1. Document
number
Product name CDMA
Used by Huawei engineers Product version
Drafted by CDMA RNP Document version 1.0
CDMA System RSSI Exceptional
Troubleshooting Guideline V1.0
Prepared by Si Binhe (54736) Date March 2007
Reviewed by Date
Approved by Date
Tempus Telcosys (P).,Ltd.
Time is Almighty
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2. Contents
1 Overview..................................................................................................................3
2 RSSI Exceptional Analysis...................................................................................4
2.1 RSSI Exceptional Phenomena......................................................................................................4
2.1.1 Subscriber Experience.............................................................................................................4
2.1.2 Terminal Phenomena...............................................................................................................4
2.1.3 Traffic Statistics OMC Phenomena .......................................................................................4
2.1.4 Other Phenomena....................................................................................................................4
2.2 RSSI Exceptional Classifications..................................................................................................5
2.2.1 RSSI Exceptional Caused by Poor Engineering Quality........................................................5
2.2.2 RSSI Exceptional Caused by Parameter Settings...................................................................5
2.2.3 RSSI Exceptional Caused by Equipment Abnormality...........................................................5
2.2.4 RSSI Exceptional Caused by Unallocated Terminals.............................................................6
2.2.5 RSSI Exceptional Caused by Base Station Blocking..............................................................6
2.2.6 RSSI Exceptional Caused by Heavy Traffic...........................................................................6
2.2.7 RSSI Exceptional Caused by External Interference...............................................................6
2.2.8 Summary of RSSI Exceptional and Relevant Causes.............................................................8
2.3 RSSI Exceptional Analysis Steps..................................................................................................9
2.3.2 Traffic Statistics Analysis......................................................................................................11
2.3.3 Alarm Data Analysis.............................................................................................................12
2.3.4 Historical Operations Analysis.............................................................................................12
2.3.5 Parameter Checking.............................................................................................................13
2.3.6 Antenna and Feeder Checking..............................................................................................14
2.3.7 Interference Testing...............................................................................................................14
2.3.8 Summary and Conclusions....................................................................................................15
3 RSSI Exceptional Troubleshooting...................................................................16
3.1 Interference Testing.....................................................................................................................16
3.2 Interference Data Analysis..........................................................................................................16
3.3 Determining Interference Troubleshooting Solution..................................................................17
3.4 Eliminating Interference.............................................................................................................17
3.5 Verification..................................................................................................................................17
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3. 1 Overview
Reverse received signal strength indicator (RSSI) is the reverse signal
reception indicator in 1.2288 MHz band of base station. Normal RSSI
indicates that the reverse channel is operational.
In actual networks, RSSI exceptional may be contributed to
engineering quality, equipment, terminal, parameter settings, and
interference. That is, RSSI exceptional does not means the
interference exists in the network.
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4. 2 RSSI Exceptional Analysis
2.1 RSSI Exceptional Phenomena
2.1.1 Subscriber Experience
 User average access time is larger than 5 seconds.
 In serious conditions, the subscribers are hard to access the
system.
 Audio discontinuity, noise, silence, monologue call or even call
drop exists during a call.
2.1.2 Terminal Phenomena
 Terminal transmit power is very high, Rx + Tx > -70dBm.
 The terminal cannot access the system for a long period of time.
20 seconds later, the terminal is dropped from the network and
researches a network.
2.1.3 Traffic Statistics OMC Phenomena
 RSSI of carrier with slow access speed is larger than-95dBm.
 RSSI of carrier that access unavailable is larger than -80dBm.
 RSSI is too small, and is smaller than -120dBm for a long period
of time.
 The difference between main RSSI and diversity RSSI exceeds
6dB for a long period of time.
2.1.4 Other Phenomena
In the RFMT data tracing, the indicators, such as RevBadFrame,
RevSetEbNt, FwdFer, FwdSetEbNt, and MsRxPwr are degraded.
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5. 2.2 RSSI Exceptional Classifications
2.2.1 RSSI Exceptional Caused by Poor Engineering
Quality
RSSI exceptional is caused by base station equipment, for example,
the improper installation, connectors loosen, antenna soaked, or
antenna aging. In such cases, the difference between main RSSI and
diversity RSSI is large or RSSI is too small.
2.2.2 RSSI Exceptional Caused by Parameter Settings
 Initial access power parameter is set to a large value.
