Towards a Hybrid Access to Resource Units in Multi-user OFDMA Communications

Abstract

Orthogonal Frequency Division Multiple Access (OFDMA) is one of the main features introduced in the new IEEE 802.11ax standard, in order to enable Multi-User (MU) communications in the next generation of High Efficiency (HE) Wireless Local Area Networks (WLANs). The basic principle is dividing a single 20 MHz transmission channel into multiple sub-channels called Resource Units (RUs), and allocating them to multiple stations for Down-Link (DL) and Up-Link (UL) simultaneous transmissions. To manage MU communications in the UL direction, it is necessary first to collect UL needs of network stations. For this end, there are two access modes to RUs: scheduling access and random access. In scheduling mode, all stations are scrutinized either they have or not UL data. In random mode, the stations having UL data share the same RUs to send their UL requests. In this paper, we propose a Hybrid Access protocol to RUs (HA-RUs protocol) in WLAN networks-based OFDMA MU transmission technique. The goal is combining the advantages of scheduling and random access modes while avoiding their disadvantages. The main idea is privileging, in the current communication cycle, the stations receiving DL data to send in a deterministic manner their UL requests. The other stations having UL data will use random mode to express their UL needs. The effectiveness of the HA-RUs protocol has been evaluated and compared with OHCA protocol. The simulation results prove that HA-RUs protocol enhances the success ratio of UL requests, the UL service rate, and the UL throughput.