UL RSSI Mitigation Techniques

UL RSSI MitigationUL RSSI MitigationUL RSSI MitigationUL RSSI Mitigation

March 1, 2012March 1, 2012March 1, 2012March 1, 2012

Why is UL RSSI Important? Every UMTS Operator will at one time or another

experience an Radio Environment degradation as it relates to UL RSSI

especially during the initial launch or when rolling out additional carriers.

Deviating from the expected UL RSSI levels severely impacts the performance

of the sites in terms of coverage and capacity.

An effort has been initiated by Ericsson to author a Decision Process Flow

Chart along with a UL RSSS Mitigation Guideline to assist the Customer

(Regions/Markets) in identifying and resolving UL RSSI problems. This

presentation will provide the Process Flow Chart along with supplementing the

algorithm with examples of actual interference issues discovered and resolved

in a live 3G Network.

Purpose

UL RSSI, Counters & Unloaded System Value

› What is UL RSSI?– Received Signal Strength Indicator of the total wideband received power within the

entire channel bandwidth

– Note that RSSI does not distinguish between own, other, or any other unwanted internal 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 every

second and stored as a PDF step range, [65] long (-110 to -65 dBm, with the resolutions 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 the thermal

noise N = 10log(kTBNf)(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 and

– The total effective noise = -172 + 10*log(3,840,000) = -106 dBm

UL RSSI, Counters & Unloaded System Value

› What impact will my traffic have on the UL RSSI?– If the system load (Mpole) increases to 50%, a 3 dB noise rise may be observed.

– This means that one may expect an uplink interference level of -106 + 3 = -103 dBm

› How does the system configurable parameters affect the UL RSSI?– No TMA: Value Reported = Value Measured in RBS + UL Attenuation MO:

AntFeederCable

– With TMA: Value Reported = Value Measured in RBS + Ul Attenuation MO: AntFeederCable – ULGainMO:ExternalTMA

– So, if one assumes an RBS without a TMA, and the UL Attenuation set to 3 dB, than we should investigate a site if the UL RSSI exceeds -100 dBm (-103 dBm + 3 dB).

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Noise rise [dB]

Sample UL RSSI Environment

Shown below is a nationwide RTWP “snapshot”– reflecting the current performance

of an Ericsson Customer (at the market level) in terms of Elevated and Deficient UL

RSSI over a 1 week interval. It’s apparent for this customer that a significant

number of their markets are experiencing severe elevated UL RSSI.

Percentage of Cells per ED Market - Ericsson UTRAN

Based on RTWP Busy Hour

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

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16.00%

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South

Texas

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Los A

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%)

VERY_HIGH HIGH LOW

For the Customer shown in the previous slide – one of their more challenged markets (S. Florida)

in terms of UL RSSI performance was surveyed to produce a listing of the sources/contributors

identified by the RF Performance Team. Shown below is a representation or breakdown of the

interference issues in terms of Faulty H/W, RF Design/Configuration & 3Rd Party External Sources.

Surveyed Market – Compiled ISSUEs

Faulty Hardware

› Failing Diplexers (RFS). Raises the noise floor to an average of -85 dBm and often goes undetected in some markets.

› Poor Antenna Connections

› RxAIT (Receive Antenna Interface Tray) Duplexer

› MCPA

RF System Design / Configuration Optimization

- Loss and Delay parameters were not set correctly in the cable system.

- TMA object created for RxAIT for a single antenna branch only (known Ericsson corruption issue)

- RxAITs mistakenly configured in the RBS (TMA object created on both branches)

- MAI (Multiple Access Interference) list error

Surveyed Market – Compiled ISSUEs

3rd Party External Interference Sources

› Bi-Directional Amplifier (BDA) Interference

– Marine Traffic

– Fixed Locations

– Recreational Vehicles (RVs)

› Cable TV (CATV) Interference

– Improper terminations on trunk lines

– Housing to housing leaks

– End user attaching CATV line to an outdoor antenna

› Wireless Cameras

› RFID Scanners for vehicle entry systems

› Wi-Fi Amplifiers

› 840 MHz Wireless Microphones imported from Europe

› Cell Phone Jammers

– Used by a teacher to stop children from sharing notes / answers

– Jails / Prisons

– Ambulance driver to get people off of their phones

› TV Station Transmitters

› On Star System

› Power over Ethernet

› Symbol Inventory Systems

› 9th Order Harmonics from Commercial FM Radio Transmitters

› Sierra Wireless Air Card (stuck in transmit mode @ high power – Model # 881)

Top Reasons/Sources – Nationwide

Expanding on the previous slide – categorization of the aforementioned issue (at National Level)

was undertaken in terms of identifying them as resulting in either Elevated or Deficient UL RSSI

as shown below:

Elevated UL RSSI

› External Sources

- External Interference (Bi-Directional Amplifiers, Digital TV Antennas, CATV Cable Failures, etc.)