 TCH minimum gain is too large.
 LAC division error, Reg_zone boundary zone, Total_zone, and
Zone_timer settings are improper or Reg_zone setting is incorrect,
resulting in frequency registrations of terminals. In such cases, the
RSSI may be increased.
 Open access macro diversity (partial exceptional terminals).
 Layer 2 acknowledgment of base station is not enabled (mainly for
IS95 MSs).
In such cases, main RSSI and diversity RSSI are high simultaneously.
2.2.3 RSSI Exceptional Caused by Equipment
Abnormality
RSSI exceptional caused by equipment abnormality has two types:
 RSSI exceptional is caused by RF front end. The RF front end
problems contain passive intermodulation due to antenna
damaged. The power capacity limit is insufficient, and the RSSI is
worse after the multi-carrier is enabled. RSSI exceptional also can
be caused by the connector intermodulation, or lightning arrester
abnormality.
 RSSI exceptional is caused by BAM abnormality, for example,
transmission or BSC resource allocation module failure, and many
calls are rejected frequently, result in the repeated calls. There are
too many network busy hour attempts, for example, over 3000
attempts. The traffic statistics or CSL shows that many calls are
released abnormally.
In such cases, main RSSI and diversity RSSI are high simultaneously.
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6. 2.2.4 RSSI Exceptional Caused by Unallocated
Terminals
When some MSs and FWTs whose techniques are inconsistent with
the CDMA industry standards access the network, the terminals
neglect the power control messages delivered by the network, or the
power control commands delivered by the system are invalid for the
terminals.
In actual networks, the unallocated MSs or FWTs whose techniques
are inconsistent with industry specifications increase the noise floor of
network.
In such cases, main RSSI and diversity RSSI are high simultaneously.
2.2.5 RSSI Exceptional Caused by Base Station
Blocking
When the base station is blocked or the baseband gain is set to a
small value, the base station becomes a receiver. The MSs within its
coverage range cannot receive the signals of this site, and access the
surrounding base stations for launching services.
The MSs near the site are far away from surrounding base stations.
When the MSs access the surrounding base stations for launching
services, large transmit power is required to ensure the communication
with surrounding base stations. The RSSI of this site is affected
dramatically.
In such cases, main RSSI and diversity RSSI are high simultaneously.
2.2.6 RSSI Exceptional Caused by Heavy Traffic
When the RSSI is too high or the difference between main RSSI and
diversity RSSI is large, check the traffic of this carrier first.
If the traffic is heavy (>30Erl) and RSSI is changed with the traffic, the
RSSI exceptional may be caused by the heavy traffic. We exploit the
potentials of existing network or consider network expansion to reduce
the carrier load and realize the load sharing. When the traffic is
reduced, RSSI is restored to a normal value.
In such cases, main RSSI and diversity RSSI are high simultaneously.
2.2.7 RSSI Exceptional Caused by External
Interference
Interphone interference
The interphone interference is mainly present in the hotels, office
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7. buildings, and governmental organizations. The interference of
interphone system is generated at random.
Generally, it is used almost 24 hours one day. Therefore, the
interference is hard to control. The interphone transmits small power
and the interference range is small, so the adjacent channel
interference and intermodulation interference have small impact.
This kind of interference can be avoided if the frequency band used by
the interphone system is far away from the frequency band we use.
Repeater interference
At the early stage of network construction, the repeater was used to
extend the coverage range of base station. It increases the noise floor
of CDMA system.
If the use of repeater in the network is inappropriate, the interference
to the base station is generated easily, affecting the CDMA coverage
range and reducing the quality of service.
The following types of repeater interference are available:
(1) RSSI is increased because of large reverse gain.
(2) The components of repeater are invalid.
(3) The repeater installation is not standardized, and insufficient
isolation exists between donor antenna and user antenna and the self-
excitation is generated, affecting the normal operation of base station
that the repeater is attached.
 Self-excitation
After the signals transmitted from the repeater are received again
through the donor antenna, the signals are amplified through the
repeater and then are transmitted. The amplified signals are received
and then amplified. Such circle results in a bad condition.
Radar station and TV station interference
The frequency used by Some decimetric wave radars designed in
1970’ and 1980’ is similar to 800MHz frequency of CDMA system.
