Why Channel Hopping Makes Sense, even with IEEE802.15.4 OFDM at 2.4 GHz

Since its 2015 revision, IEEE802.15.4 now supports the OFDM physical layer at 2.4 GHz, on top of the popular O-QPSK modulation. Chips capable of both O-QPSK and OFDM are currently available. The question now is whether OFDM is relevant for low-power wireless mesh networking; given its prevalence in 4G cellular, it could be a game-changer. We start by collecting a comprehensive connectivity dataset, 141,587,000 data points, continuously over 21 days. We then show, in an entirely counter-intuitive manner, that OFDM alone is not enough to cope with external interference and multi-path fading, and we recommend combining OFDM with channel hopping at the link layer. In the presence of WiFi interference, we further recommend using OFDM option 1 MCS3, a fast 800 kbps mode, which does not use frequency repetition, even though the latter is meant to increase frequency diversity.