intro(4)ifnet(9)wlan(4)ieee80211(9)802.11n Demystified. Key considerations for n-abling the Wireless Enterprise: http://www.winncom.com/images/stories/Motorola_802.11nDEM_WP_v4_0209.pdf
What is an antenna chain and how do I figure out the correct setting for my router? (A post about 802.11n features): https://superuser.com/q/744065/442991
Nomadic Communications. 802.11n/ac: MIMO and Space Diversity: http://disi.unitn.it/locigno/didattica/NC/15-16/04_802.11n-ac_MIMO.pdf
FreeBSD Architecture Handbook. Chapter 9. Writing FreeBSD Device Drivers: https://www.freebsd.org/doc/en/books/arch-handbook/driverbasics.html
Getting started with kernel projects: Graphics/Getting started with kernel projects
How to write a Device Driver in FreeBSD: https://www.bsdcan.org/2006/papers/freebsd.device.driver.slides.pdf
iwn(4)iwm(4)indicates that I've not read it yet (and most often just scanned through)