6.10.1 Cell-specific Reference Signal (CRS)
36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS
The UE may assume cell-specific reference signals are, unless otherwise stated in [4, clause 12], transmitted in
– all downlink subframes for frame structure type 1,
– all downlink subframes and DwPTS for frame structure type 2,
– non-empty subframes for frame structure type 3
in a cell supporting PDSCH transmission.
If special subframe configuration 10 is configured by the higher layer signalling ssp10-CRS-LessDwPTS, the UE cannot assume that cell specific reference signals are transmitted in the 5th OFDM symbol of the special subframe.
Cell-specific reference signals are transmitted on one or several of antenna ports 0 to 3.
Cell-specific reference signals are transmitted in subframes where 
only.
6.10.1.1 Sequence generation
The reference-signal sequence 
is defined by
where 
is the slot number within a radio frame and 
is the OFDM symbol number within the slot. The pseudo-random sequence 
is defined in clause 7.2. The pseudo-random sequence generator shall be initialised with 
at the start of each OFDM symbol where
6.10.1.2 Mapping to resource elements
The reference signal sequence 
shall be mapped to complex-valued modulation symbols 
used as reference symbols for antenna port 
in slot 
according to
where
The variables 
and 
define the position in the frequency domain for the different reference signals where 
is given by
The cell-specific frequency shift is given by 
.
Resource elements 
used for transmission of cell-specific reference signals on any of the antenna ports in a slot shall not be used for any transmission on any other antenna port in the same slot and set to zero.
In an MBSFN subframe, cell-specific reference signals shall only be transmitted in the non-MBSFN region of the MBSFN subframe.
Figures 6.10.1.2-1 and 6.10.1.2-2 illustrate the resource elements used for reference signal transmission according to the above definition. The notation 
is used to denote a resource element used for reference signal transmission on antenna port
.
Figure 6.10.1.2-1. Mapping of downlink reference signals (normal cyclic prefix)
Figure 6.10.1.2-2. Mapping of downlink reference signals (extended cyclic prefix)