Internet Engineering Task Force A. Ratilainen
Internet-Draft Ericsson
Intended status: Informational July 8, 2016
Expires: January 9, 2017
NB-IoT characteristics
draft-ratilainen-lpwan-nb-iot-00
Abstract
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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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)
complexity.
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
operation
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
above.
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
conditions.
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
bps.
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
[TGPP23720]
3GPP, "TR 23.720 v13.0.0 - Study on architecture
enhancements for Cellular Internet of Things", 2016.
[TGPP33203]
3GPP, "TS 33.203 v13.1.0 - 3G security; Access security
for IP-based services", 2016.
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[TGPP36201]
3GPP, "TS 36.201 v13.2.0 - Evolved Universal Terrestrial
Radio Access (E-UTRA); LTE physical layer; General
description", 2016.
[TGPP36300]
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.
[TGPP36321]
3GPP, "TS 36.321 v13.2.0 (Available soon) - Evolved
Universal Terrestrial Radio Access (E-UTRA); Medium Access
Control (MAC) protocol specification", 2016.
[TGPP36322]
3GPP, "TS 36.322 v13.2.0 (Available soon) - Evolved
Universal Terrestrial Radio Access (E-UTRA); Radio Link
Control (RLC) protocol specification", 2016.
[TGPP36323]
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.
[TGPP36331]
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
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: antti.ratilainen@ericsson.com
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