If the tablet is initially able to connect to the Wi-Fi network, but loses connection, this can be due to a number of factors. Firstly, check that the tablet is within operational range of the Wi-Fi router. For 802.11n routers, the range is around 250m, and for 802.11b/g routers the range is approximately 140m. It is important to note, however, that these ranges are often heavily reduced in real-world scenarios, and this reduction can be brought about by a number of factors, such as:
Interior and exterior walls, particularly those that may contain pipes or steel reinforcement.
Adverse environmental conditions, e.g. Electrical storms.
Other Wi-Fi routers operating on the same channel
Other devices operating in the 2.4GHz/5GHz frequency band.
In order to eliminate these factors as a possible cause, it is necessary to test the connection under a variety of conditions. To make sure that the signal is not being blocked by walls, connect your tablet to the router, and monitor the state of the connection while the tablet is physically next to the router. If the connection does not drop, then this indicates the cause is related to the blocking of the signal by a physical barrier.