OpenWrt in default uses the reverse engineered b43 driver for BCM47xx and BCM53xx devices. With this driver only 802.11g is supported, but you can easily get wireless 802.11n working by installing the Broadcom open source brcmsmac driver. You can easily do make wireless N working by following below steps.
By running the following commands you will remove kmod-b43 and other unnecessary drivers, install kmod-brcmsmac and kmod-brcmutil package.
rm -f /etc/config/wireless
Comment out “option disabled 1” by adding “#” in front of it or delete it “option disabled 1” completely. After that, run the following command and you will see SSID named OpenWrt on your other devices.
*Note: brcmsmac does not support 40mhz (yet).