LTE: How an UE get to know cell is running on MIMO mode or not ?

Question

Why dBm unit is used in case of doing measurement for RSRP and why dB is used for RSRQ ?
What reasoning is behind it ?

Answer 1

With the CRC mask of PBCH data

• Transmitter (eNB) will calculate CRC for 24 bits of MIB information and masked with 16teen 0's if there is one antenna, 16teen 1's if there is two antennas and alternate 1010101010101010 if there are 4 antennas.

• Receiver (UE) will remove this CRC bits (16 bit) and calculate CRC for remaining data i.e. 24 bits of MIB data.

• Calculated CRC is again masked with 16teen 0's at UE side and CRC out come is cross checked with received CRC bits. If both are matching then UE comes to know about number of antennas = 1 used.

• If above is not matching, then Calculated CRC is again masked with 16teen 1's for this received 24 bits of MIB information at UE side. CRC Mask Outcome is matches with received CRC bits then UE comes to know about number of antennas = 2 used

• If above is not matching, then Calculated CRC is again masked with 1010101010101010 for this received 24 bits of MIB information, at UE side. CRC Mask Outcome is matches with received CRC bits then UE comes to know about number of antennas = 4 used.

• If nothing is matched then UE come to know that the received MIB data contain Errors, so can not be decoded and should look for new MIB data in sub sequent frames.

Comments

well explained

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What if more than 4 antennas are used i.e. 8X8 MIMO for e.g. ?

Answer 2

After decoding the PBCH, UE will come to know number of Tx antenna .
And when it successfully decodes the DCI intended to itself, it will come to know the transmission mode.

Answer 3

I would add one thing to the answer above which is well presented and quite comprehensive.

With regard to transmission mode, The UE is given the transmission mode in the dedicated portion of the RRC_Connection_Setup message.

So the way you should think about it is: You can certainly determine the number of antennas from the CRC on the MIB, and if the eNB has more than 1 it is required to use transmit diversity for broadcast, PDCCH, and SIB messaging.

You'll be instructed what to use based on the DCI and your assigned transmission mode. This does not need to be blindly determined.

It's a small nuance.

Jeff