If I understand you correctly, you want to improve the signal strength of your wifi capability. There are two ways to do that increase the power of the transmitter and get a bigger antenna.
Increasing power on a tablet's internal wifi is almost impossible, but check your software and see if yours is at max power (some wifi implementations set the power at 50% for a default setting). If you're willing to go with a PCMCIA alternative or try an aftermarket internal mini-PCI card, Engenious/Senao has a wifi cards with outstanding power ~200/400/600mW depending on how much you want to spend. These are outstanding systems I've used for years. Yet that's only half of the equation.
More power doesn't equal better reception. So just because you can transmit for a mile if the system on the other end can't you're still screwed so a bigger antenna is required. Most Wifi access points (AP) come stock with a 0dB or 2dB antenna that transmits reliably about 4-600feet. If you were to upgrade to an 8dB antenna that range would be extended threefold at least depending on location. If you can't upgrade the AP, adding an external antenna to your tablet can increase you range just as significantly. Some PCMCIA cards com with connectors for external antennae.
In my own opinion you will make out better getting a good external antenna because that will improve both transmit and receive.