Some articles on acwmin:

IEEE 802.11e-2005 - 802.11e MAC Protocol Operation - Enhanced Distributed Channel Access (EDCA)
... The CWmin and CWmax values are calculated from aCWmin and aCWmax values, respectively, that are defined for each physical layer supported by 802.11e ... of contention window boundaries AC CWmin CWmax Background (AC_BK) aCWmin aCWmax Best Effort (AC_BE) aCWmin aCWmax Video (AC_VI) (aCWmin+1)/2-1 aCWmin Voice (AC_VO) (aCWmin+1)/4-1 (aCWmin+1)/2-1 ...