- GSM Interference

- UMTS High Sites (Boomer sites which could be over-serving and carrying a very high level of traffic)

› Internal Sources

- Faulty Diplexers

- Incorrect Parameter Settings

- Faulty Antenna/TMA

- Incorrect Installation

Deficient UL RSSI

- Faulty or Non-Powered TMAs

- Incorrect Parameter Settings

- Faulty Diplexers/Cable/Connectors

- Incorrect Installation (RX-AIT Attenuators, etc.)

UL RSSI Investigative techniques & UL RSSI Investigative techniques & UL RSSI Investigative techniques & UL RSSI Investigative techniques & Process Flow ChartProcess Flow ChartProcess Flow ChartProcess Flow Chart

UL RSSI Investigation approach

› How do we determine which sites should be investigated?

– Investigate sites with reported UL RSSI values outside of the normal range:

Normal

The normal range depends on the

market design and traffic load

Low UL RSSI

This example site is considered “deaf” since all samples are below -110 dBm

High UL RSSI

This example has a considerable number of samples outside of the normal range.

Comparison between UL RSSI Mitigation & Decision Flow Process

A Decision Flow Process has been developed to assist the Customer in determining the cause or

source of the Elevated or Deficient UL RSSI – shown below is a Level 1 Process Layer. A more

detailed process covering the decision blocks will be presented in the slides that follow.

Overview of Decision Process Flow

Comprehensive overview of the steps one might take to identify the root causes behind an

Elevated or Deficient UL RSSI situation.

DECISION PROCESS FLOW – DEFICIENT UL RSSI SCENARIO [1.1]

INPUT

a) Average UL RSSI reading over a seven day

interval to encompass the busy hour window.

b) Site/Cell Parameter Readout and RF Design

Database.

PROCESS DESCRIPTION

a) Based on the results from the Business Objects or

Prospect report determine if the site/cell is

exhibiting deficient UL RSSI.

b) Rule out any incorrect parameter settings or site

configuration inconsistencies through the use of

OSS and the various RF Design Databases.

OUTPUT

a) Finalize list of sites/cells that are exhibiting

extremely low UL RSSI.

b) Move on to the TMA Audit Process.

DECISION PROCESS FLOW – ELEVATED UL RSSI SCENARIO [1.2]

Problem Description

Issue Resolved?

Rule outs

INPUT

a) Average UL RSSI reading over a seven day

interval to encompass the busy hour window.

b) Site/Cell Parameter Readout and RF Design

Database.

PROCESS DESCRIPTION

a) Based on the results from the Business

Objects or Prospect report determine if the

site/cell is exhibiting elevated UL RSSI.

b) Rule out any incorrect parameter settings or

site configuration inconsistencies through the

use of OSS and the various RF Design

Databases.

OUTPUT

a) Finalize list of sites/cells that are exhibiting

extremely low UL RSSI.

b) Move on to the TMA/Site Audit Process.

DECISION PROCESS FLOW – TMA AUDIT [1.3]

TMA Audit [1.3]

Sector

Confgured for

TMA in RBS

EM?

TMA Powered

by Sector in

RBS EM

TMA is

Powered by

GSM, Other

Band or Ext

Source

Yes

No 850 MHz Site?

TMA 850

Bypass Model

in RND-CIQ/

RFDS

Yes

Yes

TMA Current

Reading

TMA is not

Powered

No

Incorrect TMA

Installed

< 130 mA

> 180 mA

YesNo

No

From 1.1

Go To 1.4 [Site

Audit]

INPUT

a) Current/Voltage measurement

readings for installed TMAs and

b) Existing Site/Cell Configuration and

original RF Design Database.

PROCESS DESCRIPTION

a) Employ RBS Element Manager (EM)

to determine if the Site/Cell is

configured for a TMA and identify

the Power Source for the amplifier.

b) Utilize AMOS or NCLI to determine if

the Voltage/Current presently used

by the TMA is within the specified

limits. Should note that the readings

are only valid for Ericsson TMAs.

OUTPUT

a) List of Cells with improperly

configured or malfunctioning TMAs.

b) Move on to the Site Audit Process

DECISION PROCESS FLOW – SITE AUDIT [1.4]

INPUT

a) Existing Site/Cell Configuration

along with the original RF Design

Database and

b) Equipment logs collected from the

effected sites/cells for the

RUIF/RAXB.

