CDMA System RSSI Exceptional

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CDMA System RSSI Exceptional

  1. 1. DocumentnumberProduct name CDMAUsed by Huawei engineers Product versionDrafted by CDMA RNP Document version 1.0CDMA System RSSI ExceptionalTroubleshooting Guideline V1.0Prepared by Si Binhe (54736) Date March 2007Reviewed by DateApproved by DateTempus Telcosys (P).,Ltd.Time is Almightywww.TempusTelcosys.com
  2. 2. Contents1 Overview..................................................................................................................32 RSSI Exceptional Analysis...................................................................................42.1 RSSI Exceptional Phenomena......................................................................................................42.1.1 Subscriber Experience.............................................................................................................42.1.2 Terminal Phenomena...............................................................................................................42.1.3 Traffic Statistics OMC Phenomena .......................................................................................42.1.4 Other Phenomena....................................................................................................................42.2 RSSI Exceptional Classifications..................................................................................................52.2.1 RSSI Exceptional Caused by Poor Engineering Quality........................................................52.2.2 RSSI Exceptional Caused by Parameter Settings...................................................................52.2.3 RSSI Exceptional Caused by Equipment Abnormality...........................................................52.2.4 RSSI Exceptional Caused by Unallocated Terminals.............................................................62.2.5 RSSI Exceptional Caused by Base Station Blocking..............................................................62.2.6 RSSI Exceptional Caused by Heavy Traffic...........................................................................62.2.7 RSSI Exceptional Caused by External Interference...............................................................62.2.8 Summary of RSSI Exceptional and Relevant Causes.............................................................82.3 RSSI Exceptional Analysis Steps..................................................................................................92.3.2 Traffic Statistics Analysis......................................................................................................112.3.3 Alarm Data Analysis.............................................................................................................122.3.4 Historical Operations Analysis.............................................................................................122.3.5 Parameter Checking.............................................................................................................132.3.6 Antenna and Feeder Checking..............................................................................................142.3.7 Interference Testing...............................................................................................................142.3.8 Summary and Conclusions....................................................................................................153 RSSI Exceptional Troubleshooting...................................................................163.1 Interference Testing.....................................................................................................................163.2 Interference Data Analysis..........................................................................................................163.3 Determining Interference Troubleshooting Solution..................................................................173.4 Eliminating Interference.............................................................................................................173.5 Verification..................................................................................................................................17www.TempusTelcosys.co
  3. 3. 1 OverviewReverse received signal strength indicator (RSSI) is the reverse signalreception indicator in 1.2288 MHz band of base station. Normal RSSIindicates that the reverse channel is operational.In actual networks, RSSI exceptional may be contributed toengineering quality, equipment, terminal, parameter settings, andinterference. That is, RSSI exceptional does not means theinterference exists in the network.www.TempusTelcosys.com
  4. 4. 2 RSSI Exceptional Analysis2.1 RSSI Exceptional Phenomena2.1.1 Subscriber Experience User average access time is larger than 5 seconds. In serious conditions, the subscribers are hard to access thesystem. Audio discontinuity, noise, silence, monologue call or even calldrop 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 andresearches 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 periodof time. The difference between main RSSI and diversity RSSI exceeds6dB for a long period of time.2.1.4 Other PhenomenaIn the RFMT data tracing, the indicators, such as RevBadFrame,RevSetEbNt, FwdFer, FwdSetEbNt, and MsRxPwr are degraded.www.TempusTelcosys
