“…Only recently has the noise shaping characteristics of first and second-order spatial and cascaded space-time Σ∆ architectures been studied for a few array processing applications. In particular, applications have been considered for massive MIMO [40], [41], [42], [43], [44], phased arrays [45], [46], interference cancellation [35], and spatio-temporal Σ∆ circuit implementations [47], [48]. With the exception of our preliminary studies in [42], [49], there has been no prior work focused on channel estimation for spatial Σ∆ massive MIMO systems.…”