Many wireless routers and wireless access points offer either a "bridge" mode or a "repeater" mode, both of which perform a similar function. Wireless routers, access points, and bridges are available that utilize each of the commonly used wireless frequencies (used in the wireless-B, wireless-A (and -G), and wireless-N standards). The frequency bands for these wireless standards can be used license-free in most countries.
Unless a user has a wireless card with a PXE-ROM chip built into it, it is not easy to directly netboot over a wireless connection. BIOS-based PXE algorithms usually only search for a wired NIC to be used in a PXE netboot.
It is possible to connect a "wireless bridge" (i.e. a wireless router or access point set to the "bridge" mode) to the wired NIC of a PC. The PC then netboots through the wired ethernet NIC as usual, but the data is then transmitted from the NIC to the wireless AP/router connected to it and then wirelessly "across the bridge" to a central wireless access point/router.
This solution works reasonably well but requires two wireless access points/routers (one on each side of the "bridge") making it a more expensive solution. It is sometimes, however, easier than running extra ethernet cables throughout a building.