To answer your question from purely an rf prospective, yes, such items exist. You would need a bi-directional amplifier with an operating range in the 2.4 GHz band, as well as low pass filters on the transmit side to handle any higher order effects.

However, this amplifier would need to have the same input/output impedance to ensure that the SWR was low and therefore most of the power (S21) is getting to the amp and then to the antenna. With this in mind, as @Kartman suggested, have you looked into the input impedance of the WiFi antenna? If the antenna is made for, say 75 Ohms, and the WiFi AP is expecting 50 Ohms, then a serious amount of loss is going to be occurring. If you have something like a VNA, you can measure this to be sure that both the AP and Antenna match, as well as look at how lossy the coax is if it is separate. Also, if you are on the 9th floor, is the antenna outside (such as on a deck)? This can make a huge difference based on the attenuation of things like concrete, steel, or brick.

As for the legal implications, in the US at least, the FCC limits everything you do RF. It is there job. For the US, the maximum RF output power is 30dBm or 1 Watt. Some WiFi APs have this as an option, so it could be possible that to save power for normal applications the AP only runs at 1/2 the possible power. So you could check the settings for your manufacture to see.

Finally, from a distributed systems prospective, WiFi tends to be expanded by WiFi repeaters or via cabled connections. The repeater option is slow but cheap, as it introduces latency for each hop back to the main, and can cause other issues if the mesh becomes large (see Aloha Protocol for more details). The best way to do this is to have an AP at least on each floor of a building, and bring all of those back to a switch and manage them with a common controller (think DHCP, DNS, etc. being consistent so you can move through the building as if one there is one connection).

Your configuration was not explained well, so I am not sure if the building is the provider or ISP or ? If you could maybe explain this better it would help with options, as well as your country of origin to look into maximum power restrictions.

To answer your question from purely an RF perspective, yes, such items exist. You would need a bi-directional amplifier with an operating range in the 2.4 GHz band, as well as low pass filters on the transmit side to handle any higher order effects.

However, this amplifier would need to have the same input/output impedance to ensure that the SWR was low and therefore most of the power (S21) is getting to the amplifier and then to the antenna. With this in mind, as @Kartman suggested, have you looked into the input impedance of the WiFi antenna? If the antenna is made for, say 75 ohms, and the WiFi AP is expecting 50 ohms, then a serious amount of loss is going to be occurring. If you have something like a VNA, you can measure this to be sure that both the AP and antenna match, as well as look at how lossy the coax is if it is separate. Also, if you are on the 9th floor, is the antenna outside (such as on a deck?) This can make a huge difference based on the attenuation of things like concrete, steel, or brick.

As for the legal implications, in the US at least, the FCC limits everything you do RF. It is their job. For the US, the maximum RF output power is 30dBm or 1 watt. Some WiFi APs have this as an option, so it could be possible that to save power for normal applications the AP only runs at 1/2 the possible power. You could check the settings for your manufacture to see.

Finally, from a distributed systems prospective, WiFi tends to be expanded by WiFi repeaters or via cabled connections. The repeater option is slow but cheap, as it introduces latency for each hop back to the main, and can cause other issues if the mesh becomes large (see Aloha Protocol for more details.) The best way to do this is to have an AP at least on each floor of a building, and bring all of those back to a switch and manage them with a common controller (think DHCP, DNS, etc. being consistent so you can move through the building.)

Your configuration was not explained well, so I am not sure if the building is the provider or ISP or something else. If you could maybe explain this better it would help with options, as well as your country of origin to look into maximum power restrictions.