UMTS
UL Interference E. Eter
2
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.
3
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 TMA Gain 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
In the OSS element manager
4
TMA Gain
5
Feeder Attenuation and delays
6
Feeder Attenuation and delays
7
pmAverageRssi
8
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.
9
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
< -110
dBm
-108
.5..-
108
dBm
-106
.5..-
106
dBm
-104
.5..-
104
dBm
-102
.5..-
102
dBm
-100
.5..-
100
dBm
-98.5..-
98 dBm
-96.5..-
96 dBm
-94.5..-
94 dBm
-92.5..-
92 dBm
-90.5..-
90 dBm
-88.5..-
88 dBm
-86.5..-
86 dBm
-84.5..-
84 dBm
-82.5..-
82 dBm
-80.5..-
80 dBm
Signal Level
Nu
mb
er
of
Sam
ple
s
CNU3007A
10
How to identify the cause of high UL RSSI
:
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.
11
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:
12
LUCENT
1. TMA equipped and controlled by the Node B
2. No TMA equipped
13
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
14
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
15
Other Cases
• There are variants of the "TMA equipped but NOT controlled by the
Node B" scenario described in Configuration 2, above. For example,
there are certain RxAIT configurations in Cingular's network where
RxAIT is equipped without the presence of TMA. In some cases the
RxAIT components appear to the Node B as the equivalent of a TMA in
the external path. Similarly, there are configurations where the Nokia
GSM base station hosts the Rx path. For this case the path through
the host GSM base station and antenna system appears as a TMA
equivalent.
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