I have a friend who works in the back office for a large nationwide organisation with retail outlets. The retail outlets offer free wifi which anyone can connect to. The problem is that she works on the first floor and her phone will only pickup the wifi as far as the stairwell but not at her desk.
I suggested maybe a wifi repeater/booster but don't know if it will work as there's no access to the router and one will have to manually set it up with the network name and password. The wifi network is open, no password is required but you do go to a landing page to accept the T&C's and register with your mobile number which a confirmation code is then sent to.