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RSSI troubleshooting
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RSSI Troubleshooting
Purpose of this presentation
The purpose of this presentation is to point out the main sources that aresusceptible to cause 3G UL interference, as well as the best practices that can help
finding and solving them.
The UL RSSI counters are Ericsson performance indicators designed to identifycells that experience abnormal high or low interference levels. Site visits might stillbe required and could potentially provide additional important information
The site design and parameter configurations play an important part in RSSItroubleshooting. Components that impact the UL RSSI are, for example:
Indoor Distributed Antenna System (DAS)
Ericsson Diplexer-Duplexer units (DDU)
Receive Antenna Interface Tray (RX-AIT)
Enhanced Uplink (EUL) represents an important step towards mobile broadbandservices. Ensuring the UL interference is kept under control, will ensure no seriouslimitation exists over services performance in P5MD.
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RSSI Troubleshooting
Some Frequent Asked Questions
What is UL RSSI?
Received Signal Strength Indicator of the total wideband received power withinthe entire channel bandwidth
Note that RSSI does not distinguish between own, other, or any other unwantedinternal or external interference
How is UL RSSI measured in the Ericsson system?
The RSSI is measured every 100 ms. An average value is then calculated everysecond and stored as a PDF step range, [65] long (-110 to -65 dBm, with theresolutions 0.5 dBm and 5 dBm).
Counter pmaverageRSSI , MO Class Carrier and incremented on the RBS level
How high is the actual noise floor for an unloaded system?
The expected uplink interference level in an unloaded system is given by thermalnoise (kTB = -174 dBm/Hz) plus the ASC Noise Figure of the Node B (~2 dB)
Thus the Receiver Noise Density = -174 + 2 = -172 dBm/Hz.
The total effective noise = -172 + 10*log(3,840,000) = -106 dBm
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RSSI Troubleshooting
Some Frequent Asked Questions (continue)
What impact will my traffic load have on the RSSI?
If the system load (Mpole) is increased to 50%, a 3dB Noise rise can be expected
This means we can expect a uplink interference level of -106 + 3 = -103 dBm
How does the system configurable parameters affect the RSSI? No TMA: ValueReported= ValueMeasured in RBS + ULAttenuationMO:AntFeederCable
With TMA: ValueReported= ValueMeasured in RBS + ULAttenuationMO:AntFeederCable ULGainMO:ExternalTMA
So if we assume a RBS without a TMA, and the ULAttenuation set to 3 dB, thenwe should investigate if the RSSI increase over -103 + 3 = -100 dBm
0
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Loading
Noise
rise
[dB]
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RSSI Troubleshooting
What is new in P5MD?
RBS P5ED
RBS P5MD
RNC P5MD
New
New
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RSSI Troubleshooting
Selecting sites for troubleshooting
Investigate sites with reported RSSI values outside the normal* range:
*The normal range depends on the market design and traffic load
Normal
Low RSSI
This example site is considered deafsince all samples are below -110 dBm
High RSSI
This example site has to many high RSSIsamples
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RSSI Troubleshooting
Low RSSI
Possible reasons for sites experiencing a Low UL RSSI
1. No IP communication (unable to ftp xml from the site)
2. Component failures:
i. Cable, connectors and/or diplexers
ii. Antenna
iii. TMA
iv. RX-AIT
v. Distributed antenna system (DAS)
3. Incorrect parameter settings
4. Incorrect installation
Sites that are not integrated or locked, wont show any counter values
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Case L1
TMA not powered
Notes
The TMA power to thissite was not enabled,causing a low RSSI.This was corrected on
6/19
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RSSI Troubleshooting
High RSSI
Possible reasons for sites experiencing a High UL RSSI
1. Internal Causes
i. RBS Internal Interference (Case H1)
ii. Faulty diplexers (Case H2,H3)
iii. Faulty Antenna/TMA (Case H4)
iv. Incorrect parameter settings (Case H5)
v. Incorrect installation (Case H6,H7,H8,H9)
vi. Traffic load (Case H10)
2. External Causes
i. GSM Interference (Case H11)
ii. High sites (Case 12)
iii. External interference (Case 13)
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Case H1
RBS Internal Interference
RF Cable connection
Notes
In order to eliminate possible interferencecreated internally to the RBS, the RFjumper ports can be connected to aspectrum analyzer or a dummy load
If the RSSI values of the site returns tonormal, it means interference is generatedexternal to the RBS
In case of the RBS3202, the set ofconnectors H1, H2 and H3 are related to RxDiversity, while J1, J2 and J3 are the ones
with Tx/Rx combined. In the case of theRBS3206, the lower cables are the oneswith the Rx Diversity, while the upper onesare the Tx/Rx branch
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Case H2
Faulty Diplexers
SFL RSSI tracker during Rollout
Notes
A faulty diplexer can causeunwanted interference onthe uplink.
The SFL team found a specificRSS diplexer model thatincreased the uplinkinterference. Once these werereplaced, the UL RSSIrecovered
Vs.
Before
After
Vs.
Before
After
Vs.
Before
After
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Case H3
Faulty Diplexers
Notes
The Tampa teamfound a baddiplexer on 6/9,and replaced it.The average RSSIremained withinthe normal range
afterward
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Case H4
Faulty Antenna/TMA
Notes
A TMA or an Antenna can also be a source of
interference. TMAs are usually replaced, whileAntennae dont typically fail.
