LTE UL and DL Power Measurements

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This page describes UL and DL power and path loss measurements that can be made with the YateENB, as of r7472.

UL power-related measurements

The ENB can provide real-time measurements of UL transmitted power, received power, and path loss.

  • Transmitted power is calculated from http://www.sharetechnote.com/html/Handbook_LTE_PHR.html reported power headroom], assuming that the UE is in the standard power class, with a maximum output of 23 dBm.
  • RSSI is calculated based on the known receiver gain for the radio hardware.
  • Path loss is calculated from transmitter power and RSSI. This is a port-to-port path loss, where all antennas and cables are included in the measured "path".

Setting fixed UL power on PUSCH

The ENB uses dynamic power control to adjust the output power of the UE so that the per-resource-block RSSI at the ENB receiver meets a configured target level. Because the number of resource blocks in an UL transmission vary depending on load, this means that the total transmitted power of the UE changes always even though the power per resource block is fixed.

To make path loss and power measurements easier from outside the ENB, the ENB supports fixed UL assignment sizes as a special test mode. This mode does not really fix the UL power to a constant level, but if the path loss is constant, UL power on PUSCH will also be constant.

To enable fixed UL assignment sizes, set the PuschFixedPower configuration parameter to true:

[basic]
; Fixed UL grant sizes for easier power measurement.
PuschFixedPower=true

This parameter is not supported in the LMI, and needs to be set in the enb-custom.conf file in the /etc/yate/sdr directory. (If you do not already have such a file, just create one. Be sure to indicate the "[basic]" section at the start of the file.)

The default size for the fixed UL grant is 4 resource blocks.

Note: This mode is not necessary for UL power, RSSI and power loss measurements.

Note: This control does not affect PUCCH or PRACH.

Note: This mode severely limits UL data throughput.

Getting PUSCH power and path loss measurements

For PUSCH, the ENB measures:

  • power headroom, in dB per resource block
  • RSSI in dBm and dBm per resource block
  • path loss in dB

These measurements are accurate to about +/-3 db. These measurements are for PUSCH only and do not include PUCCH or PRACH.

PHR in dB/RB?

Q: What is power headroom in dB per resource block?

A: It is the reported power headroom adjusted by the number of resource blocks in the UL assignment that carried the power headroom report.

Specifically:

PhrPerRb = PHRdB + 10 * log10(RBs)

On a linear scale, this is the maximum number of resource blocks that can be sent on PUSCH, given the current UE PUSCH power control state.


Getting the information with "enb uepool chans"

The "enb uepool chans" command shows:

  • short-term average RSSI per resource block in dBm ("RSSIdBm")
  • power headroom per resource block in dB ("PHRdB")
  • path loss in dB ("Lp dB")

for each active UE.

Example with two active UEs:

enb uepool chans
RNTI    PHRdB   Lp dB   RSSIdB  RSSIdBm UL-SNR  UL-FER  UL-HFER UL-eff  64QAM   ULbytes DL-eff  256QAM  DLbytes DL-NACK UC-RSSI UC-SNR  UC-miss Age     Idle    RSRPdBm RSRQdB  UL-BSR  DL-BSR
62      47      43      -25     -79     11      0%      4%      15      false   679k    153     false   11M     0%      -44     19      43%     121     0       -74     -3      0       0
61      37      54      -24     -79     9       18%     0%      15      false   1555k   23      false   834k    0%      -28     39      1%      6912    0       -81     -3      0       0

With a fixed allocation size of 4 resource blocks, the total RSSI on PUSCH is 4 dB above the value reported here. In this example, both UEs have a total RSSI of -75 dBm.

Getting the information with "enb measurements pat="

The YateeNB KPI-related measurements track these values for all connected UEs:

  • TB.UlPhrAvg - Average power headroom in dB per resource block
  • TB.UlPathLossAvg - Average path loss in dB
  • TB.UlRssiAvg - Average RSSI in dBm
  • TB.UlRssiPerRbAvg" - Average RSSI per resource block in dBm

Example of accessing a measurement:

enb measurements pat= Ul.*Avg
TB.UlPathLossAvg=59
TB.UlRssiPerRbAvg=6
TB.UlPhrAvg=32
TB.UlRssiAvg=-61
RRU.UlMcsAvg=1
LastClearTime=1531905255
CurrentTime=1531905314

The "enb measurements clear" command clears and restarts the averaging period.

DL power-related measurements

The UE reports to the ENB a received power level called "RSRP". RSRP is the power level in dBm-per-resource element for the CSRS part of the LTE signal.

Total LTE DL power varies with activity. The total output power of and idle ENB, averaged over a frame, is about 10 dB higher than RSRP, depending on the bandwidth, CFI setting, and SIB sizes and scheduling. For an active ENB, the output is 20 - 30 dB higher than RSRP, depending on the configured bandwidth.

Getting RSRP

"enb uepool chans"

The "enb uepool chans" command shows short-term average RSRP for each active UE under the heading "RSRP".

"enb measurements pat= TB.UlRssiAvg"

The YateeNB KPI-related measurements track long-term average PHR for all connected UEs. The measurement name is "RRC.MeasReportRSRP".

enb measurements pat= RRC.MeasReportRSRP
RRC.MeasReportRSRP=-85
LastClearTime=1529780687
CurrentTime=1529782819

The "enb measurements clear" command clears and restarts the averaging period.