Choosing Wireless Connectivity: Part 1
This is the first article in a series. It gives an overview of the factors you should consider when choosing connectivity for your IoT device. The second article talks about how network technologies differ in four of these factors: bandwidth, latency, power, and range.
In the near future connectivity will be a requirement for industrial equipment. This coming wave, referred to as the "Industrial Internet of Things" (IIoT), is pushing companies in industries such as solar, waste management, and farming to become experts in communication technology. It is not uncommon for manufacturers to spend months evaluating communication options before starting a device design, and then change course several times during development as new information is uncovered or new technologies start getting deployed. This series of articles will hopefully reduce both planning time and design rework. In this first post we overview all the factors that affect the choice of communication technology. Future posts will delve into various subject matters in more detail. As always, contact us if you have questions.
There are eleven important factors in choosing connectivity. These are:
4. Service level
9. Product life
10. Form factor
There are other factors as well, such as end-of-life and build vs buy but we're assuming you are already familiar with how these factors affect decision making.
Let's start with the obvious one. If your device needs to stream video to the cloud (e.g.- Dropcam) you cannot use networks such as Sigfox, LoRa, 2G, and Iridium SBD. You will also need to buy an unlimited data plan with a carrier. However, most IIoT devices do not use that much data. In fact, there are huge benefits to aggressively reducing your bandwidth requirements through compression or edge computing. Not only will you reduce your bills on cellular networks, but you will also open up a new range of very attractive options such as Sigfox, LoRa, and even satellite communications.
Latency is the time it takes for data to go from the originating device to its intended destination. Soil temperature readings are tolerant of high latency communication channels so a solution like Sigfox or Ingenu, which take multiple seconds to send small packets of data, is fine. Control systems on the manufacturing floor are very time sensitive so communication latencies in the of seconds are not acceptable.
Every wireless connection requires power (measured in watts) to communicate because it takes effort to get an electric signal over the airwaves. More important than power however is energy (power over a period of time, such as watt-hours). Energy dictates battery size. If you're building a device that has readily available electricity (from the electric grid or a large solar installation) then power is not something you need to worry about. Otherwise power will factor into your connectivity decision.
There are two ways to address power constraints. First, you can spend money and use larger batteries and/or off-grid energy sources like solar panels to increase the energy available to your device. Second, you can decrease the amount of energy your device uses by reducing the number of times your device wakes up to send data or going to a lower power network such as LoRa or Sigfox.
You often hear of SLAs (service level agreement) for services such as web hosting. It applies to connectivity as well. Consumers do not expect any kind of SLA from their wireless carriers, but industrial customers absolutely expect a wireless SLA. Is your device expected to connect anywhere, guaranteed? If so, then you might opt to offer satellite communications as an option, or at least support for multiple networks and technologies. Can you offload the responsibility of the SLA to another company, such as a third party that is responsible for installing and maintaining the device? If so, then you might be able to get away with providing a standard interface such as USB or Ethernet and have the third party worry about the connectivity. Keep in mind however that the third party may have influence in equipment decisions and if your solution is too hard or expensive to connect it may affect your sales.
Where will your device be installed? If you are focused on a single homogeneous market such as the USA or Western Europe it dramatically reduces complexity. However, if you have plans to expand internationally in the near future you need to support many more cellular frequencies, different unlicensed band rules, and multiple government agency certifications. You'll also need multiple carrier and reseller contracts to go global. For example, in the US you can get 99% of the coverage you need with five frequency bands. For worldwide coverage, you need to think about supporting all 30+ LTE frequency bands used around the world in some way or another.
This factor is often overlooked. When your device is installed in the field, will there be a cluster of them within a certain distance or just a single device? For example, smart home devices are clustered in a house. Farm sensors are clustered in a 10 mile radius. Solar micro-inverters may have multiple communication nodes (one for each micro inverter) clustered in a single installation. If there are a cluster of devices you have the option of connecting them to a private wireless network that uses a single gateway for backhaul communications. If there is only one device in the installation (such as an alarm panel) you're better off putting the backhaul capability (such as LTE) directly into the device.
