The Internet of Things invades our daily lives, more and more ordinary everyday things are becoming "smart" and therefore using communication with other devices and/or the Internet. The number and specificity of smart things construct new requirements for the networks they operate in and therefore require new approaches and technologies, or the adaptation of old technologies to new realities and challenges. One such network technology is the Narrowband (NB) IoT, which allows numerous low-power devices to work in the cellular mobile network along with smartphones and modems. Note that the data collected from these devices can be transferred to a centralized cloud, or processed at mobile operator base stations using mobile ad hoc cloud technology, which is one of the most promising approaches to edge computing.
1. Short Range and Long Range radio networks
NB-IoT is one of the many standards for cellular data transmission. It has developed relatively recently. The first completed version of the standard was released in June 2016, but is now formally supported by most of the world's mobile operators. However, to understand what NB-IoT is, what makes this technology better (or worse) than others, we should understand what other technologies are and how they work. In this context, we should talk only about wireless or radio networks, because the specifics of wired networks do not allow their use everywhere and reduce the overall flexibility of systems built on them. Depending on the coverage radius, wireless data transmission technologies are divided into Short Range and Long Range radio networks.
1.1 Short Range networks
Consists of low-power short-range devices (SRD), which communicate within a few hundred meters. Such devices have little effect on the operation in the working frequency range, as their transmitter power limit is around 25–100 mW or less. Short-range wireless technologies include well-known common protocols such as Bluetooth, Wi-Fi, near-field communication (NFC) and lesser-known but IoT important standards, such as IEEE 802.15.4 (the basis for Zigbee, ISA100.11a, WirelessHART, MiWi, 6LoWPAN specifications and other wireless personal area networks (WPAN)), or Radio-frequency identification (RFID). You can find more interesting information about RFID tags in our article.
1.2 Long Range or wide-area networks
Includes several classes of networks that differ by frequency range and principle of operation. For trouble-free transmission of data over long distances, it is necessary to control the load of the frequencies the network operates on. Therefore, some long-distance networks use licensed cellular frequencies and, in most cases, are part of cellular networks or are subject to 3rd Generation Partnership Project (3GPP) standards. NB-IoT also belongs to this list.
The advantage of this approach is worldwide control over the use of only tested devices in these frequency bands, guarantees the absence of extraneous noise, and so on. The disadvantages are the high congestion of large cities and the payment of a license, which increases the cost of communication modules. In contrast, other networks use unlicensed ISM (industrial, scientific and medical) bands. Here, there may be interference from third-party devices. Such networks include LoRa, Sigfox, Ingenu and others. The last class of long-distance networks can be satellite communication, which is developing dynamically in recent times. It has a significant advantage, because it actually covers the whole world, but it also needs a high-power transmitter for data transmission.
It is worth assessing which networks and approaches are most applicable to IoT tasks. The main data transmission technologies parameters we are interested in are the distance at which data transmission operates, the power consumption of the device with the transmitter, or standard battery "life" (we will represent the time based on the fact that a standard battery has a capacity of 5 W*h), and the volume or speed of data transfer.
A technology designed, as the name implies, to interact over very short distances (dozen centimetres). Communication between devices using NFC begins almost instantly, and data rates up to 424 kbps. The low power of the transmitter allows the NFC module to run long battery life, on the order of a week continuously. Given that in many uses the module will not work constantly, the "life" time can be significantly longer. Short interoperability blocks the use of NFC to collect data from IoT devices, but allows the use of this technology for secure authentication, as it prevents interception of data at a long distance.
One of the most common data transmission standards, due to a combination of characteristics: low module price, low consumption (up to three days battery life), a range of 10-15 m, which fully covers the area of the personal network, and data rate enough for continuous data transmission of the audio stream. All this has allowed Bluetooth technology to become the basis for interaction between personal gadgets, such as smartphones, smartwatches and smart bands, headphones, and more. Bluetooth can be used to collect data from sensors from a small area, such as an apartment or house, but there is a problem with power consumption, as such devices will need to be charged every few days, or to be connected to the power network.
Probably the best option for creating a local area network. This technology provides high data rates (up to 1 Gbps over short distances), a sufficient range of operation to cover work or home area, and low device consumption, which allows you to use them for up to 3 days in a row.
