Internet of Things Wireless Networks: which are the most common IoT Wireless communication protocols?
Working with Internet of Things applications in 2020 almost surely means working with many Wireless communication protocols, based on different technologies. Nowadays, many home or industrial automation applications use Low Power and Long Range communication protocols to enable what we call Wireless Sensors Networks, which are the basis of the Internet of Things world.
However, there are many different Wireless communication protocols that can be used in these kind of applications. Which are the most suitable for a certain kind of application? Which are their characteristics and differences? How can these Internet of Things Wireless communication protocols be classified?
In these article I’ll try to classify the main and most used Internet of Things Wireless communication protocols adopted in many modern applications.
Which are the most common Internet of Things Wireless communication protocols?
Among the different technologies available on the market to connect several devices for smart city, smart farming or industrial Internet of Things (IoT) applications from small to large range area Wireless Sensors Networks (WSNs), the main alternatives are Wi-Fi technology (IEEE 802.11 a/g/n/ac/ah), Bluetooth technology (IEEE 802.15.1), both Classic and Low Energy (BLE) variant, ZigBee technology (IEEE 802.15.4), LoRaWAN protocol and LTE-M, followed by Narrowband Internet of Things (NB-IoT) Protocol and the upcoming fifth cellular generation network (5G).
When dealing with large WSNs, it is common have to deal with wide-range wireless networks characterised by subnets with smaller ranges based on more energy-saving protocols, in order to ensure an adequate endurance even for battery-powered end-node devices. Thus, it is useful to classify the aforementioned protocols on their typical coverage range and applications use cases. Therefore, it is possible to divide them into three main classifications: Short Range Communication Protocols, Mid Range Communication Protocols and Long Range Communication Protocols. A brief comparison of the main characteristics of the aforementioned standards can be seen in the following graph.
Short Range Internet of Things Wireless Communication Protocols
There are many short range communication protocols that can be used to create Wireless Personal Area Network (WPAN), which typically have a range between few meters up to 20 m in Line-of-Sight (LoS) applications. The most common protocol used for this kind of Wireless network is Bluetooth, which can be used in the Classic variant for synchronous data transfer operations, or BLE, which is often used for low power multi-nodes networks and indoor localisation through beacons, since its good range paired with a very low power consumption fits perfectly for asynchronous data communication between peripheral battery powered nodes and a central master node. Usually this kind of WPANs have a typical star topology, but when dealing with applications dedicated to environmental sensing and the IoT use cases, it is quite typical to use mesh Wireless networks, in order to increase the operating ranges. A short analysis of Bluetooth Classic and Low Energy variant is done below.
Bluetooth Classic Protocol – IEEE 802.15.1
Bluetooth Classic is mainly used for all that types of connections that require continuous synchronisation (Synchronous Connection Oriented Link), such as, for example, a connection between a smartphone and a Bluetooth speaker, a pair of headsets, or during a real data transfer between two neighbour smartphones. The latest version of the Bluetooth Classic standard, called 5.2, operates on 79 channels with a 1 MHz band and a 1 MHz spacing. It adopts Gaussian Frequency Shift Keying (GFSK) modulation, and uses the mechanism called Frequency Hopping Spread Spectrum (FHSS) to minimize the destructive effects of fading and channel noise from Wi-Fi networks operating within the same 2.4 GHz ISM band.
The transmission speed (bitrate) depends on the type of Phase Shift Keying modulation adopted from the standard. Typically, the theoretical transfer rate goes from 1 Mbps up to 3 Mbps, depending on the modulation variant used and the Bluetooth standard used. The operating range of Bluetooth Classic technology depends on the power radiated by the antenna. Generally, devices operating with Bluetooth Classic protocol belongs to Class 2, so they have a typical range up to 20 m in an open field.
