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Low Power IoT Integration with WiFi Access Points

by Hemant Chaskar on Jan 5, 2017

Local wireless connectivity is critical for IoT. Early IoT applications such as appliances remote control have used WiFi due to its prevalence in homes and offices. That said, WiFi is not suitable for many other IoT applications, particularly those requiring low power operation on coin batteries. Also for many IoT applications, WiFi data rates are much higher than needed. WiFi also does not provide elegant approach to create self-organizing mesh network of IoT nodes. These gaps are filled by Zigbee, Thread and BLE.

Low Power IoT

Zigbee standard has been around for a decade, mostly used in industrial control applications. It is now a contender for home and office IoT. Zigbee operates in 2.4 GHz ISM band using IEEE 802.15.4 standard and supports maximum data rate of 250 Kbps on 2 MHz channel. The IEEE 802.15.4 MAC is Carrier Sense Multiple Access (CSMA) based. The Zigbee networking protocol is designed for mesh topology. Thread is a more recent standard using the same IEEE 802.15.4 radio and MAC, but has defined a mesh networking protocol that is based on IPv6 and that is more generic and application agnostic compared to Zigbee (the recent version of Zigbee, called Zigbee IP, has tried to achieved similar objective via dual stack approach). Thread specifies mechanisms for node authentication and link layer encryption. BLE is a low energy communication protocol that runs on Bluetooth radio and supports maximum data rate of 1 Mbps on 1 MHz channel.

WiFi AP as Gateway for IoT

The low power IoT nodes require connectivity to the network. The IoT node may connect to the network directly or through one or more intervening IoT nodes in the mesh topology. And what better way to connect IoT nodes to the network than to use WiFi access point as the gateway. The gateway also implements border router function for the mesh network.

Multi-function 2.4 GHz Radio on AP

All WiFi APs today include 2.4 GHz radio. The 2.4 GHz band is inferior to 5 GHz band for heavy network access and some will argue that there isn’t a need in the future for the AP to support 2.4 GHz radio. However, with the prospect of AP serving as a gateway for low power IoT that runs in 2.4 GHz, the 2.4 GHz radios may never go away from APs, rather become mission critical!

The gateway function requires the 2.4 GHz radio on the AP of the future to be multi-functional. It needs to support WiFi, Zigbee/Thread and BLE. There are challenges and opportunities here. Since all these technologies operate in 2.4 GHz, there will be interference from a local transmitter in the gateway to a local receiver. For example, WiFi could be receiving when Zigbee/Thread/BLE could be transmitting and vice versa. Chip vendors and standards will devise innovative solutions to solve this co-existence problem. For instance, WiFi can reserve the medium using frames like CTS-TO-SELF to silence WiFi radios in the proximity leaving a clear channel for the low power IoT. Another method could be to share information about channels and interference among radio drivers to help steer IoT to clean channels (notably, some 2 MHz 802.15.4 channels can even sit in the crest between adjacent 20 MHz WiFi channels). There is also opportunity for chip vendors to produce multi-function SOC (system on chip). And there is opportunity for WiFi vendors to add IoT management to their AP consoles. 

Intelligent Gateways

Another interesting point is the prospect of local intelligence built into the gateway. Since low power IoT technologies are IP based, networking possibilities among the nodes connected via various wireless technologies is possible. Instead of all information flowing to the cloud, some processing at the local gateway would benefit the application. As an example, detection of motion outside the windows or doors could be used to trigger lights to come on and locks to be shut without user intervention or data traversal to the cloud. So, you could actually be installing apps on your AP!

Early multi-function silicon designs are already out (this OnHub teardown shows both Zigbee and Bluetooth modules inside) and more are in works for homes and enterprises. It is going to be exiting time again for the 2.4 GHz radios on APs, quite a change of fortune for them!

Learn about Mojo's High Performance AP's