4. IEEE 802.15.4
A technical standard of the physical layer and access control in low-power short-range wireless networks. Many protocols used in IoT are based on this standard (they are, in fact, solutions for building the upper layers of the network). Although most devices of this standard use low data rates, the standard supports speeds of up to 480 Mbps, and power consumption is low enough to operate for several years without service. The biggest disadvantage of IEEE 802.15.4 is the short range of up to 100 m. It allows one to build a personal area network (PAN), but not a global one.
We have already discussed the work of RFID tags and their application. It is worth mentioning that, although they operate at a short distance from the transmitter, tags themselves may not have power at all, and their cost is extremely low, which allows to use them en masse. The similarity of the technology with NFC also suggests the possibility of application for authentication and tagging of items.
A collective name for many international organizations involved in the standardization of mobile cellular networks. All known cellular standards since 1998, such as GPRS and EDGE, 3G standards, including HSPA, LTE and related 4G, 5G and 5G-Advanced, have been developed by this group of organizations. Mobile telecommunications networks are now widespread around the world, and they can transmit large amounts of information at high speeds. Conventional GSM/LTE devices from a standard battery can "live" up to a week, and the distance to the base station can reach 30 km at high data rates. However, from the point of view of IoT developers, more interesting are the standards, which, sacrificing the speed and volume of transmitted data, allow the creation of communication modules with very low power consumption. Such standards include LTE-M, or LTE-MTC (Machine Type Communication), NB-IoT and EC-GSM-IoT. By optimizing power consumption, devices based on these technologies can "live" on the battery for several years.
A proprietary technology of a low-power network with a large range creating, which uses unlicensed frequencies lower than 1 GHz. A very low data rate of up to 30 kbit/s is already in the design stage (the first version of the standard in 2015), but a large radius of coverage and low power consumption are expected.
8. Satellite communication
This area of network technology is developing at a simple breakneck tempo, because it has an extraordinary advantage over others - in fact, unlimited range and high data rates with minimal delays. But along with the advantages, there are huge disadvantages, the cost of both, the client module and the operation of the network, and high power consumption, because to transmit a useful signal into space requires high transmitter power and high sensitivity receiver. But IoT central stations that collect data and send it to the cloud can be equipped with satellite network devices, which will help use Internet of Things technology in the most remote corners of the planet.
2. What are Low-power Wide-area Networks?
Modern IoT tasks impose severe restrictions on devices, including protocols and data modules. IoT devices should work for a long time without service, and therefore without replacing the power supply (read more about Fuel for IoT devices), so consumption should be minimal. Simultaneously, the device itself should be cheap enough and production must be simple enough to be manufactured and used in large quantities. Device data needs to be collected from a long distance to cover as much area as possible, but there can be numerous devices in a small area, in smart cities, for example. Therefore, based on these requirements, the concept of LPWAN (Low-power Wide-area Network) was formed, the devices of which must meet next requirements:
- Long range: The operating range of LPWAN technology varies from a few kilometers in urban areas to over 10 km in rural settings. It can also enable effective data communication in previously infeasible indoor and underground locations.
- Low power: Optimized for power consumption, LPWAN transceivers can run on small, inexpensive batteries for up to 20 years.
- Low cost: LPWAN's simplified, lightweight protocols reduce complexity in hardware design and lower device costs.
The most common applications of such networks are resource meters and emergency sensors. In these cases, the need for a long operation without maintenance of devices and a wide geography of distribution, in contrast to, for example, smart homes, where all devices are concentrated compactly.
3. Standards that meet all LPWAN requirements
1. Sigfox is a global wireless network operator for low-power facilities. Sigfox uses Ultra Narrowband (UNB) technology at unlicensed frequencies of 868 MHz and 902 MHz and its proprietary standards to transmit data. Close ties with hardware manufacturers and a large network of providers around the world allowed the operator to cover areas with almost a quarter of the world's population. The disadvantage of Sigfox is the restriction of up to 140 uplink messages a day per device and the low data rate.
2. NB-Fi. This is an open protocol, which operates in unlicensed ISM radio bands, data transmission can be executed at a distance of 10 km even in urban conditions, and module power consumption is low enough to work in some scenarios for up to 10 years. NB-Fi Protocol is actively implemented by Internet of Things hardware manufacturers. The only significant disadvantage of this technology is the need to build the infrastructure of NB-Fi devices and base stations.