PROCESS DESCRIPTION

a) Employ RBS Element to determine if

the Site/Cell properly incorporates

the losses associated with an RX-

AIT and the respective attenuator.

b) Utilize NSA/NCLI to review the H/W

log files for any errors that were not

present in the Alarm Log.

OUTPUT

a) List of Cells deployed with the wrong

attenuators, incorrect data fill in RBS

EM or exhibiting H/W Faults.

b) Implement Corrective Action(s)

DECISION PROCESS FLOW – TMA/SITE AUDIT [1.5]

INPUT

a) Current/Voltage measurement

readings for installed TMAs and

b) Existing Site/Cell Configuration and

original RF Design Database.

PROCESS DESCRIPTION

a) Employ RBS Element Manager (EM)

to determine if the Site/Cell is

configured for a TMA and utilize

AMOS or NCLI to determine if the

Voltage/Current is within the

specified limits.

b) Utilize RBS EM to determine if the

Site/Cell properly incorporates the

losses associated with an RX-AIT

and the respective attenuator.

OUTPUT

a) List of Cells deployed with the wrong

attenuators or incorrect data fill in

RBS EM.b) Implement Corrective Action(s)

Elevated / Deficient UL RSSI Elevated / Deficient UL RSSI Elevated / Deficient UL RSSI Elevated / Deficient UL RSSI ----Detailed Market ExamplesDetailed Market ExamplesDetailed Market ExamplesDetailed Market Examples

Elevated UL RSSI: Bi-Directional Amplifier

Majority of the External Elevated UL RSSI cases appear to

be associated with BDAs and other Consumer Related

Devices (Digital TV Antennas, etc.). S. Florida Performance

Team has seen numerous occurrences of BDAs negatively

impacting their network – pictures/tables depicted are taken

from a UL RSSI Mitigation Activity which identified a BDA at

the SBC NOC.

Similar to the situation in the previous slide –

South Florida along with Connecticut/Boston

and other coastal markets have seen a

proliferation of problems associated with

consumers employing BDAs to boost the signal

on Yachts, Oil Platforms, etc.

Elevated UL RSSI: BDAs Continued

In addition to the BDAs - S. Florida Performance Team discovered a nearby CATV

installation where the connections were aging and emitting spurious emissions

negatively impacting the UMTS site approximately 1500 ft away. For whatever reason –

Florida Team is detecting and resolving a very high number of Elevated UL RSSI

situations based on self reporting by the Market.

Elevated UL RSSI: CATV Plant Aging

Elevated UL RSSI: Faulty Diplexers

Market RSSI tracker during Rollout

Vs.

Before

After

Vs.

Before

After

Vs.

Before

After

A faulty diplexer can be

the source of unwanted

interference on the Uplink.

During the course of

conducting a site

investigation – local RF

Performance Team & Site

Technicians discovered

that a specific RSS

Diplexer Model resulted in

an increase to the Uplink

RSSI. Once the diplexers

were replaced, the UL

RSSI recovered to the

normal and expected

levels.

Elevated UL RSSI: Faulty Antenna/TMA

RBS

TMA

A Tower Mounted Amplifier (TMA) or

Antenna may also be a source of

interference. TMAs due to their active

components have a higher failure rates and

are replaced while Antennas generally do not

experience high MTBF rates.

Troubleshooting is typically accomplished

through the use of a dummy load and/or

spectrum analyzer to isolate the interference

source.

Elevated UL RSSI: Incorrect Parameter Setting

When utilizing a RX-AIT

(Antenna Sharing Unit) and/or

TMA, it is very important that one

takes the necessary steps to

ensure that the configurations

are correctly in the NodeB.

Typically, an RX-AIT Uplink Gain

is 10 dB for 1900 MHz and 20 dB

for 850 MHz. The attenuator loss

is typically 4 dB, unless it is an

850 MHz installation

accompanied by a TMA, where

the attenuation will be 15 dB.

Elevated UL RSSI: Incorrect Parameter Setting

UL Attenuator values in the clusters were fixed to include the 6 dB gain.

If a site reports 6 dB lower RSSI than other cells, it could be that that RX-AIT is down

6 dB

6 dB

Another example of

how an incorrect

parameter setting

may result in the site

experiencing an

elevated UL RSSI

level. For this

particular case – RX-

AIT attenuator values

were improperly set.

Elevated UL RSSI: Faulty Installation

During the design of an

antenna sharing solution –

engineering team

determined the need for a

15 dB attenuator (on the

Rx Path) to prevent the

receivers from being

saturated. Unfortunately,

the attenuators were

never installed and

resulted in an average UL

RSSI of 88 dBm being

observed at the site.

Elevated UL RSSI: Faulty Installation

For this situation – local Operations

Team added the incorrect attenuator

pads at the site and it resulted in a

spike to the UL RSSI. Installing the

proper attenuation moved the UL RSSI

to the expected range.

