Reset Wi-Fi, mobile data communication, and Bluetooth from [Settings] → [System] → [Reset options]. Resetting may improve the connection; however, it will also initialize the following settings, so they will all need to be reconfigured.
Reset your Network Settings from [Settings] → [General] → [Transfer or Reset iPhone] → [Reset]. Resetting may improve the connection; however, it will also initialize the following settings, so they will all need to be reconfigured.