zxc10 bssb rssi alarm troubleshooting guide_r1.1

ZXC10 BSSB RSSI Alarm Troubleshooting Guide

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ZXC10 BSSB RSSI Alarm Troubleshooting Guide Internal Use Only▲

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Revision History

Product Version Document Version Serial Number Reason for Revision1.0 First published1.1 Second amendment

Author

Date Document Version Prepared by Reviewed by Approved by2010-7-15 1.0 Xiang Yijie2010-8-19 1.1 Xiang Yijie

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Applicable to: ZXC10-BSS technical support engineers

Proposal: Before reading this document, you had better have the following knowledge and skills.SEQ Knowledge and skills Reference material1 CDMA-BSSB Skills Certification Level II23

Follow-up document: After reading this document, you may need the following informationSEQ Reference material Information123

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About This Document

SummaryChapter Description

1 Overview Introduces the summary, application and readers of this document, as well as the skill requirements for onsite support engineers.

2 Starting Here Discusses the basic RSSI knowledge.3 Fault Phenomenon Describes the common abnormal RSSI phenomena.4 Fault Location Tool Lists the tools required for handling an abnormal RSSI

problem.5 Troubleshooting Steps Details the methods and procedures for handling abnormal

RSSI problems.6 Case Study Analyzes several abnormal RSSI cases.AppA References Introduces RSSI query method and reverse spectrum

scanning method.

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TABLE OF CONTENTS

1 Overview.............................................................................................................11.1 Summary.............................................................................................................11.2 Abbreviation.........................................................................................................11.3 Product Version...................................................................................................11.4 Intended Reader..................................................................................................11.5 General Skill Requirements for Onsite Support Engineers of ZTE CDMA

Devices...............................................................................................................2

2 Starting Here......................................................................................................22.1 Meaning of RSSI.................................................................................................22.2 Normal RSSI Range............................................................................................2

3 Fault Phenomenon............................................................................................3

4 Fault Location Tool...........................................................................................4

5 Troubleshooting Steps.....................................................................................45.1 Checking BTS Alarm and Radio Parameter........................................................45.1.1 Finding and Confirming an RSSI Fault..........................................................45.1.2 Checking BTS Alarm......................................................................................55.1.3 Checking Radio Parameter............................................................................55.2 Analyzing Characteristics of Abnormal RSSI Values..........................................65.2.1 Time-variant Characteristics of RSSI Strength..............................................75.2.2 Relation between Traffic and RSSI Strength.................................................95.2.3 Geographic Distribution Diagram of RSSIs...................................................95.3 Checking Relation between Abnormal RSSIs and OMC / Engineering /

Optimization Operation.....................................................................................115.3.1 OMC Operation............................................................................................115.3.2 Engineering and Optimization Operation.....................................................125.3.3 Forwarding the Problem to Related Departments.......................................125.4 Checking BTS Devices......................................................................................125.4.1 BTS Running Status....................................................................................125.4.2 BTS Type.....................................................................................................135.4.3 External or Internal Interference..................................................................135.4.4 BTS Problem or Other Device Problem.......................................................145.5 Checking Passive/Active Parts..........................................................................185.6 Checking Antenna Feeder System....................................................................205.7 Finding External Interference............................................................................26

6 Case Study.......................................................................................................276.1 Abnormal RSSI Arisen from External Interference............................................276.2 Abnormal RSSI Arisen from Repeater Problem................................................286.3 Abnormal RSSI Arisen from Loose Link Connection.........................................286.4 Abnormal RSSI Arisen from Hardware Problem...............................................296.5 Abnormal RSSI Arisen from Terminal Problem.................................................29

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AppA References.......................................................................................................31A.1 RSSI Query Method..........................................................................................31A.2 Reverse Spectrum Scanning.............................................................................31

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FIGURES

Figure 1 Statistical RSSI Data..................................................................................................3

Figure 2 RSSI Values of a Region............................................................................................7

Figure 3 Abrupt Increase of RSSIs in a Period........................................................................8

