There are many very different IoT applications today from soil sensors that send a few bytes every few hours, up to the driverless car that sends many Megabytes of data constantly. Many if not all these applications depend upon good connectivity, but a question arises…what is a good connectivity for IoT?
When planning IoT networks there are three major factors to pick from and these are power consumption, range and bandwidth/data rate. If your sensors can connect to a stable power source then it’s quite easy to reach good range and bandwidth, but in most applications this is not the case, batteries must be used, so there must be some kind of a trade-off. Other important factors are also the cost of the communications chips and devices and of course reliability. Due to all these factors and many trade-offs currently there are lots of connectivity options like WiFi, LoRaWAN, NbIoT, LTE etc. to just name a few.
To easily understand these options it’s always convenient to group them:
1. Unlicensed: WiFi, Bluetooth, RFID/NFC, ZigBee, Z-Wave
2. Cellular/licensed: 4G LTE, LTE Cat-M, NbIoT and 5G
3. LPWAN: SigFox, LoRa/LoRaWAN, Ingenu, Weightless
5. Hybrid/combinations: combinations of the previous four types
These five groups can be shown nicely on a bandwidth vs range chart so it’s easier to see and choose a right connectivity solution for the appropriate IoT application:
Unlicensed networks don’t need the license from the frequency regulator to use the frequencies. A typical example would be a WiFi access point that anyone can use freely, compared to the licensed 4G LTE base station that your smartphone connects to. LTE frequencies are licensed by your operator and they actually cost quite a lot annually. It’s normal to ask a question: why would anyone pay for something that he can get for free? By using unlicensed solutions you are limited in transmit power so you can’t reach very far and also typically you get to experience interference from other users since no one protects/restricts others from using the same frequencies. However, unlicensed is great for building smaller private networks and when you don’t want to pay any fees to the telco operator. Popular unlicensed frequency bands are 433 MHz, 868 MHz, 915 MHz, 2.4 GHz, 5.4 GHz and 60 GHz.
The most popular unlicensed standard is WiFi. In it’s latest ac version it can provide more than 1 Gbps, but the range is limited to typically 100 meters, even less than this indoors. Additionally, there are new WiFi standards developed for IoT: WiFi HaLow (802.11ah) and HEW (802.11ax).
Other very popular unlicensed standard but with even smaller range <30m is Bluetooth and the Low Energy variant (BLE) that is ideal for IoT. Compared to WiFi, BLE is more power efficient, it’s set up more easily and it’s also more resistant to interference (works better in noisy environment), however it has lower range and much lower capacity that is measured in hundreds of kilobits per second. The latest version of Bluetooth, the version 5 brings many useful features like 4x the range, 2x the speed and it supports mesh so it’s easier then before to make bigger Bluetooth networks.
Other unlicensed standards are ZigBee that has been on the market for more than 10 years and also Thread that is quite similar, used mostly for smart home applications by Google and Nest. There is also Z-Wave, standard designed mostly for home automation.
Cellular licensed networks are based on the so called 3GPP standards (3rd Generation Partnership Project), upon which most of the mobile communications from 2G/GSM, 3G UTMS, 4G LTE and now 5G is based. Smartphones nowadays mostly use 4G LTE networks that can provide more than 100 Mbps, large range and good reliability but on the other hand we are all aware of the fact that we charge our phones every two days or even every day.
To overcome this power consumption problem 3GPP has issued standards for networks that are low power, narrowband and yet still licensed. The two most well-known types are LTE Cat-M and NbIoT (short for Narrowband IoT). These networks provide well known service based upon the SIM card and they provide similar level of coverage, security and QoS as 4G LTE networks. One of the biggest benefits of cellular IoT networks is that the current LTE base stations can easily be upgraded to Cat-M or NbIoT so a full national coverage can be reached in matter of days, while some other new entrants in the market must spend quite a lot time and effort to build the network from scratch.
One of the most popular LPWAN standards today is LoRa (short for Long Range). LoRa uses unlicensed <1 Ghz frequency so a good coverage and indoor penetration is possible. LoRa uses spread spectrum technology that increases robustness of the link to interfence and also provide good gain and coverage. LoRa can support distances of up to 15 km (rural/suburband, urban is mostly 1-2 km) and bandwidths from a few hundred bytes up to 50 kbps. An open protocol that is used to build region-wide or nation-wide networks is called LoRaWAN (WAN for Wide Area Network). LoRa has good security levels and it can even be used for rough positioning without the use of the GNSS.
Other major LPWAN player is definitely SigFox. Opposite to LoRa that is open-standard, SigFox is a proprietary protocol, and a closed system since SigFox appoints one network operator per each country and controls the back-end and connectivity and IoT customers are left to use the system and pay the fee to connect to the SigFox network. SigFox also uses unlicensed <1 Ghz frequency but since the capacity is even smaller than LoRa (around 100 bps and up to 140 messages per day), SigFox devices can have even better range of up to 40 km and/or bigger battery life of up to 20 years. SigFox is not appropriate for any application that transmits lots of data often, and since it’s designed for “uplink” communications it’s not good to be used for applications that have to often send data from the base station to the sensors.
Other LPWAN technologies are Ingenu, Weightless, SymphonyLink etc.
Because of its characteristics Sigfox is used mostly for static devices that only upload very small amounts of data with very large latency (smart meters etc.). LoRa on the other hand is better for moving devices with a medium level of bidirectional data. If a better level of quality of service is needes and worldwide coverage then cellular is the way to go.
Satellite typically use microwave frequencies and their coverage and range is the biggest. Due to high cost, this solution is mostly used when there are no other options i.e. in very remote areas, on ships or platforms in the open sea or when security is very important i.e. for military or security applications.
Apart from the higher cost, satellite can have poor latency, it may require a big parabolic dish antenna and for higher frequencies it can be unreliable. Satellite typically can’t be battery powered so it’s mostly used to connect gateways to the Internet and not sensors.
For the real world IoT applications very often a hybrid solution is used. Hybrid solution would consist of two parts. The first part is called access and it includes everything from sensors/devices to the local gateway. The communications used here are typically WiFi or LoRa, but it can also be Bluetooth or ZigBee. The gateway is put on a higher ground (rooftop or a small mast) and the gateway is directly connected to the power source.
The second part is called backhaul since it includes the part from the Gateway to the Internet. Here typically a 4G LTE router is used, fiber where it is available, satellite in the very remote areas or microwave link where it is feasible.
To conclude, today there are more than 30 types of connectivity (standards, protocols) made for IoT networks and to pick the correct one, you should consider power consumption, range, current and future coverage, needed bandwidth, latency cost and reliability. One has to be very careful not to base its IoT solution around the “wrong” standard that may disappear from widespread use some day and hence the end solution might be swept from the market as well.
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