System information & DL-SCH data in LTE
1920 bits or 1728 bits are to be transmitted for normal or extended CP resp..
The PBCH is transmitted every 40 ms. The bit scrambling depends on the cell id and is starting in radio frames 0, 4, 8 … . PBCH uses QPSK.
I.e. 960 (864) symbols need to be allocated.
Mapping and precoding is possible for
- single antenna port
- transmit diversity
4 OFDM-symbol durations x 72 RE’s are used, placed in the centre of the cell BW. The occupied RE’s are located at the begin of the 1st subframe, 2nd slot of each frame. Hence, there are 4 x 72 = 288 symbols per radio frame; 1152 QPSK symbols in total for 40 ms.
The physical resource is given by resource elements not assigned by the channels/ signals described above. It can be used to transmit information of higher layer, i.e. control and user data, on the PDSCH. The DPSCH resource will be scheduled on a TTI basis (subframe) by means of the DCIs.
Quadruplets of symbols are formed, permuted and mapped to the REs which are left free, i.e. not used by synchronization signals, RS, PBCH, PCFICH, PHICH, PDCCH. Normally there is one code word mapped, in case of spatial multiplex two code words may be transmitted.
The bits of each code word are scrambled for PDSCH depending on UE id and cell id; for the PMCH depending on NID MBSFN.
Modulation schemes QPSK, 16QAM and 64QAM are supported.