Invest in a Wi-Fi Site Survey

But Ekahau also has a less capable freeware version called Heat Mapper. There are other freeware, evaluation and inexpensive site survey products, including VisiWave Site Survey SO from AZO Technologies and Covera Zone from Celtrio.
If you conduct a site survey and discover you need more than one AP to eliminate all potential dead spots, there are a few possible ways to deploy and configure them. In enterprise networks, each AP is typically connected to an Ethernet "backbone" that connects them to the Internet.

More and more new homes today are wired with Ethernet in every room, so it may be possible to design a network in a large new home the same way. But in most homes and many small offices, running Ethernet to all APs will be difficult or impossible.
One router or AP, connected to the Internet, functions as the root, while others, configured in bridge mode and located nearer the dead spots, connect wirelessly to the root, and at the same time, provide wireless connectivity to nearby client devices.

Even if you assume you’ll only need one AP and don’t want to go to the trouble or expense of conducting a site survey, it makes sense to select a router or AP that can support bridge mode. Most enterprise products do, but only newer and higher-end SOHO products do.
If you start with a SOHO device that cannot support bridge mode and later discover you need additional APs, you will have to abandon the first product and start over (or use Band-Aid solutions).

Some APs can only function in point-to-point bridge mode, meaning they can only connect wirelessly to one other AP. Some support point-to-multipoint mode, connecting in bridge mode to multiple other APs.
With products supporting point-to-multipoint bridging, mostly enterprise products, you can create a wireless mesh, making it even easier to eliminate dead spots caused by transient multipath effects. Mesh networks have many potential routes for sending traffic and can pick the route with the best throughput at any given moment.

In the absence of a site survey, if you’re lucky, you can eliminate dead spots with minimal expense and effort -- but count on having to install additional infrastructure.