UMTS
UL Interference
E. Eter
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.
2
UL RTWP
(Ericsson)
Antenna
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
Rx Reference Point
Where, FAtt is the Attenuation antenna feeder cable and TMAG is the TMA Total Gain
RUG and FUG are internal to the NodeB
TMA
TMAG
FAtt
NodeB
K_dBm
FUG
FU
RUG
RU
RU
Feeder attenuation and TMA Gain are provided by site
configuration. So it’s important the loss FAtt and gain TMAG
are accurate.
Power Sensor
pmAverageRSSI
Next 3 slides show how to input the TMA gain and feeder attenuation
In the OSS element manager
3
TMA Gain
4
Feeder Attenuation and delays
5
Feeder Attenuation and delays
6
pmAverageRssi
7
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.
8
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
40000
30000
25000
20000
CNU3007A
15000
10000
5000
0
-1 < 08 11
0
.
-1 5..- dB
06 10 m
.
-1 5..- 8 dB
04 10 m
.
-1 5..- 6 dB
02 10 m
.
-1 5..- 4 dB
00 10 m
.5 2
.
d
-9 .- 10 Bm
8. 0
5
d
-9 ..-9 Bm
6. 8
5
d
-9 ..-9 Bm
4. 6
5
d
-9 ..-9 Bm
2. 4
5
d
-9 ..-9 Bm
0. 2
5
d
-8 ..-9 Bm
8. 0
5
d
-8 ..-8 Bm
6. 8
5
d
-8 ..-8 Bm
4. 6
5
d
-8 ..-8 Bm
2. 4
5
d
-8 ..-8 Bm
0. 2
5. d
.-8 Bm
0
dB
m
Number of Samples
35000
Signal Level
9
How to identify the cause of high UL RSSI
In case one or two sectors of a site has high UL RSSI
Antenna
Rx Reference Point
 Swap antenna feeders between good and bad sectors on RBS cabinet top.
A
TMA
 Wait for the next ROP and check the UL RSSI.
NodeB

If the high interference stays with the antenna:
- then it may be external interference or TMA (A)
- otherwise check the FU/RU. (B)
FU
B
 Use spectrum analyzer to detect external interference sources
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.
10
RU
RU
Power Sensor
pmAverageRSSI
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:
11
LUCENT
1. TMA equipped and controlled by the Node B
2. No TMA equipped
12
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
TTLNA
Feeder Cable
Filter panel
Filter panel
attenuator
Cable
to
Radio
824 MHz
Total
Gain (dB)
12.00
-3.00
-0.15
30.50
13
-8.00
-0.70
30.65
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.
RTWP reference point
_
LNA
Variable
Attenuator
1:3 Splitter
Cable to radio
Total
NodeB Filter
Gain (dB)
38.00
-3.00
-7.00
14
-1.60
26.40
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.
15