Balance the SWaP-C for your IoT Wireless Solution

All innovations in IoT, from medical devices to industrial equipment to consumer products, need an integrated approach to optimise wireless technology applications. Adding a random wireless connection would be an unnecessary expense in terms of power and cost

End-devices will come in almost unlimited shapes and sizes, but they will probably have many commonalities: cost, closely followed by size and weight. But all of those demands could easily be overshadowed by a fundamental need to be low power, and regardless of the technical specifications, it is necessary to make strategic trade-offs to successfully solve your SWaP-C equation (size, weight, power, and cost) during development.

Balancing the SWaP-C equation is well understood in the military and aerospace industries and just as applicable in the IoT. Many end-devices in the IoT are expected to operate for many years with little or no maintenance, including changing the batteries. As they will most likely use some form of wireless connectivity, the choice of wireless technology will be a major part of the SWaP-C calculations. No matter the specifications of the IoT product your company is bringing to market, you'll need to make strategic trade-offs to solve your SWaP-C equation successfully. A large part of this will depend on understanding the differences between wireless technologies and which is right for your product.

Figure 1: Wireless Connectivity IoT Technology

A Plethora of Wireless Connectivity Solution

Choosing the right wireless technology for more complex products is rarely a simple one-to-one affair. In other words, a combination of variously configured Wi-Fi, Bluetooth, LPWAN, and cellular technologies is often needed. Looking at it from a single node's point of view, the power needed to get a message to the network's server is effectively distributed across all nodes actively participating in the network.

For a size of a mesh network, for example, that functions in a self-healing way, one message could be picked up and passed on by multiple nodes, in some cases consuming power unnecessarily. This is characteristic of wireless networking technologies that occupy the PAN (Personal Area Network) and LAN (Local Area Network) space and adopt a mesh topology, such as Bluetooth and ZigBee. We certainly know what this is, but the range of Wi-Fi networks is often too limited by their frequency, transmission power, antenna type, location, and environment. Whilst Wi-Fi is well established, Wi-Fi 6 is the next generation of this technology and holds game-changing possibilities for new product development. More on this is described in my previous SCMR column.

It is less characteristic of WAN wireless technologies like cellular and Low Power Wide Area (LPWA), designed to transmit over kilometers instead of just a few meters for PANs and LANs. This includes technologies developed for the licensed spectrum such as LTE-M and NB-IoT and LPWAs operating in the unlicensed spectrum, like Sigfox and LoRaWAN.

Features and	PAN	PAN	LAN	WAN	WAN	WAN	WAN	WAN
Specification	BLE/Bluetooth 5	Zigbee	Wi-Fi	5G	NB-IoT	LTE-M	Sigfox	LoRA
Network Size	up to 750 m	<30 m	<=100m	500m- 10km	>15km	>10km	>15km	>10km
Module Weight	0.3g-2g	2-4g	3-6g	4-5g	2-3g	2-3g	2-3g	2-3g
Power Efficiency	~10 yr	6-12 month	<10 days	<10 days	~10 yr	~10 yr	10-20 yr	10-20 yr
Module Cost	Very Low	Low	Medium	Very High	Low	Low	Very Low	Low

Creating and operating a cellular network in the licensed spectrum is expensive, so developing solutions like LTE-M and NB-IoT could be precluded based on cost, at least in the early stages of deployment. Similarly, networks that rely on many local nodes to guarantee connectivity and extend range (Bluetooth, ZigBee) could also put the total cost of ownership (TCO) up, particularly when large areas and/or long distances are involved.

The solutions presented by the likes of Sigfox and LoRaWAN attempt to overcome these limitations by offering long range connectivity (10s of kilometers) for low bandwidth messages (10s of bytes) at very low power (years of service on a single battery), without the responsibility of becoming a network operator. Whilst they can't be considered cellular networks in the conventional sense, LPWANs operating in the license-free spectrum do require base stations to provide coverage.

We know these technologies can intersect, but the appropriate technologies and suitable configuration for each to optimise performance and SWaP-C trade-offs will vary depending upon the requirements for use cases and the value that particular functionality can offer your target market. The question of which wireless technologies? and which combinations? are just one piece of a larger puzzle. It is worth mentioning that each connectivity solution has its strengths and weaknesses, and obviously, there is no 'one size fits all’ approach. Rather, it is important to understand the variety of options available and other factors that influence the decision, such as data rates, latency, mobility, range, coverage, security, and many others. In addition, requirements for the underlying use cases of an IoT application are likely to change during its life cycle, as the volumes or selection of data gathered from machines etc., might need to be adjusted once patterns have been analysed.

To gain in-depth understanding on wireless connectivity solutions and their used cases, read our whitepaper on "Wireless Connectivity Solutions for the IoT"