From yesterday, the wireless network coverage of my router has reduced due to unknown reasons. I require some assistance.

I am using the router inbuilt modem Smart RG SR505n ( https://www.acanac.com/hardware/smar...?package=fibre ) for the DSL connection. I am noticing the reduction in the range of the wireless network. I used to get the signals from my bedroom , but I can't see the signals now. I can get signals only in the hall where the router is placed and the kitchen which i nearby. There are no fluctuations in the speed while in the range. So, the internet issue can be ruled out.

Please help me solve this issue.