However, the same CSI-RS resource may be configured to many or all UEs served by the eNB to save CSI-RS overhead, that is, they all measure on the same CSI-RS resource. The CSI-RS is UE specifically configured, that is, per dedicated signaling to each UE. Note that CSI-RS port numbering for a CSI-RS in LTE always begins with port 15. ![]() This example shows an antenna port layout with 2 and 4 ports in first and second dimensions, respectively, a total of 16 ports. The UE is placed at the position of the reader, where port 15 is in the lower left corner. Numbering is across first dimension first (for one polarization) followed by second spatial dimension and lastly across polarizations. 3GPP convention of CSI-RS port numbering and mapping to antennas for the 2×4 port layout. The number of ports N 1 and N 2 in each dimension is configured by the network for the UE to use the correct codebook.įigure 8.11. Note that the 2D antenna port layout (i.e., N 1 × N 2 ports in first and second dimensions) is not part of the CSI-RS resource configuration, but instead it is part of the MIMO precoder codebook configuration for CSI feedback. The 2D layouts allow precoding or beamforming in a given direction defined by both a vertical and a horizontal angle. The need for more ports was motivated by the introduction of 2D antenna port layouts. Therefore the concept of a CSI-RS resource was defined and a UE in TM 10 can have multiple such resources configured simultaneously and perform independent measurements on each of them.įurthermore, in release 13 the definition of a CSI-RS resource was extended to have a larger number of antenna ports. This enables the UE to perform measurements and reporting of CSI for more than one transmission point for example. In release 11, there was a need to be able to configure multiple CSI-RS to a UE simultaneously. Therefore a UE specifically configured and dedicated measurement signal, the CSI-RS, was introduced in release 10 with 1, 2, 4, or 8 orthogonal antenna ports. When using TM 8 with reciprocity, the full benefit is not achieved since measurements are made on the CRS. ![]() Moreover, to fully benefit from reciprocity-based operation, channel-dependent precoding/beamforming toward a specific UE was seen necessary both for the measurement signals and for the PDSCH transmission. It makes it difficult to fully utilize the antenna gains of AAS since the measurement RS will not benefit from beamforming gain. In addition, CRSs are shared by all UEs in the cell and hence, a CRS transmission cannot be channel-dependent, that is, it cannot be beamformed to a specific UE. The LTE-Advanced requirements of a peak spectral efficiency of 30 bps/Hz implied a requirement of eight-layer transmission and extending the CRS-based transmission for this purpose (i.e., increasing the number of CRS ports to eight) was inefficient. ![]() When evolving LTE network deployments for heterogeneous networks and when introducing beamforming with advanced antenna arrays it was observed that the CRS-based measurement signals were too inflexible and restrictive. The CSI-RS is introduced as a dedicated RS used for CSI measurement purposes and replaces the CRS for measurement purpose, at least for some TMs. Erik Larsson, in Advanced Antenna Systems for 5G Network Deployments, 2020 8.3.1.4 Downlink channel state information reference signals
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |