Kavli Affiliate: Xiang Zhang
| First 5 Authors: Xiang Zhang, Xiang Zhang, , ,
| Summary:
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
emphProxySelect, 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.
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