This value determines the final contention resolution
back-off window used by the SU when attempting to
transmit data packets. The SU randomly selects a
number within the back-off window defined by this
parameter then defers this number of contention
transmit opportunities before actually attempting the
transmission. Expressed as a power of 2. A value of 16
at the HE indicates that a proprietary adaptive retry
mechanism is to be used.