NB-IoT Architecture: Understanding LTE NB-IoT Network

This page covers NB-IoT Architecture as per 3GPP LTE-NB Specifications. It describes various elements used in the LTE NB-IoT architecture.

Introduction

3GPP has released specifications for a narrowband cellular IoT solution known as LTE-NB or NB-IoT, utilizing 200 KHz bandwidth. It has been released in Rel.13, Rel.14 and Rel.15.

NB-IoT is known as LPWAN (Low Power Wide Area Network) technology. The technology mainly focuses on improving indoor coverage, low cost, long battery life and a larger number of connected devices.

Let’s understand the overall network architecture as shown in Figure 1.

As shown, there are two main parts in the NB-IoT architecture: the access network and the core network. UEs (User Equipments) are connected to eNBs (evolved NodeBs, i.e., base stations) using the Uu interface. The eNBs are connected together via the X2 interface. The eNBs are connected to the Core Network side using the S1 interface. This S1 interface carries either NB-IoT control packets or data packets. Though NB-IoT does not support handover, the X2-interface is used to enable fast resume from the IDLE state of the UE. One can refer to RRC Connection Establishment Procedure to know more about different states of UE. Overall, the access network part is similar to LTE.

LTE NB-IoT Architecture | Core Network Side

There are two optimizations used in CIoT (Cellular IoT) based architectures such as NB-IoT. The control plane is marked in red and the user plane is marked in blue. In NB-IoT, a new node called SCEF (Service Capability Exposure Function) is designed to handle machine type data. It is used for delivery of non-IP data over the control plane. It also provides an abstract interface for the network services such as authentication, authorization, discovery, and access network capabilities.

Figure 2 depicts data transmission and reception.

• UL (Uplink) data are transmitted from eNB to MME (Mobility Management Entity). From there, it may either follow the SGW (Serving Gateway) to PGW (Packet Data Network Gateway) path or to the SCEF path. From this node, they are forwarded to the application server for CIoT services.
• DL (Downlink) data is transmitted over the same paths but in reverse direction.
• This LTE NB-IoT architecture does not require data radio bearer setup. Data packets are sent on the signaling radio bearer instead. Hence, this architecture-based solution is most ideal for transmission of infrequent and small data packets.

Reference: 3GPP 36 series Rel.13, 14, 15