If you plan on using a private network such as WiFi, Bluetooth, Zigbee, or LoRa you need to consider range limitations. The first three technologies have range that is measured in the tens of meters. LoRa has range that is in the tens of miles. LoRa is great for spread out farms and oil fields. WiFi and Zigbee are more suited for factories and buildings.
Value refers to how much a working device is worth to the end customer. It is effectively how much your customer is willing to pay for the device. If the device is a tracking system for low-priced products the customer is not going to spend thousands of dollars on a service when the value of the goods is a fraction of that. However, for a device that detects structural damage in a dam thousands of dollars is a drop in the bucket. Low value devices will most likely be relegated to low-cost wireless technologies such as Zigbee and Sigfox. High cost devices can afford expensive satellite communications that ensure coverage wherever there's a view of the sky.
Value also is related to maintenance strategy. A high value device can support regular truck rolls to change batteries or upgrade communication technology. A low value device needs to minimize maintenance requirements. That's why the 2G sunset was so damaging to the residential alarm industry. Monthly subscriptions for residential security are in the double digits. The cost to replace an alarm panel in the field is the triple digits, including material and labor cost. You do the math.
As we've mentioned before, industrial devices are in the field longer than consumer devices. Smart meters are in service for 10 years. Residential solar installations are expected to last more than 30 years. Many industrial devices will outlast the networks they're connected to. Cellular technologies sunset because consumer demand for bandwidth keeps increasing and the only way carriers can satisfy this demand is to replace inefficient old technologies like 2G with more efficient technologies like 4G, 5G, and beyond. Choosing 3G for a solar inverter will lead to network replacement costs that far outweigh the small material cost advantage 3G has over LTE. However, a telematics system that is upgraded every 5 years might be able to get away with 3G.
Device size can limit your choice of communication technology. Satellite communications require the most real estate to support- the Iridium 9602 module is 45mm x 41mm x 13mm. The smallest LTE Cat 1 modules are around 20mm x 20mm. The smallest Zigbee modules are around 10mm x 10mm. For ultra small devices that have backhaul requirements you will need to have your Zigbee device connect to a WWAN gateway (e.g.- cellular) for backhaul communications.
Form factor also dictates antenna location. Metal enclosures or underground installations require external antennas, often with long coax cables.
Security in industrial deployments can no longer be an afterthought. It must be considered when choosing your wireless connectivity. Certain networks are more secure than others. Zigbee has security flaws and WiFi security often is too reliant on the user to maintain adequate passwords. Sigfox is secure because it uses 128-bit AES security keys (which aren't as good as 256-bit keys BTW) but you must trust Sigfox because they know the keys. The same is true for LoRa networks. LTE secures communications over the airwaves, but not over the wired networks that get data to your server. The end customer may implement their own end-to-end security system but you need to make sure it's compatible with the wireless technology you are using, especially if you use non-IP-based connectivity. The end customer may mandate a closed loop system and disallow packets going over a public or third-party network, which would rule out a vast multitude of standards that require access to the Internet for provisioning.
One Last Thing
Now that we've given you the factors to consider for a successful product launch you might have to throw all that out because the one factor that trumps all is the end customer. Let me give you some examples of end customer requirements that can derail any careful analysis you may have done up-front:
1. You pick Iridium because of its global footprint, but your big contract is in India which outlaws any satellite communications except for Inmarsat.
2. Your high-bandwidth security camera installation is for a state-run company in China that has close ties with China Mobile. China Mobile uses TD-LTE which is different than anything else in the world.
3. Your reseller supports AT&T, T-Mobile, and Sprint, but your end customer has done a lot of custom integration with Verizon so now you're at a disadvantage to competing bidders.
The complexity of wireless connectivity is overlooked 99% all IoT solution providers. The common assumption is that support for WiFi or 3G cellular is all you need. That is naive. We hope these articles helps your planning and prevents you from missteps when designing your device.
By Alfred Tom on March 23, 2017