Master Information Block (MIB) in LTE


The very first step for UE to gain initial access to the network after completing initial cell synchronization is to read the Master information block (MIB) on BCCH (Logical channel), BCH (Transport channel) and PBCH (Physical channel). Resource elements used by MIB are the first 4 OFDMA symbols of second slot of first subframe of a radio frame. On frequency domain it occupies 72 subcarriers. MIB carries very little but most important information for UE initial access. The content of MIB includes

·         Downlink channel bandwidth in term of resource blocks (RBs)
·         PHICH configuration (PHICH duration and PHICH resource)
·         System Frame Number

New MIB is broadcasted every radio frame for which SFN mod 4 = 0 (40ms repetition) while its copies are broadcasted in the middle 10ms radio frames as shown in the figure below



Why PHICH is carried by MIB? 
After decoding MIB, UE has to decode PDCCH to read other system information blocks (SIBs).  PDCCH, PHICH and PCFICH share the resources in the control region of a subframe. So to find the available resources for PDCCH, UE has to know the PHICH configuration only, as PCFICH resources are fixed and known

15 comments:

  1. This comment has been removed by the author.

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  2. No not the copies are broadcasting in the middle 10ms.. extracting all the data in 40ms at this position i.e SFN mod 4 = 0,1,2 and 3 forms complete 1920 bits MIB block..

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  3. Each of the repeated transmission is self decodable to make one complete MIB provided the radio conditions are very good. Otherwise in bad SIR, soft combination over four radio frames is used to improve decoding performance

    See page 191,192 "LTE - The UMTS Long Term Evolution: From Theory to Practice"

    Please share your source of information

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    Replies

    1. hi, i saw your blogs, they are very helping, do u hav any material on dual connectivity architecture which can help in undrstanding it? can u gv me ur contact info fb id or email plz so that i cn take hlp from u in some topics

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  4. Can a UE read the MIB information in the camped but non-attached state?

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    1. If you mean ECM idle (EMM Registered) then yes it can ..

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  5. SFN field in the MIB records only the most significant 8 bits of the actual SFN; the remaining 2 bits are determined by which of the 4 repetitions the UE is looking at (00 for the first copy, 01 for the second, and so on can any one explain me wt it means..

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  7. Suppose an eNB receives some how the MIB from a neighbor cell working on different freq. and the eNB wants to transfer this information to a specific connected UE. How can the eNB do that?
    1- in a dedicated RRC control message?
    2- on what logical channel ?
    3- will that specific UE interrupts its data during the reception of that information?
    Any answers?

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  8. What is the use of sending the PHICH configuraton in MIB.

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    Replies

    1. Please see the updated post above for answer to your question..

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  10. Great, A descriptive yet crisp information

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