I used the common Wifi for all rooms and put the router in the living room, but the signal transmission is quite weak if I work in my classroom. However, I cannot install another Wifi network. What do I have to do to make sure all rooms can use strong wifi?
… A common setup for large spaces, or spaces where high density or high performance is needed, is to have multiple access points providing wifi access for what appears as a single WiFi network.
The client device will just pick the physical wireless access point to talk to depending on which one has the strongest signal.
Signal strength is limited by regulation, different channels have different regulatory limits (e.g. if you’re using 5GHz try changing to channel 100/5500MHz, or try 149 if you’re in the US, avoid 149 if you’re in Europe).
Signal strength also degrades with distance and obstacles… e.g. moving your current wifi gateway/router to a different part of the room or outside of a cabinet or to not be behind the TV for example might get you a bit better signal.
Also, if the device has external antennas changing the angle on them so they’re pointing in different directions (it won’t do miracles but might help a little which may be enough for you???)
Tell us more about your ISP, what speeds are you hoping to get?
Next, how strong is the signal reported next to your router, and how strong is it in the classroom?
Can you get the readouts in decibels using an app like “wifi analyzer” on Android?
Knowing the two numbers can tell us how much “stuff” you have in between, and whether there’s any hope in getting the speeds you want? (folks around here can look stuff up based on that info).