Bluetooth Low Energy Protocol – IEEE 802.15.1
Bluetooth standard has also a Bluetooth Low Energy (BLE) variant, available since the version 4.0 of the protocol. As name suggests, BLE sacrifices performance and operating range in favour of lower power consumption. The considerable difference in the use of channel and protocol resources, has made it necessary to divide the equipment related to the two standards, giving rise to Dual-Mode chipsets, which are able to operate with both Bluetooth variants, and Single-Mode chipset, able to support only one of the two standards (at the manufacturer’s discretion). As Bluetooth Classic, also BLE operates in the free ISM band of 2.4 GHz and uses the same modulations and FHSS technique, but it works differently at higher protocol levels. In contrast to Bluetooth Classic, the BLE variant uses only 40 channels in the 2.4 GHz band, with a channel spacing that goes from 1 to 2 MHz. Between the 40 channels provided by the BLE, three of them are reserved exclusively for the Advertising process, namely channels 37, 38 and 39. The remaining 37 channels, instead, are used for data transfer between Master and Slave.
As opposed to Bluetooth Classic, there are no power classes, but an operating range between two extremes, i.e. the maximum and minimum power values at the transmitter output. These limits are respectively 10 mW and 0.01 mW, so they are much lower than the Bluetooth Classic devices. Unlike the latter, the operating range also decreases, ranging from a minimum of one meter to a maximum around 10 m. This limited operating range can be considerably increased by using mesh network topology instead of the typical star topology.
The key of BLE efficiency is certainly the lower number of channels (40 compared to 79 defined for the Bluetooth Classic), of which only three, those of Advertising, are actually used for advertising, scanning and establishing a connection between two nodes. Also, compared to Bluetooth Classic, BLE packet are smaller. BLE is the mostly used protocols for wearables, smart devices and cheap battery powered environmental sensors, which can communicate their data periodically to a central master that acts as gateway, assuring good battery life in a tiny format.
For a detailed explanation of Bluetooth Low Energy protocol, its Internet of Things use cases and its limits, you can check my dedicated article.
Mid Range Internet of Things Wireless Communication Protocols
Mid range communication protocols can be used to create a Wireless Local Area Network (WLAN), which usually have a coverage between 10 to 100 m without any obstacles. However, using directional antennas can increase operating range up to hundreds of meters for some particular applications. Among many protocols, the mostly used are Wi-Fi IEEE 802.11 and ZigBee IEEE 802.15.4 protocols. While Wi-Fi has now become present in almost any smart device, ZigBee has achieved a relevant role for wide IoT WSNs with a wide range, such as entire buildings in industrial environments. However, even if Wi-Fi and Zig-Bee use the same carrier frequency of 2.4 GHz, they are completely different with distinct applications.
Wi-Fi Protocol – IEEE 802.11 a/b/g/n
The Wi-Fi term refers to a family of wireless standards related to IEEE 802.11 protocol, in particular, the most common and widely used versions are the Wi-Fi a/b/g/n and the last announced Wi-Fi 6. Wi-Fi uses two free ISM bands: 2.4 GHz and 5.8 GHz. However, mostly Internet of Things application use 2.4 GHz. given its higher operating range and properties, which enough appropriate to most IoT use cases. The Wi-Fi 2.4 GHz band uses 14 channels with a bandwidth of 22 MHz each and spacing of 5 MHz, but usually only the first 13 channels are usable in Europe.
Some of the main advantages of the Wi-Fi standard are the high diffusion and device integration, but, above all, the high transmission capacity (11-300 Mbit/s), low latency and the operating range, wide enough to cover small houses with a single central Access Point (AP), since it can easily reach 50 m of range with obstacles and walls. In a free open space environment, the operating coverage can go up to 100 m and more. However, the biggest draw back of Wi-Fi protocols is the high power consumption, which, for IoT applications, makes it suitable only for some particular use cases, like data transfers between gateways, nodes which can be powered from power grid or devices with high deep sleep times, such as my solar powered ESP8266-based weather station.