Figure 4 High Main RSSIs after a DO Carrier Being Added.....................................................8

Figure 5 Relation between RSSI Strength and Traffic.............................................................9

Figure 6 Distribution of Abnormal RSSIs in a Region............................................................10

Figure 7 Antenna Swapping Method: Main or Diversity RSSIs Are Abnormal.......................15

Figure 8 Antenna Swapping Method: Main and Diversity RSSIs Are Abnormal....................16

Figure 9 Procedure of Antenna Swapping Method................................................................16

Figure 10 Procedure of Dummy Load Connection Method....................................................18

Figure 11 Indoor Coverage of Active/Passive Devices..........................................................19

Figure 12 Checking 1/2" jumpers on top of the cabinet..........................................................21

Figure 13 Checking Lightning Arresters.................................................................................22

Figure 14 Checking 7/8” Feeders...........................................................................................23

Figure 15 Checking the 1/2" jumpers at the antenna side......................................................24

Figure 16 Procedure of Dummy Load Connection Method for Checking Antenna Feeder System.....................................................................................................................................25

Figure 17 Procedure of Swapping Method for Checking Antenna Feeder System................26

Figure 18 Reverse Spectrum Scanning: Main RSSIs Are Normal, while Diversity RSSIs Are Low..........................................................................................................................................32

Figure 19 Reverse Spectrum Scanning: Narrowband Interference Signals Present in Main and Diversity Bandwidth..........................................................................................................32

TABLES

Table 1 Abbreviations and Acronyms.......................................................................................1

Table 2 Product Version...........................................................................................................1

Table 3 Abnormal RSSI Phenomenon.....................................................................................4

Table 4 Typical Abnormal RSSI Phenomena and Possible Reasons....................................11

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1 Overview

1.1 SummaryThis guide first describes the phenomena of faults arisen from abnormal RSSIs and then discusses the approach to fault location as well as the handling procedure.

1.2 AbbreviationThe following table lists abbreviations and acronyms used in this guide.

Table 1 Abbreviations and Acronyms

Abbreviations/Acronyms Full NameRSSI Received Signal Strength IndicatorRFE Radio Frequency Front EndTRX Transceiver ModulePA Power Amplifier

1.3 Product VersionThis document is applicable to the following product versions:

Table 2 Product Version

Product VersionZXC10-BSSB V8.20.04 and higher

1.4 Intended ReaderThis document is intended for the following persons:

CDMA technical support engineer

CDMA maintenance engineer

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1.5 General Skill Requirements for Onsite Support Engineers of ZTE CDMA DevicesThe onsite support engineers, including technical support engineers or onsite maintenance engineers, should take certain training on the operations of ZTE’s CDMA devices before they operate or maintain these devices. Specifically, they should have the following knowledge or pass certain certification level.

Knowledge about ZXC10-BSSB product;

ZXC10-BSSB OMC-related specifications;

Handling methods of common ZXC10-BSSB faults

Passing ZXC10-BSSB Level-2 skill certification

2 Starting Here

2.1 Meaning of RSSIRSSI stands for received signal strength indicator. As an index indicating the strength of a signal received at antenna interface, it can be used to analyze the received signals of a BTS.

Generally, the TRX module of a BTS detects the strengths of received signals and then works out the power strength of the antenna interface based on the receiver link gain. Once the signals are too strong or too weak, a high RSSI or low RSSI alarm is raised.

2.2 Normal RSSI RangeFirst of all, it should be made clear that abnormal RSSI should be treated as a long-term statistical value, while a high or low RSSI at a moment or short period should not be regarded abnormal. Moreover, the normal RSSI range varies in different cases.

In the absence of subscribers and interference, RSSIs should range from -115 dBm to -95 dBm and the difference between main and diversity RSSIs should be within 10 dB.

RSSIs may fluctuate with traffics. In busy hours, RSSIs may rise, while in non-busy hours, RSSIs may return normal. Figure 1 shows RSSIs of 11 days of a RRU, where we can see the difference between busy hours and non-busy hours.



