# Transmission Delay-Based Uplink Multi-User Scheduling in IEEE 802.11 ax Networks +
Footnote †: This paper is an extended version of our paper published in IEEE International Conference on Consumer Electronics (ICCE), Las Vegas, NV, USA, 4-6 January 2020. [PERSON]  
1 Samsung Electronics, Suwon 16677, Korea; [EMAIL_ADDRESS]  
[PERSON]  
2 School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea; [EMAIL_ADDRESS]  
[PERSON]  
3 Department of Computer Engineering, Chosun University, Gwangju 61452, Korea; [EMAIL_ADDRESS]  
[PERSON]  
3 Department of Computer Engineering, Chosun University, Gwangju 61452, Korea; [EMAIL_ADDRESS]  
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uplink data to the AP [4]. With the proper selection of uplink stations, the channel can be efficiently utilized in data transmissions in a network with many stations rather to avoid excessive competition. Although centralized scheduling at the AP increases network throughput performance compared to the fully random access-based channel competition of densely deployed stations, scheduling is still an important issue to increase channel use and spectral efficiency in a Wi-Fi network. An AP allocates frequency-time resource units to stations trying to transmit uplink data, and the number of resource units allocated for each station may be different from each other. For example, by allocating more frequency resources to stations, the stations can transmit much amount of data for the same time. Hence, if stations with different amounts of data are selected for uplink multi-user transmissions, an AP may allocate many resources to stations with a large amount of data to align uplink transmissions to increase channel use. However, if the available resources are limited or in a scenario that multiple stations are supported by multi-user beamforming on a single radio frequency band, transmission delays of selected stations for uplink multi-user transmissions become important to increase channel use. When the transmission delays of scheduled stations are significantly different, the uplink channels during the time between triggering message and block ACK are underutilized, while non-scheduled stations are waiting for transmission opportunities. Inefficient station scheduling without considering the transmission delays of stations degrades channel use, and a delay-considered scheduling method for uplink multi-user transmission is required to improve service performance. In this paper, we study the open issue regarding the multi-user scheduling process in IEEE 802.11 ax networks and propose a transmission delay-based uplink multi-user scheduling method. The proposed scheduling method consists of two parts: station clustering and scheduling of clusters. In the first part, the proposed method creates clusters of stations trying to participate in the uplink transmission process. The clustering is based on the expected transmission delays of stations, and stations with similar transmission delays are clustered together for simultaneous uplink transmission. With transmission delay-based clustering, communication channels between uplink multi-user transmissions from the stations and block ACK transmissions from the AP can be efficiently utilized. Increasing the channel use of the transmission delay-based clustering approach enhances the network throughput performance of the uplink multi-user transmission process specified in the IEEE 802.11 ax. In the second part, the proposed method selects the cluster, and stations in the selected cluster are scheduled to transmit uplinks.