IEEE 802.11ax introduces orthogonal frequency division multiple access (OFDMA) to WiFi to support concurrent transmissions to a larger number of users. As bandwidth continues to grow, WiFi channels exhibit increased frequency selectivity, which poses new challenges for MU-MIMO user selection: the optimal user set varies across frequency and is interleaved over subbands (called resource units, or RUs). This frequency selectivity, coupled with the complex subband allocation pattern, renders conventional narrowband user selection algorithms inefficient for 802.11ax. In this paper, we propose \emph{ProxySelect}, a scalable and frequency selectivity-aware user scheduling algorithm for joint OFDMA and MU-MIMO usage in 802.11ax under zero-forcing beamforming (ZFBF). The scheduling task is formulated as an integer linear program (ILP) with binary variables indicating user (group)-RU associations, and linear constraints ensuring standard compatibility. To reduce complexity, we introduce a novel proxy rate--a function of individual channel strengths and their correlations--that approximates the ZFBF rate without requiring cubic-complexity matrix inversion. Additionally, we develop a sampling-based candidate group generation scheme that selects up to $T$ near-orthogonal user groups for each RU, thereby bounding the ILP size and ensuring scalability. Simulations using realistic ray-tracing-based channel models show that ProxySelect achieves near-optimal rate performance with significantly lower complexity.

翻译：IEEE 802.11ax将正交频分多址接入（OFDMA）技术引入WiFi，以支持面向更多用户的并发传输。随着信道带宽持续增长，WiFi信道呈现出更强的频率选择性，这为MU-MIMO用户选择带来了新的挑战：最优用户集合随频率变化，并在子带（称为资源单元，RU）间交织分布。这种频率选择性，结合复杂的子带分配模式，使得传统的窄带用户选择算法在802.11ax中效率低下。本文提出\textit{ProxySelect}——一种面向802.11ax在迫零波束成形（ZFBF）下OFDMA与MU-MIMO联合使用的、可扩展且感知频率选择性的用户调度算法。调度任务被建模为一个整数线性规划（ILP）问题，其中二元变量表示用户（组）与RU的关联关系，线性约束确保标准兼容性。为降低复杂度，我们引入了一种新颖的代理速率——该函数基于各用户信道强度及其相关性——可在无需立方复杂度矩阵求逆的情况下近似ZFBF速率。此外，我们设计了一种基于采样的候选用户组生成方案，为每个RU选取最多$T$个近似正交的用户组，从而限制ILP问题规模并保证可扩展性。基于实际射线追踪信道模型的仿真表明，ProxySelect能以显著更低的复杂度实现接近最优的速率性能。