NR-LTE Interworking

NR-LTE Interworking refers to the interoperability between 5G New Radio (NR) and Long-Term Evolution (LTE) networks. It is necessary for seamless transition from LTE to 5G and vice versa, and allows devices to operate on both networks simultaneously.

In this article, we will discuss the technical aspects of NR-LTE Interworking, including the key components and protocols involved, network architecture, and the types of interworking scenarios.

Components and Protocols

The interworking between NR and LTE networks is achieved through several key components and protocols, including:

Dual Connectivity (DC)

Dual Connectivity is a key feature that allows devices to be simultaneously connected to both NR and LTE networks. With DC, a device can communicate with both networks and benefit from the higher speeds and lower latency of 5G while still maintaining coverage and compatibility with the existing LTE infrastructure. The two types of DC are Non-Standalone (NSA) and Standalone (SA). In NSA mode, the device is connected to both NR and LTE networks, but the LTE network is used for control plane functions and the NR network is used for data plane functions. In SA mode, the device is connected to both NR and LTE networks, but the NR network is used for control plane and data plane functions.

Xn Interface

The Xn Interface is a new interface introduced in 5G that enables communication between two adjacent gNBs (Next-Generation NodeB) in the 5G network. The Xn interface is used for inter-gNB communication and is responsible for functions such as handover, load balancing, and traffic steering.

NG Interface

The NG Interface is a new interface introduced in 5G that enables communication between the 5G Core Network and the gNBs. It is responsible for functions such as network slicing, authentication, and charging.

S1 Interface

The S1 Interface is the interface between the eNodeB (Evolved NodeB) in the LTE network and the 5G Core Network. It is responsible for functions such as handover, mobility management, and packet forwarding.

Network Architecture

The network architecture for NR-LTE Interworking consists of the following components:

LTE Network

The LTE network is the existing cellular network infrastructure that provides connectivity to LTE-enabled devices. The LTE network consists of eNodeBs, which are responsible for controlling the radio access network, and the EPC (Evolved Packet Core), which is responsible for managing the data traffic between the LTE network and the Internet.

5G Network

The 5G network is the new cellular network infrastructure that provides connectivity to 5G-enabled devices. The 5G network consists of gNBs, which are responsible for controlling the radio access network, and the 5G Core Network, which is responsible for managing the data traffic between the 5G network and the Internet.

Xn Interface

The Xn Interface is used for inter-gNB communication and is responsible for functions such as handover, load balancing, and traffic steering.

NG Interface

The NG Interface is used for communication between the 5G Core Network and the gNBs. It is responsible for functions such as network slicing, authentication, and charging.

S1 Interface

The S1 Interface is used for communication between the eNodeBs in the LTE network and the 5G Core Network. It is responsible for functions such as handover, mobility management, and packet forwarding.

Interworking Scenarios

There are several interworking scenarios between NR and LTE networks, including:

LTE to NR Handover

In this scenario, a device that is connected to an LTE network moves into an area that has 5G coverage. The device then initiates a handover procedure to switch from LTE to NR. The handover procedure is managed by the 5G Core Network and the gNBs, which coordinate with the LTE eNodeBs to ensure a smooth handover.

During the handover procedure, the device maintains connectivity with both the LTE and NR networks through Dual Connectivity, which allows the device to seamlessly switch between the two networks without interrupting the data transfer. Once the handover is complete, the device is fully connected to the NR network and can benefit from the higher speeds and lower latency of 5G.

NR to LTE Handover

In this scenario, a device that is connected to a 5G network moves into an area that only has LTE coverage. The device then initiates a handover procedure to switch from NR to LTE. The handover procedure is managed by the 5G Core Network and the gNBs, which coordinate with the LTE eNodeBs to ensure a smooth handover.

During the handover procedure, the device maintains connectivity with both the NR and LTE networks through Dual Connectivity, which allows the device to seamlessly switch between the two networks without interrupting the data transfer. Once the handover is complete, the device is fully connected to the LTE network and can continue to operate normally.

LTE and NR Coexistence

In this scenario, a device is connected to both the LTE and NR networks simultaneously through Dual Connectivity. The LTE network is used for control plane functions, while the NR network is used for data plane functions. This allows the device to benefit from the higher speeds and lower latency of 5G while still maintaining compatibility with the existing LTE infrastructure.

During normal operation, the device communicates with both networks simultaneously, but when a handover is required, the 5G Core Network and the gNBs coordinate with the LTE eNodeBs to ensure a smooth transition.

LTE and NR Data Aggregation

In this scenario, a device is connected to both the LTE and NR networks simultaneously through Dual Connectivity, but the data is aggregated across both networks to achieve higher throughput. The LTE network is used for low-bandwidth applications, while the NR network is used for high-bandwidth applications.

During normal operation, the device communicates with both networks simultaneously, but the data is routed through the network that can provide the best performance for the specific application. This allows the device to achieve higher throughput than would be possible using either network alone.

Conclusion

NR-LTE Interworking is essential for the smooth transition from LTE to 5G and vice versa. The interworking is achieved through Dual Connectivity, Xn Interface, NG Interface, and S1 Interface, and allows devices to operate on both networks simultaneously. The network architecture for NR-LTE Interworking consists of the LTE network, 5G network, Xn Interface, NG Interface, and S1 Interface. The interworking scenarios include LTE to NR Handover, NR to LTE Handover, LTE and NR Coexistence, and LTE and NR Data Aggregation. These scenarios ensure that devices can benefit from the higher speeds and lower latency of 5G while still maintaining compatibility with the existing LTE infrastructure.