Before revision:  In this new framework, it has been decided that the transmission for all the users in an multi-user OFDMA should end end at the same time , and the users with insufficient data should transmit null data (i.e. padding) to fill the duration.
After revision:  In this new framework, it has been decided that the transmission for all the users in an multi-user OFDMA should end end at the same time . In order to realize that condition, the users with insufficient data should transmit null data (i.e. padding) to fill the duration.