How to use Android in Wi-Fi repeater mode by bridging Wi-Fi with Access Point? I would like to extend a WiFi signal. I could buy a WiFi repeater, but a much cheaper solution would be using an older Android 4 device, which I own and don't use. The Android device is capable of creating a WiFi AP. So if I bought an external WiFi USB adapter for it, with a large antenna used as the receiver and the Android device itself as the AP, I could bridge the network.

The hardware should be possible. But how about the Android software? Will there be any issues, or any considerations I need to take note of?
That's not worth the trouble.

It's not supported out of the box by Android and you would have to (re)compile and configure and script many things. The dedicated router is the more reasonable and stable solution (and it's also cheap).

Reasons are the following. You would need:  


USB host support
finding a USB wifi module that's supported by linux
Compile a kernel module or a new kernel (to support the USB module)
bridge utilities (maybe), bridge module in linux
a working wpa_supplicant binary for the new USB dongle
time
17EUR+ costs (Wifi USB dongle (starting around 12EUR) + USB OTG cable (5EUR))


In contrast to this the cheapest repeater-mode wifi router I found on Amazon was 18EUR and requires null additional fiddling (plus has a better antenna).