ul rssi mitigation techniques
DESCRIPTION
UL RSSI Mitigation and OptimizationTRANSCRIPT
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).
0
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Loading
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%
12.00%
14.00%
16.00%
18.00%
Ark
ansas/O
kla
hom
a
Illin
ois
/Wis
consin
Mic
hig
an/India
na
Mis
souri/K
ansas
ND
/SD
/NE
/MN
/IA
Nort
h T
exas
Ohio
/Weste
rn P
ennsylv
ania
South
Texas
E. P
A/S
. N
J/D
E
New
Engla
nd
NY
C/N
NJ
Upsta
te N
Y
VA
/WV
A
Washin
gto
n D
.C./M
ary
land
Ala
bam
a/M
issis
sip
pi/L
ouis
iana
Georg
ia
Nort
h C
aro
lina/S
outh
Caro
lina
Nort
h F
lorida
Puert
o R
ico
South
Flo
rida
Tennessee/K
entu
cky
AZ
/NM
CO
/UT
/WY
/MT
/So. ID
Los A
ngele
s
San D
iego/L
as V
egas/H
aw
aii
San F
rancis
co/S
acra
mento
Seattle
/Ore
gon/N
o. ID
ED Market
Perc
en
tag
e o
f C
ell
s (
%)
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
0 A
M
2:0
0 A
M
3:0
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M
4:0
0 A
M
5:0
0 A
M
6:0
0 A
M
7:0
0 A
M
8:0
0 A
M
9:0
0 A
M
10
:00
AM
11
:00
AM
12
:00
PM
1:0
0 P
M
2:0
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M
3:0
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4:0
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:00
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:00
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.