IEEE 802.11 standard develops novel medium access control (MAC) protocol called orthogonal frequency division multiple access (OFDMA) in IEEE 802.11ax. The OFDMA divides channel into many resource unit (RUs). The nodes transmit the data packet using the RUs at the same time in the OFDMA MAC protocol. Especially, the random access (RA) can use in uplink. The nodes generate OFDMA backoff (OBO) counter in OFDMA contention windows (OCW) value to access the channel. However, the OCW value is fixed value. If the number of nodes increases, collision rate increase too. As a result, the network performance decrease. Thus, if the access point (AP) can control OCW value according to exact the number of nodes, the network performance increases. However, it is difficult to the AP estimates exact the number of nodes without overhead. Therefore, we propose the OCW control algorithm without overhead. The AP estimates the number of nodes using states of RUs and controls OCW value according to the estimated nodes. Simulation results show that the performance of proposed algorithm outperforms that of the conventional algorithm. Also, the performance of the proposed algorithm is almost same that of the ideal algorithm.
ACKNOWLEDGMENT This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2021R1A4A1030775), and by the MSIT(Ministry of Science and ICT), Korea, under the ITRC(Information Technology Research Center) support program(IITP-2022-2018-0-01424) supervised by the IITP(Institute for Information & communications Technology Promotion).
