Decoupling beam steering and user selection for scaling multi-user 60 GHz WLANs

Multi-user transmission at 60 GHz promises to increase the throughput of next generation WLANs via both analog and digital beamforming. To maximize capacity, analog beams need to be jointly configured with user selection and digital weights; however, joint maximization requires prohibitively large training and feedback overhead. In this paper, we scale multi-user 60 GHz WLAN throughput via design of a low-complexity structure for decoupling beam steering and user selection such that analog beam training precedes user selection. We introduce a two-class framework comprising (i) single shot selection of users by minimizing overlap of their idealized beam patterns obtained from analog training and (ii) interference-aware incremental addition of users via sequential training to better predict inter-user interference. We implement a programmable testbed using software defined radios and commercial 60 GHz transceivers and conduct over-the-air measurements to collect channel traces for different indoor WLAN deployments. Using trace based emulations and high resolution 60 GHz channel models, we show that our decoupling structure experiences less than 5% performance loss compared to maximum achievable rates via joint user-beam selection.