Do you know, ubuntu power management software making your wifi speed slow. Yes what you heard is true. So Here I found a way to fix this. Follow these bellow steps, and Enjoy the speed of your internet..
1. goto /etc/pm/power.d dir
cd /etc/pm/power.d
2. create a script file to execute some commands
sudo vim wireless
3. copy following text to that file
#!/bin/sh
iwconfig eth0 power off
