RSSI Overwiev Troubleshooting

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2006 AT&T Knowledge Ventures. All rights reserved.

AT&T is a registered trademark of AT&T Knowledge Ventures.

RSSI troubleshooting


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January 8, 2012Page 2 2006 AT&T Knowledge Ventures. All rights reserved.


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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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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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

3

6

9

12

15

010

20

30

40

50

60

70

80

90

100

Loading

Noise

rise

[dB]


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What is new in P5MD?

RBS P5ED

RBS P5MD

RNC P5MD

New

New


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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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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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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


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


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

RSSI Overwiev Troubleshooting

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