Narrowband Internet of Things Whitepaper

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  • Narrowband Internet of ThingsWhitepaper

    As part of Release 13, 3GPP has specified a new radio interface, the Narrowband Internet of Things (NB-IoT). NB-IoT is optimized for machine type traffic. It is kept as simple as possible in order to reduce devicecosts and to minimize battery consumption. In addition, it is also adapted to work in difficult radio condi-tions, which is a frequent operational area for certain machine type communication devices. Although NB-IoT is an independent radio interface, it is tightly connected with LTE, which also shows up in its integra-tion in the current LTE specifications.

    In this whitepaper we introduce the NB-IoT technology with an emphasis on the tight connection to LTE.

    Note:

    Visit our homepage for the most recent version of this application note (www.rohde-schwarz.com/appnote/1MA266).

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  • Contents

    2Whitepaper NarrowBand_IoT 1MA266_0e

    Contents1 Introduction............................................................................................ 3

    2 Overview................................................................................................. 5

    3 Physical Layer........................................................................................9

    4 Cell Access...........................................................................................24

    5 Data Transfer........................................................................................33

    6 Summary and Outlook.........................................................................39

    7 References............................................................................................40

    8 Additional Information.........................................................................41

    9 Rohde & Schwarz.................................................................................42

  • Introduction

    3Whitepaper NarrowBand_IoT 1MA266_0e

    1 IntroductionOne of the characteristics of Machine Type Communication (MTC) is the broad spec-trum of capabilities. For example surveillance cameras have to deliver a huge amountof UL data while being almost stationary, whereas devices for fleet tracking have asmall amount of data while performing a lot of handovers.

    Yet another class of devices has neither of these capabilities. Examples are devicesfor meter reading like electricity, gas, or water consumption. They are often stationary,thus need not an optimized handover. Only a small amount of data is usually transfer-red, which is even not delay sensitive. However, the number of these MTC devicesmay become quite big, even up to several orders of magnitude compared to the tradi-tional devices. Using existing LTE technology would lead to a network overload,because despite of their small amount of user data the amount of signaling is about thesame. The first specification of NB-IoT focusses on this class of devices.

    These devices are often installed at places without power supply. Consequently theyrun completely on battery and it may be very expensive to change the battery, becausethey may only be accessed by trained staff. Hence, in some cases the battery lifetimecan even determine the lifetime of the whole device. An optimized power consumptionis therefore essential for a proper operation. In addition, the coverage at these placesis often quite bad. Therefore, the indoor coverage has to be significantly improved, upto 23 dB are regarded as necessary.

    Due to their sheer amount of required devices, they have to be in the low cost range.As a goal, each module shall be in the price range of less than 5 US$.

    In order to evaluate possible solutions, a study item was discussed in 3GPP in theGERAN TSG [1]. The main requirement in addition to the above ones was the coexis-tence with existing GSM, UMTS and LTE systems and the hardware used for thosetechnologies.

    Figure 1-1: The three different solutions for specifying an optimized internet of things standard

    Two solutions, the NB-IoT and the EC-GSM have been identified from this study,where the latter is building upon the GSM standard. In parallel, also a pure LTE solu-

  • Introduction

    4Whitepaper NarrowBand_IoT 1MA266_0e

    tion, LTE-M, was brought into 3GPP. It continues the optimizations already done inRelease 12 with the introduction of a new device category cat-M1.

    In this whitepaper, the NB-IoT is presented. Although it is integrated in the LTE stan-dard, it can be regarded as a new air interface. Therefore, it is not backward compati-ble with LTE. The coexistence is realized by specifying the time and frequency resour-ces used from the existing standards, or in the neighborhood thereof.

    The whitepaper is structured in the following way: We first give an overview of themore specific requirements and the network architecture and provide the details of thephysical layer. After having described the access to the cell, we show how the datapackets are transported over the air interface. Finally, an outlook to further develop-ments of this technology is given.

