Internet DRAFT - draft-zuniga-lpwan-sigfox-system-description
draft-zuniga-lpwan-sigfox-system-description
LPWAN Working Group JC. Zuniga
Internet-Draft B. Ponsard
Intended status: Informational SIGFOX
Expires: June 7, 2018 December 04, 2017
SIGFOX System Description
draft-zuniga-lpwan-sigfox-system-description-04
Abstract
This document presents an overview of the network architecture and
system characteristics of a typical SIGFOX Low Power Wide Area
Network (LPWAN). It is intended to be used as background information
by the IETF LPWAN group when defining system requirements of
different LPWAN technologies that are suitable to support common IP
services.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. System Architecture . . . . . . . . . . . . . . . . . . . . . 3
4. Radio Spectrum . . . . . . . . . . . . . . . . . . . . . . . 5
5. Radio Protocol . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Uplink . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.1. Uplink Physical Layer . . . . . . . . . . . . . . . . 6
5.1.2. Uplink MAC Layer . . . . . . . . . . . . . . . . . . 6
5.2. Downlink . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2.1. Downlink Physical Layer . . . . . . . . . . . . . . . 7
5.2.2. Downlink MAC Layer . . . . . . . . . . . . . . . . . 7
5.3. Synchronization between Uplink and Downlink . . . . . . . 8
6. Network Deployment . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This document presents an overview of the network architecture and
system characteristics of a typical SIGFOX LPWAN, which is in line
with the terminology and specifications defined by ETSI [etsi_unb].
It is intended to be used as background information by the IETF LPWAN
group when defining system requirements of different LPWANs that are
suitable to support common IP services.
LPWAN technologies are a subset of IoT systems which specifically
enable long range data transport (e.g. distances up to 50 km in open
field), are capable to communicate with underground equipment, and
require minimal power consumption. Low throughput transmissions
combined with advanced signal processing techniques provide highly
effective protection against interference. LPWAN technologies can
also cooperate with cellular networks to address use cases where
redundancy, complementary or alternative connectivity is needed.
Because of these characteristics, LPWAN systems are particularly well
adapted for low throughput IoT traffic. SIGFOX LPWAN autonomous
battery-operated devices send only a few bytes per day, week or month
in an asynchronous manner and without the needed for central
coordination, which allows them to remain on a single battery for up
to 10-15 years.
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2. Terminology
The following terms are used throughout this document:
Base Station (BS) - A Base Station is a radio hub, relaying
messages between DEVs and the SC.
Device Application (DA) - An application running on the DEV or EP.
Device (DEV) - A Device (aka end-point) is a leaf node of a LPWAN
that communicates application data between the local device
application and the network application.
End Point (EP) - An End Point (aka device) is a leaf node of a
LPWAN that communicates application data between the local device
application and the network application.
Low-Power Wide-Area Network (LPWAN) - A system comprising several
BSs and millions/billions of DEVs, characterized by the extreme
low-power consumption, long-range of transmission, and typically
connected in a star network topology.
Network Application (NA) - An application running in the network
and communicating with the device(s).
Registration Authority (RA) - The Registration Authority is a
central entity that contains all allocated and authorized Device
IDs.
Service Center (SC) - The SIGFOX network has a single service
centre. The SC performs the following functions:
* DEVs and BSs management
* DEV authentication
* Application data packets forwarding
* Cooperative reception support
3. System Architecture
Figure 1 depicts the different elements of the system architecture:
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+---+
|DEV| * +------+
+---+ * | RA |
* +------+
+---+ * |
|DEV| * * * * |
+---+ * +----+ |
* | BS | \ +--------+
+---+ * +----+ \ | |
DA -----|DEV| * * * | SC |----- NA
+---+ * / | |
* +----+ / +--------+
+---+ * | BS |/
|DEV| * * * * +----+
+---+ *
*
+---+ *
|DEV| * *
+---+
Figure 1: SIGFOX network architecture
SIGFOX has a "one-contract one-network" model allowing devices to
connect in any country, without any need or notion of either roaming
or handover.