ZigBee Protocol – IEEE 802.15.4
ZigBee was developed in 2004 as an alternative to Wi-Fi and Bluetooth for low-power applications in the field of Wireless Mesh Networks (WMNs). Therefore, compared to Wi-Fi, it boasts extremely low power consumption and a very low bitrate (20-250 Kbit/s), too small for enhanced data transfers between multimedia devices but enough for IoT applications.
ZigBee nodes are characterised by a low power nature, that allow them to be easily battery powered for years, but also, their low power radio trans-receiver limits the operating range to a small range, usually between 10 to 20 m. Thus, ZigBee protocols is usually associated as an alternative to Bluetooth and Bluetooth Low Energy, given its power consumption efficiency, range and data rates, as shown in the comparison figure below.
Anyway, given the protocol mesh nature, a network of ZigBee devices can easily scale up to 100 and more meters range when many nodes are involved. However, it is decidedly less widespread than standards such as BLE and Wi-Fi, as a limited number of devices support this technology, which today remains mainly conned to the industrial sector. Also the license costs of ZigBee are slightly higher than BLE devices, another reason why this standard, although interesting, has not had a great response in customer-oriented applications as happened for the other two standards.
Long Range Internet of Things Wireless Communication Protocols
Long Range communication protocols are often used to create Low Power Wide Area Networks (LPWANs) with an operating range that goes from 300 m up to 10 km, but, using certain protocols that rely on existing mobile networks, it is possible to a create network with many nodes located at tens of kilometres from each others. Also, some protocols can be used for mobility applications, adding more possibilities and use cases. However, such wide networks could have different implementations costs that rely on the protocol used, which also depends on the applications and usage.
In fact, some protocols use existing mobile networks managed by operators, while others lean on an existing free open architecture network, managed by many community members such as companies and also users. The most common and used LPWANs has been analysed and characterised by their costs, characteristics, advantages and disadvantages in the following.
A detailed description of LoRaWAN protocol can be found in a dedicated article (you can find it HERE). However, here you can find a shorter description of this protocol. LoRaWAN is a Long Range communication protocol often used to create Low Power Wide Area Networks (LPWANs) with an operating range that goes from hundreds of meters up to 10 kilometres. It is based on LoRa modulation (PHY Layer) while the Medium Access Control (MAC) layer is an open network architecture regulated by the LoRa Alliance. The most used and large LoRaWAN network is The Things Network, with more than 10’000 LoRaWAN Gateways and 110’000 community members.
LoRaWAN has different end nodes classes: Class A, B, and C. All LoRaWAN devices must implement Class A, whereas Class B and C are extensions of Class A devices. These classes, defines the behaviour about downlink packets from gateways to end nodes. Usually LoRaWAN gateways acts as Class C devices, since they are constantly listening for incoming transmission. Also, in order to transmit and receive data over LoRaWAN network, LoRaWAN end nodes must be registered and enabled on the Application Server provider.
Given the LoRaWAN protocol nature, there are many limitations regarding payloads sizes, usage policy and operating range. That’s because LoRa modulation is characterised by a Spreading Factor (SF) which defines the airtime duration of the chirp. Increasing the SF increases the symbol time, allowing the signal to travel over a longer distance. A lower SF allows the greater data rate and lower symbols airtime, while an higher one allows the highest transmission range with the lowest data rate, thus higher energy consumption. Also, as shown in the following table, SF affects the maximum packet payload, which is equal to 222 bytes with the lowest SF (SF7), while the minimum, instead, is reached with SF set to 12, with a limit of 51 bytes for user’s data.
For a detailed explanation of LoRaWAN protocol and its limits, you can check my dedicated article.
