There are many discussions on the internet over whether 2.4GHz is dead or not. My opinion is that it is not dead at all. Should it be used by some applications like voice over Wi-Fi? No. But with having more devices that want to connect with the internet, there are some that are very suitable for the 2.4 GHz band. Internet of Things (IoT) are most of the time devices that will only work at 2.4 GHz. With 802.11ac, some people hoped that we were done with the 2.4GHz, but with the upcoming 802.11ax, 2.4GHz is back on the radar. The question was really, whether 2.4GHz was really off the radar, because all the access point vendors still produce dual-band access points. I do know that there are access points that can do both 5 GHz band instead of one 2.4 GHz and one 5GHz.
As said, why is 2.4GHz great for IoT devices? Those devices are most of the time sensors that are used to collect data. You don’t need speed for that; you don’t need 3×3 devices. Most of the time wireless sensors are devices that use only 1×1, a low power, devices that can penetrate through walls (further distance), and so on… So, the conclusion is what you want is a cheap 2.4GHz only chipset for your device.
What will bring 802.11ax to this and what makes it better? With Target Wake Time, it allows an access point to define specific time with individual stations. That one sensor that you have in your company that needs to send its data every hour can now sleep 59 minutes and save the battery power. TWT is also available in 802.11ah, but this uses the 900MHz band.
WirelessHART
WirelessHART is a self-healing, self-optimizing, and secure mesh technology that is used in an industrial environment. WirelessHART is a technology that uses low data rates (250 kb/s), low speed, and low cost. It started out as a wired protocol, and in 2007 WirelessHART standard 7 came out that supported Wi-Fi. It is based on IEEE 802.15.4, like ZigBee. A funny fact about WirelessHART is that it uses 15 channels in the 2.4GHz. The channels are only 2 MHz wide, 5 MHz apart and named channel 11 (2405) to channel 25 (2475), channel 26 is not used in WirelessHART. Another change is in the modulation technique: it uses Orthogonal QPSK, which means that the signal transition is not going through the ‘zero-axe’. WirelessHART uses beacon frames (for joining the network), data frames, ACK frames (10ms within the data frame), and MAC command frames.
WirelessHART uses five types of devices in their mesh network. First, there are the sensors that gather the information, second are the WirelessHART adapters (those are for the legacy WirelessHART devices which can only be used on the wired network), third are the ‘access points’ or the gateways, fourth is the management, and fifth is a device to configure the sensors.
To finish up this blog, there are some best practices for WirelessHART. Some examples are 100 devices per gateway, not more than 7-hops away, the rule of five and rule of three (meaning five devices within 1 hop from the gateway and within a range of three neighbors), and twenty-five (25) percent of your devices should be within 1 hop of your gateway.
