Performance Analysis of Channel-Dependent Rate Adaptation for OFDMA transmission in IEEE 802.11ax WLANs

This paper investigates the application of the Received Bit Information Rate (RBIR) mapping technique to abstract the physical (PHY) layer in performing rate adaptation for IEEE WLAN 802.11ax systems. We observe that the modulation and coding scheme (MCS) obtained by PHY Layer Abstraction (PLA) is too conservative when used in practice. Motivated by this observation, we propose Hybrid Channel-Dependent Rate Adaptation (HCDRA) to map the measured SNR to an MCS value that maximizes the throughput while keeping the average Packet Error Rate (PER) below a threshold value. We evaluate HCDRA for a user on a Resource Unit (RU) in the OFDMA mode of transmission. The proposal of channel-dependent rate adaptation in OFDMA mode of transmission for IEEE WLAN 802.11ax is novel to the best of our knowledge. We implement and evaluate HCDRA in the standard-compliant MATLAB WLAN Toolbox and compare its performance with other well-known rate adaptation algorithms such as Automatic Rate Fallback (ARF), Adaptive ARF (AARF), Minstrel, and MutFed. More realistic situations with PHY impairments such as carrier frequency offset (CFO) and symbol timing offset are considered in all our simulations. Results show that HCDRA has better throughput performance compared to the four other algorithms we have evaluated. HCDRA is eminently implementable without any modification in the standard frames, and hence it is suitable for practical deployment.