Why is Frequency Channel Diversity so Beneficial in Wireless Sensor Networks?

In the context of dense sensor networks, a multichannel MAC is a good means to reduce channel contention and increase frame reception probability. In the paper, we report on experiments with transmissions on various channels in the 2.4GHz ISM band and find more channel diversity than expected: this effect is particularly exacerbated at a short range, but it also has a significant impact at any distance.

In our experiments, it appears that wireless sensor nodes have a radiation
pattern that changes significantly from one frequency channel to another, which often results in the overall channel gain considerably changed.
This feature is inherent to the size of the sensor node, in which the antenna necessarily interferes with other components. The first consequence of this finding is that frequency diversity in sensor networks is even more effective than generally thought, and conversely, single channel communication schemes should be avoided as long as the power budget is not very comfortable.