Previously I installed Ububtu 15.04 on my Raspberry Pi 2 that has Wi-Fi connectivity provided by Edimax EW-7811Un:
$ lsusb
Bus 001 Device 005: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]
One annoyance is that the Wi-Fi will be off automatically after no network traffic for a while.
Today I learned from Rasberry Pi Forum that the power management feature can be turned off by adding /etc/modprobe.d/8192cu.conf with the following content:
# Disable power management
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0