CoAP protocol

[Thedude]

I'm a big fan of "everything over WiFi" and I hate zwave, zigbee and alike for many reasons explained elsewhere in this forum. The problem is that WiFi is battery drainer for battery powered devices so that battery powered WiFi devices will last 2-3 months while zigbee equivalent will last 1-2 years. Big advantage.
Apparently there is a low power WiFi protocol called CoAP designed specifically for battery powered devices.
Unfortunately I do not see many CoAP devices in the marketplace. I'm particularly interested in motion sensors and door locks with long battery life.

[Michael McSharry]

CoAP is for limited resource devices and provides a means for short message communications which will use less battery. It still carries the lower levels of the ISO model at the socket layer used for WiFi. At the next layer it uses UDP rather than TCP. The typical scenario for battery powered microcontroller devices is that the CPU is put to sleep and awaken by an event or periodically. This sleep mode is where the power savings comes. When it awakens it needs to establish a connection onto the WiFi network which includes the power-hungry RF transmitter used for the WiFi connection. CoAP spits out short messages and this conserves the time the RF transmitter is active vs. TCP-oriented protocols that have other layers of protocol that extend the time the RF is active and draining the battery.

When the device wakes up it will take some time to establish a connection on the WiFi network. This latency is usually a problem for the effectiveness of event-based devices such as motion sensors. With things like door locks the problem is that the Ouality Of Service is fire-and-forget. If you keep the communication channel open to allow a handshake then the battery gets drained. This means that the world of use-cases is limited. Other solutions are available so not a strong need for a new IOT protocol with limited use.

Espressif has also come out with a ESPNow protocol that has a similar effect of reducing the time it takes to establish communication via WiFi. You can find this on ESP32 and ESP8266 microcontrollers. I am not aware of commercial products that use this protocol, but a firmware change in the products could. These uses cases are machine-to-machine as there will need to be some node in this ESPNow network that is also able to get onto the standard network where messages can be routed.

A more common solution is some form of hub that is mains-powered and specialized RF communications. Pretty much similar in concept to Zigbee, Zwave and Weather Stations. The battery-efficient RF at 433 MHz - 900 MHz bursts a short digital pattern that is decoded by the hub receiver and converted to something the host computer recognizes. USB on the host is common, but could be an ethernet socket as well.