How to do connectionless UDP broadcast using Wi-Fi?
Yes, it's possible, but you must learn IEE802.11 Datagram very well. There are two ways, the first provides two-way data exchange, the second only broadcasts to receivers:


use the beacon frame and Probe request/response frame to send data from AP to clients without connection


Broadcasting Information in Variably Dense Environment Using Connectionless Data Exchange (CoLDE)

use the length field in the data frame to broadcast only. You should develop a communication protocol with the encoded length. The receiver should:


enter Promiscuous Model
switch channels
Provide a 100ms timer interrupt at least.