Can you practically illustrate the interference problem ?

Please take the following as one reference Multi-Dwelling-Unit (MDU or apartment complex) example of the unlicensed 2.4 Ghz and 5 Ghz spectrum usage (from my current residence):

The figure on the left shows the 2.4 Ghz spectrum usage while the figure on the right shows the 5 Ghz spectrum usage (with my 5 Ghz AP only). It should be clear that the 2.4 Ghz band is congested while the 5 Ghz is empty and free for my outdoor AP use.

The results I got are like this:

1. My 2.4 GHz AP gives best case (client  device right over antenna) of around 40-45 Mbps while the 5 Ghz AP gives best case result of 90-95 mbps. A factor of two in the ideal case
2. In longer range, I could extract a performance of max. 7-8 mbps from the 2.4 Ghz Outdoor AP while the 5.0 Ghz AP gave me results of 15-16 Mbps. A factor of two again. I had line of sight between client device and and AP with only an occasional tree and leaves as obstacle. 

The interference problem is particularly severe in apartments because of the density of flats (and each has a wifi routers). If we go to a villa or large bungalow community, the problem is less severe.

Please note that the 5 Ghz  suffers great attenuation from walls and based on that the results could change the other way round. But the above case clearly demonstrates quantitatively the impact of interference when both the 2.4 Ghz and 5 Ghz APs are theoretically rated to be able to do the same speeds.

- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee