There's an unusual problem that I'm facing. I have ubuntu 12.04 installed with Broadcom STA Wireless driver installed. When I connect to wifi then other devices get ~1Mbps instead of 15Mbps. However, when I switch off my wifi or connect using ethernet cable, then other devices get desired ~15Mbps speed.
I also deactivated Broadcom STA Wireless driver and restarted the system, but it didn't help.