RSRP, RSSI and RSRQ

In LTE network, UEs need to measure signal strength of its own and neighbor cells constantly, during idle, connected mode or handovers in order to keep the signal quality constant. UE measures RSRP and RSRQ in LTE

Reference Symbol Received Power (RSRP):

  • RSRP is the linear average of the downlink reference signals across the channel bandwidth 
  • RSRP provides information about signal strength and  gives no indication of signal quality 
  • RSRP measurements are used in handover, cell selection and cell re-selections 
  • The reporting range of RSRP is defined from -140 dBm to -44 dBm with 1 dB resolution as shown in table below
RSRP measurement report mapping (3GPP Reference: TS 36.133)

Received Signal Strength Indicator (RSSI):

  • RSSI represents the total received wide-band power by UE
  • RSSI is measured only in symbols containing Reference signals 
  • RSSI includes power from serving cell as well as co-channel interference and noise
  • RSSI helps in determining interference and noise information 
  • RSSI is never reported by UE

Reference Signal Received Quality (RSRQ):

  • RSRQ indicates quality of received reference signal. RSRQ measurement and calculation is based on RSRP and RSSI since RSRP determines signal quality and RSSI determines co-channel interference and noise. RSRQ formula is shown below (N represents number of resource blocks)
  • The reporting range of RSRQ is defined from -19.5 dB to -3 with 0.5 dB resolution
RSRQ measurement report mapping (3GPP Reference: TS 36.133)

Example

Lets try to calculate RSRP, RSSI and RSRQ for one very simple case of one resource block with 12 sub carriers and 0.5 ms in time domain. For sake of simplicity, lets assume the power of reference symbols  (shown by red square) and power of other symbols carrying other data channels (shown by blue square) is same i.e. 0.021 watt


Since RSRP is linear average of downlink reference signal for given channel bandwidth therefore
RSRP = 10*log (0.021*1000) = 13.2 dBm

While RSSI is total received wide-band power. Therefore we have to add power of all 12 carriers in the given resource block
RSSI = 10*log(0.021*1000)+10*log(12) = 24 dBm

RSRQ is now simple ratio of RSRP to RSSI with N=1
RSRQ = 10*log(0.021/(12*0.021)) = -10.79 dB


Why do we use dBm as a unit of Power

We use decibels-milliwatts to measures power levels in telecommunication and other fields instead of Watt. The reason to use logarithmic scale is that it helps in reducing massive values to smaller number

Example : 0.00000000000080 watt which apparently looks very small value but
can still be received by antenna. The logarithmic value is just -91 dbm by using below formula
P (dBm) = 10 x Log (1000*P)

dBm vs dB

dB is ratio between two power values while dBm is used to express an absolute value of power. So when we mention RSRP and RSSI we shall always use dBm since we are talking about absolute power values but we need to use dB with RSRQ since it is the ratio of RSRP to RSSI

39 comments:

  1. Maybe you can mention how to derive "SINR = 12/((1/RSRQ)-x) where x is cell load". I think it is also important.

    ReplyDelete
    Replies
    1. Sure let me read a bit on SINR before..

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    2. Hi, you can find information about it in our website: www.laroccasolutions.com in the training session

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    3. Can anybody tell me that how we measure these parameter from SIM card.

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    4. Can anybody tell me that how we measure these parameter from SIM card.

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    5. You cannot! If you idea is to dev some "Agent" on SIM, you need some API on the mobile that will connect to the radio interface of the mobile. These API can be shared only from Mobile Producers...

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  2. RSRQ = 10*log(0.021/(12*0.021)) = -10.79 dbm => The parameter of RSRQ is db not dbm.

    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
    Replies
    1. This comment has been removed by the author.

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    2. Yes it should be same,eNodeB coverage footprint remains the same it doesn't matter if UE is in connected/idle mode.
      Well you can check the drive testing kit setup and do couple of stationary up-link/down-link test cases to verify this mismatch.

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  4. Hi Imad,

    Thanks for the info.

    We have performed several tests and the results are almost the same. One thing I noticed was RSRP reporting by UE was different in Idle/Connected modes, but not sure if that can impact the calculation. Another suspect could be AGC functionality in computing antenna gain (this was suggested by a friend and I am still checking on that).

    Regards!

    ReplyDelete
  5. Hello Aresh,

    Can you explain the below terms:
    RSSI In Band
    RSSI Total Band
    RSSI Broad Band

    thanks

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  6. This comment has been removed by the author.

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  7. You can find a APP in Google Play, it can help you to find the mapping quickly. Its name is "RSRP/RSRQ report mapping".

    https://play.google.com/store/apps/details?id=com.rsrp_q

    ReplyDelete
  8. Why did you multiple 0.021*(1000) , why 1000 for RSRP calculation ? where did you get this number 1000

    ReplyDelete
    Replies
    1. 0.021 is Watt, 0.021*1000 is mW, and 10*log(0.021*1000) is dBm~

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  9. Related link:
    http://www.rfwireless-world.com/Terminology/LTE-RSRP-vs-RSRQ.html

    ReplyDelete
  10. Thanks you vary much for your valuable post which is very informative and helpful for my life. I have read very attentively your article’s quotation’s which has increase my knowledge. I think, your website is a great bank of informative and useful article. It’s a great job. Thanks you again.

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  11. I think cellular networks are playing great role in network communication..

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  13. Why in calculation RSSI is 24dBm? if RSSI=2RS+10PDSCH

    ReplyDelete
  14. As mentioned in example, "For sake of simplicity, lets assume the power of reference symbols (shown by red square) and power of other symbols carrying other data channels (shown by blue square) is same i.e. 0.021 watt". As in question, RSSI=2RS+10PDSCH = 2 * 0.021 + 10 * 0.021 = 12 * 0.021. Expressing in log,
    = 10 log (12*0.021*1000) = 24 dBm.

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  17. Quite good and crisp information for a complex topic

    ReplyDelete
  18. I like it!
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  21. U mentioned "RSSI is measured only in symbols containing Reference signals"

    But, RSSI is the measure of total power i.e., all the symbols power at a given time. Isn't?

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