How To and Other References
Yocto Project images use systemd for startup management instead of Sys-V init. One implication of this change is that interfaces configured in /etc/network/interfaces are not always automatically brought up on boot. As a result, bringing up a WiFi interface on boot in systemd-based images cannot be done in the interfaces file.
These instructions will walk you through enabling WiFi from a terminal on a Yocto Project image.