Figure 1 Statistical RSSI Data

When there is no signal at the antenna interface or there is interference, the statistical RSSI values (i.e. more than 95%) should be -110 ± 6 dBm, typically -110 ± 3 dBm. The fluctuation of ±3 dBm or ±6 dBm depends on RFE module, TRX module and BTS type.

In the case there are a few subscribers and there is no interference, due to small-scale fading and multipath effect in mobile radio propagation, as well as the power control mechanism and rate of the CDMA network, the reverse power at the antenna interface may rise by 10-20 dB in a short time. Accordingly, RSSIs rise instantaneously. In this case, as long as the statistical RSSI values are less than -105 dBm, reverse link is regarded in good condition and external interference is within an acceptable range.

When there are lots of subscribers, the useful signals at the antenna interface cannot be ignored. In this case, the upper limit of the statistical RSSI values are 3 ~ 5 dB more than the case where there are a few subscribers. That is to say, as long as the statistical RSSI values are less than -100 dBm, reverse link is regarded in good condition and external interference is within an acceptable range.

In addition, main and diversity RSSIs may differ due to such factors as subscriber distribution and landform. On the average, there is a difference of 10 dB between them.

Specific to ZXSDR RF products, which currently include distributed RRU and RSU installed in BS8800, RSSI alarm thresholds are -120 dbm and -89 dbm. If RSSIs are continuously more than -89 dbm or less than -120 dbm, they are regarded abnormal, so is the reverse link.

3 Fault PhenomenonThe abnormal RSSI-arisen fault phenomena are described in Table 3.



Table 3 Abnormal RSSI Phenomenon

Aspect Phenomenon

ServiceThe sensitivity and capacity of the reverse link of a BTS decrease. The BTS may not deliver normal services in case of a serious fault. The subscribers far from the BTS can receive signals but cannot access the network.

AlarmRSSI of reverse link is low;Reverse link of TRX (main/diversity) raises low RSSI alarm;RSSI of reverse link is high.

4 Fault Location ToolThe following tools may be needed to locate an RSSI-related fault:

150W /40 dB attenuator or 150 W load: used to check the BTS device for proper running;

Frequency sweeper and Yagi antenna: used to find any external interferences;

RF cable, DING connector, N-SMA adapter and N-type female connector: used to check the antenna feeder system.

5 Troubleshooting Steps

5.1 Checking BTS Alarm and Radio Parameter

5.1.1 Finding and Confirming an RSSI Fault

Objective

To verify if an RSSI value is in normal range.

Procedure

Extract RSSI value of a BTS from the OMC.

Judge whether the RSSI values of a BTS is normal based on such factors as, statistic period, traffic and distribution.

Reference Information

For details about RSSI query method, please refer to Appendix A.1.

5.1.2 Checking BTS Alarm



Objective

To check alarms of related devices of the BTS whose RSSI value is found abnormal.

Procedure

1. In the Alarm Management of OMC system, double-click related modules.

2. If an alarm is found, check its occurrence time to see if it is time correlated to RSSI abnormality. If yes, process the alarm.

3. After all alarms of related modules are processed, observe the RSSI value again and see if it returns to normal.


1. The modules that are related to RSSI values include: RFE, TRX and PA.

2. RSSI-related alarms involve the following aspects: VSWR, over power of PA, LNA, lock-loss of TRX’s phase-locked loop, and transmission.

5.1.3 Checking Radio Parameter

Objective

To make sure settings of related radio parameters are correct.

Procedure

The incorrect settings of some parameters may cause RSSI to rise. If an RSSI fault is reported but related devices are found normal, check the settings of the following radio parameters:

1. Registration parameters: TOTAL_ZONE, ZONE_TIMER, etc.;

2. Access parameters: INIT_PWR, PWR_STEP, NUM_STEP, ACC_TMO, etc;

3. Power control parameters: ER_LEN1/2/3/4, Up_INI1/2/3/4, Up_ER1/2/3/4, etc.


Parameter Description

INIT_PWR

A large value may increase both access success rate and interference on access channels;A small value may reduce interference on access channel but let the MS send more access probes before it receives the acknowledgement message from the BTS, thus increasing the load of access channel as well as the access channel collision probability.

