Efficiency analysis of burst transmissions with block ACK in contention-based 802.11e WLANs

The channel utilization efficiency of the standard 802.11 networks is severely compromised when high data transmission rates are employed, since physical layer headers and control frames are transmitted at low rate, thus wasting more channel time, proportionally. The extensions defined in the emerging 802.11e for quality-of-service (QoS) provisioning include some new mechanisms developed in order to improve the efficiency. Those include data transmission bursting (referred to as TXOP operation) and acknowledgment aggregation (referred to as block ACK). These two features allow it to offer new data transmission services, in which the data delivery and acknowledgment unit is not a single frame, but a block of frames. In this paper, we evaluate the performance of these operations for both basic and RTS/CTS access cases. We quantify how the data bursting and block ACK mechanisms can affect the system efficiency for different environments, and derive the maximum achievable throughput. We also discuss the operating conditions at which the switch from one channel utilization method to another is desired.