这是我第一次使用 Ubuntu。我安装了 ubuntu 14.4，但 WiFi 无法使用。我不知道如何激活它们。我该怎么办？
lspci -knn | grep Net -A2 && rfkill list：
02:00.0 network controller [0280]: Broadcom corporation BCM43142 802.11b/g/n [14e4:4356](rev 01)
subsystem: lenovo Device [17aa:0621]
kernel driver in use:bcma-pci-bridge
rfkill list：
02:00.0 network controller [0280]: Broadcom corporation BCM43142 802.11b/g/n [14e4:4356](rev 01) subsystem: lenovo Device [17aa:0621]
0:ideapad_wlan: wireless LAN
soft blocked: no
hard Blocked: no
1: ideapad_blutooth: Bluetooth
spft blocked:yes
hard blocked:no
iwconfig：
eth0 no wireless extensions
lo no wireless extensions