First thing- move the router to the middle of the house. This will help with signal distribution.
Secondly- if it has to be in the basement, which I do not recommend, get it as close to the ceiling/ floor joists as possible.
I would start with this, as the basement is the worst place you can put it, which is typically full of electrical, conduits, HVAC, etc. I would also look at your config, wider channels may theoretically provide more bandwidth but only at a relatively close range, if 2.4GHz then use 20MHz and for 5Ghz don't go over 40mhz. You should provide more details on the options/config you have selected. APs, whether they are consumer grade or enterprise are not typically optimized by selecting defaults.
I use the Ubiquity AP's at work and find them frustratingly complicated for a simple task.
Assuming that the router is not in metal lined room, I'd try changing its orientation. Personally, I'm a huge fan of the Asus routers with external antennas. These allow you to manipulate the radiation pattern to eliminate holes.
Most APs and wireless environments are frustrating even for network engineers but a little knowledge goes a long way. In this case these APs have either a single or dual radio that is integrated into them, so there is no diversifying or manipulating the antennas for coverage, just physically moving it. Typically these APs provide the best coverage located centrally on the ceiling and often have a small dead spot directly under them, something to keep in mind. Also avoid placing it anywhere close to a microwave, it will interfere as consumer microwaves operate @ 2.45GHz band and some have better shielding than others. Other sources of EMI to avoid would be electrical and things light ballasts for lights.
Bottom line, if the AP, and your devices, support 5GHz then use it and just shut off the 2.4GHz which will allow you to optimize it for a single frequency, this is because some of the optimize options are not meant to be enabled when in mixed mode, such as short guard interval.
These are popular and have gained market share for one reason, they are inexpensive for the features and quality as well as have centralized web management. You see them popping up in retails stores and small businesses all over the place, I just set one up for a cafe I visit. Not to sound argumentative, but as far as the class of product, they are certainly a better design than the rest of the consumer pack, but Ubiquiti are not Enterprise class, they wish. Having said that it's a good choice for this application if you can fill the dead spots.
