IoT Connectivity Technologies
- Ankur Gupta
- May 30, 2020
- 7 min read
Paul was sufficiently impressed that we were making progress in designing his IoT for aeroponics system. We had identified the sensors that we were going to use.
“How are you going to connect the sensors to each other? How are you going to connect to the remote monitoring server so that all the sensor data gets transferred and visible on my dashboard?”
IoT Connectivity
Connectivity is what gives IoT its popularity and widespread adoption. Sensors for measurement and actuators for control have existed for centuries, but the numerous connectivity options that exist now have come to play only in the recent past. Adding to this the sheer variety of connectivity technologies available in the market are enough to make even IoT veterans’ heads spin with options.
A few factors make IoT connectivity technology different from connectivity technology of say the Internet. In a farm, 1000s of sensors of multiple types can be placed far and wide from each other. With so many sensors deployed, and many times in remote and inaccessible locations, changing a sensor’s battery might be unfeasible. It would be easier just to throw the sensor away and replace it with a new system. Thus, to conserve costs, each system has to last for as long as possible, which means power consumed has to be as low as possible.
But with sensors spread far and wide, some IoT applications might need to transfer data over a ‘wide-area’. At the same time, depending on the type of application, the bandwidth of data required to be transmitted across the network can also vary.
In summary, each IoT connectivity option has to take into consideration the following three factors: 1) Power requirements 2) Range 3) Data Bandwidth. Range and data bandwidth have a directly proportional relationship with power required. With each other, range and data bandwidth don’t have a mathematical relationship. In fact, each IoT connectivity technology defines the ideal range and bandwidth that it can transfer. A brief list of some of the popular connectivity technologies are plotted on an x-y plane below:
Towards the lower-left corner you have RFID and Bluetooth which are used to transfer only bytes of data upto a few meters away. On the lower right corner, there is LPWAN technology (more of that will be explained later). Towards the upper left, there is Wifi, which can be used to transfer Gigabytes of data but has a range of again only a few meters. Finally, towards the upper right corner there is cellular technology, which is the most capable of transferring large amounts of data over kilometers.
What is LPWAN?
LPWAN, or Low Power Wide Area Network, technology offers connectivity options that consumer mAs of current (very low power) and can transfer data over large distances, such as kilometers. They are very useful to connect devices that are far apart and transfer small amounts of data (typically kilobytes of data).
RF vs Wifi vs LPWAN vs Cellular Technology
RF (Radio Frequency) technology such as RFID, Bluetooth, Zigbee are useful for transferring data over short distances. However, as compared to LPWAN technology, which consumes lesser power and can transfer data over larger distances, RF technology such as Zigbee is witnessing a technology-obsolescence of sorts. Other proprietary networks, such as Digimesh, are taking over. The advantage that most of the proprietary networks offer over LPWAN technologies is that they are able to form relatively robust mesh networks among the sensors. This makes the network more fail-proof in terms of data loss. The downside is that data-transfer across the network takes time and consumes more power than a simple P2P LPWAN network. For these reasons, RF networks are slowly going out-of-favour only to be replaced by other forms of connection technology.
Wifi connectivity works very well at close distances and is able to transfer enormous amounts of data. But as soon as the distance increases to a 100m+, a wifi network becomes useless. And it also consumes too much power to be a viable option for an IoT sensor network.
Among the numerous LPWAN technologies existing in the market and still being actively developed, the most popular ones are 1) Lora 2) Sigfox 3) LTE-M 4) NB-IOT.
Lora Technology
Lora is a modulation technique that primarily caters to applications that need low power, low data latency, and have long distances. Lora modules can transfer bytes of data over distances of more than 10km. This feature makes it attractive for monitoring remote areas and locations that might not be very convenient for humans to visit multiple times.
Advantages of Lora include:
Low Cost ($10/$20) for one module
Can cover wide distances of 10km+
Low power
Can transmit when object is in motion
Disadvantages of Lora include:
Very low bandwidth (Bytes/second)
Transmission time is high
Gateway (in non P2P networks) can be an expensive investment
SigFox Technology
Similar to Lora, Sigfox is a low-power, low bandwidth technology that is uplink only (one-side data transfer). It introduced the concept of LPWAN before Lora did.
