  Due to their sparsity, 60GHz channels are characterized by a few dominant
paths. Knowing the angular information of their dominant paths, we can develop
various applications, such as the prediction of link performance and the
tracking of an 802.11ad device. Although they are equipped with phased arrays,
the angular inference for 802.11ad devices is still challenging due to their
limited number of RF chains and limited phase control capabilities. Considering
the beam sweeping operation and the high communication bandwidth of 802.11ad
devices, we propose variation-based angle estimation (VAE), called VAE-CIR, by
utilizing beam-specific channel impulse responses (CIRs) measured under
different beams and the directional gains of the corresponding beams to infer
the angular information of dominant paths. Unlike state-of-the-arts, VAE-CIR
exploits the variations between different beam-specific CIRs, instead of their
absolute values, for angular inference. To evaluate the performance of VAE-CIR,
we generate the beam-specific CIRs by simulating the beam sweeping of 802.11ad
devices with the beam patterns measured on off-the-shelf 802.11ad devices. The
60GHz channel is generated via a ray-tracing simulator and the CIRs are
extracted via channel estimation based on Golay sequences. Through experiments
in various scenarios, we demonstrate the effectiveness of VAE-CIR and its
superiority to existing angular inference schemes for 802.11ad devices.
