In the previous tutorial, various physical and data link layer protocols specified for computers and mobile devices were discussed. Continuing the subject of physical and data link protocols, in this tutorial, network access protocols specified for LPWAN will be discussed.
LPWAN stands for Low Power Wide Area Network. In general, LPWAN is a low power long range wireless network in which battery powered IOT devices surrounded by wireless sensors (Wireless Sensor Network) are interconnected. LPWAN are designed for machine to machine communication. They typically have a coverage network greater than Wi-Fi but less than cellular technologies.
The major challenges in an LPWAN remains power efficiency, network coverage, security, penetration level and network cost. These networks operate at very limited bandwidth and must be extremely efficient by their power budget. So, a careful choice of sensors, controllers, IOT boards and batteries need to be made in designing an LPWAN considering penetration level, coverage area, bandwidth limitations, cost efficiency and security of the network. The prime focus in designing of LPWAN remains power consumption. The IOT devices in these networks should ideally need a battery replacement in years or at least in months.
There are many physical and data link layer protocols specified particularly for LPWAN. Some of these protocol stacks include the following –
• Weightless / Neul
• NB-IOT/LTE Cat NB1
• LTE Cat 0, 1, & 3
• LTE-M1/ LTE-MTC (LTE-Machine Type Communication)
• Symphony Link
• EC-GSM-IOT (Extended Coverage GSM-IOT)
1) Sigfox – Sigfox is a French telecom company and a global telecom service provider. It provides an LPWAN networking technology stack by the same name. It is a proprietary networking technology spanning across Europe and United States. Sigfox uses license free ISM bands (868 MHz in Europe and 902 MHz in United States) in a narrow spectrum, which it calls Ultra Narrow Band (UNB) for M2M communication in urban as well as rural areas. The company has set up towers at various locations (just like cellular towers) which use differential binary phase-shift keying (DBPSK) and Gaussian frequency shift keying (GFSK) for data communication.
These towers have a coverage area of 3 to 10 Km in urban and metropolitan areas and 30 to 50 Km in rural areas. The Sigfox transceivers are extremely power efficient with only 50 Microwatt power consumption. Ideally, any Sigfox transceiver won’t need a battery replacement for 15 to 20 years. The IOT devices can exchange data with these transceivers at low speeds ranging from 10 to 1000 bits per second. For connecting to and utilizing Sigfox network, an IOT developer needs to contact Sigfox operator or partner in her area. The developer can also negotiate network coverage and bandwidth with the operator to suit her application requirements. Currently, Sigfox networks are widely used in smart city and transportation IOT applications.
2) Weightless/Neul – Neul now known as Weightless is an LPWAN technology stack proposed by Weightless Special Interest Group (SIG).
It uses white space in TV transmission bands for M2M communication between IOT devices and a base station. The weightless transceivers operate at license free radio bands (458 MHz in United Kingdom and 900 MHz ISM band in United States and Europe) and White Space TV Spectrum (470 to 790 MHz). As it uses UHF spectrum (which is actually used for TV transmission), it is highly scalable competing to Mobile IOT standards in terms of network coverage. Also, UHF spectrum allows quality link between the devices and the station.
Like Sigfox, Weightless transceivers are mounted to towers with each tower having a network coverage up to 10 Km. Weightless has been developed for M2M communication at low speeds ranging from few bits per second to 100 kbps. The transceivers usually operate on AA batteries and consume 15 to 30 mA current. With such low power consumption, a transceiver can stand by 10 to 15 years without battery replacement.
There are three protocol stacks offered under Weightless –
Weightless-W – This standard uses TV White Space for communication between IOT devices and the central station. It uses quadrature amplitude modulation (QAM) and other modulation techniques for linking between antennas operating at different frequencies. The major challenge in Weightless-W standard remains to accommodate RF system with antennas operating at different frequencies (which can be anywhere between 400 MHz to 800 MHz) as different TVWS frequencies are available at different locations.
Weightless-N – This protocol stack is much similar to Sigfox as it utilizes sub-1GHz band just like Sigfox. It is designed by N-Wave and is intended for sensor based networks. Instead of being an end to end enclosed system, it is formed by a network of partners. The standard uses binary phase shift keying (BPSK) with focus to uplink sensor data to a base station.
Weightless-P – Developed by ubiik, Weightless-P is designed for local area networks and private area networks. It uses a 12.5 KHz channel for data transmission using Gaussian minimum shift keying (GMSK) and quadrature phase shift keying (QPSK).
Weightless is an open standard which not only minimizes its cost but also let it evolve in future.
3) NB-IOT – NarrowBand-IOT is another LPWAN standard which is about to release in 2018. It will use cellular telecommunication bands (unused carrier bands in 4G LTE network) for M2M communication. It is proposed by 3rd Generation Partnership Project (3GPP) and is a kind of Mobile IOT (MIoT) technology.
