LPWAN Working Group JC. Zuniga Internet-Draft B. Ponsard Intended status: Informational SIGFOX Expires: December 15, 2017 June 13, 2017 SIGFOX System Description draft-zuniga-lpwan-sigfox-system-description-03 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 defined by ETSI. 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 provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Zuniga & Ponsard Expires December 15, 2017 [Page 1] Internet-Draft SIGFOX System Description June 2017 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 . . . . . . . . . . . . . . . . . . . . . . . . . 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. Zuniga & Ponsard Expires December 15, 2017 [Page 2] Internet-Draft SIGFOX System Description June 2017 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: Zuniga & Ponsard Expires December 15, 2017 [Page 3] Internet-Draft SIGFOX System Description June 2017 +---+ |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 Zuniga & Ponsard Expires December 15, 2017 [Page 4] Internet-Draft SIGFOX System Description June 2017 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. Zuniga & Ponsard Expires December 15, 2017 [Page 5] Internet-Draft SIGFOX System Description June 2017 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 Zuniga & Ponsard Expires December 15, 2017 [Page 6] Internet-Draft SIGFOX System Description June 2017 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 Zuniga & Ponsard Expires December 15, 2017 [Page 7] Internet-Draft SIGFOX System Description June 2017 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 12 countries, with ongoing deployments on 26 other countries, giving in total a geography of 2 million square kilometers, containing 512 million people. The one-contract one-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. Zuniga & Ponsard Expires December 15, 2017 [Page 8] Internet-Draft SIGFOX System Description June 2017 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 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 at the application level or not, depending on the criticality of the use case, allowing hence to balance cost and effort vs. risk. 9. Acknowledgments The authors would like to thank Olivier Peyrusse for the useful inputs and discussions about ETSI. 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. Zuniga & Ponsard Expires December 15, 2017 [Page 9] Internet-Draft SIGFOX System Description June 2017 [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/ Zuniga & Ponsard Expires December 15, 2017 [Page 10]