802.11ac Frame Aggregation is Bottlenecked
Muhammad Inamullah, Bhaskaran Raman · 2019
Frame aggregation improves performance of 802.11 networks by eliminating many overheads the single-frame transmissions incur. An originator builds and sends an aggregate (A-MPDU) of packets (MPDUs or subframes) from a window of 64 sequence numbers, and a block ACK then acknowledges the same window. The mechanism works fine till there are no packet losses. With the advent of packet losses (and their subsequent reporting by the block ACK), holes appear in the originator's aggregation window. An A-MPDU constructed immediately after by the originator then becomes smaller in size due to these holes. We discuss the effect of such inadvertent shortening of transmitted A-MPDUs on the performance of WLAN. We propose modifications to the block ACK and aggregation mechanisms, and show through our ns-3 simulations that the change improves the network throughput by up to 20% in hidden node scenario in simple basic service sets (BSSs) consisting of 32 to 48 STAs. Our analysis shows that improvement in the worst case throughput can be as high as 400% for the highest VHT MCS indexes with our proposed modifications.