Yes the Wi-Fi can be an issue @Zheng49
Some wire free cameras connect directly to the Wi-Fi signal and others use a hub. The TP-link has a hub that you physically plug into the modem, and the communication is then between the camera(s) and the hub (so the actual camera doesn't connect to the Wi-Fi). @Rose2635 it may be good to read up a bit about hub vs. no hub, maybe it helps to identify what's been bothering you with the cameras that you've tried so far. Or hopefully we have a camera expert around who knows more?