802.11ah - Contender for low power IoT?

The race to become the dominant low-power wireless access technology for IoT is on. While Wi-Fi has become the preferred access method for mobile devices in homes and business, for low powered IoT Wi-Fi is overkill, and too power hungry, making it unsuitable for sensors and devices which are not mains powered. Enter Bluetooth and 802.15.4 technologies such as ZigBee and Thread, and a host of new low-power wireless standards including LoRa, 802.11ah and NB-LTE. How do some of these alternatives compare?

Bluetooth

The massive opportunity represented by low-power IoT applications is driving standards innovation. For example, Bluetooth Low Energy (BLE) A.K.A. Bluetooth Smart, which was introduced in 2010 in version 4.0, significantly reduced the energy requirements.

Much of the BLE power efficiency was the direct result of a 95% reduction of the scan time required to detect other devices. This dropped from 22.5 milliseconds (ms) for classic Bluetooth to a mere 0.6 to 1.2 ms for BLE. Additionally BLE only supports data rates up to 270 Kbps, not the 2.1 Mbps for classic Bluetooth. Together these and other optimizations extended battery life 20-25 times over classic Bluetooth, which dramatically increases the market potential for Bluetooth for IoT wireless access.

Not satisfied with that, in November 2015 the Bluetooth SIG announced its roadmap for 2016 stating its intentions to boost range from the current maximum of 20-30 to nearly 100 meters, to improve performance and introduce meshing capabilities.

But Bluetooth is still limited by the number of concurrent devices it can practically handle, and it must play in the 2.4 GHz spectrum which is becoming more crowded by the day. Could 2.4 GHz congestion ultimately be its downfall?

Zigbee

Zigbee (IEEE 802.15.4) already has a head start over many newer alternative low-power wireless technologies, with a large number of deployments already out there in Smart Grid and building automation applications. It has been around since 2005, around the time that Bluetooth was popularized.

One of its advantages is its ability to operate in both star and mesh topologies. In a mesh network, each device can talk with nearby devices, enabling data to “hop” from one device to another until it reaches its final destination. The mesh topology also provides a level of redundancy and self-healing capabilities in the event that one node fails.

Like Bluetooth, Zigbee operates at 2.4GHz but has a greater range (100 meters or more). Combine this with meshing, and Zigbee becomes quite suitable for outdoor sensor networks for applications such as Smart Parking, Waste Management and Smart Grids where the devices are static, but relatively far apart. Another advantage of Zigbee is its low power requirements. Powered by a button- or coin-cell battery, a typical Zigbee device can last several years before needing a batter replacement or recharge.

Since Zigbee also shares the 2.4 GHz spectrum with Wi-Fi and Bluetooth and operates in much the same way as Wi-Fi in that it requires channel selection, ZigBee can be vulnerable to co-channel interference from Wi-Fi devices, if prudent channel selections are not made. Zigbee’s relatively low data rate which peaks at 250 Kbps is also considered a limitation for some applications.

As Wi-Fi becomes even more pervasive in business and homes, co-channel interference between neighboring networks is a growing problem, which is likely to also impact any low-power IoT sensor networks sharing the same spectrum. embedUR has been developing automated Radio Resource Management solutions to enable service providers to manage the spectrum better.

802.11ah

Meanwhile the Wi-Fi standard is downshifting to target the low-power market with the introduction of a new standard 802.11ah. In 2010 the IEEE formed a Task Group to investigate the specification of an unlicensed sub-1GHz worldwide wireless local area network (WLAN) standard for future M2M communications supporting a wide set of scenarios based on a large number of devices, a long range and energy constraints. It is slated for approval in July 2016.



Although 802.11ah is not compatible with 802.11a/b/g/n/ac it is based on a 10 times down-clocked version of the 802.11ac PHY. PHY and MAC layer enhancement which include long sleep time and optimizations for small packets, help to achieve ultra-low power consumption and multi-year battery life. 802.11ah will transmit on unlicensed bands in sub 1 GHz frequencies in 1 MHz wide channels, the availabilities of which vary greatly by region. For more bandwidth channels can be bonded, just as they are in 11ac.