The transmit power is large, so the power level reaches several tens to
hundreds kw range and the outband spurious emission is large, easily
interfering to the adjacent 800MHz base stations.
The TV station mainly operates at 450 MHz frequency band, and
easily interferes to 450MHz CDMA system.
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8. AMPS interference without frequency retire
The original military AMPS system operates at the same frequency
band with CDMA2000 1X.
If the frequency band used by original military AMPS system was not
retired and is still used in some regions, it interferes to CDMA20001x
system operating at 800MHz frequency band.
Microwave transmission interference
The transmission microwave transmission links exist in many places.
These microwave transmissions operate at a high frequency band
(about 2 GHz). They have a small impact on existing 800MHz CDMA
network but interfere to the network operating at about 2000 MHz,
such as CDMA 1900MHz.
Other interference
The types of communication devices are various. Some companies
use the frequency band inconsistent with the industry standard and
occupy the frequency band for CDMA 1x being constructed.
The placement and isolation are inappropriate, so many dedicated
communication devices interfere to the coverage areas of CDMA
network.
In addition, there are broadband noises generated by the electric arc
and sparkles of electricity factor and electricity station.
Other types of interference sources are available, such as conference
interference system, computer screen interference unit, neon light
strike, TV active receiver, and high voltage transformer.
In such cases, the main RSSI and diversity RSSI are increased
simultaneously or the unipolarization RSSI is high.
2.2.8 Summary of RSSI Exceptional and Relevant
Causes
RSSI Exceptional Phenomenon Possible Causes
RSSI too low Main/diversity RSSI is smaller
than -110dBm for a long period of
time.
The connectors of antenna
and feeder are connected
insecurely or antenna and
feeder, TRX, CDU, or power
amplifier are faulty.
RSSI too high Main/diversity RSSI is higher than
-95dBm for a long period of time
or within a certain period of time.
Switch and jumper errors,
hardware faulty, water
penetrated in connectors,
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9. antenna and feeder standing
wave, parameter settings
(registration and access
message settings
inappropriate), system faulty,
spurious emission and
intermodulation, and external
interference
RSSI main and
diversity difference
large
The difference between main
RSSI and diversity RSSI is over
6dB or RSSI main/diversity
comparison alarm and TRM
main/diversity reception alarm
exist.
Antenna and feeder standing
wave, antenna installation
problems, hardware faulty,
diversity bypass switch setting
error, and external
interference
2.3 RSSI Exceptional Analysis Steps
The analysis of reverse RSSI is showed in Figure 1.1.
Analyze the RSSI data collected first.
If main/diversity RSSI is higher than -95dBm for a long period of time
or within a certain period of time, or The difference between main RSSI
and diversity RSSI is over 6dB, it may be caused by the heavy traffic,
equipment fault, manual operation, or external interference.
In such cases, collect the RSSI data within a week and check the
change of RSSI within this period of time. According to the information,
as well as alarms and historical operations, determine roughly the
causes of RSSI exception, and identify the causes according to the
following flowchart to tackle the RSSI exceptional problem.
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11. Figure 1.1 Flowchart of RSSI exceptional analysis
2.3.2 Traffic Statistics Analysis
Heavy traffic
When finding that the RSSI is too high or the difference between main
RSSI and diversity RSSI is large, check the traffic of carrier first. If the
traffic is high (> 30Erl) and RSSI is changed with the traffic, the RSSI
exceptional may be caused by heavy traffic.
We exploit the potentials of existing network or consider network
expansion to reduce the carrier load and realize the load sharing.
When the traffic is reduced, check whether RSSI is restored to a
normal value.
ACH occupation and call attempts analysis
Check the ACH occupation.
If the ACH occupation exceeds 60%, analyze the ACH occupation
according to the registrations and call attempts, and determine
frequency registrations or frequent accesses originated by the user
results in the high ACH occupation.
If it is caused by the frequent registrations, modify the registration
parameters and reduce the registrations.
If the user originates frequent access when the traffic is not heavy,
identify the real reasons. Check the operating status of equipment and
eliminate the cause of system abnormality.
Generally, the high ACH occupation is caused by incorrect settings of
LAC zone parameters, or system operation abnormality.
For details, refer to section 2.3.3Alarm Data Analysis and section
2.3.5Parameter Checking.