The architecture consists of a single cloud-based core network, which
allows global connectivity with minimal impact on the end device and
radio access network. The core network elements are the Service
Center (SC) and the Registration Authority (RA). The SC is in charge
of the data connectivity between the Base Stations (BSs) and the
Internet, as well as the control and management of the BSs and
Devices. The RA is in charge of the Device network access
authorization.
The radio access network is comprised of several BSs connected
directly to the SC. Each BS performs complex L1/L2 functions,
leaving some L2 and L3 functionalities to the SC.
The Devices (DEVs) or End Points (EPs) are the objects that
communicate application data between local device applications (DAs)
and network applications (NAs).
Devices can be static or nomadic, as they associate with the SC and
they do not attach to any specific BS. Hence, they can communicate
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with the SC through one or multiple BSs without needing to signal for
handover or roaming.
Due to constraints in the complexity of the Device, it is assumed
that Devices host only one or very few device applications, which
most of the time communicate each to a single network application at
a time.
4. Radio Spectrum
The coverage of the cell depends on the link budget and on the type
of deployment (urban, rural, etc.). The radio interface is compliant
with the following regulations:
Spectrum allocation in the USA [fcc_ref],
Spectrum allocation in Europe [etsi_ref],
Spectrum allocation in Japan [arib_ref].
At present, the SIGFOX radio interface is also compliant with the
local regulations of the following countries: Australia, Brazil,
Canada, Kenya, Lebanon, Mauritius, Mexico, New Zealand, Oman, Peru,
Singapore, South Africa, South Korea, and Thailand.
5. Radio Protocol
The radio interface is based on Ultra Narrow Band (UNB)
communications, which allow an increased transmission range by
spending a limited amount of energy at the device. Moreover, UNB
allows a large number of devices to coexist in a given cell without
significantly increasing the spectrum interference.
Since the radio protocol is connection-less and optimized for uplink
communications, the capacity of a SIGFOX base station depends on the
number of messages generated by devices, and not on the actual number
of devices. Likewise, the battery life of devices depends on the
number of messages generated by the device. Depending on the use
case, devices can vary from sending less than one message per device
per day, to dozens of messages per device per day.
Both uplink and downlink are supported, although the system is
optimized for uplink communications. Due to spectrum optimizations,
different uplink and downlink frames and time synchronization methods
are needed.
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5.1. Uplink
5.1.1. Uplink Physical Layer
The main radio characteristics of the UNB uplink transmission are:
o Occupied bandwidth: 100 Hz / 600 Hz (depending on the region)
o Uplink baud rate: 100 baud / 600 baud (depending on the region)
o Modulation scheme: DBPSK
o Uplink transmission power: compliant with local regulation
o Link budget: 155 dB (or better)
o Central frequency accuracy: not relevant, provided there is no
significant frequency drift within an uplink packet transmission
For example, in Europe the UNB uplink frequency band is limited to
868.00 to 868.60 MHz, with a maximum output power of 25 mW and a
maximum mean transmission time of 1%.
5.1.2. Uplink MAC Layer
The format of the uplink frame is the following:
+--------+--------+--------+------------------+-------------+-----+
|Preamble| Frame | Dev ID | Payload |Msg Auth Code| FCS |
| | Sync | | | | |
+--------+--------+--------+------------------+-------------+-----+
Figure 2: Uplink Frame Format
The uplink frame is composed of the following fields:
o Preamble: 19 bits
o Frame sync and header: 29 bits
o Device ID: 32 bits
o Payload: 0-96 bits
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o Authentication: 16-40 bits
o Frame check sequence: 16 bits (CRC)
5.2. Downlink
5.2.1. Downlink Physical Layer
The main radio characteristics of the UNB downlink transmission are:
o Occupied bandwidth: 1.5 kHz
o Downlink baud rate: 600 baud
o Modulation scheme: GFSK
o Downlink transmission power: 500 mW / 4W (depending on the region)
o Link budget: 153 dB (or better)
o Central frequency accuracy: Centre frequency of downlink
transmission are set by the network according to the corresponding
uplink transmission
For example, in Europe the UNB downlink frequency band is limited to
869.40 to 869.65 MHz, with a maximum output power of 500 mW with 10%
duty cycle.
