LTE PBCH

LTE Physical Broadcast Channel (PBCH)

• Physical Broadcast Channel (PBCH) is used to broadcast the Master Information Block (MIB) using the BCH transport channel and BCCH logical channel
• For both FDD and TDD,
• the PBCH is allocated the central 72 subcarriers belonging to the first 4 OFDMA symbols of the second time slot of every 10 ms radio frame (time slot 1 in subframe 0, with time slot numbering starting from 0)
• Reference Signal Resource Elements (including those which would be allocated if antenna ports 0 to 3 were used, irrespective of the actual antenna ports used) are excluded from the PBCH allocation
•  The PBCH can be broadcast using only antenna port 0, or transmit diversity can be used to broadcast the PBCH using antenna ports {0, I} or {0, I, 2, 3}

Resource Element allocation for the PBCH

normal cyclic prefix:-

• The PBCH occupies 240 Resource Elements when using the normal cyclic prefix,i.e. (72 x 4)- 48, where 48 is the number of Resource Elements allocated to the Reference Signal.

extended cyclic prefix:-

• The PBCH occupies 216 Resource Elements when using the extended cyclic prefix, i.e. (72 x 4) - 72, where 72 is the number of Resource Elements allocated to the Reference Signal (in this case, the third column of Reference Signals also overlaps with the set of PBCH Resource Elements)

modulation:-

• The PBCH uses QPSK modulation so the 240 Resource Elements provide 480 bits when using the normal cyclic prefix, and the 216 Resource Elements provide 432 bits when using the extended cyclic prefix

* 3GPP References: TS 36.211

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