Advantages of Sigfox include:
Even lower cost modules than Lora ($5/$10)
Disadvantages of Sigfox include:
Uplink only
Sigfox can’t transmit while the device is moving
Sigfox devices have to be part of the ‘Sigfox’ network, which is deployed mostly in Europe. Outside Europe, there is no option of using Sigfox.
LTE-M Technology
LTE-M, an abbreviation for LTE Cat-M1 or Long Term Evolution Cat-M1, is a technology that allows devices to connect to the cellular LTE network. How does it then differ from the conventional cellular technology? For that you’ll have to understand the basics of cellular technology and the terminology associated with cellular networks.
Cellular Technology
Cellular technology involves a lot of popular buzzwords such as ‘2G’, ‘3G’, ‘4G’, ‘HSPA’, ‘LTE’ among others. Here is a brief description of the popular words:
2G/3G/4G/5G: These are standards and NOT technologies that define how fast internet speeds should be (among other requirements). For example, for any network to meet 4G standards, it had to allow data transfer of at least 100 megabits/second for mobile devices, and at least 1 gigabit/second for stationary devices. Only if a network provider was able to allow these speeds on its network and a device manufacturer was able to comply with such a network’s requirements were they termed as ‘4G compliant’.
LTE: Long-term evolution is the technology or the method of achieving the speeds dictated by a 4G standard network. An analogy that I can think of to represent the difference between LTE and 4G is that 4G is like an island, and LTE is the boat to get there. That also means that there are other possible technologies that network providers can use to achieve the 4G standards. This is when technologies like HSPA+ became popular. Again, HSPA+ was like another boat that network providers and device manufacturers provided to reach the LTE island. In India, for example, Vodafone, Jio, and Airtel have all deployed LTE networks. More information about the differences between the two can be found HERE
LTE-M Technology (continued)
So coming back to LTE-M technology for IoT, it is a specialized set of technology that the cellular body 3GPP is implementing to cater to IoT devices.
As compared to other LPWAN technologies, the advantages of LTE-M are:
It can transfer data upto about 400 kbps and the data transfer rates are as fast as the current LTE network
It can connect directly to existing LTE networks, thus requiring no additional hardware investment by network providers. Although it needs a software upgrade from the side of the network providers.
It can be used to talk to devices kilometers away, riding on the existing LTE networks in the area
It has certain disadvantages though:
It is expensive as compared to Lora/Sigfox modules
It consumes more power
It is a half-duplex technology (can only transfer data one-way)
As compared to cellular technologies, the advantages of LTE-M are:
It is cheaper then existing 3G/4G modules
It consumes much less power
The disadvantages are:
Data rates are as fast as regular LTE technology
It is half-duplex
NB-IoT Technology
NB-IoT (or Narrowband IoT) technology, is another technology developed by the cellular body 3GPP apart from LTE-M technology. It differs from LTE-M because it uses another modulation technique (DSSS Modulation) as compared to the typical LTE modulation technique, which means that it isn’t compatible with the existing LTE network.
Apart from the fact that network providers will have to spend time and money to make their networks compatible with NB-IoT, the prime advantages this technology offers over LTE-M are:
It is potentially cheaper to deploy
It consumes lesser power
The disadvantages are:
Speed of transfer is lower than LTE-M by upto 4 times
Summary & Takeaway
With so many IoT buzzwords, it can be difficult to determine what technology to use for which application. Of course, there is no right answer, and determining the technology needs one to completely understand the application that it is going to be used for, but here are a few take-aways from the article:
For most IoT applications, technologies like Wifi, BLE, RFID, Zigbee might not be suitable. The most important technologies to consider are cellular and LPWAN technologies
The primary considerations to be taken into account while deciding the technology to use are: 1) Cost 2) Power Consumption 3) Speed 4) Distance
A list of cellular and LPWAN technologies to be considered are: Lora, Sigfox, NB-IoT, LTE-M, and cellular 3G/4G. Even in this list, Sigfox is not feasible to be used outside Europe. Thus, the list contracts to Lora, NB-IoT, LTE-M, and cellular 3G/4G.
Each of the 4 technologies has its specific use-cases:
In an area where there is no or weak cellular network, Lora is the only option.
In an area with cellular network, Lora is useful if one wants to conserve power but transfer only bytes of data. The higher the data amount to be transferred, the more power will be consumed by the device.
LTE-M seems like the technology with the highest potential in terms of power-consumption, distance, and speed. Let’s see what the future holds.
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