Elevated UL RSSI: Faulty Installation

For this particular site which is an

Indoor Site – design required an

attenuator to be installed for the

Distributed Antenna System (DAS).

This task was never completed and the

result was an elevated UL RSSI

environment.

Elevated UL RSSI: Increased CS Speech Traffic

Increase in RSSI

Sometimes the

source of an

increase to the UL

RSSI can be a

simple as elevated

traffic levels. As a

rule – if the noise

rise is higher than

3-4 dB while the

load is less than

50-60%, than

further investigation

should be

performed.

Neighboring cells and external interference are examples

that may be the source of interference.

Elevated UL RSSI: External Interference

DL CE Usage

MapInfo and the Statistics were used to narrow down the location of the source

and a Yagi + Spectrum Analyzer confirmed that it was a 1500 ft broadcast

tower which was generating a network wide harmonic interference.

For this example –

more than 280 sectors

were effected in a S.

Texas City. Avg. RSSI

was generally

acceptable, but the

No. of samples > “-

90.5 to -90 dBm”

indicated the

presence of an

external interferer.

Have not had many occurrences of GSM Interference reported from the Markets but the

cases have proven to be quite difficult to resolve. TelCel, a Mexican Wireless Operator,

was using the same band as AT&T’s UMTS network in San Diego and resulted in a

significant impact the 3G Network’s performance.

200kHz GSM spikes will impact the RTWP

on UMTS

Elevated UL RSSI: Cross Border External Interference

High Interference

Border with Mexico

Elevated UL RSSI: GSM Interference

DL Code Usage

-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

-85.00

1:0

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2:0

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6:0

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9:0

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10

:00

AM

11

:00

AM

12

:00

PM

1:0

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M

2:0

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:00

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AM

UL RSSI measured by sites experiencing GSM interference

Ave. UL RSSI measured by sites with configuration issues

Ave. Network UL RSSI

Narrow band GSM

interference is easily

identified by the fact

that the reported UL

RSSI follows a

similar pattern as

the GSM traffic

profile as seen the

accompanying

graph.

Elevated UL RSSI: RRC request Congestion

High congestion of RRC Connection Requests can lead to increased UL RSSI level due to the

number of re-attempts that in turn affects Quality of Service for both voice and data (Call Drops,

BLER, etc.)

The failure can affect the serving cell and the neighbor cells for the reasons listed below:

� IP Stack failure

� Iub Congestion

� Wrong parameter configuration of “RRC Load Control” Feature

� Wrong parameter configuration of “Admission Control”

Abnormal increase of

RRC Connection

Requests and Rejections

Elevated UL RSSI: RRC request Congestion

High percentage of RRC Connection Requests rejected which increases the UL RSSI level, affecting voice and data

performance

Deficient UL RSSI – Faulty or Incorrectly Powered TMA

One of the most prevalent causes or source of Deficient UL RSSI resulting in “Deaf” Sites

have been Faulty or Improperly Powered TMAs. Problem was widespread in two Market

Launches where the sites were built with internalpower = NO for both the GSM and UMTS

RBSs.

System assumes that a 12 dB

gain has been applied -

resulting in the RSSI floor that

should be -105 dBm being

reported as -110 dBm

Altering the GSM BTS IDB to

properly denote the power

source for the TMA remedied

the problem.

Deficient UL RSSI – Incorrect Attenuation

Incorrect Attenuators at sites employing the RX-AIT Solution has been one of the other main

reasons or causes behind the site experiencing Deficient UL RSSI. An example taken from one

of several markets where the wrong attenuator pad was corrected and the UL RSSI returned to

the expected levels. This type of problem was observed to occur more often during the initial

Network Launch and resulted in both Deficient and Elevated UL RSSI measurements.

The table below reflects the correct attenuation padding that should be employed at the RX-AIT

for the different Frequency Bands.

Deficient UL RSSI – Equipment Failures/Configuration

Site in Northeast Region where the Operations

Team changed the site configuration by

removing the RX-AIT and TMA without notifying

the Performance Team which had not updated

the configuration in the OSS/RBS Element

Manager.

Customer opted

to zero out the

UL Gain as

opposed to

removing the

TMA Definition at

the site.

Conclusions

› High and Low UL RSSI Measurements usually indicates a

problem within the system setup or equipment functionality.

› Hourly and Daily Statistics can help to identify if the

interference is constant or systemic with the 2G and 3G Traffic levels.

› It is important to ensure that all system parameters and installation issues have been checked/resolved before one

initiates a search for possible external interferer.

› Using a GIS Tool combined with statistical data can help to

narrow down the location of the external interference source.