Use of Rank Indication in LTE


Probably all of you must have heard of something called rank indication in LTE. The rank indication or the RI in LTE is one of the control information that a UE will report to eNodeB on either PUCCH or PUSCH based on uplink scheduling.

The eNodeB configures the RI reporting periodicity for every UE during the attach procedure and UE has to honour it. The RI reporting periodicity can overlap with CQI reporting periodicity in which case the UE will drop CQI and report RI.

Now coming to the RI itself, the contents of RI is just a couple of bits. The number depends on antenna configuration. If the eNodeB is configured with 2 transmit antennas on downlink then the number of bits reported in RI will be one and if its 4 then number of RI bits will be 2.

Lets consider the two antenna case where RI is indicated using one bit, so a bit 0 indicates RANK1 and a bit 1 indicates RANK2. RANK1 means the UE is seeing a good SINR only on one of its receive antenna so asking the eNodeB to bring down the transmission mode to single antenna or transmit diversity. A RANK2 from the UE means good SINR on both the antenna ports and eNodeB can schedule MIMO.

Its very essential for the eNodeB to decode a UEs RI report to know the channel conditions so that it can schedule downlink appropriately. The LTE specifications also say that if the UE is not reporting any RI then the eNodeB should assume RANK1.

So thats all about rank indication. I hope it was useful 🙂

|| Pradeep Prabhu ||

15 thoughts on “Use of Rank Indication in LTE

  1. can you please specify which portion of 3GPP supports the comment “The LTE specifications also say that if the UE is not reporting any RI then the eNodeB should assume RANK1”

  2. Dear,
    good explanation.
    but this part“The LTE specifications also say that if the UE is not reporting any RI then the eNodeB should assume RANK1″ i think not right.
    If the UE not reporting any RI Report that’s mean it is single layer antenna.
    we use the RI in the Spatial Multiplexing (Open-loop or Closed loop).

  3. What will be the Radio UEs RI report to know the channel conditions so that it can schedule downlink appropriately.
    e.g what will be CQI,SINR,Buffer data,RSRP so that it can report R1 or R2.
    Is there any Mapping on what radio condition it will report

  4. Thanks for sharing.
    I have a question:
    I activated the MIMO 4×4 function for an LTE site:
    MIMO counters are:
     L.ChMeas.MIMO.PRB.CL.Rank1
     L.ChMeas.MIMO.PRB.CL.Rank2
     L.ChMeas.MIMO.PRB.CL.Rank3
     L.ChMeas.MIMO.PRB.CL.Rank4

    I when I run a querry for these counters after being activated for LTE 2600 MHZ frequency band, I got the following results:

    L.ChMeas.MIMO.PRB.CL.Rank1 = 40188901
    L.ChMeas.MIMO.PRB.CL.Rank2 = 63413974
    L.ChMeas.MIMO.PRB.CL.Rank3 = 0
    L.ChMeas.MIMO.PRB.CL.Rank4 = 0

    What does this mean ?
    why Rank3 and Rank4 are NULL

    thank you for your feedback and help

    B.AFETTOUCHE

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