Since the IEEE 802.15.4-2015 standard is released a new frame format for 802.15.4, tagged as frame version 2, is defined. This is, e.g., required for the TSCH mode of 802.15.4 (or at least for 6TiSCH). Unfortunately, to the best of my knowledge, this frame version is not supported by any transceiver yet, so we would have to implement it in software. Since, AFAIK, the 2015 version of the standard is still not available for free, one might look into the 802.15.4e-2011 amendment.