The NB-IOT transceivers will be similar to mobile transceivers but will have a bandwidth of only 180 KHz. The devices could communicate with these transceivers at a speed of 250 Kbits per second. There could be a latency of 1.5 seconds to 10 seconds in these networks. Being based on mobile networks, NB-IOT will have security features similar to mobile devices.
NB-IOT is developed for deep indoor penetration intended for deployment in rural areas. Its transceivers will be deployed on towers as in case of mobile towers. These transceivers will be extremely power efficient and won’t need battery replacement for 10 to 15 years. An IOT developer could avail NB-IOT networks by contacting telecom operators in her area. The main advantages of NB-IOT will be network security, interoperability at global scale and co-existence with existing 2G, 3G and 4G mobile networks.
4) LTE Cat 0, 1, & 3 – The LTE Cat 0, 1 and 3 are actually LTE (Cellular Network) User Equipment Categories differentiated by headline data rates. Typically, the LTE UE categories have the following uplink and downlink speeds –
The LTE classes with lower data speeds are well suitable for LPWAN IOT applications as transceivers in these mobile LTE networks have very low power consumption. The LTE Cat 0, 1 and 3 are deemed to most suitable for large scale IOT deployment using existing mobile network.
5) LTE-M1 – LTE-M1 also known by names LTE-A, eMTC (Machine Type Communication), CAT-M1 and LTE-MTC is a futuristic LTE standard under development for M2M communication using LTE cellular networks. It is one of the three protocol stacks proposed by 3rd Generation Partnership Project (3GPP) under its Release 13. The other being NB-IOT and EC GSM-IOT. It will utilize the existing hardware infrastructure for mobile services with software upgrade to suit the IOT M2M requirements. There are lot of expectations with this upcoming standard as it is expected to be scalable and highly cost efficient.
It is also referred as BL/CE where BL stands for Bandwidth Limited and CE stands for Coverage Enhanced. This standard will be based on LTE Cat 1 and LTE Cat M1 classes which will make it highly energy efficient. The network will have a three layer architecture with end nodes (mobile IOT devices), radio access network and core network lying at different layers. The network will be using Orthogonal Frequency Division Multiple Access (OFDMA) for Media Access Control Protocol.
6) LoRaWAN – LoRaWAN stands for Long Range Wide Area Network. It is a Media Access Control (Data Link or Network Access) protocol with some functions of network layer also implemented. It is developed by LoRa Alliance. In this protocol stack, multiple end nodes (IOT devices) are connected to a gateway in star topology for M2M communication. This protocol stack has been developed to cater battery powered IOT devices that need to frequently connect wirelessly with a base station. It is somewhat similar to Sigfox and Weightless technologies. The transceivers in this network typically have a coverage area of about 2 to 5 Km in urban areas and 10 to 15 Km in deep indoors. The IOT devices can communicate with a gateway at data speed ranging from few hundred bits per second to 50 Kbps.
LoRaWAN is setup like a classroom environment where end nodes (IOT devices) are seen as students and gateway or base station is seen as professor. The end nodes try to communicate with gateway all times but gateway could cater to only one end node at a time. So, it has three classes operating simultaneously – A, B and C. In class A, the endnotes transmit the data to the gateway in asynchronous manner, that is, the end notes transmit data to the gateway whenever required and stay idle until serviced. In class B, the gateway transmits a beacon every 128 seconds and the message is received by the end nodes within the 128 second cycle. The end nodes in such case are configured to listen one after the other. In class C, the end nodes always remain active to receive data from the gateway and messages can be sent to the end nodes (IOT devices) any time.
7) Symphony Link – This is another LPWAN technology stack developed by LoRa Alliance. It is similar to LoRaWAN except that it has additional features to suit industrial and enterprise IOT applications.
8) Extended Coverage GSM-IOT – EC GSM-IOT is another LPWAN protocol stack proposed by 3rd Generation Partnership Project (3GPP) under its Release 13. However, it has not been included in the official Release. It will be using existing 2G mobile networks for M2M communication. Like LTE-MTC, it is expected to be cost efficient as it will only require software upgrade and will be utilizing existing mobile network infrastructure.
It will have high data rates (474 Kbps for EDGE networks and 2 Mbps for eGPRS 2G networks) and latency as low as 700 ms. The transmission channels will have a bandwidth of 200 KHz. This LPWAN standard is expected to be operational by 2019.
9) RPMA – Developed by Ingenu, random phase multiple access (RPMA) is a mobile network protocol stack based on direct-sequence spread spectrum (DSSS) modulation. It is somewhat similar to code division multiple access (CDMA) protocol. RPMA was first deployed for smart energy grids and deems to be an IOT protocol stack for other IOT verticals as well.
In the next tutorial, physical and network access protocols developed for Personal Area Network (PAN) and Local Area Network (LAN) IOT applications will be discussed.
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