Wireless connection slow when back from sleep.

I have a macbook 2.4ghz 2gb or ram and I'm having issues with my wireless connection.
It works perfectly fine except when I come back from the macbook being asleep. When it wakes it's very slow and the only way to get it back to normal is to turn airport off and on and reconnect.
Is there a reason for this? Also, can I set it to turn off airport when I sleep so if I have to turn it back on anyways it saves some time?

A problem I've seen with both my first MacBook and now my new MacBook is that the wireless connection drops while on battery power.

I'm not the only one who has seen this. I have read in many forums that many people have the same problem. It seems to be related to particular wireless routers, and Apple recommends buying one of their AirPort products to fix the problem, but the problem only occurs on battery power, so it seems to be related to how OS X deals with power management.