3. LoRa is a proprietary modulation technology for low-power networks that also use unlicensed sub-gigahertz frequencies. The standardization is carried out by the LoRa Alliance, which involves more than 500 member organizations from more than 100 countries. The disadvantages of this technology are the low data rate and the limit on the number of messages.
4. NB-IoT and EC-GSM-IoT are technologies that are regulated by 3GPP and allow the use of existing mobile networks for data transmission with minimal change that does not affect the operation of other devices. The fundamental difference between NB-IoT and EC-GSM-IoT is the operating frequencies (open and protected LTE bands for NB-IoT and GSM bands for EC-GSM-IoT). Modules of both standards operate with 20 dB lower signal levels than conventional devices, which significantly increases the working distance, and the "life" of the battery can reach 10 years with 1-2 messages per day. Need to say that there is no limit on the number of messages, and the data transfer rate is about 200 kbps for NB-IoT and 74 kbps for EC-GSM-IoT. Up to 10,000 NB-IoT and EC-GSM-IoT devices can be connected to one mobile network base station.
4. Narrow Band IoT – radio technology of the future?
Now we know in what context to consider NB-IoT, so let's take a closer look at how this technology works. To meet the requirements for IoT devices, NB-IoT devices have made significant simplifications that reduce the complexity of the device, and therefore its cost and power consumption:
- refusal of the need to register in the network under normal mode of operation;
- simplified hybrid automatic repeat request (HARQ) process for both directions of data streams;
- support only serial data transfer mode in both directions;
- left the opportunity to work only in economic half duplex operation (HD-FDD) mode;
- bandwidth and data rate restrictions;
- reducing the size of the transport unit.
Such simplifications ease the scheme of the module and increase the one-battery lifetime to 10 years by transmitting one message per day. The NB-IoT standard is also designed to be as compatible with existing LTE networks as possible.
The first time the NB-IoT device is turned on, it selects one of the possible scenarios provided by the base station of the mobile network in the same way as other LTE devices. In this case, the carrier band can be placed only in certain physical resource blocks (PRB).
The downlink of NB-IoT, based on the Orthogonal Frequency-Division Multiple Access (OFDMA) method and uses the same subcarrier intervals as LTE – 15 kHz. According to the LTE standard, NB-IoT technology uses subframe durations of 1 ms, slot 0.5 ms and frame durations of 10 ms. In fact, an NB-IoT carrier uses twelve 15 kHz subcarriers of 180 kHz in total, or one LTE PRB (200 kHz).
The uplink of NB-IoT supports both multi-tone and single-tone transmissions. Multi-tone transmission is the same as in the LTE standard. Single-tone transmission supports two numerologies, 15 kHz and 3.75 kHz. The 15 kHz numerology is identical to LTE and thus achieves the best coexistence performance with LTE in the uplink. The 3.75 kHz single-tone numerology uses a 2 ms slot duration. Like the downlink, an uplink NB-IoT carrier uses a total system bandwidth of 180 kHz.
There are three NB-IoT PRB position options:
- Stand-alone. This option is used for GSM networks of older generations. One 200 kHz band is allocated for NB-IoT devices.
- Guard band. The band for NB-IoT devices is allocated in the unused band close to the LTE band – in the guard band. This position does not affect the throughput of the LTE network.
- In-band. One of the LTE blocks is allocated for NB-IoT devices. It allows flexible assignment of resources between LTE and NB-IoT: it will be possible for an NB-IoT carrier to time-share a resource with an existing LTE carrier.
New tasks nowadays require new solutions. Combining the ready-made infrastructure of cellular networks, which cover almost the entire planet, with new approaches of data transmission and power-saving allows such technologies as NB-IoT, EC-GSM-IoT, LoRa to breakthrough in the foreground. Until a decade ago, the challenges posed by such technologies were unsolvable because they combined two opposing requirements: low power consumption and long communication range. All those involved in IoT devices and systems should closely monitor the development of these technologies.
Related: IoT Solution Anatomy: A Deep Dive into Remote IoT Technology