MMRU-ALLOC: An Optimal Resource Allocation Framework for OFDMA in IEEE 802.11ax

Abstract

IEEE 802.11ax introduces OFDMA (Orthogonal Frequency Division Multiple Access) that allows multiple users to transmit or receive frames concurrently. The OFDMA transmission duration is decided by the client with maximum transmission duration. We focus on minimizing the maximum transmission duration. The standard restricts assignment of at max one RU to a client and provides a specific way of splitting the channel into smaller RUs. In this paper, we come up with a generic framework, MMRU-Alloc (Min Max Resource Unit Allocation) to allocate RUs to clients under the given constraints for a single OFDMA transmission. The framework allows one to define any non-negative cost function such as data transmission time or the padding length required for synchronized end time of all clients for a client-RU pair and we believe this can capture a wide variety of scenarios. We design provably efficient and optimal algorithms for this general problem. We demonstrate the applicability of our framework for two specific problems pertaining to transmission of one OFDMA frame. (1) Minimizing the transmission duration of one OFDMA frame for a given set of clients. (2) Minimizing the maximum padding length required by any client to ensure synchronized end time. We implemented (1) in NS-3 and evaluated its performance. We compare it with two popular scheduling and resource allocation algorithms: Max Rate (MR) and Proportional Fairness (PF). We find that it outperforms both MR and PF by upto 91.3% in terms of frame transmission time and upto 91.1% terms of throughput achieved.