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Network Working Group                                         JC. Zuniga
Internet-Draft                                                B. Ponsard
Intended status: Informational                                    SIGFOX
Expires: April 30, 2017                                 October 27, 2016


                       SIGFOX System Description
            draft-zuniga-lpwan-sigfox-system-description-01

Abstract

   This document presents an overview of the network architecture and
   system characteristics of a typical SIGFOX Low Power Wide Area
   Network (LPWAN), which is in line with the terminology and
   specifications being defined by the ETSI ERM TG28 LTN group.  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

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 30, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  System Architecture . . . . . . . . . . . . . . . . . . . . .   3
   4.  Radio Spectrum  . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Radio Protocol  . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Uplink  . . . . . . . . . . . . . . . . . . . . . . . . .   5
       5.1.1.  Uplink Physical Layer . . . . . . . . . . . . . . . .   5
       5.1.2.  Uplink MAC Layer  . . . . . . . . . . . . . . . . . .   6
     5.2.  Downlink  . . . . . . . . . . . . . . . . . . . . . . . .   6
       5.2.1.  Downlink Physical Layer . . . . . . . . . . . . . . .   6
       5.2.2.  Downlink MAC Layer  . . . . . . . . . . . . . . . . .   7
     5.3.  Synchronization between Uplink and Downlink . . . . . . .   7
   6.  ETSI LTN  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Network Deployment  . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   11. 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 being defined by the ETSI ERM
   TG28 Low Throughput Networks (LTN) group [etsi_ltn].  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.

   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 used in this document are in accordance to the
   ones defined by ETSI ERM TG28 Low Throughput Networks (LTN)
   [etsi_ltn]:

      Base Station (BS) - A Base Station is a radio hub of an LTN
      system.

      Device Application (DA) - An application running on the End Point
      or device.

      End Point (EP) - An End Point is a leaf node (aka device) of an
      LTN system that communicates application data between the local
      device application and the network application.

      Low Throughput Networks (LTN) - Terminology used in ETSI to define
      Low Power Wide Area (LPWA) networks.

      Network Application (NA) - An application running in the network
      at the opposite extreme of the device.

      Registration Authority (RA) - The Registration Authority is a
      central entity that contains all allocated and authorized End
      Point IDs.

      Service Center (SC) - Each LTN system has a single service centre.
      The SC performs the following functions:

      *  EPs and BSs management

      *  EP 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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                +--+
                |EP| *                    +------+
                +--+   *                  |  RA  |
                         *                +------+
                +--+       *                 |
                |EP| * * *   *               |
                +--+       *   +----+        |
                             * | BS | \  +--------+
                +--+       *   +----+  \ |        |
        DA -----|EP| * * *               |   SC   |----- NA
                +--+       *           / |        |
                             * +----+ /  +--------+
                +--+       *   | BS |/
                |EP| * * *   * +----+
                +--+         *
                           *
                +--+     *
                |EP| * *
                +--+




                      Figure 1: ETSI LTN architecture

   The architecture consists of a single 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 Station (BS) and the Internet, as
   well as the control and management of the BSs and End Points.  The RA
   is in charge of the End Point 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 or End Points (EPs) are the objects that communicate
   application data between local device applications (DAs) and network
   applications (NAs).

   EPs (or devices) can be static or nomadic, as they associate with the
   SC and they do not attach to a specific BS.  Hence, they can
   communicate with the SC through one or many BSs.

   Due to constraints in the complexity of the EP, it is assumed that
   EPs host only one or very few device applications, which communicate
   to one single network application at a time.



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4.  Radio Spectrum

   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 LTN 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.

   Both uplink and downlink communications are possible with the UNB
   solution.  Due to spectrum optimizations, different uplink and
   downlink frames and time synchronization methods are needed.

5.1.  Uplink

5.1.1.  Uplink Physical Layer

   The main radio characteristics of the UNB uplink transmission are:

   o  Channelization mask: 100 Hz (600 Hz in the USA)

   o  Uplink baud rate: 100 baud (600 baud in the USA)

   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






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   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

   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  Channelization mask: 1.5 kHz

   o  Downlink baud rate: 600 baud

   o  Modulation scheme: GFSK

   o  Downlink transmission power: 500 mW (4W in the USA)

   o  Link budget: 153 dB (or better)



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   o  Central frequency accuracy: Centre frequency of downlink
      transmission are set by the network according to the corresponding
      uplink transmission.

   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

   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 querying the
   network for existing data from the device.

   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 LTN network transmits
   the downlink message for a given device during the reception window.




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   The LTN network selects the 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.  ETSI LTN

   The ETSI TC EMC and Radio Spectrum Matters (ERM) group has multiple
   work items dealing with LTN.  The objective is to define use cases,
   system architecture and radio protocols for LTN (or LPWAN), using
   shared spectrum bands, allowing to offer very low cost subscriptions
   per device.

   According to ETSI TG28, LTN is particularly well suited for low
   throughput machine to machine communication where data volume is
   limited and low latency is not a strong requirement.  Some foreseen
   applications include remote measurement for agriculture and
   environment, smart metering for utilities, smart cities applications
   such as air pollution monitoring or public lighting, etc.

   LTN could also cooperate with cellular networks to address use cases
   where redundancy, complementary or alternative connectivity is
   needed.  Low power, very low throughput, very long battery life,
   simple, effective and robust radio communication principles are the
   key features of ETSI LTN systems.

7.  Network Deployment

   As of today, SIGFOX's network has been fully deployed in 6 countries,
   with ongoing deployments on 18 other countries, which in total will
   reach 397M people.  The "one-contract one-network" model allows
   devices to connect in any country, without any notion of roaming.

   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/LTN 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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8.  IANA Considerations

   N/A.

9.  Security Considerations

   The radio protocol provides mechanisms to authenticate and ensure
   integrity of the message.  This is achieved by using a unique device
   ID and a message authentication code, which allow ensuring that the
   message has been generated and sent by the device with the ID claimed
   in the message.

   Security keys are independent for each device.  These keys are
   associated with the device ID and they are pre-provisioned.
   Application data can be encrypted by the application provider.

10.  Acknowledgments

   The authors would like to thank Olivier Peyrusse for the useful
   inputs and discussions about ETSI LTN.

11.  Informative References

   [arib_ref]
              "ARIB STD-T108 (Version 1.0): 920MHz-Band Telemeter,
              Telecontrol and data transmission radio equipment.",
              February 2012.

   [etsi_ltn]
              "ETSI Technical Committee on EMC and Radio Spectrum
              Matters (ERM) TG28 Low Throughput Networks (LTN)",
              February 2015.

   [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.

   [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.








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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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