International telecommunication union
Multiple heterogeneous radio access networks
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- Fixed-mobile convergence
- Operation and management
- Structuring of IMT-2020 requirements
- Access network-agnostic and unified core network
- Distributed network architecture
- Integrated management of multi-RAT and fixed access networks
- Flexible signaling
Multiple heterogeneous radio access networksThe use of multiple heterogeneous radio access networks, including Wi-Fi networks, and their interworking with each other in existing IMT networks are becoming prevalent with various approaches: LTE/WiFi link Aggregation (LWA), interworking with ePDG or TWAG (trusted wireless access gateway), etc. The trend is also expected to be continued in IMT-2020 networks, but with more advanced and efficient ways. The multi-connectivity through the multiple available radio access networks improves the robustness of the network as well as the throughput performance. Especially, the dual connectivity of an existing IMT-network and a new IMT-2020 network will help ensure the smooth introduction of IMT-2020 networks. Gap A.14: Multi-RAT connectivity. See Clause: 7.1.1 of the main body of this report. IMT-2020 core network is envisioned as a converged access-agnostic core (i.e., where identity, mobility, security, etc. are decoupled from the access technology), which integrates multiple heterogeneous radio access networks as well as fixed networks on an IP basis. Gap A.15: Fixed mobile convergence. See Clause 7.1.1 of the main body of this report. Enhanced on-demand mobility management IMT-2020 should support a wide range of mobility options. Only around 30 % of total subscribers are actually mobile even in the current IMT networks according to some of MNOs’s observation. Therefore, IMT-2020 should not assume the same mobility support for all devices and application services but rather provide mobility on demand only to those that need it. While mobility is not required for some stationary devices such as smart meters and CPE devices, but we also need to provide mobility for high-speed trains running at 500 km/h. The service continuity levels also varies: seamless mobility, nomadic mobility, mobility for sporadic transmission, etc. Gap A.16: Flexible mobility. See Clause 7.1.1 of the main body of this report. Gap A.17: Mobility management for distributed flat network. See Clause 7.1.1 of the main body of this report.
The current status of having its own proprietary network management protocol in every different vendor should be enhanced by supporting a standard open interface so that a convergence network management system can control all different network devices as shown Figure . In addition to the standard management protocol, an IMT-2020 network should support common OAM protocols in IP-based transport network to enhance sustainability and reliability. 
Figure . Standardized network management and OAM. Gap A.18: End-to-end network management in a multi-domain environment. See Clause 7.1.1 of the main body of this report. Gap A.19: OAM protocols. See Clause 7.1.1 of the main body of this report.
Figure . Structuring of requirements. Figure 2 describes the structuring IMT-2020 requirements based on the gap analysis to give an overview of vision of IMT-2020 network architecture.
The introduction of a new mobile technology has been accompanied with a new packet core network in the legacy IMT networks. Therefore, the interworking issue between the new core network and legacy core networks has always been a technical challenge to overcome. The IMT-2020 network is envisioned to be an access network-agnostic architecture whose core network will be a common unified core network for emerging new radio access technologies for IMT-2020 as well as existing fixed and wireless networks (e.g., Wi-Fi). The access technology-agnostic unified core network should be accompanied by common control mechanisms which are decoupled from access technologies.
The IMT-2020 network should be flexible enough to handle the explosive increase of traffic from the new emerging bandwidth-hungry services such as ultra-high definition (UHD) TV, augmented reality (AR), video conferencing, remote medical treatment, etc. The heavily centralized architecture onto an anchor node of existing IMT networks is expected to be changed to cope with the explosion of mobile data traffic. This will require the gateways to the core network are expected to be located closer to the cell sites resulting in a distributed network architecture. The distributed network architecture will bring a significant reduction on backhaul and core network traffic by enabling placing content servers closer to mobile devices and also be beneficial to the latency of the services.
The IMT-2020 network should facilitate an integrated access network management for multiple radio access networks including Wi-Fi and fixed access networks. The integrated multi-RAT and fixed network management should support seamless and consistent user experience while moving across different access networks, and also steer mobile devices to choose the most suitable access technology in a seamless way. In addition, simultaneous multiple connections for a mobile device to multiple RATs and fixed access networks should be supported to increase user experienced data rate through the integrated management of multi-RAT and fixed access networks.
In the existing IMT networks, all different types of traffic are treated in a uniform procedure by a monolithic bearer management and its accompanied signaling protocol. The characteristics of traffic are expected to vary significantly from devices to devices and from applications to applications in IMT-2020 networks. For example, as the number of IoT devices is expected to increase, the intermittent short burst traffic from massive number of devices will cause signaling bottleneck. Meanwhile, a full-fledged signaling may be still essential for the devices/applications in which the support of mobility is more critical. Therefore, the IMT-2020 network should support flexible signaling architecture.
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