  5. 5. 2.2 RSSI Exceptional Classifications2.2.1 RSSI Exceptional Caused by Poor EngineeringQualityRSSI exceptional is caused by base station equipment, for example,the improper installation, connectors loosen, antenna soaked, orantenna aging. In such cases, the difference between main RSSI anddiversity 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, andZone_timer settings are improper or Reg_zone setting is incorrect,resulting in frequency registrations of terminals. In such cases, theRSSI may be increased. Open access macro diversity (partial exceptional terminals). Layer 2 acknowledgment of base station is not enabled (mainly forIS95 MSs).In such cases, main RSSI and diversity RSSI are high simultaneously.2.2.3 RSSI Exceptional Caused by EquipmentAbnormalityRSSI exceptional caused by equipment abnormality has two types: RSSI exceptional is caused by RF front end. The RF front endproblems contain passive intermodulation due to antennadamaged. The power capacity limit is insufficient, and the RSSI isworse after the multi-carrier is enabled. RSSI exceptional also canbe caused by the connector intermodulation, or lightning arresterabnormality. RSSI exceptional is caused by BAM abnormality, for example,transmission or BSC resource allocation module failure, and manycalls are rejected frequently, result in the repeated calls. There aretoo many network busy hour attempts, for example, over 3000attempts. The traffic statistics or CSL shows that many calls arereleased abnormally.In such cases, main RSSI and diversity RSSI are high simultaneously.www.TempusTelcosys
  6. 6. 2.2.4 RSSI Exceptional Caused by UnallocatedTerminalsWhen some MSs and FWTs whose techniques are inconsistent withthe CDMA industry standards access the network, the terminalsneglect the power control messages delivered by the network, or thepower control commands delivered by the system are invalid for theterminals.In actual networks, the unallocated MSs or FWTs whose techniquesare inconsistent with industry specifications increase the noise floor ofnetwork.In such cases, main RSSI and diversity RSSI are high simultaneously.2.2.5 RSSI Exceptional Caused by Base StationBlockingWhen the base station is blocked or the baseband gain is set to asmall value, the base station becomes a receiver. The MSs within itscoverage range cannot receive the signals of this site, and access thesurrounding 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 launchingservices, large transmit power is required to ensure the communicationwith surrounding base stations. The RSSI of this site is affecteddramatically.In such cases, main RSSI and diversity RSSI are high simultaneously.2.2.6 RSSI Exceptional Caused by Heavy TrafficWhen the RSSI is too high or the difference between main RSSI anddiversity RSSI is large, check the traffic of this carrier first.If the traffic is heavy (>30Erl) and RSSI is changed with the traffic, theRSSI exceptional may be caused by the heavy traffic. We exploit thepotentials of existing network or consider network expansion to reducethe carrier load and realize the load sharing. When the traffic isreduced, 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 ExternalInterferenceInterphone interferenceThe interphone interference is mainly present in the hotels, officewww.TempusTelcosys
  7. 7. buildings, and governmental organizations. The interference ofinterphone system is generated at random.Generally, it is used almost 24 hours one day. Therefore, theinterference is hard to control. The interphone transmits small powerand the interference range is small, so the adjacent channelinterference and intermodulation interference have small impact.This kind of interference can be avoided if the frequency band used bythe interphone system is far away from the frequency band we use.Repeater interferenceAt the early stage of network construction, the repeater was used toextend the coverage range of base station. It increases the noise floorof CDMA system.If the use of repeater in the network is inappropriate, the interferenceto the base station is generated easily, affecting the CDMA coveragerange 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 insufficientisolation exists between donor antenna and user antenna and the self-excitation is generated, affecting the normal operation of base stationthat the repeater is attached. Self-excitationAfter the signals transmitted from the repeater are received againthrough the donor antenna, the signals are amplified through therepeater and then are transmitted. The amplified signals are receivedand then amplified. Such circle results in a bad condition.Radar station and TV station interferenceThe frequency used by Some decimetric wave radars designed in1970’ and 1980’ is similar to 800MHz frequency of CDMA system.The transmit power is large, so the power level reaches several tens tohundreds kw range and the outband spurious emission is large, easilyinterfering to the adjacent 800MHz base stations.The TV station mainly operates at 450 MHz frequency band, andeasily interferes to 450MHz CDMA system.www.TempusTelcosys
  8. 8. AMPS interference without frequency retireThe original military AMPS system operates at the same frequencyband with CDMA2000 1X.If the frequency band used by original military AMPS system was notretired and is still used in some regions, it interferes to CDMA20001xsystem operating at 800MHz frequency band.Microwave transmission interferenceThe 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 CDMAnetwork but interfere to the network operating at about 2000 MHz,such as CDMA 1900MHz.Other interferenceThe types of communication devices are various. Some companiesuse the frequency band inconsistent with the industry standard andoccupy the frequency band for CDMA 1x being constructed.The placement and isolation are inappropriate, so many dedicatedcommunication devices interfere to the coverage areas of CDMAnetwork.In addition, there are broadband noises generated by the electric arcand sparkles of electricity factor and electricity station.Other types of interference sources are available, such as conferenceinterference system, computer screen interference unit, neon lightstrike, TV active receiver, and high voltage transformer.In such cases, the main RSSI and diversity RSSI are increasedsimultaneously or the unipolarization RSSI is high.2.2.8 Summary of RSSI Exceptional and RelevantCausesRSSI Exceptional Phenomenon Possible CausesRSSI too low Main/diversity RSSI is smallerthan -110dBm for a long period oftime.The connectors of antennaand feeder are connectedinsecurely or antenna andfeeder, TRX, CDU, or poweramplifier are faulty.RSSI too high Main/diversity RSSI is higher than-95dBm for a long period of timeor within a certain period of time.Switch and jumper errors,hardware faulty, waterpenetrated in connectors,www.TempusTelcosys
