Systems, methods, apparatuses, and computer program products for supporting a narrow serving beam in a hierarchical beam configuration. For example, certain embodiments may provide a UE that may receive, from a network node, information of a quasi co-location (QCL) configuration of self-contained, aperiodic, and/or semi-persistent tracking reference signals (TRSs) for sub-beams, where a source for one or more TRSs may be channel state information (CSI-RS) without repetition. In addition, the UE may determine these TRSs as self-contained, for which there are no associated periodic TRSs, if there is a TRS configured for an SSB sub-beam.