UMTS
UL Interference
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Possible Causes for UL interference
Too high UL RSSI (>-100 dbm) can be caused by:
External sources of uplink interference Inter-mod product
Incorrect plumbing
Parameter TMA ulGain setting does not match the real TMA gain Faulty devices along the Rx path
Loose Connectors Tight Cable Bends
High UL RSSI caused by external interference has significant impact on UL capacity and coverage of a cell.
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UL RTWP
(Ericsson)
UL RSSI pmAverageRSSI is measured in the RU power sensor.
The result is translated to dBm at the Rx reference point by the factor K_dBM.
K_dBm = (RUG – FUG) + FAtt – TMAG
Where, FAtt is the Attenuation antenna feeder cable and TMAG is the TMA Total Gain
RUG and FUG are internal to the NodeB
Feeder attenuation and TMAGain are provided by site configuration. So it’s important the loss FAtt and gain TMAG
are accurate. TMA FU RU Power Sensor RU FAtt TMAG K_dBm Rx Reference Point NodeB pmAverageRSSI RUG FUG Antenna
Next 3 slides show how to input the TMA gain and feeder attenuation
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Ericsson Uplink RSSI Measurement
pmAverageRssi
UL RSSI counter can be checked through either RBS Performance Statistics
counter pmAverageRssi. It can be read by Business Object or
Prospect.
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UL Interference Monitoring
A macro was developed to graph ( see figure below) and flag any cell that has a RTWP at least 2dB greater or less than the mean RTWP for all cells in a given RNC.
A daily summary for the worst performing sectors will be available on NetTrack (Ericsson and Lucent ).
Ericsson Measured Interference
0 5000 10000 15000 20000 25000 30000 35000 40000 < -1 10 d Bm -108 .5 ..-108 dBm -106 .5 ..-106 dBm -104 .5 ..-104 dBm -102 .5 ..-102 dBm -100 .5 ..-100 dBm -98. 5..-9 8 dB m -96. 5..-9 6 dB m -94. 5..-9 4 dB m -92. 5..-9 2 dB m -90. 5..-9 0 dB m -88. 5..-8 8 dB m -86. 5..-8 6 dB m -84. 5..-8 4 dB m -82. 5..-8 2 dB m -80. 5..-8 0 dB m Signal Level N u m b e r o f S a m p le s CNU3007A
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How to identify the cause of high UL RSSI
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Swap antenna feeders between good and bad sectors on RBS cabinet top. Wait for the next ROP and check the UL RSSI.
If the high interference stays with the antenna: - then it may be external interference or TMA (A) - otherwise check the FU/RU. (B)
Use spectrum analyzer to detect external interference sources
TMA FU RU Power Sensor RU Rx Reference Point NodeB pmAverageRSSI Antenna
In case one or two sectors of a site has high UL RSSI
A
B
Too low UL RSSI (<-110 dbm) will cause PRACH preamble detection problem because UE uses too low power to access the site. It may also cause UL synch loss drop call if the initial power of the Radio Link is too low during handover.
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LUCENT Uplink RSSI Measurement
RTWP
VS.RF.Rtwp.LE110 to VS.RF.Rtwp.GT90
Description
• The measurement provides a distribution of the Received Total
Wideband Power(RTWP) within the granularity period.
• The RTWP provides separate counters on a 1dB step size in the
typical range used for detailed evaluation. This range is 110 dBm to
-90 dBm.
• Trigger condition
For every 100 ms sampling period the mean RTWP value for the
sampling period will be calculated and the appropriate counter
incremented. The ranges are defined as listed:
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LUCENT
1. TMA equipped and controlled by the Node B
2. No TMA equipped
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TMA equipped Node B
The reference point for RTWP is at the TMA input port (antenna side of the TMA). For this configuration RTWP is computed by adding the Rx Path Gain
(consisting of the Node B's internal path gain plus the external path gain) to the RSSI measured at the radio's receiver. The external path gain (between the reference
point and the Node B's External Antenna Connector (EAC)) is the combination of the Rx
Gain data contained in the associated TTLNA Descriptor plus that contained in the Antenna Path Descriptor.
RTWP reference point 824 MHz Gain (dB) TTLNA 12.00 Feeder Cable -3.00 -0.15 Filter panel 30.50 Filter panel attenuator Cable to Radio -0.70 Total 30.65 -8.00
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No TMA equipped NodeB
The reference point for RTWP is the Node B's External Antenna Connector
(EAC). In this case RTWP is computed by adding the RSSI measured at the radio to the Node B's internal path gain. The Antenna Path Descriptor's Rx Gain
parameters are set to zero.
Gain (dB) LNA _ _ 38.00 _ Variable Attenuator _ _ -3.00 1:3 Splitter _ _ -7.00 Cable to radio _ _ -1.60 Total 26.40 NodeB Filter RTWP reference point
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