Internet Engineering Task Force                            A. Ratilainen
Internet-Draft                                                  Ericsson
Intended status: Informational                              July 8, 2016
Expires: January 9, 2017

                         NB-IoT characteristics


   Low Power Wide Area Networks (LPWAN) are wireless technologies
   covering different Internet of Things (IoT) applications.  The common
   characteristics for LPWANs are large coverage, low bandwidth, small
   data sizes and long battery life operation.  One of these
   technologies include Narrowband Internet of Things (NB-IoT) developed
   and standardized by 3GPP.  This document is an informational overview
   to NB-IoT and gives the principal characteristics and restrictions of
   this technology in order to help with the IETF work for providing
   IPv6 connectivity to NB-IoT along with other LPWANs.

Status of This Memo

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   This Internet-Draft will expire on January 9, 2017.

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Overview of the NB-IoT technology . . . . . . . . . . . . . .   3
   3.  System architecture . . . . . . . . . . . . . . . . . . . . .   4
   4.  NB-IoT worst case performance . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The purpose of this document is to provide background information and
   typical link characteristics about NarrowBand Internet of Things (NB-
   IoT) to be considered in IETF's 6LPWA work.

   NB-IoT is a Low Power Wide Area (LPWA) technology being standardized
   by the 3GPP.  NB-IoT has been developed with the following objectives
   in mind:

   o  Improved indoor coverage

   o  Support of massive number of low throughput devices

   o  Low delay sensitivity

   o  Ultra-low device cost

   o  Low device power consumption

   o  Optimized network architecture

   The standardization of NB-IoT was finalized with 3GPP Release-13 in
   June 2016, but further enhancements for NB-IoT are worked on in the
   following releases, for example in the form of multicast support.
   For more information of what has been specified for NB-IoT, 3GPP
   specification 36.300 [TGPP36300] provides an overview and overall
   description of the E-UTRAN radio interface protocol architecture,
   while specifications 36.321 [TGPP36321], 36.322 [TGPP36322], 36.323
   [TGPP36323] and 36.331 [TGPP36331] give more detailed description of
   MAC, RLC, PDCP and RRC protocol layers respectively.  The new
   versions of the specifications including NB-IoT are not yet available

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   due to novelty of the feature, but should be shortly available in the
   3GPP website.

2.  Overview of the NB-IoT technology

   Machine type communication (MTC) refers to the emerging type of
   wireless communications where machine-like devices talk to each other
   through mobile networks or locally.  Its requirements range from
   Massive MTC type of data with low cost, low energy consumption, small
   data volumes and massive numbers to critical MTC type of high
   reliability, very low latency and very high availability.

   NB-IoT has been designed to satisfy a plethora of use cases and
   combination of these requirements, but especially NB-IoT targets the
   low-end Massive MTC scenario with following requirements: Less than
   5$ module cost, extended coverage of 164 dB maximum coupling loss,
   battery life of over 10 years, ~55000 devices per cell and uplink
   reporting latency of less than 10 seconds.

   NB-IoT supports Half Duplex FDD operation mode with 60 kbps peak rate
   in uplink and 30 kbps peak rate in downlink.  Highest modulation
   scheme is QPSK in both uplink and downlink.  As the name suggests,
   NB-IoT uses narrowbands with the bandwidth of 180 kHz in both,
   downlink and uplink.  The multiple access scheme used in the downlink
   is OFDMA with 15 kHz sub-carrier spacing.  On uplink multi-tone SC-
   FDMA is used with 15 kHz tone spacing or as a special case of SC-FDMA
   single tone with either 15kHz or 3.75 kHz tone spacing may be used.
   These schemes have been selected to reduce the User Equipment (UE)

   NB-IoT can be deployed in three ways.  In-band deployment means that
   the narrowband is multiplexed within normal LTE carrier.  In Guard-
   band deployment the narrowband uses the unused resource blocks
   between two adjacent LTE carriers.  Also standalone deployment is
   supported, where the narrowband can be located alone in dedicated
   spectrum, which makes it possible for example to refarm the GSM
   carrier at 850/900 MHz for NB-IoT.  All three deployment modes are
   meant to be used in licensed bands.  The maximum transmission power
   is either 20 or 23 dBm for uplink transmissions, while for downlink
   transmission the eNodeB may use higher transmission power, up to 46
   dBm depending on the deployment.

   For signaling optimization, two options are introduced in addition to
   legacy RRC connection setup, mandatory Data-over-NAS (Control Plane
   optimization, solution 2 in [TGPP23720]) and optional RRC Suspend/
   Resume (User Plane optimization, solution 18 in [TGPP23720]).  In the
   control plane optimization the data is sent over Non Access Stratum,
   directly from Mobility Management Entity (MME) in core network to the

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   UE without interaction from base station.  This means there are no
   Access Stratum security or header compression, as the Access Stratum
   is bypassed, and only limited RRC procedures.

   The RRC Suspend/Resume procedures reduce the signaling overhead
   required for UE state transition from Idle to Connected mode in order
   to have a user plane transaction with the network and back to Idle
   state by reducing the signaling messages required compared to legacy

   With extended DRX the RRC Connected mode DRX cycle is up to 10.24
   seconds and in RRC Idle the DRX cycle can be up to 3 hours.

