Enriching Multi-User OFDMA in Wi-Fi Networks with Frequency-Selective Channel Awareness

Recent studies on multi-user (MU) orthogonal frequency division multiple access (OFDMA) in IEEE 802.11ax high-light its advantages in terms of network efficiency under low traffic loads by mitigating channel access overheads. They also claim that MU-OFDMA becomes only susceptible to extra overheads under saturated traffic conditions, even leading to throughput loss compared to legacy single-user (SU) transmissions. Against this perspective, we notice that MU-OFDMA potentially enhances overall capacity of Wi-Fi networks by harnessing small resource units (RUs) flexibly over frequency-selective channels. Through measurements, we find that current RU allocation in commercial APs cannot achieve optimal performance due to the lack of consideration for detailed channel characteristics. We conceptualize a resource allocation strategy that accounts for distinct link quality across RUs, with its effectiveness verified through proof-of-concept study as well as extensive performance analysis. Based on these findings, we present ChORUS, a standard-compliant framework to realize optimal RU allocation by fully exploiting frequency-selective channels and their diversity among users. Our trace-driven simulation using standard channel models and real-world traces demonstrates that ChORUS significantly enhances throughput performance over SU, ensuring network capacity elevation through MU-OFDMA.