I posted this just before I went to bed last night. As no one else has responded and my reply may have seemed a little flippant, I’ll give you a bit more context.
The majority of people in industry will tell you, you only use wireless, (or powerline adapters), when you can’t put wires in for some reason. As with a lot of things, wireless has been sold to the public because it is quick and easy for the provider to install, not because it’s really any good. They can’t be held responsible for connections/speed inside your house anyway, so why should they worry about it. (In fact, as an aside, with FTTP they don’t offer a wireless connection from the ONT to the router. I wonder why?)
If you insist on using wireless however, the first thing to do with poor wireless performance is download a network analyser, like inSSIDer, and take a look at what channels are being used locally. Try to pick channels that are not in use, (good luck with that today), or the lesser used channels.
There are a lot of very clever (minor) error correction techniques in play today, but ultimately if a packet is unreadable the receiving end discards it. When the sending end does not receive an acknowledgement for that packet it will send it again. (It does this a number of times before it gives up). This really screws with the speed. For example, if every other packet needs sending twice that reduces your effective speed by a third. While this applies to both wired and wireless, wireless suffers from the problem far more because of interference from other radio sources & weak signals because of too many walls etc. Not to mention the lag involved in converting from wired format to wireless and back again, encrypting and decrypting, (because anyone can potentially listen in to wireless), etc.
If you are using 2.4GHz stick to channels 1, 6 or 11. While there appear to be many other channels available, they can cause more problems than they solve. This is because a mechanism exists to allow wireless access points on the same channel to cooperate and share the channel. If you use, say, channel 8 and your neighbour is using 6 they are still close enough to interference but they can’t cooperate and so the problem is actually worse.
Similarly, with 5GHz. Those channels are already four apart and you can use any of them. Most things default to 36 so I would pick 40, 44 or 48. Anything above 48 can potentially clash with radar and if it detects a signal it is obliged to automatically switch to a different channel. This can make those channels unstable.
Another big thing with wireless is the position of the wireless access point. Radio signals do pass through things but only up to a point. Water, metal etc. are very good at absorbing signals, so if you have a radiator, water tank, aquarium, fridge etc. in the way, forget it. In fact, as I understand it, modern plasterboard is foil backed. Ideally the wireless access point needs to be in the centre of the house, fairly high up. (Above head height, as after all, you are merely a bag of water to a radio signal – no offense).
One of the advantages of running cable is that you can then put multiple wireless points in different rooms connected to the router by cable. (Keep the same SSID but use different channels to avoid interference, as above). Even if you get a wireless mesh system, using a hardwired backhaul will perform much better.
Oh, and while I think about it, 5GHz is far less able to go through walls etc. than 2.4GHz. On the up-side, the shorter range makes it less prone to interference.
