Scheduled Trigger Frames: Enabling Worst-case Latency Bounds for Wi-Fi Industrial Use

The centralized nature of OFDMA (i.e., the AP coordinating uplink and downlink transmissions) introduced in IEEE 802.11ax provides the foundation towards deterministic transmissions in Wi-Fi. Yet, the problem of deterministic channel access and resource allocation still exists. This work presents two time-triggered resource allocation mechanisms which guarantee worst-case latencies for UL transmissions based on scheduled Trigger Frames in OFDMA-based Wi-Fi. These mechanisms support converged networks, i.e., periodic, aperiodic and best effort traffic transmitted on the same network infrastructure. Combined with a previously presented modification that allows the AP to reliably access the channel with a worst-case delay of 55 μs, we show that the proposed resource allocation strategies based on OFDMA can support worst-case latency bounds. Our simulation results show that we can provide a bounded latency of 10 ms for up to 18 STAs for periodic deterministic traffic and a bounded latency of 30 ms for up to 31 STAs for aperiodic deterministic traffic in a 20 MHz channel.