tion for an MS, the BS adds the MS to an existing group. If the existing groups are not appropriate for the MS, or if no groups currently exist, the BS may form a new group. The BS signals group configuration information via Group Configuration MAC control message, which includes the Group ID of the group (to which the MS is added) and the assigned User Bitmap Index, to the MS. Once the MS is added to the group, the resources used for initial transmission of the HARQ data burst may be allocated as part of the group until the MS is deleted from the group. On receiving Group Configuration MAC control message, the MS obtains the required information to interpret the assigned MIMO mode, HARQ burst size, and resource size from the bitmaps in the corresponding MAC management message. Once the MS receives a Group Configuration MAC control message, it monitors its allocations until it is deleted from the designated group. The BS may delete an MS from a group based on either or both of the following conditions: (1) all the GRA-enabled connections are terminated and (2) the MIMO mode/nominal MCS/HARQ burst size suitable for the MS no longer belongs to the MIMO Mode Set/nominal MCS set/HARQ burst size set corresponding to the group. The BS may delete a number of mobile stations from a group in a subframe. The deletion information is signaled via the Group Resource Allocation MAC control message. The de-allocation information is sent by listing De-allocated MS Index. The De-allocated MS Index is determined based on the order of the MS among inactive mobile stations in the user bitmap. The length of the De- allocated MS Index is determined according to the number of inactive users. Figure 6-24 shows an example de-allocation with de-allocated MS index. The deletion of an MS takes effect from the subframe in which the deletion information is sent to the MS. After sending the deletion information, the BS will for an ACK from the MS. The BS does allocate the corresponding bitmap position to another MS until an ACK for deletion is