   To recap, the following is a list of the most important
   characteristics of NB-IoT:

   o  Narrowband operation (180 kHz bandwidth) in licensed bands, either
      in in-band, guard band or standalone operation mode

   o  Support for 1 Data Radio Bearer (DRB) is mandatory, 2 additional
      DRBs are optional

   o  Maximum peak rate is 60 kbps in UL and 30 kbps in DL

   o  No channel access restrictions (up to 100% duty cycle)

   o  The maximum size of PDCP SDU and PDCP control PDU is 1600 octets
      in NB-IoT

   o  Data over non-access stratum is supported

   o  With eDRX, DRX cycle is up to 10.24 seconds in connected mode and
      up to 3 hours in idle mode

3.  System architecture

   NB-IoT network architecture is based on the network architecture of
   legacy LTE, which is illustrated in Figure 1.  It consists of core
   network, called Evolved Packet Core (EPC), Evolved UMTS Terrestrial
   Radio Access Network (E-UTRAN) and the User Equipment (UE).  Next we
   take a look at the key components of EPC.

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   |UE| \              +------+      +------+
   +--+  \             | MME  |------| HSS  |
          \          / +------+      +------+
   +--+    \+-----+ /      |
   |UE| ----| eNB |-       |
   +--+    /+-----+ \      |
          /          \ +--------+
         /            \|        |    +------+     Service PDN
   +--+ /              |  S-GW  |----| P-GW |---- e.g. Internet
   |UE|                |        |    +------+
   +--+                +--------+

                    Figure 1: 3GPP network architecture

   Mobility Management Entity (MME) is responsible for handling the
   mobility of the UE.  MME tasks include tracking and paging UEs,
   session management, choosing the Serving gateway for the UE during
   initial attachment and authenticating the user.  At MME, the Non
   Access Stratum (NAS) signaling from the UE is terminated.

   Serving Gateway (S-GW) routes and forwards the user data packets
   through the access network and acts as a mobility anchor for UEs
   during handover between base stations known as eNodeBs and also
   during handovers between other 3GPP technologies.

   Packet Data Node Gateway (P-GW) works as an interface between 3GPP
   network and external networks.

   Home Subscriber Server (HSS) contains user-related and subscription-
   related information.  It is a database, which performs mobility
   management, session establishment support, user authentication and
   access authorization.

   E-UTRAN consists of components of a single type, eNodeB. eNodeB is a
   base station, which controls the UEs in one or several cells.

   The illustration of 3GPP radio protocol architecture can be seen from
   Figure 2.

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   +---------+                                       +---------+
   | NAS     |----|-----------------------------|----| NAS     |
   +---------+    |    +---------+---------+    |    +---------+
   | RRC     |----|----| RRC     | S1-AP   |----|----| S1-AP   |
   +---------+    |    +---------+---------+    |    +---------+
   | PDCP    |----|----| PDCP    | SCTP    |----|----| SCTP    |
   +---------+    |    +---------+---------+    |    +---------+
   | RLC     |----|----| RLC     | IP      |----|----| IP      |
   +---------+    |    +---------+---------+    |    +---------+
   | MAC     |----|----| MAC     | L2      |----|----| L2      |
   +---------+    |    +---------+---------+    |    +---------+
   | PHY     |----|----| PHY     | PHY     |----|----| PHY     |
   +---------+         +---------+---------+         +---------+
               LTE-Uu                         S1-MME
       UE                     eNodeB                     MME

                Figure 2: 3GPP radio protocol architecture

   The radio protocol architecture of NB-IoT (and LTE) is separated into
   control plane and user plane.  Control plane consists of protocols
   which control the radio access bearers and the connection between the
   UE and the network.  The highest layer of control plane is called
   Non-Access Stratum (NAS), which conveys the radio signaling between
   the UE and the EPC, passing transparently through radio network.  It
   is responsible for authentication, security control, mobility
   management and bearer management.

   Access Stratum (AS) is the functional layer below NAS, and in control
   plane it consists of Radio Resource Control protocol (RRC)
   [TGPP36331], which handles connection establishment and release
   functions, broadcast of system information, radio bearer
   establishment, reconfiguration and release.  RRC configures the user
   and control planes according to the network status.  There exists two
   RRC states, RRC_Idle or RRC_Connected, and RRC entity controls the
   switching between these states.  In RRC_Idle, the network knows that
   the UE is present in the network and the UE can be reached in case of
   incoming call.  In this state the UE monitors paging, performs cell
   measurements and cell selection and acquires system information.
   Also the UE can receive broadcast and multicast data, but it is not
   expected to transmit or receive singlecast data.  In RRC_Connected
   the UE has a connection to the eNodeB, the network knows the UE
   location on cell level and the UE may receive and transmit singlecast
   data.  RRC_Connected mode is established, when the UE is expected to
   be active in the network, to transmit or receive data.  Connection is
   released, switching to RRC_Idle, when there is no traffic to save the
   UE battery and radio resources.  However, a new feature was
   introduced for NB-IoT, as mentioned earlier, which allows data to be

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   transmitted from the MME directly to the UE, while the UE is in
   RRC_Idle transparently to the eNodeB.