  9. 9. antenna and feeder standingwave, parameter settings(registration and accessmessage settingsinappropriate), system faulty,spurious emission andintermodulation, and externalinterferenceRSSI main anddiversity differencelargeThe difference between mainRSSI and diversity RSSI is over6dB or RSSI main/diversitycomparison alarm and TRMmain/diversity reception alarmexist.Antenna and feeder standingwave, antenna installationproblems, hardware faulty,diversity bypass switch settingerror, and externalinterference2.3 RSSI Exceptional Analysis StepsThe 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 timeor within a certain period of time, or The difference between main RSSIand 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 thechange of RSSI within this period of time. According to the information,as well as alarms and historical operations, determine roughly thecauses of RSSI exception, and identify the causes according to thefollowing flowchart to tackle the RSSI exceptional problem.www.TempusTelcosys
  10. 10. www.TempusTelcosys
  11. 11. Figure 1.1 Flowchart of RSSI exceptional analysis2.3.2 Traffic Statistics AnalysisHeavy trafficWhen finding that the RSSI is too high or the difference between mainRSSI and diversity RSSI is large, check the traffic of carrier first. If thetraffic is high (> 30Erl) and RSSI is changed with the traffic, the RSSIexceptional may be caused by heavy traffic.We exploit the potentials of existing network or consider networkexpansion to reduce the carrier load and realize the load sharing.When the traffic is reduced, check whether RSSI is restored to anormal value.ACH occupation and call attempts analysisCheck the ACH occupation.If the ACH occupation exceeds 60%, analyze the ACH occupationaccording to the registrations and call attempts, and determinefrequency registrations or frequent accesses originated by the userresults in the high ACH occupation.If it is caused by the frequent registrations, modify the registrationparameters 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 andeliminate the cause of system abnormality.Generally, the high ACH occupation is caused by incorrect settings ofLAC zone parameters, or system operation abnormality.For details, refer to section 2.3.3Alarm Data Analysis and section2.3.5Parameter Checking.Many call resources allocation failureRSSI exceptional is caused by equipment abnormality, for example,transmission or BSC resource allocation module failure, and manycalls are rejected frequently, result in the repeated calls.There are too many network busy hour attempts, for example, over3000 attempts. The traffic statistics or CSL shows that many calls arereleased abnormally.If the allocation of many call resources fails, the ACH load may be alsohigh.Check whether many calls are rejected because of the transmission,www.TempusTelcosys
  12. 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 AnalysisCheck the alarms, such as RSSI main/diversity received channel faultalarm, TRM main/diversity comparison exceptional, or standing wavealarm.If these kinds of alarms are available, check the alarm date and theassociation between RSSI exceptional and alarm data.If the RSSI exceptional is associated with the alarm data, RSSIexceptional may be caused by the equipment faults.To locate the problems, do as follows (before performing the followingoperations, check the regularity of RSSI exceptional and perform thefollowing 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 screwsof DDU, power amplifier and TRM at near end are secure. Checkwhether 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 theindicators flash abnormally, reset and insert or remove the units andobserve the status.4) Trace the RSSI of base station through TELNET. 10 minutes later,save the records, and analyze whether RSSI is changed or isrestored to a normal value.5) If RSSI is still exceptional, conduct the next round.Main/diversity received channel fault mechanism checks themain/diversity RSSI and reports the alarm. The alarm report dependson the difference between main RSSI and diversity RSSI and thedifference duration. In different versions, the alarm thresholds of thesetwo input values are also different.2.3.4 Historical Operations AnalysisCheck the historical operation records of RSSI exceptional cell andobserve the added or modified base station hardware and the changeddata, and the association between the interference occurrence timeand operation time.If the carrier is conducted within the near end time and RSSIexceptional time is associated with the operation time, the RSSIwww.TempusTelcosys
  13. 13. exceptional is caused by this operation.The RSSI rise may be contributed to the upgrade, parameteradjustment and RF adjustment.UpgradeThe RSSI exceptional caused by the upgrade mainly represents theBSC upgrade. If the RSSI is increased after the BSC is upgraded,check the change of parameters before and after upgrade, and restorethe changed parameters to the parameters before upgrade aspossible. Check whether RSSI is restored to a normal value.Parameter adjustmentThe RSSI rise may be caused by the parameters, such asTOTAL_ZONES, ZONE_TIMER, initial access power controlparameter, and baseband gain.RF adjustmentCheck whether the RSSI rise time is associated with RF adjustmenttime. If yes, check the change of traffic. If the RSSI exceptional iscaused by heavy traffic, exploit the potentials of existing network orconsider network expansion to reduce the carrier load and realize theload sharing.When the traffic is not changed, check the antenna and feeder areconnected securely.If the RSSI is restored to a normal value, the process ends. Otherwise,conduct the next round.2.3.5 Parameter CheckingThe 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 aresult, the noise floor and RSSI are increased.B. TCH minimum gain: If the TCH gain is too large, the terminaltransmits large power over TCH. As a result, the voice quality isimproved, and the RSSI is increased. If the TCH gain is set toolarge, it has a small impact on the voice quality, but the systemcapacity and RSSI are affected largely.C. Inappropriate settings of Reg_zone, Total_zone, and Zone_timer orReg_zone setting error result in the frequent terminal registrations.As a result, the RSSI may be increased.www.TempusTelcosys
