Large homes or poor placement of WiFi routers can cause issues with WiFi connections. Extending an existing WiFi network is a fairly simple task.
Using one of the many free apps available for smartphones and computers one can easily asses the signal strength in each room of the house. Doing a quick survey, noting locations where signal level drops below -70dB (as signal levels drop to -80dB and below connection speed and reliability suffer). There is a solution.
To remedy this you can add a “hard wired” (wired back to your ethernet router or switch) Wireless Access Point to areas with low or no signal. Hard wiring the access point maintains internet speeds. You can also set the AP (access point) to perform as a wireless repeater if you are unable to fish a wire back to the router/switch but please note, putting an access point in repeater mode will reduce your overall speed on that node. You can also add a wire access point and then use an AP in repeater mode to extend the WiFi signal further.
After placing the access point, be sure to configure the AP to use the same wireless network name (SSID) of your existing WiFi network, all SSIDs should be the same throughout all of your wireless access points, but be sure to vary the channels as you do not want them sharing the same channel. Using the same SSID throughout your network allows wireless devices to determine the best AP to connect to and makes roaming seamless as you move from AP to AP throughout the house.