Frame Aggregation in 802.11ac: Need for Modified Block ACK

Frame aggregation in 802.11n and ac gives higher throughputs because larger aggregates reduce inter-frame timing overheads. When aggregate (A-MPDU) sizes are forced to be smaller the throughput benefit dwindles. During normal operation the A-MPDU sizes fall from the maximum possible due to the loss of individual constituent subframes. In the worst case, the size can be as low as a single subframe. We show that, compared to the worst case, full-sized A-MPDUs can give up to 400% higher throughput for the highest MCS indexes of 802.11ac. In this paper, we explain how fixed block ACK size coupled with subframe retransmission are the main causes of reduction in A-MPDU size. We present the modification in the block ACK mechanism needed to attain larger sizes of aggregates even in the presence of subframe losses.