Interworking between the 3G network and the LTE network was developed by the Core Network-level interworking solution, in which a 3G Core Network entity, SGSN (Serving GPRS Support Node), directly interfaces with LTE Core Network Entities, MME (Mobility Management Entity) and S-GW (Serving Gateway). For 4G-5G interworking, two kinds of solutions, RAN-level interworking and CN-level interworking, are under discussion in 3GPP. RAN-level Interworking RAN-level interworking provides the interworking service between LTE and 5G using a direct interface between LTE eNB and 5G NB. The control protocol (RRC) message is transmitted over the LTE radio interface, so the connection and the mobility of UE are controlled by LTE eNB. User traffic is simultaneously transmitted through LTE eNB and 5G NB (PDCP aggregation) or by using 5G NB (CN-split Bearer) only. Although the RRC message can be processed stably by LTE eNBs that provide coverage larger than 5G NBs, LTE radio interface always remains connected, even though user traffic is transmitted over the 5G radio interface (NR). RAN-level interworking is necessary in NSA (Non- Standalone Architecture), where 5G Radio (NR) cannot be used without LTE Radio. Two different core networks can be used for RAN-level interworking, as shown in Figure 1. Architecture for RAN-Level Interworking Figure 1. When using EPC (Evolved Packet Core) for an existing LTE network, basically only EPC-based service can be provided, even though 5G radio technology is used. Only high-speed data service can be provided to users using NR (New Radio) technology.

3 4G-5G Interworking @2017 Samsung. All rights reserved. LTE and 5G interworking can be achieved by upgrading some LTE eNBs connected to 5G NBs and by increasing the gateway capacity in EPC. The new 5G Core Network, which is called 5GC (5th Generation Core), can be introduced to support RAN-level interworking. In this solution, the new 5G core network features, e.g. network slicing, can be supported and the 5G service can be differentiated from the LTE service. However, all LTE eNBs will be upgraded to eLTE eNBs that can be connected to 5GC. CN-level Interworking CN-level interworking does not require a direct interface between the LTE eNB and the 5G NB, but the EPC entity is connected to the 5GC entity. The UE manages LTE and NR radio interface connection independently, and can be connected to a single network, either LTE or 5G. When the UE is located in 5G coverage, it can only connect to the 5G network and receive 5G service. When the UE moves out of 5G coverage, it releases NR radio interface connection and establishes LTE radio interface connection. Even though the network that the UE connects to changes, the IP address assigned to the UE is maintained and seamless service can be provided to the user. CN-level interworking is necessary in SA (Standalone Architecture), where 5G Radio (NR) can be used without LTE Radio. For CN-level interworking, the single registration solution and the dual registration solution are possible, as shown in Figure 2. With the single registration, the UE registers to either one of the LTE or 5G networks at any moment, and the UE context can be delivered through the control interface between MME in EPC and AMF (Access and Mobility Management Function) in 5GC when the connected network for the UE is changed. In order to support the single registration solution, MME will be upgraded to support the MME-AMF interface (Nx) and S-GW needs to be connected to UPF in 5GC. LTE eNB should also be upgraded to support the mobility between LTE and 5G. The dual registration solution is a way to allow the UE to register individually with EPC and 5GC. Thus, it does not need to forward the UE context between MME and AMF, and the interface between M........