By Smart TV, do you mean controlling the TV with your smart phone? Or are you streaming television from your wifi like netflix to your TV?
In either case, there's probably something interfering between your point of origin and the television. Distance is the largest problem, other electrical and frequency noise from devices can also sometimes cause problems, if you're trying to do something from another room, your signal may have issues penetrating some types of walls. Wifi works 'BEST' with direct line of sight.
Try to best eleminate anything that could be interfering and reduce the distance between the two devices that you want to communicate. If you're doing anything related to Netflix and you're having poor wifi transmissions then you may want to move the router or directly connect via cable.