Uplink Access Protocol in IEEE 802.11ac

Abstract

The IEEE 802.11ac amendment enhances WLAN throughput by exploiting the spatial diversity of the antennas in a multi-user multi-input multi-output downlink transmission. Still, network resources remain under-utilized in uplink transmission due to single-user communication. In this paper, we propose an access point-controlled MAC protocol (A-MAC) that enables simultaneous transmissions from multiple STAs in uplink. The protocol uses the EDCA channel access technique to initiate multi-user transmission and the OFDMA method to transmit multiple RTSs simultaneously. It also introduces the explicit channel sounding technique by using dedicated OFDM subcarrier blocks for each user. Performance measurement shows that network throughput of the A-MAC is 150% higher than that of a single uplink transmission, thanks to the availability of concurrent multiple RTS transmissions in the uplink. The proposed protocol shortens the backoff time by up to 50% for all traffic categories due to concurrent multiple transmissions and thus enhances the battery life of the nodes. We observe that although the smaller backoff window of high-priority traffic category enhances the network throughput, higher intensity of high-priority traffic drives the network faster to saturation. Furthermore, better network stability and fairness among different traffic categories can be achieved when the dominant traffic has low priority.

Performance analysis of IEEE 802.11ax heterogeneous network in the presence of hidden terminals

“…as discussed in [6]. Finally, probability of successful transmission in the presence of hidden nodes can be expressed as γ k,h = γ k f ncoll , where γ k is the probability of successful transmission but without any hidden node.…”

“…When a non-HE STA wins the contention, a single user transmission will take place. This limitation has been removed in a recently proposed multi-user access protocol for uplink [6] which allows multiple legacy STAs to transmit in uplink direction using MU-MIMO technique.…”