  In the IEEE 802.11ax standard, a mode of operation called target wake time
(TWT) is introduced towards enabling deterministic scheduling in WLAN networks.
In the TWT mode, a group of stations (STAs) can negotiate with the access point
(AP) a periodically repeating time window, referred to as TWT Service Period
(TWT-SP), over which they are awake and outside which they sleep for saving
power. The offset from a common starting time to the first TWT-SP is referred
to as the TWT Offset (TWT-O) and the periodicity of TWT-SP is referred to as
the TWT Wake Interval (TWT-WI). In this work, we consider communication between
multiple STAs with heterogeneous traffic flows and an AP of an IEEE 802.11ax
network operating in the TWT mode. Our objective is to maximize a long-term
weighted average timely throughput across the STAs, where the instantaneous
timely throughput is defined as the number of packets delivered successfully
before their deadlines at a decision instant. To achieve this, we obtain
algorithms, composed of (i) an inner resource allocation (RA) routine that
allocates resource units (RUs) and transmit powers to STAs, and (ii) an outer
grouping routine that assigns STAs to (TWT-SP, TWT-O, TWT-WI) triplets. For
inner RA, we propose a near-optimal low-complexity algorithm using the
drift-plus-penalty (DPP) framework and we adopt a greedy algorithm as outer
grouping routine. Via numerical simulations, we observe that the proposed
algorithm, composed of a DPP based RA and a greedy grouping routine, performs
better than other competitive algorithms.
