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20 several kilometers, which makes it a good candidate for IoT applications such as smart lighting or security. IEEE 802.11af offers 6, 7, and 8MHz channels, of which four can be bonded into one or two contiguous blocks. The technology also supports MIMO (with up to four spatial streams). Its throughput ranges from 1.8Mbps for a single-stream- 6MHz channel to 570Mbps for four- bonded-8MHz channels with four spatial streams, 256-QAM modulation, and a 5/6 coding rate. IEEE 802.11af was designed to operate like a traditional WLAN while avoiding the congested 2.4GHz spectrum allocation and the range limitations of the 5GHz allocation. Throughput on an IEEE 802.11af single channel has more limitations than IEEE 802.11ac, but by bonding channels and employing MIMO, satisfactory Wi-Fi WLAN performance is achievable. IEEE 802.11af was adopted in February 2014. While some chipsets with this technology began to appear in early 2016, broad use of the technology has been slow, and this is primarily because spectrum allocations vary not only from country-to-country but even from region- to-region, making it tough for chip makers to introduce chipsets that cater to all applications. IEEE 802.11ah IEEE 802.11ah (dubbed "HaLow") complements the "af" amendment by introducing IoT-targeted capabilities, such as sensor-traffic priority and low-power consumption. Employing a low duty cycle operation restricts power consumption, allowing a sensor to spend long periods in sleep mode. Claims suggest that the technology's power consumption is around one percent of a conventional Wi-Fi chip's consumption. The technology also employs TWT and other power saving techniques such as restricted access windows. Figure 2: Sub-1GHz Wi-Fi offers the long range essential for external, wireless monitoring deployments. Source: (Getty Images) Wi-Fi also provides a key advantage over many competing IoT wireless technologies, such as Bluetooth ® Low Energy (BLE) and Zigbee, because its firmware typically incorporates TCP/IP upper layers that enables a connection to the Internet without the recourse of expensive and complex gateways. IEEE 802.11af IEEE 802.11af is sometimes referred to as a "White-Fi" and was designed to employ licensed very high frequency (VHF) and ultrahigh frequency (UHF) TV channels from 54 to 790MHz—enabling more efficient use of that part of the electromagnetic spectrum. Because Wi-Fi access power transmits at relatively low power, minimal interference should affect other devices, like analog/digital TV and wireless microphones, that use the spectrum allocation. However, to ensure that these primary users don't suffer from interference, IEEE 802.11af includes measures such as cognitive radio technology, which allows a system to detect transmissions and move to alternative channels when it detects these signals. IEEE 802.11af borrows much from IEEE 802.11ac, including OFDM modulation and 256-QAM, and because of its lower operating frequency, IEEE 802.11af experiences a much lower attenuation from obstacles such as walls and ceilings. Its indoor range can exceed 100m (compared to IEEE 802.11ac's 35m), and its outdoor range can exceed IEEE 802.11ah operates in the 900MHz ISM band in the US and in other sub- 1GHz bands elsewhere in the world, supporting up to a 1km range. The technology's channel widths are 1, 2, 4, 8, and 16MHz, and it supports MIMO, OFDM modulation, and up to 256-QAM. With a single spatial stream, 1/2 coding rate, and a 2MHz channel width, throughput is 650kbps. At the top end, using three spatial streams, 256-QAM modulation, a 3/4 coding rate, and an 8MHz channel width, throughput is 234Mbps. The amendment supports mesh networking and includes IP support at the node, which is crucial for IoT-targeted technologies. IEEE 802.11ah was adopted at the end of 2016, and while the introduction of commercial products that embody this new standard has been slow, some chipsets, firmware, and development tools are now starting to trickle into the market. Qorvo has a family of <1GHz FEMs to mate across multiple chipset solutions on the market. Conclusion The IEEE 802.11 amendments underpinning Wi-Fi have continued to evolve since the adoption of the original standard over two decades ago. Amendments such as IEEE 802.11ay progressively address consumer demands for greater throughput for applications such as high-definition video streaming, and other amendments such as IEEE 802.11ax address the challenge of creating the best use for increasingly congested RF spectrum allocations while also continuing to enhance the IEEE 802.11's overall performance standard.

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