Low power wireless technologies for the IoT

The predictions for how big the so-called IoT will eventually be are widespread and large. What is less sure is what wireless technologies will be used to connect these devices, with the proponents of each already setting out their stalls for what should be a tense few years as they jockey for position.

Among the favourites are the likes of Zigbee and Bluetooth, boosted by the recent launch of 4.2, but also low-power radio technologies such as LoRa are likely to have a say and even WiFi, and of course there is the IPv6 6LowPan option, supported by Zigbee and Bluetooth 4.2. And let’s not forget cellular, which while not low power at all will be in many edge devices. There are others as well all hoping for a slice of what looks like could be a very big pie.

Some pundits are hedging their bets and giving support to as many technologies as they can while they wait to see who will be the winners and losers. Others do not believe there will be losers, as such, with each technology finding its place.

“I think all the technologies will have a part to play in different roles,” said Jonathan Pearce, European Marketing Manager, Wireless Products, Microchip. “Even in the edge devices there are a wide range of requirements in data rate, range, cost and so on.”

Nick Pummell, Strategic Business Development Manager, Alpha Micro, agreed: “The key for IoT is finding the right wireless tool for the application and it relates to what they need to connect to. It depends on the use-case.”

What will be key, though, is low power; some of the devices will need to survive for more than ten years without changing batteries and/or rely on energy harvesting. Yet WiFi, not really seen as a low-power choice, will still be used for providing a basic connection to the internet. Some of this need could be erased by the profile in version 4.2 of the Bluetooth core specification, which will enable direct IP connectivity.

BLE, also known as Bluetooth Smart, is already showing growth because of its ability to connect with smartphones and laptops as it provides direct links with many of the apps. “With BLE, because the technology is in consumer electronics, there is an easy route for connecting into,” said Pummell. “And Bluetooth 4.2 is now there to take on WiFi. It lets them attach to the internet, removing the biggest selling point that WiFi has. This will make Bluetooth the predominant technology in the short term. 4.2 really opens it up and I suspect the WiFi guys are a bit worried about it.”

But he pointed out that some companies have ripped out bits of the WiFi stack leaving just the parts that are optimised for low power. This has reduced the 300 to 400mA during peak transmission to just 70 to 80mA. “I don’t think we can count WiFi out,” said John Wells, Senior Director, Cypress. “They are pushing the power consumption down. And if you have a billion devices, about half of them won’t need really low power. The smart meter is a good example.”

Pummell added: “With WiFi, we see it being used predominantly where someone needs access to a piece of equipment, not just locally but from outside.” Zigbee is carving out its own niches in the smart meter sector and connected smoke detectors. It is a mesh technology that suits this type of application well. For example, if there are some smoke detectors in an office it is easy to add more and for them to join an existing Zigbee network. “Zigbee is a strong low-power technology for home automation and IoT,” said Pearce. “The propagation is not so good because the higher the frequency the less distance and the less it penetrates through buildings, so there are pros and cons. It is strong in America where the houses are made of timber and cardboard but less in Europe where building are made of bricks, concrete and steel.” Here, the sub-GHz radio technologies are more likely to make an impact.

Asymmetry

When considering the problem with low-power radios, the attention often falls on the transmit side when it really burns up the battery. But Pearce believes more attention should be played to the receive side for IoT applications as he sees this as being the biggest difficulty: “When you look at it, the current consumption looks high for the transmit side and the receive side is much smaller,” he said, “but the receive current can become the decider on battery life.”

This, he said, is because in IoT applications the devices have to sit there for a long time in receive mode waiting for a signal, whereas the transmit times are very infrequent. Technologies such as LoRa get round this by letting the end devices initiate the connections. “In cellular, mobile phones wake up every second to see if there is a signal and that draws current,” he said. “With LoRa the devices wake up say every ten minutes or an hour. They only listen for a receive signal when they send something. It makes the power budget extremely efficient. It is these sorts of tricks that can be used to save power. Zigbee does something similar. You could do that with the higher power technologies, such as WiFi, which is why any technology has the potential to go forward.”

Winners and losers

Hardy Schmidbauer, Director of Wireless Products at Semtech, thinks that low-power radio will be a winner in over half the connected devices. He sees commercial devices such as smartphones and tablets making up 35% of the IoT and they will continue to use cellular, Bluetooth and WiFi. Another 10% will be taken up by cellular M2M. But it is the other 55%, what he calls the Internet of Objects, where technologies such as LoRa will score.

“Some think much higher than 55%,” he said. “For these we need low cost and long battery life. They may be outdoors for things like asset tracking and positioning. Until today, that has been the undecided segment.” He said he did not think Bluetooth 4.2 would change that landscape. And he does not think mesh technology is adequate to drive volumes.

“That is what we are targeting with LoRa, and others such as Weightless are targeting as well,” he said. “I think for the Internet of Objects, that is not a play for Bluetooth and Zigbee. You are going to need something like LoRa for that.”

Wells believes that Bluetooth and WiFi will dominate and that Zigbee will be squeezed out: “There is just not enough infrastructure for Zigbee,” he said. “Whether Zigbee is better or worse is not relevant, as there is no deployment. There are lots of Zigbee devices out there but they are not turned on because there is no-one for them to talk to. If you have WiFi or Bluetooth there are things to talk to already.”

While he acknowledged there would be a place for technologies such as LoRa, he said it would be small: “It depends on the market,” he said. “The US market tried to deploy a lot of Zigbee a few years ago and failed. Longer range technologies, such as sub-GHz radios and cellular, have been used in neighbourhood area networks. The range is pretty good. Range could be a barrier for Bluetooth but when Bluetooth 4.2 rolls out the objections on range will go away. Bluetooth outperforms the other technologies. Bluetooth will be a major winner with WiFi a strong second.”

Not surprisingly, Dave Egan, Senior Product Manager at Silicon Labs, and who is involved with the Zigbee Alliance, disagrees: “Zigbee has a very specific role,” he said. “It will be used in smart meters and home area networks. Zigbee is very good for that. This is because of the application protocols. They provide interoperability and an open standard that can be used for home automation. There is nothing else that has the full range of device application level support that Zigbee does.” He said Bluetooth and WiFi had a role in connected homes, in that WiFi gives access to the internet and Bluetooth to the consumer devices, but neither provided the ability to talk with 200 connected things in the home.

“All the home automation people are testing with 200 to 300 devices in the home,” he said. “Today it is ten to 15 devices, or even three to four, but within five years there will be hundreds. Start adding up the windows, doors, light bulbs, power sockets, thermostats, sensors and so on and you get to hundreds. That is where Zigbee is strong, on mesh networks and with the number of profiles it has.”

There is disagreement, as seen, over which technologies will win, but most seem to think that the battle has a long way to run. As Pummell said: “There is a place for all these technologies. There will be winners and losers, but in ten years there will be lots of radios all coexisting next to each other. It will depend on the application.”