A Modified Back off Mechanism for Uplink Orthogonal Frequency Division Multiple Access Random Access 802.11ax

Abstract

Uplink Orthogonal Frequency Division Multiple Access (OFDMA) Random Access (UORA) is prime trademark of IEEE 802.11ax protocol and meritoriously used in Wireless Local Area Network (WLANs). UORA working is based on two prime factors OFDMA Backoff (OBO) and OFDMA Contention Windows (OCW). OBO is a randomly selected positive integer value and decision for accessing available Resource Unit (RU) is totally based in OBO, however, OCW is a range (Minimum to Maximum) value used to select OBO counter value. The calculation of OCW value is the responsibility of Access Point (AP) and further share with all user station available in network. The OCW value calculation is very decisive specially in over populated network and to overcome this issue, a number of experience has been carried out with the addition of overhead, additional signaling mechanism or extensive calculation methods. By adding additional burden on UORA network, the performance of UORA network will be compromised, especially in densely populated network. The proposed scheme is very simple and associated with OBO with the name Modified OBO (M-OBO). The scheme entail in UORA process in re-transmission phase, once the transmitted packet is failed to deliver then the user station have to re-transmitted it again after due calculation of OCW value and randomly selection of OBO counter value. The randomly selection of OBO counter value after collision is between new incremented OCWInc value and OCWMax (i.e. OBO = (OCWInc, OCWMax)) instead of 0 and OCWInc (i.e. OBO = (0, OCWInc)). The simulation results validate the proposed M-OBO scheme and enhanced channel efficiency when it is compared to the Standard UORA scheme (UORA Std) and Efficient Backoff Scheme (E-OBO).