Enhanced backoff mechanism for uplink OFDMA in Wireless Local Area Network

Abstract

Uplink Orthogonal Frequency Division Multiple Access (OFDMA) Random Access (UORA) is a prominent feature within the IEEE 802.11ax protocol, widely employed in Wireless Local Area Networks (WLANs). UORA’s operation centers on two critical elements: OFDMA Backoff (OBO) and OFDMA Contention Windows (OCW). OBO involves the random selection of a positive integer and the decision to access available Resource Units (RUs) hinges entirely on this OBO value. In contrast, OCW represents a range spanning from a minimum to a maximum value, dictating the selection of the OBO counter value. The calculation of OCW is the responsibility of the Access Point (AP), which subsequently shares this value with all user stations in the network. Precisely determining the OCW value is pivotal, particularly in densely populated networks. Addressing this concern has prompted various experiments, often involving the introduction of additional overhead, signaling mechanisms or complex calculation methods. However, augmenting the UORA network with these elements can potentially compromise its performance, especially in highly populated environments. To mitigate these issues, a straightforward solution known as M-OBO has been proposed. The scheme arises when user required re-transmission of data due to collision or non-receipt of acknowledgment of already transmitted data. This re-transmission is subject to the calculation of the OCW value and a random selection of the OBO counter value. The calculated OCW value is correlate with its maximum (i.e. M-OBO = (OCWInc, OCWMax)) and randomly select M-OBO counter value as opposed to the standard approach, which uses the range (0, OCWInc) (i.e. OBO = (0, OCWInc)). The proposed scheme is based on the selection criteria of OBO counter value without demanding complex mathematical calculation or additional signaling overhead. The implementation of suggested scheme is align with standard IEEE 802.11ax UORA structure. This selected OBO counter value further reduced according to the standard UORA process and access RU. Simulation results provide validation for the proposed M-OBO scheme. The proposed M-OBO scheme enhanced 6 to 8 % channel efficiency in static network when compared with Efficient Backoff Scheme (E-OBO).