Many call resources allocation failure
RSSI exceptional is caused by equipment abnormality, for example,
transmission or BSC resource allocation module failure, and many
calls are rejected frequently, result in the repeated calls.
There are too many network busy hour attempts, for example, over
3000 attempts. The traffic statistics or CSL shows that many calls are
released abnormally.
If the allocation of many call resources fails, the ACH load may be also
high.
Check whether many calls are rejected because of the transmission,
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12. CE configuration, FMR resources, SPU load or roaming restriction.
Through the previous operations, RSSI is restored to a normal value,
and the process ends. Otherwise, conduct the next round.
2.3.3 Alarm Data Analysis
Check the alarms, such as RSSI main/diversity received channel fault
alarm, TRM main/diversity comparison exceptional, or standing wave
alarm.
If these kinds of alarms are available, check the alarm date and the
association between RSSI exceptional and alarm data.
If the RSSI exceptional is associated with the alarm data, RSSI
exceptional may be caused by the equipment faults.
To locate the problems, do as follows (before performing the following
operations, check the regularity of RSSI exceptional and perform the
following operations when the RSSI is exceptional):
1) Trace the RSSI of base station through TELNET. 10 minutes later,
check the change of RSSI and find the regularity.
2) If the RSSI is exceptional, check the connection cables and screws
of DDU, power amplifier and TRM at near end are secure. Check
whether RF cables are damaged and the connectors are secure.
Ensure the antenna SWR is within the receivable range.
3) Check the DDU, power amplifier, and TRM at near end. If the
indicators flash abnormally, reset and insert or remove the units and
observe the status.
4) Trace the RSSI of base station through TELNET. 10 minutes later,
save the records, and analyze whether RSSI is changed or is
restored to a normal value.
5) If RSSI is still exceptional, conduct the next round.
Main/diversity received channel fault mechanism checks the
main/diversity RSSI and reports the alarm. The alarm report depends
on the difference between main RSSI and diversity RSSI and the
difference duration. In different versions, the alarm thresholds of these
two input values are also different.
2.3.4 Historical Operations Analysis
Check the historical operation records of RSSI exceptional cell and
observe the added or modified base station hardware and the changed
data, and the association between the interference occurrence time
and operation time.
If the carrier is conducted within the near end time and RSSI
exceptional time is associated with the operation time, the RSSI
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13. exceptional is caused by this operation.
The RSSI rise may be contributed to the upgrade, parameter
adjustment and RF adjustment.
Upgrade
The RSSI exceptional caused by the upgrade mainly represents the
BSC upgrade. If the RSSI is increased after the BSC is upgraded,
check the change of parameters before and after upgrade, and restore
the changed parameters to the parameters before upgrade as
possible. Check whether RSSI is restored to a normal value.
Parameter adjustment
The RSSI rise may be caused by the parameters, such as
TOTAL_ZONES, ZONE_TIMER, initial access power control
parameter, and baseband gain.
RF adjustment
Check whether the RSSI rise time is associated with RF adjustment
time. If yes, check the change of traffic. If the RSSI exceptional is
caused by heavy traffic, exploit the potentials of existing network or
consider network expansion to reduce the carrier load and realize the
load sharing.
When the traffic is not changed, check the antenna and feeder are
connected securely.
If the RSSI is restored to a normal value, the process ends. Otherwise,
conduct the next round.
2.3.5 Parameter Checking
The inappropriate parameter settings also may result in the RSSI rise.
When the RSSI is increased, check the following parameters:
A. Initial access power parameter: If this parameter is set too large,
MS transmits at large power when accessing a network. As a
result, the noise floor and RSSI are increased.
B. TCH minimum gain: If the TCH gain is too large, the terminal
transmits large power over TCH. As a result, the voice quality is
improved, and the RSSI is increased. If the TCH gain is set too
large, it has a small impact on the voice quality, but the system
capacity and RSSI are affected largely.
C. Inappropriate settings of Reg_zone, Total_zone, and Zone_timer or
Reg_zone setting error result in the frequent terminal registrations.
As a result, the RSSI may be increased.
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14. D. Open the access macro diversity (some exceptional terminals).
E. Base station layer 2 acknowledgment switch is not enabled (mainly
for IS-95 MS).
F. Check the diversity bypass switch (when a sector has two
carriers).
