“…JPTA can be used to reduce the overheads in beam training [17], [22], [24]- [28], [41] which can be realized by a pure TTD network [24], [29], [30], JPTA [25]- [28], or hybrid (multiple RF-chains) JPTA [17]. All of these works assume a uniform delay model, where the delay difference between any two consecutive antennas (∆t) is uniform, and it is sufficient to set ∆t proportional to the inverse of the bandwidth to achieve the near-optimal gain across the whole 180 • angular region under the narrow-band assumption.…”