Narrowband Internet of Things (NB-IoT) Protocol
Narrowband Internet of Things (NB-IoT) is a LPWAN protocol created by 3GPP which focus on indoor coverage for low power and low cost IoT applications. As LTE-M, it uses a subset of the existing LTE networks managed by many operators, in order to guarantee an high connection density over a wide regions. NB-IoT uses OFDM modulation for downlink communication and SC-FDMA for uplink communications, while the bandwidth is limited to a single narrow-band up to 200 kHz. Given its high link budget, it is mostly used for urban IoT applications with battery powered device (e.g., smart meters).
Given its very narrow band, it is usually allocated inside guard-bands of existing LTE networks using one or more Resource Blocks of 180 kHz each. Otherwise, it can be deployed as standalone network as a result of one or more GSM carrier frequency re-farming operation. It is a cheaper-to-implement protocol, since relays on the existing LTE infrastructure of radio base stations. The implementation of the standard requires only a software upgrade of the infrastructure.
Compared to LoRaWAN, it has an higher per-nodes cost, since each node needs a subscription with an Internet Service Provider, but the overall coverage should be greater, allowing also an high devices density per squared kilometer. It has a power consumption comparable to LoRaWAN, allowing the creation of battery powered devices that can last for some years.
NB-IoT is believed to be a great alternative to LoRaWAN for Long Range Internet of Things applications, and is a far way better the the old but still used GSM, given its higher efficiency and lower end nodes costs.
LTE-M protocol, also known as LTE Machine Type Communication protocol, is a type of LPWAN radio standard developed by 3GPP to power a wide range of cellular devices and services. As the name suggests, LTE-M uses the same carrier frequency adopted by LTE networks, which can be different from region to region. However, in order to limit the power consumption of the transceiver, the signal bandwidth is limited to 5 MHz or 1.4 MHz, while downlink and uplink data rates are more than ten times lower than a common LTE connection, since the typical uplink data rate for an LTE-M device can reach up to 7 Mbit/s, while the downlink data rate can reach up to 4 Mbit/s, while in some version it is limited to 1 Mbit/s.
One of the main advantage of LTE-M over NB-IoT and LoRaWAN protocols is its higher data rate, followed by the mobility opportunity offered by this connection, which overcomes some of LoRaWAN and NB-IoT great limits. However, its deployment cost is higher, since a contract with LTE-M operators is needed. Also, the power consumption is higher than LoraWAN and NB-IoT, making it suitable for mobility applications with limited battery life.
Wi-Fi ah (HaLow)
Wi-Fi HaLow is a new Wi-Fi standard announced back in 2016. Almost all Wi-Fi standards (IEEE 802.11 a/b/g/n/ac) operates at either 2.4 GHz or 5 GHz, which allow them to reach a relatively high data rate but a lower sensitivity over wide operating range with obstacles and walls. Therefore, these Wi-Fi versions are often limited to Wireless Local Area Networks (WLANs) within an operating range below 50 m. Wi-Fi HaLow solved the limited range problem of typical Wi-Fi standards using 900 MHz as carrier frequency, which can easily penetrates through walls compared to 5 and 2.4GHz.
Also, it has a lower power consumption when compared to the more used Wi-Fi standards. Given its low power and wider operating range, which can reach up to 1 kilometre, it could be an interesting standard for LPWANs IoT applications. However, considering the need for new radio equipments, since it uses a complete different frequency than the other versions, it is actually rarely used. Even if HaLow was released in 2016, actually there are almost no products on the market that uses this standard. This could partly depend on the lack of a global standard, but it is likely also due to the fact that there are competing technologies on the market that better address the needs of IoT.
Currently in an early stage, 5G networks will probably revolution the Internet of Things world, allowing unprecedented devices density for squared kilometre. Its very low latency nature, combined with an ubiquitous coverage, will support the development of Smart City, Farming and Industry applications with thousands of sensing nodes, vehicles such as autonomous cars, trucks and even drones, but also real time services of data analysis over large area networks, exceeding all the limits of current protocols. However, it is too early to talk about 5G IoT devices, since networks are still under deployment and costs are actually too higher for that kind of use cases.