Quasi Co-location Type-D relation between hierarchical beams in a Grid of Beams setup

In NR, Beam forming based directional links, require fine alignment of the transmitter and receiver beams, achieved through a set of operations known as beam management. One mode of operation is beam management with indication, where a concept known as Quasi-co-location (QCL) is used to provide an instruction to the UE which it can use to adjust receiver settings. Different QCL types and relations were defined by 3GPP. This work sheds light on QCL-Type-D relation specifically, which governs spatial relations between different antenna ports/beams. An investigation of the accuracy of the QCLType-D relation between Parent(Wide) and children(Narrow) beams in LOS and NLOS scenarios is presented, using field measurements from a 3GPP Release 15-compliant Ericsson 5G test-bed. The analysis showed higher accuracy in the reception of the children beams (strongest child beam) and their(its) parent beam in LOS scenarios compared to NLOS scenarios when using spatial QCL indication. Moreover, the QCLType-D accuracy between the parent/children beams is shown to improve as the children tend to look similar to their parent beam. Finally, an estimate of the power losses endured in the reception of the strongest child beam due to a wrong QCL indication was provided.