Troubleshooting can commence using dummyloads and/or a spectrum analyzer toisolated the source of interference
RBS
TMA
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Case H5
Incorrect parameter settings
Notes
When using a RX-AIT or/and a TMA, it isimportant to ensure the configurations areset correctly in the RBS
Typically, the RX-AIT uplink gain is 10 dBfor 1900 MHz and 20 dB for 850 MHz. Theattenuator loss is typically 4 dB, unless it is
a 850 MHz installation with a TMA, where theattenuation will be 15 dB
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Case H5
Incorrect parameter settings
A Cluster in Charlotte got theULAttenuator values fixed toinclude the 6 dB gain
If a site reports 6 dB lowerRSSI than other cells, itcould be that that RX-AIT isdown
6 dB
6 dB
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Case H5
Incorrect parameter settings
TMA
DlAttenuationMO:AntFeederCable = Feeder_loss
UlAttenuationMO:AntFeederCable = Feeder_Loss
DlAttenuationMO:ExternalTMA = TMA_Ins_Loss
ULGainMO:ExternalTma = 12 dB (typical value)
DlAttenuationMO:AntFeederCable= Feeder_Loss + RXAIT_Losses_DL
ULAttenuationMO:AntFeederCable = Feeder_Loss + RXAIT_Losses_UL RXAIT_Gain
DlAttenuationMO:ExternalTma = TMA_Ins_Loss
ULGainMO:ExternalTma = 12 dB (typical value)
TMA
DlAttenuationMO:AntFeederCable= Feeder_Loss + RXAIT_Losses_DL + Jumper_loss
ULAttenuationMO:AntFeederCable = Feeder_Loss + RXAIT_Losses_UL + Jumper_loss
ULGainMO:ExternalTma = RXAIT_Gain (need to define the TMA object)
TMA
DlAttenuationMO:AntFeederCable = Feeder_loss + Jumper_loss
UlAttenuationMO:AntFeederCable = Feeder_Loss + Jumper_loss
TMA
System configuration calculations
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Case H6
Faulty installation
Notes
During the design of the
antenna sharing solution itwas identified that the RXpath to the UMTS receiver
would require 15dBattenuation to prevent thereceivers from being overpowered.
These attenuators werenever installed for this
example site. This resultedin the average RSSI of -88dBm on all affectedsectors.
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Case H7
Faulty installation
Notes
The Tampa team added thecorrect attenuator pads, andthis moved the UL RSSI to theexpected range
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Case H8
Faulty installation
Notes
This Atlanta design called for anattenuator to be installed with theDistributed Antenna System (DAS).This was never completed, resultingin a high UL RSSI
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Case H9
Faulty installation
Notes
This site example had cablingproblems affecting GSM aswell. The Tampa teamcorrected it, and this restoredthe UL RSSI
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Case H10
Impact of Traffic load on the UL Interference
Increase in RSSI
Notes
If the noise rise ishigher than 3-4 dBwhile the load is lessthan 50-60%, thenfurther investigationshould be performed.
Neighboring cells andexternal interferenceare examples that maycause the increase
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Case H11
GSM Interference
200kHz GSM spikeswill impact the RTWP
on UMTS
TelCel, a mexican
operator, was using the
same band as Cingulars
UMTS network
High interference
Mexican border
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Case H11
GSM Interference (continue)
-101.57
-103.42
-99.52
-96.13
-99.23
-97.13
-98.73
-96.13
-99.33
-101.82
-105.00
-103.00
-101.00
-99.00
-97.00
-95.00
-93.00
-91.00
-89.00
-87.00
-85.001:00AM
2:00AM
3:00AM
4:00AM
5:00AM
6:00AM
7:00AM
8:00AM
9:00AM
10:00
AM
11:00
AM
12:00
PM
1:00PM
2:00PM
3:00PM
4:00PM
5:00PM
6:00PM
7:00PM
8:00PM
9:00PM
10:00
PM
11:00
PM
12:00
AM
UL RSSI measured by s ites experiencing GSM interference
Ave. UL RSSI measured by sites with configuration issuesAve. Network UL RSSI
Notes
Narrow band GSM interferenceis easily identified by the factthat the reported UL RSSIfollows a similar pattern to theGSM traffic profile
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Case H12
High sites
Mount Soledad High site (2400ft)Notes
High sites normally share thetower with multipletechnologies. Unwantedcoupling is always a risk if
minimum separation betweenantennas are not maintained.
Containing this site is almost
impossible due to its relativeheight. This sector wasmeasuring UL RSSI at -97dBm
while the surrounding siteswere reporting the noise floorat -104dBm.
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Case H13
External interference
1500 ft broadcast tower wasidentified as the cause for thisnetwork wide harmonic interferer
San Antonio
Notes
More than 280 sectorswere affected in SanAntonio
Ave. RSSI wasgenerally acceptable,but the No. samples>= -90.5 to -90 dBmindicated that therewas an external
interferer present
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High and Low UL RSSI measurements usually points towards aproblem within the system setup or equipment functionality
Hourly and daily statistics can help to indicate if the interferenceis constant, or trend with 2G and/or 3G traffic load
It is important to ensure all system parameters and theinstallation are implemented correctly, before searching for anexternal interferer
Conclusions
Summary