When you have a secure network, the security settings of your Wi-Fi should be set to WPA TKIP or WPA2 CCMP, with the channel set to 802.11n or 802.11g/n. We also recommend to add the MAC address of your Fire TV to the list of permitted devices in your router settings.
When the frequency of your Wi-Fi network is set to 2.4 GHz, use one of the following channels: 1, 6, 7, 8 or 11. When it's set to 5 GHz, please use channel 36, 40, 44 or 48. If one of these suggested channels is activated, test one of the other recommended channels to avoid overlaps with other networks. When your router uses both frequencies at the same time, ensure that the network names (SSID) for the 2.4 GHz and the 5 GHz network are different.