  • Overview

    5Whitepaper NarrowBand_IoT 1MA266_0e

    2 Overview

    2.1 Requirements

    From the general MTC requirements mentioned in the previous chapter, the followingstandard specific requirements for NB-IoT were derived:

    Minimize the signaling overhead, especially over the radio interface Appropriate security to the complete system, including the core network Improve battery life Support delivery of IP and non-IP data [2, 3] Support of SMS as a deployment option [4]

    In order to fulfill these requirements, many advanced and even basic features of LTERelease 8/9 are not supported [5]. The most striking example is the lack of handoverfor UEs in the connected state. Only cell reselection in the idle state is supported,which is even restricted to be within the NB-IoT technology. As there is no interactionwith other radio technologies, also the associated features are not supported. Exam-ples are the lack of LTE-WLAN interworking, interference avoidance for in-device coex-istence, and measurements to monitor the channel quality.

    Most LTE-Advanced features are also not supported. This concerns e.g. Carrier Aggre-gation, Dual Connectivity, or device-to-device services. In addition, there is no QoSconcept, because NB-IoT is not used for delay sensitive data packets. Consequently,all services requiring a guaranteed bit rate, like real time IMS, are not offered in NB-IoTas well.

    With these requirements, 3GPP uses a different approach than before. Instead of cre-ating one air-interface for all types of applications, the air-interface for small non-delaysensitive data packets is split off and optimized separately. UEs which support to workon NB-IoT technology are tagged with the new UE category cat-NB1.

    2.2 Network

    2.2.1 Core Network

    In order to send data to an application, two optimizations for the cellular internet ofthings (CIoT) in the evolved packet system (EPS) were defined, the User Plane CIoTEPS optimisation and the Control Plane CIoT EPS optimisation, see Figure 2-1. Bothoptimisations may be used but are not limited to NB-IoT devices.

    Network

  • Overview

    6Whitepaper NarrowBand_IoT 1MA266_0e

    Figure 2-1: Network for the NB-IoT data transmission and reception. In red, the Control Plane CIoTEPS optimisation is indicated, in blue the User Plane CIoT EPS optimisation.

    On the Control Plane CIoT EPS optimisation, UL data are transferred from the eNB(CIoT RAN) to the MME. From there, they may either be transferred via the ServingGateway (SGW) to the Packet Data Network Gateway (PGW), or to the Service Capa-bility Exposure Function (SCEF) which however is only possible for non-IP data pack-ets. From these nodes they are finally forwarded to the application server (CIoT Ser-vices). DL data is transmitted over the same paths in the reverse direction. In this solu-tion, there is no data radio bearer set up, data packets are sent on the signaling radiobearer instead. Consequently, this solution is most appropriate for the transmission ofinfrequent and small data packets.

    The SCEF is a new node designed especially for machine type data. It is used fordelivery of non-IP data over control plane and provides an abstract interface for thenetwork services (authentication and authorization, discovery and access neworkcapabilities).

    With the User Plane CIoT EPS optimisation, data is transferred in the same way as theconventional data traffic, i.e. over radio bearers via the SGW and the PGW to the appli-cation server. Thus it creates some overhead on building up the connection, however itfacilitates a sequence of data packets to be sent. This path supports both, IP and non-IP data delivery.

    2.2.2 Access Network

    On the overal access network architecture there is no difference to LTE [6]:

    Network

  • Overview

    7Whitepaper NarrowBand_IoT 1MA266_0e

    Figure 2-2: Network architecture towards the air--interface

    The eNBs are connected to the MME and S-GW using the S1 interface, with the differ-ence of carrying the NB-IoT messages and data packets. Even though there is nohandover defined, there is still an X2 interface between two eNBs, which enables a fastresume after the UE goes to the idle state, see Chapter 4.5.1, "RRC Connection Estab-lishment", on page 28 for details, even for the case that the resume process is toanother eNB.

    2.3 Frequency Bands

    For the frequency bands, the same frequency numbers as in LTE are used, with a sub-set defined for NB-I