   Packet Data Convergence Protocol's (PDCP) [TGPP36323] main services
   in control plane are transfer of control plane data, ciphering and
   integrity protection.

   Radio Link Control protocol (RLC) [TGPP36322] performs transfer of
   upper layer PDUs and optionally error correction with Automatic
   Repeat reQuest (ARQ), concatenation, segmentation and reassembly of
   RLC SDUs, in-sequence delivery of upper layer PDUs, duplicate
   detection, RLC SDU discard, RLC-re-establishment and protocol error
   detection and recovery.

   Medium Access Control protocol (MAC) [TGPP36321] provides mapping
   between logical channels and transport channels, multiplexing of MAC
   SDUs, scheduling information reporting, error correction with HARQ,
   priority handling and transport format selection.

   Physical layer [TGPP36201] provides data transport services to higher
   layers.  These include error detection and indication to higher
   layers, FEC encoding, HARQ soft-combining.  Rate matching and mapping
   of the transport channels onto physical channels, power weighting and
   modulation of physical channels, frequency and time synchronization
   and radio characteristics measurements.

   User plane is responsible for transferring the user data through the
   Access Stratum.  It interfaces with IP and consists of PDCP, which in
   user plane performs header compression using Robust Header
   Compression (RoHC), transfer of user plane data between eNodeB and
   UE, ciphering and integrity protection.  Lower layers in user plane
   are similarly RLC, MAC and physical layer performing tasks mentioned

4.  NB-IoT worst case performance

   Here we consider the worst case scenario for NB-IoT.  This scenario
   refers to the case with high coupling loss and the UE being the least
   capable.  The link characteristics are listed assuming such

   o  180 kHz bandwidth

   o  Uplink transmission

      *  1 Data Radio Bearer (DRB)

      *  Single-tone transmission, 3.75 kHz spacing

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   o  164 dB maximum coupling loss (see Table 1

   |                       Numerology                       | 3.75 kHz |
   |                (1) Transmit power (dBm)                |   23.0   |
   |           (2) Thermal noise density (dBm/Hz)           |   -174   |
   |             (3) Receiver noise figure (dB)             |    3     |
   |          (4) Occupied channel bandwidth (Hz)           |   3750   |
   |  (5) Effective noise power = (2) + (3) + 10*log ((4))  |  -135.3  |
   |                         (dBm)                          |          |
   |                 (6) Required SINR (dB)                 |   -5.7   |
   |       (7) Receiver sensitivity = (5) + (6) (dBm)       |  -141.0  |
   |        (8) Max coupling loss  = (1) - (7) (dB)         |  164.0   |

                        Table 1: NB-IoT Link Budget

   Under such conditions, NB-IoT may achieve data rate of roughly 200

   For downlink with 164 dB coupling loss, NB-IoT may achieve higher
   data rates, depending on the deployment mode.  Stand-alone operation
   may achieve the highest data rates, up to few kbps, while in-band and
   guard-band operations may reach several hundreds of bps.  NB-IoT may
   even operate with higher maximum coupling loss than 170 dB with very
   low bit rates.

5.  IANA Considerations

   This memo includes no request to IANA.

6.  Security Considerations

   3GPP access security is specified in [TGPP33203].

7.  Informative References

              3GPP, "TR 23.720 v13.0.0 - Study on architecture
              enhancements for Cellular Internet of Things", 2016.

              3GPP, "TS 33.203 v13.1.0 - 3G security; Access security
              for IP-based services", 2016.

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              3GPP, "TS 36.201 v13.2.0 - Evolved Universal Terrestrial
              Radio Access (E-UTRA); LTE physical layer; General
              description", 2016.

              3GPP, "TS 36.300 v13.4.0 (Available soon) - Evolved
              Universal Terrestrial Radio Access (E-UTRA) and Evolved
              Universal Terrestrial Radio Access Network (E-UTRAN);
              Overall description; Stage 2", 2016.

              3GPP, "TS 36.321 v13.2.0 (Available soon) - Evolved
              Universal Terrestrial Radio Access (E-UTRA); Medium Access
              Control (MAC) protocol specification", 2016.

              3GPP, "TS 36.322 v13.2.0 (Available soon) - Evolved
              Universal Terrestrial Radio Access (E-UTRA); Radio Link
              Control (RLC) protocol specification", 2016.

              3GPP, "TS 36.323 v13.2.0 (Available soon) - Evolved
              Universal Terrestrial Radio Access (E-UTRA); Packet Data
              Convergence Protocol (PDCP) specification (Not yet
              available)", 2016.

              3GPP, "TS 36.331 v13.2.0 (Available soon) - Evolved
              Universal Terrestrial Radio Access (E-UTRA); Radio
              Resource Control (RRC); Protocol specification", 2016.

Author's Address

   Antti Ratilainen
   Hirsalantie 11
   Jorvas  02420


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