Performance analysis of greedy fast-shift block acknowledgement for high-throughput WLANs

The techniques of frame aggregation and block acknowledgement (ACK) are utilized in the IEEE 802.11n standard for achieving high throughput performance from the medium access control perspective. Conventional greedy scheme for block ACK adopts the transmitterdefined starting sequence number (SSN) to construct the ACK window for recognizing the correctness of data packets. However, there exists correctly received packets that lie outside of the ACK window which will unavoidably be retransmitted by adopting the conventional scheme. In this paper, a greedy fast-shift (GFS) block ACK mechanism is proposed to provide the receiver-defined SSN, which can both implicitly acknowledge the correctly received packets before the SSN and explicitly identify the correctness information for the packets after the SSN. In order to evaluate the effectiveness of the GFS scheme, the analytical models for these two mechanisms are proposed based on the window utilization. Compared to the conventional greedy scheme, it is observed from the simulation results that the proposed GFS method can provide better performance owing to its fast-shift behavior on ACK window.