For the settings of parameters A, B, and C, refer to the network
planning common parameters.
For the settings of parameters D and E, refer to Technical Notice No.
[2006] CDMA002--Technical Notice on Enabling BTS Layer 2 ACK
Switch and Technical Notice No. [2006] CDMA003--Technical Notice
on Disabling Access Macro Diversity Switch.
2.3.6 Antenna and Feeder Checking
Exchange the antenna and feeder of adjacent two cells, and check
whether the high RSSI is caused by the antenna and feeder.
For the omnidirectional sites, exchange the main antenna and feeder
with diversity antenna and feeder, re-trace the RSSI.
After the antenna and feeder are exchanged, if the difference between
main RSSI and diversity RSSI is changed, the RSSI exceptional may
be caused by antenna and feeder or external interference.
Check the antenna and feeder, for example, the lightning arrester is
not damaged, and the connectors between jumper and feeder and
between the jumper and antenna are secure, and then check the
change of instantaneous RSSI.
After the antenna and feeder are exchanged, if the difference between
main RSSI and diversity RSSI is not changed, the RSSI exceptional
may be caused by CDDU, TRX, and HPA or external interference.
Block the carriers, and check the change of RSSI.
After you block the carriers, if the difference between main RSSI and
diversity RSSI is small, the RSSI exceptional may be caused by TRM
or other hardware.
Through the previous operations, if the RSSI is still high, the RSSI
exceptional is caused by external interference, and conduct the
external interference testing.
2.3.7 Interference Testing
The external interference may interfere to surrounding sectors. As a
result, the RSSI values of surrounding carriers are increased.
Thus, before the interference testing, import the site informaiton by
using the Mapinfo, and check the areas to which the RSSI exceptional
cell points. According to the point direction of RSSI exceptional cell,
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15. locate roughly the position of interference source and then use
YBT250 to find the interference source.
For the procedure of identifying external interference, refer to
Interference Analysis Guideline.
2.3.8 Summary and Conclusions
This section examines the analysis of reverse RSSI exceptional. If the
personnel are sufficient and the customer has a high requirement,
analyze the RSSI exceptional through several procedures at the same
time. For example, in the equipment room, when the engineers can
check alarms, they can check the parameters and analyze the traffic
statistics. The field engineers can identify the interference through the
RSSI tracing at near end, antenna and feeder adjustment and
interference testing, together wit the engineers in the equipment room.
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16. 3 RSSI Exceptional Troubleshooting
Forward and reverse interferences degrade the network quality, so we
must assist the customer to eliminate the interference.
If the interference is determined, do as follows:
3.1 Interference Testing
Test the forward and reverse interferences according to the
Interference Testing Guideline.
3.2 Interference Data Analysis
Analyze the collected information, and locate preliminarily the reasons
of RSSI exceptional (too high or the difference between main RSSI
and diversity RSSI is large).
If the RSSI exceptional is caused by non-external interfere, identify
different solutions regarding to different reasons.
If the RSSI exceptional is caused by external interference, determine
the interference characteristics, interference types, and the
interference occurrence regularity, and confirm the interference type,
such as inband interference or outband interference, stable broadband
interference or burst interference.
On the forward link, make the quantitative analysis according to the
specific interference.
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17. 3.3 Determining Interference Troubleshooting
Solution
If the RSSI exceptional is thought to be caused by equipment fault,
disable the transmit power of power amplifier or exchange the main
antenna with diversity antenna.
If the RSSI exceptional is caused by external interference, use YBT250
to identify the interference according to the interference characteristics,
and determine the interference source.
For the procedure of interference testing, refer to
YBT250 User Manual.
3.4 Eliminating Interference
After the interference source is located, use the relevant measures to
eliminate the interference. If the RSSI exceptional is caused by
equipment fault, replace the equipment.
If the high RSSI is caused by parameter setting errors, modify the
parameters.
When other external interference sources are located, ask the wireless
committee to clear the frequency if necessary. If the frequency
clearance cannot be conducted because of some reasons, optimize
the RF, that is, increase the antenna uptilt or reduce the antenna
height or add base stations if necessary to shorten the cell radius and
decrease the interference.
This method is applicable to the dense urban and is not applicable to
the wide area coverage in rural.
3.5 Verification
Confirm whether the interference is eliminated through RSSI analysis
and dialing tests.
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