An OFDMA MAC Protocol Aggregating Variable Length Data in the Next IEEE 802.11ax Standard Mohand MOKTEFI, Mohand YAZID, Louiza BOUALLOUCHE-MEDJKOUNE and Wissam BENLALA LaMOS Research Unit, Faculty of Exact Sciences, University of Bejaia, 06000 Bejaia, Algeria Emails: moktefi.mohand@gmail.com, yazid.mohand@gmail.com, louiza medjkoune@yahoo.fr, wissambenlala@gmail.com Abstract—A new standard of the IEEE 802.11 standard is behind the scenes whose ratification is planned for the end of the current year (2019). It is the 802.11ax or HEW (High Efficiency Wireless local area network) standard dedicated to the future wireless networks. This standard promised better efficiency and throughput in more difficult use cases (dense environments) by exploiting pre-existing physical and MAC (Medium Access Control) capabilities and introducing new concepts, such as: OFDMA (Orthogonal Frequency-Division Multiple Access), 1024- QAM (1024-Quadrature Amplitude Modulation) modulation or- der, FD (Full-Duplex) communications and spatial reuse. The new OFDMA modulation technology divides the transmission channel into sub-carrier groups (known as: RUs for Ressources Units) to which up to 9 users can simultaneously access a 20 MHz channel. In order to improve the user data rate in dense areas, an OFDMA-based MAC access method is proposed in this paper by enabling the principle of aggregating frames of variable lengths while ensuring synchronization. Our proposal is followed by simulation results to demonstrate the improvement in throughput that it offers. Keywords—IEEE 802.11ax HEW, OFDMA, Medium Access, Variable Length Data, Aggregation, Simulation and validation. I. I NTRODUCTION Wireless technology has become widespread on virtually all user devices, as well as any inhabited deployment (homes, parks, airports, stadiums, etc.) since its arrival on the industrial market. However, users who are increasingly demanding, the number of connections and bandwidth intensive applications are growing. This increase will threaten the technology in its future growth to no longer serve these customers effectively. In addition to increased reliability, future networks will need to offer greater wireless capacity. This is where the sixth generation of Wi-Fi (Wireless-Fidelity) comes in. It’s the IEEE 802.11ax standard. The new 802.11ax standard, also known as HEW (High Efficiency Wireless local area network), has the ambitious goal of quadrupling average throughput per user in dense areas; it is an evolutionary improvement of the 802.11ac standard. The standard has submitted three preliminary drafts 802.11ax since its launch in May 2014, namely D1.0, D2.0 and D3.0 and provides for finalization by the end of the current year (2019) [1]. While the new 802.11ax standard is designed to maximize network efficiency, it also provides a better experience for traditional wireless LANs and more predictable performance for advanced applications, such as: 4K video, Ultra HD, wireless office, Internet of Things (IoT), etc. IEEE 802.11ax will achieve its goals taking into account the following key features: Orthogonal Frequency-Division Multi- ple Access (OFDMA), adoption of Full-Duplex transmissions, higher modulation rate 1024-QAM (1024-Quadrature Ampli- tude Modulation),Down-Link/Up-Link Multi-User Multiple- Input Multiple-Output (DL/UL MU MIMO) and spatial reuse. The implementation of these techniques poses many new challenges to the scientists who are working to achieve. Because the old Wi-Fi standards do not support these new features. In this work, we are interested to efficiently manage the OFDMA MAC communications in the next generation of IEEE 802.11ax WLANs. In fact, various methods of access to the medium based on OFDMA have been proposed by the scientific community, each aimed at optimizing the use of subcarriers and improving the transmission rate in a dense environment. The remainder of this paper is outlined as follows. Section II introduces the OFDMA and OFDM technologies. Section III introduces the main research works about multi-user MAC protocols based on OFDMA technology. In Section IV, we describe our OFDMA MAC protocol. Simulation results are given in Section VI, followed by Section VII which concludes this paper. II. BACKGROUND The main change in the 802.11ax standard is the intro- duction of OFDMA technology in both downlink and uplink transmissions. OFDMA makes it possible to multiplex more users in the same bandwidth. This is possible by allocating a contiguous subset of the sub-carriers (minimum 26, maximum 996) of the available spectrum for each user. This means that the existing 802.11ax channels (20, 40, 80 and 160 MHz wide) are divided into narrower subchannels with a pre- defined number of subcarriers. The allocated amount is referred to as the Resource Unit (RU) and it is allocated to users based on channel conditions and service requirements. The Figure 1 illustrates the allocation of RUs by the AP (Access Point). By using OFDM the entire channel is allocated to a single user, however using OFDMA several users can transmit simultaneously. The basic principle of OFDM and OFDMA is illustrated by Figure 2. 242 tones 26 26 26 26 26 26 26 26 26 52 52 26 106 106 52 52 26 Fig. 1. Configuration of RUs on a 20 MHz band [2].