This combination of features makes 802.11ah highly suitable for low-power sensor networks over moderate distances, as well as sensor and meter backhaul, aggregating multiple separate sensor networks via gateways. Its long range and ability to get thru walls, makes for a simple aggregation network.

This combination of features makes 802.11ah highly suitable for low-power sensor networks over moderate distances, as well as sensor and meter backhaul, aggregating multiple separate sensor networks via gateways. Its long range and ability to get thru walls, makes for a simple aggregation network.

While the specifications seem to hold a lot of promise, the delay in getting this standard to market may threatens its very existence. ABI research is not too bullish on its success, predicting only 11 million unit sales annually by 2020. Late 2016 delivery may be too late.

NB-LTE

One of the attractions of using 2G/3G/4G/LTE for IoT is that you can leverage the existing macro-cell infrastructure that the MNOs have already built out. However, there is a price, not only in terms of access fees, but also in terms of the power consumption. Where a Zigbee device can operate for months or years on a tiny coin-cell battery, a 4G/LTE device requires a much larger battery, which may only last a few hours or days, depending on usage.

There are several reasons contributing to the higher power requirements. First, 4G/LTE devices must power two antennas, not one, because they use MIMO techniques to improve data throughput, and second, because they must continuously scan the airwaves looking for the cell-tower with the best signal, and the more networks there are to choose from, the more scanning is required.

Needless to say, 4G/LTE is possibly the best technology for devices which are outdoors and on the move, applications such as fleet management and Smart Cars being obvious ones. In Smart Car applications LTE can enable navigation, augmented with real time traffic conditions and rerouting, while also providing the bandwidth to enable an in-car Wi-Fi hotspot for its passengers. But even here, in the fieId of transportation, there are new standards initiatives for road-to-vehicle and vehicle-to-vehicle communications.

For broader IoT applications, an initiative backed by Intel, Nokia and Ericsson seeks to create NB-LTE a Narrow Band version of LTE that would require substantially less power by using only a fraction of the spectrum - only 180 KHz versus the 20 MHz channels for today’s LTE. This is currently being evaluated by a 3GPP working group against a rival proposal called Narrowband Cellular IoT. Some are calling this future standard NB-IOT. This initiative further simplifies and further reduces power beyond the LTE-M (enhanced Machine-Type Communication) standard introduced in 2014, and nicely rounds out nicely rounds out the 3GPP cellular IoT portfolio. It will enable cellular technologies to connect a much wider variation of consumer and enterprise use cases.



NB-LTE is an attractive replacement for the 2G networks which are being phased out, and which currently carry data from IoT devices such as electricity meters and street lamps. Even though there are many viable alternatives, cellular network operators and vendors want a low-power LTE-based radio specification for IoT networking so they can leverage their LTE infrastructure.

embedUR’s role in IoT solution development

To survive through 2020 and beyond, almost every technology solution provider and many non-tech solution providers, need to fully embrace IoT technologies and new paradigms - either to protect markets they already play in, to compete in a disruptive way in existing markets they don’t play in, or to pioneer totally new markets.

But for many, this means getting into networking and wireless communications technologies that are unfamiliar territory. It also means they must build more intelligent devices which rely on embedded software, and this opens up a whole set of new challenges, such as how to upgrade devices with new software versions, how to gather data from devices and analyze it in the cloud and many more.

Vendor solutions will likely need to be a lot more open than before as well, to leverage existing frameworks, platforms and services, rather than creating everything oneself, and missing the window to market. There will be many build-buy-rent tradeoffs to be made.

With a decade of experience building embedded systems for networking and telecom products, embedUR can help you make the right technology choices, develop your IoT solution, and get to market on time, and on budget, with the least possible risk.