I get 82% from my wireless router and that runs just fine so your signal strength is not your issue. Having one bar while playing is more of an indication of what your connection is to the server your playing on and that can vary depending on where the sever is located and or the connection to the host of the game.
What do you have for internet and have you done an internet speed test?
ok i done speed test on uswitch.com and i got download speed of 1.4 i know its not very good but thats the average for my area unfortunately. but this shouldnt be a problem when i played on xbox it worked perfectly and nothing has been changed other than switching to ps3
1.4? :[ ouch man. i remember those days. yeah you are going to need a better connection man. bad days... if memory recalls, i was lagging at 4 mb
do you have any open ports on your router that can be closed? That can help with speeds if you have ports that do not need to be open. There are little things that can be done to improve your speed but your not going to see a big improvement overall w/ out a faster internet connection. Did you do the speed test I linked?