Answer by Jeremy31 for How to disable wireless N on Centos/RHEL 7?

To disable Wireless N in the module

echo "options iwlwifi 11n_disable=1" | sudo tee /etc/modprobe.d/iwl-opt.conf

Reboot

But I would suggest enabling Wireless N on the router and trying this option

echo "options iwlwifi 11n_disable=8" | sudo tee /etc/modprobe.d/iwl-opt.conf

This command enables aggressive TX on Wireless-N and fixes a lot of issues