Wednesday, 17 September 2014

LTE UE Measurement RSRP RSSI RSRQ RSTD

In LTE or any other cellular radio network, UE report some sort of signal to base station for various decision making. It could be used for better downlink scheduling (using CSI), uplink scheduling (using SRS), cell selection , handover, cell reselection , calculation of uplink and downlink path loss for power control, multipath propagation, Uplink interference  and for location based services. 

All of these achieved by parameter called RSRP, RSSI, RSRQ and RSTD.

RSRP:
RSRP Reference Signal Received Power is the average power received by UE from a single cell specific reference signal resource element spread over the full bandwidth. It is calculated by UE for cell selection, handover, cell reselection and for path loss calculation for power control. The power measurement is the energy of the OFDMA symbol excluding the energy of the cyclic prefix.  The measurement of RSRP may be based on energy of reference signal transmitted by antenna port 1 or 1 and 2. UE comes to know which antenna port can be used for measurement, when it decodes SIB3.
The range of RSRP reported by UE are between -140 dBm to -44dBm (-140dBm <RSRP<=  -44dBm).  For each 1dBm difference from -140dBm, UE report an integer value (ranging 0 to 97) to base station. Example:
Value 0 reported when UE measure RSRP less than -140dBm (RSRP< -140dBm).

Value 1 reported when UE measure RSRP between -140dBm to -139dBm (-140dBm<=RSRP<-139dBm)

Value 97 reported when UE measure RSRP greater than and equal to -44dBm (RSRP>= -44dBm).  

RSSI:
RSSI Receive Signal Strength Indicator is the total received signal power from all sources (power of each resource elements) which includes thermal noise also, unlikely to the RSRP. RSSI is never reported by UE to base station but it is the input to calculate the RSRQ.

RSRQ:
RSRQ Reference signal received quality is also used for cell selection, reselection and handover, only when RSRP is not sufficient for making decision. RSRQ is mathematically defined as (N*RSRP)/RSSI, where N is the number of Resource blocks of the LTE carrier RSSI measurement bandwidth. To calculate RSRQ, the numerator and denominator are made over the same set of RBs (like for 5MHz, RSRP and RSSI calculation will be done on 25RBs only at a time).  Since calculation of RSRQ uses RSSI, it enables the combined reporting of signal strength and interference. Range of RSRQ varies from -19.5dB to -3dB (integer value ranges from 0 to 34 ). For each .5dB variation UE report an integer value in RRC message.  
Example:
Value 0 reported by UE to base station when RSRQ measured less than -19.5dBm (RSRQ<-19.5dB).

Value 1 reported by UE to base station when RSRQ measured between -19.5 to -19 (-19.5<=RSRQ<-19dB).

Value 34 reported when RSRQ measured greater than equal to -3dB (RSRQ>=-3dB).

Integer value of RSRP and RSRQ reported by UE is included in RRC message (measurement report of serving cell) shown below:


Measurement of RSRP, RSSI and RSRQ from different antenna port are shown below:

RSTD:
RSTD (reference 3gpp 36.133 and 36.214) reference signal time difference measure the subframe timing difference of reference cell and neighbor cell. RSTD used for location based services and introduced in LTE release 9 . RSTD measurement done by UE and it uses the power received in positioning reference signal (PRS) transmitted by eNodeB. PRS is also introduced in LTE release 9. 

Questions are welcome.

9 comments:

  1. could i ask what ad do you use on top of this blog?
    i'm korean and it shows good targeted ads of korea.

    ReplyDelete
  2. Hi... Just a small doubt...

    If RSRP is solely calculated based on linear average of downlink reference signal, then why there is difference between Idle and connected mode RSRP values.

    Theoretically they should be the same, but we can see a big difference in RSRP values while plotting the DT logs of Idle and connected modes (Data session active).

    ReplyDelete
  3. Hi... Just a small doubt...

    If RSRP is solely calculated based on linear average of downlink reference signal, then why there is difference between Idle and connected mode RSRP values.

    Theoretically they should be the same, but we can see a big difference in RSRP values while plotting the DT logs of Idle and connected modes (Data session active).

    ReplyDelete
  4. Hi Aresh,

    It should be same if you have fixed number of UEs and allocated BW is same. However we can doubt the AGC functionality as RSRP computation needs to take care of Antenna gain ( this is the gain computed by an AGC) AGC can act differently in idle and connected mode.
    Couple of things you can try,
    - Use MGC (manual gain control with a fixed gain say +50dbm)
    - Ensure eNodeB power is not fluctuating
    I assume the difference should be less than 5dbm. This is possible due to OFDM symbol variance. Please let me know if it helps . Also please put some more information what difference you are observing and test scenario and configuration.

    ReplyDelete
    Replies
    1. It is not recommended to use MGC as it will increase interference in other area.

      Still, this question is remain unanswered
      I have same issuance on these measurements.

      Dedicated RSRP is a lot worse than Idle RSRP.
      (which is not possible in my opinion)

      Delete
  5. Hi Abhishek,

    Thanks for the info.

    Actually, these tests were performed in our live network with 1 UE in Idle and 1 in connected under same conditions. eNB power was very stable and the difference is much above 5dbm.

    Besides, I will check if its feasible to do testing with MGC in our next test.

    Regards!

    ReplyDelete
  6. Need frequency band for Verizon in zipcode 95837. Installing signal booster and wireless2.fcc.gov doesn't show anything for that area. Thanks!

    ReplyDelete
  7. Hi. Is anybody here for a lte question?

    ReplyDelete
  8. Does any body know how frequently a UE measure the RSRP of the serving cell?

    ReplyDelete