Performance analysis of A-MPDU and A-MSDU aggregation in IEEE 802.11n

With recent improvements in physical layer (PHY) techniques, the achievable capacity for wireless LANs (WLANs) has grown significantly. However, the overhead of IEEE 802.11 MAC layer has limited the actual throughput of a WLAN. A-MPDU aggregation suggested in IEEE 802.11n draft is a key enhancement reducing the protocol timing overheads that enables aggregation of several MAC-level protocol data units (MPDUs) into a single PHY protocol data unit (PPDU). Another aggregation scheme proposed in IEEE 802.11n is A-MSDU aggregation, which allows several MAC-level service data units (MSDUs) to be aggregated into a single MPDU. In this work we present a novel analytic model for estimating the performance of a 802.11n high throughput wireless link between a station and an Access Point (AP). We consider a 2 times 2 MIMO system and investigate how the MAC goodput under TCP and UDP traffic is affected by the aggregation size, packet error rate and PHY settings. Our results demonstrate that for UDP traffic, A-MPDU aggregation allows to achieve a high channel utilization of 95% in the ideal case while without aggregation the channel utilization is limited by just 33%. We also show that A-MPDU aggregation outperforms A-MSDU aggregation, whose performance considerably degrades for high packet error rates and high PHY rates.