  14. 14. D. Open the access macro diversity (some exceptional terminals).E. Base station layer 2 acknowledgment switch is not enabled (mainlyfor IS-95 MS).F. Check the diversity bypass switch (when a sector has twocarriers).For the settings of parameters A, B, and C, refer to the networkplanning common parameters.For the settings of parameters D and E, refer to Technical Notice No.[2006] CDMA002--Technical Notice on Enabling BTS Layer 2 ACKSwitch and Technical Notice No. [2006] CDMA003--Technical Noticeon Disabling Access Macro Diversity Switch.2.3.6 Antenna and Feeder CheckingExchange the antenna and feeder of adjacent two cells, and checkwhether the high RSSI is caused by the antenna and feeder.For the omnidirectional sites, exchange the main antenna and feederwith diversity antenna and feeder, re-trace the RSSI.After the antenna and feeder are exchanged, if the difference betweenmain RSSI and diversity RSSI is changed, the RSSI exceptional maybe caused by antenna and feeder or external interference.Check the antenna and feeder, for example, the lightning arrester isnot damaged, and the connectors between jumper and feeder andbetween the jumper and antenna are secure, and then check thechange of instantaneous RSSI.After the antenna and feeder are exchanged, if the difference betweenmain RSSI and diversity RSSI is not changed, the RSSI exceptionalmay 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 anddiversity RSSI is small, the RSSI exceptional may be caused by TRMor other hardware.Through the previous operations, if the RSSI is still high, the RSSIexceptional is caused by external interference, and conduct theexternal interference testing.2.3.7 Interference TestingThe external interference may interfere to surrounding sectors. As aresult, the RSSI values of surrounding carriers are increased.Thus, before the interference testing, import the site informaiton byusing the Mapinfo, and check the areas to which the RSSI exceptionalcell points. According to the point direction of RSSI exceptional cell,www.TempusTelcosys
  15. 15. locate roughly the position of interference source and then useYBT250 to find the interference source.For the procedure of identifying external interference, refer toInterference Analysis Guideline.2.3.8 Summary and ConclusionsThis section examines the analysis of reverse RSSI exceptional. If thepersonnel are sufficient and the customer has a high requirement,analyze the RSSI exceptional through several procedures at the sametime. For example, in the equipment room, when the engineers cancheck alarms, they can check the parameters and analyze the trafficstatistics. The field engineers can identify the interference through theRSSI tracing at near end, antenna and feeder adjustment andinterference testing, together wit the engineers in the equipment room.www.TempusTelcosys
  16. 16. 3 RSSI Exceptional TroubleshootingForward and reverse interferences degrade the network quality, so wemust assist the customer to eliminate the interference.If the interference is determined, do as follows:3.1 Interference TestingTest the forward and reverse interferences according to theInterference Testing Guideline.3.2 Interference Data AnalysisAnalyze the collected information, and locate preliminarily the reasonsof RSSI exceptional (too high or the difference between main RSSIand diversity RSSI is large).If the RSSI exceptional is caused by non-external interfere, identifydifferent solutions regarding to different reasons.If the RSSI exceptional is caused by external interference, determinethe interference characteristics, interference types, and theinterference occurrence regularity, and confirm the interference type,such as inband interference or outband interference, stable broadbandinterference or burst interference.On the forward link, make the quantitative analysis according to thespecific interference.www.TempusTelcosys
  17. 17. 3.3 Determining Interference TroubleshootingSolutionIf the RSSI exceptional is thought to be caused by equipment fault,disable the transmit power of power amplifier or exchange the mainantenna with diversity antenna.If the RSSI exceptional is caused by external interference, use YBT250to identify the interference according to the interference characteristics,and determine the interference source.For the procedure of interference testing, refer toYBT250 User Manual.3.4 Eliminating InterferenceAfter the interference source is located, use the relevant measures toeliminate the interference. If the RSSI exceptional is caused byequipment fault, replace the equipment.If the high RSSI is caused by parameter setting errors, modify theparameters.When other external interference sources are located, ask the wirelesscommittee to clear the frequency if necessary. If the frequencyclearance cannot be conducted because of some reasons, optimizethe RF, that is, increase the antenna uptilt or reduce the antennaheight or add base stations if necessary to shorten the cell radius anddecrease the interference.This method is applicable to the dense urban and is not applicable tothe wide area coverage in rural.3.5 VerificationConfirm whether the interference is eliminated through RSSI analysisand dialing tests.www.TempusTelcosys

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