Why 5G NR has not opted for CRS and instead used CSI-RS?
Disadvantages of CRS:
- Wastage of power due to always on signal
- It is transmitted (omnidirectional)across the cell area irrespective of the Ue position.
- More RE is used for sending CRS.
- It cannot be used for Beamforming because of its omnidirectional nature.
Advantages of CSI- RS:
- It is ue specific and configured via rrc reconfiguration.
- It saves energy compared to CRS
- Transmitted in less RE (1 or 2 RE)
- It is used for Beamforming because it is ue specific.
Exception: Though TM-8 defines Beamforming using CRS. But there is no deployment because of limitations of CRS omnidirectional signal characteristics.
CRS: Cell reference signal
CSI-RS: Channel state information reference signal
RE: Resource elements.