5.2.2. Downlink MAC Layer
The format of the downlink frame is the following:
+------------+-----+---------+------------------+-------------+-----+
| Preamble |Frame| ECC | Payload |Msg Auth Code| FCS |
| |Sync | | | | |
+------------+-----+---------+------------------+-------------+-----+
Figure 3: Downlink Frame Format
The downlink frame is composed of the following fields:
o Preamble: 91 bits
o Frame sync and header: 13 bits
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o Error Correcting Code (ECC): 32 bits
o Payload: 0-64 bits
o Authentication: 16 bits
o Frame check sequence: 8 bits (CRC)
5.3. Synchronization between Uplink and Downlink
The radio interface is optimized for uplink transmissions, which are
asynchronous. Downlink communications are achieved by devices
querying the network for available data.
A device willing to receive downlink messages opens a fixed window
for reception after sending an uplink transmission. The delay and
duration of this window have fixed values. The network transmits the
downlink message for a given device during the reception window, and
the network also selects the base station (BS) for transmitting the
corresponding downlink message.
Uplink and downlink transmissions are unbalanced due to the
regulatory constraints on the ISM bands. Under the strictest
regulations, the system can allow a maximum of 140 uplink messages
and 4 downlink messages per device. These restrictions can be
slightly relaxed depending on system conditions and the specific
regulatory domain of operation.
6. Network Deployment
As of today, SIGFOX's network has been fully deployed in 17
countries, with ongoing deployments on 29 other countries, giving in
total a geography of 2.6 million square kilometers, containing 660
million people. The single core network model allows devices to
connect in any country, without any notion of roaming or handover.
The vast majority of the current applications are sensor-based,
requiring solely uplink communications, followed by actuator-based
applications, which make use of bidirectional (i.e. uplink and
downlink) communications.
Similar to other LPWAN technologies, the sectors that currently
benefit from the low-cost, low-maintenance and long battery life are
agricultural and environment, public sector (smart cities, education,
security, etc.), industry, utilities, retail, home and lifestyle,
health and automotive.
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7. IANA Considerations
N/A.
8. Security Considerations
Due to the nature of low-complexity devices, it is assumed that
Devices host only one or very few device applications, which most of
the time communicate each to a single network application at a time.
The radio protocol authenticates and ensures the integrity of each
message. This is achieved by using a unique device ID and an AES-128
based message authentication code, ensuring that the message has been
generated and sent by the device with the ID claimed in the message.
Application data can be encrypted at the application level or not,
depending on the criticality of the use case, to provide a balance
between cost and effort vs. risk. AES-128 in counter mode is used
for encryption. Cryptographic keys are independent for each device.
These keys are associated with the device ID and separate integrity
and confidentiality keys are pre-provisioned. A confidentiality key
is only provisioned if confidentiality is to be used.
9. Acknowledgments
The authors would like to thank Olivier Peyrusse for the useful
inputs and discussions about ETSI UNB SRD.
10. Informative References
[arib_ref]
"ARIB STD-T108 (Version 1.0): 920MHz-Band Telemeter,
Telecontrol and data transmission radio equipment.",
February 2012.
[etsi_ref]
"ETSI EN 300-220 (Parts 1 and 2): Electromagnetic
compatibility and Radio spectrum Matters (ERM); Short
Range Devices (SRD); Radio equipment to be used in the 25
MHz to 1 000 MHz frequency range with power levels ranging
up to 500 mW", May 2016.
[etsi_unb]
"ETSI TR 103 435 System Reference document (SRdoc); Short
Range Devices (SRD); Technical characteristics for Ultra
Narrow Band (UNB) SRDs operating in the UHF spectrum below
1 GHz", February 2017.
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[fcc_ref] "FCC CFR 47 Part 15.247 Telecommunication Radio Frequency
Devices - Operation within the bands 902-928 MHz,
2400-2483.5 MHz, and 5725-5850 MHz.", June 2016.
Authors' Addresses
Juan Carlos Zuniga
SIGFOX
425 rue Jean Rostand
Labege 31670
France
Email: JuanCarlos.Zuniga@sigfox.com
URI: http://www.sigfox.com/
Benoit Ponsard
SIGFOX
425 rue Jean Rostand
Labege 31670
France
Email: Benoit.Ponsard@sigfox.com
URI: http://www.sigfox.com/
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