PWR_STEP A large value may increase both access success rate and



Parameter Descriptioninterference on access channels;A small value may reduce interference on access channel but increase the load of access channel and the access channel collision probability.

NUM_STEP

There should be a tradeoff between NUM_STEP and PWR_STEP.A large setting of this parameter may increase the probability of access with one access probe sequence but also increase interference on reverse links and setup delay; A small setting may decrease the possibility of access with one access probe sequence, leading to more access probe sequences and longer connection delay.

ACC_TMO

A large setting may increase access success rate; A small setting may increase the load of access channel as well as the access channel collision chance because the MS will send another access probe before the BTS has time to acknowledge the MS's first access probe.

ER_LEN1/2/3/4

They are the continuous error frame thresholds (RC1, RC2, RC3 and RC4).A large setting may affect the performance of reverse link as the increase of Ec/Io speeds up only when there are lots of continuous error frames; A small setting may cause Ec/Io to be increased at an early time, thus increasing the load and interference on reverse link.

UP_INI1/2/3/4

A large setting may cause Ec/Io to increase at a large step, thus increasing the load and interference on reverse link; A small setting may affect the performance of reverse link as Ec/Io increases at a small step.

UP_ER1/2/3/4

A large setting may cause Ec/Io to rise at a large step in case of continuous error frames, and reverse power increases quickly, thus increasing the load and interference on reverse link; A small setting may affect the performance of reverse link as Ec/Io increases at a small step and the reverse power cannot be increased timely.

To modify the setting of a parameter, strictly follow related procedures of ZTE or other equipment vendors. Besides, this modification operation should be done by a specialist. After a parameter setting is modified, have eyes on related performance indexes. If a performance index worsens, analyze the reasons quickly and notify related departments in order to take proper measures.

5.2 Analyzing Characteristics of Abnormal RSSI ValuesIf an RSSI alarm persists after the devices and related parameters are checked and corrected, it is required to analyze the characteristics of abnormal RSSI values to find out the reasons quickly.



RSSI values are closely related to the statistic period, traffic, regional distribution, repeaters and indoor distribution system. By collecting historical data, we can obtain corresponding RSSI values.

If RSSI values are within specified range in most cases, but become abnormal in some periods or regions, we can analyze their characteristics to find out the reasons.

5.2.1 Time-variant Characteristics of RSSI Strength

Objective

To check if an abnormal RSSI value is related to interference or main link problem of a period.

Procedure

Analyze the change in the strengths of main and diversity RSSIs over the time.


RSSI strength is often time-variant. It fluctuates on daily basis, rising in busy hours but falling in other hours. But in some special regions (e.g. tourist places), the fluctuation may be weekly, as shown in Figure 2.

Figure 2 RSSI Values of a Region

1. If in some periods, the main/diversity RSSIs abruptly increase, the reason is probably external interference, as shown in Figure 3.



Figure 3 Abrupt Increase of RSSIs in a Period

2. If the main RSSIs keep extremely high, it may be a main link problem. For example, something may be wrong with the antenna feeder system after a DO carrier is added, or a repeater is not properly installed. Figure 4 shows the high main RSSI problem arisen from a connection problem after a DO carrier is added.

Figure 4 High Main RSSIs after a DO Carrier Being Added



5.2.2 Relation between Traffic and RSSI Strength

Objective

To check if an abnormal RSSI value is related to traffic.

Procedure

Analyze main/diversity RSSIs of each carrier and see if their strengths are related to traffic.


RSSI strength is directly related to the number of subscribers. The RSSI values in busy hours are often higher than those in other hours.

Example

In Figure 5, to illustrate the relation between traffic and RSSI strength, we deduct the traffic by 110. This figure shows the traffic is indeed related to main/diversity RSSIs. The heavier the traffic, the higher RSSIs are.

Figure 5 Relation between RSSI Strength and Traffic

5.2.3 Geographic Distribution Diagram of RSSIs

Objective

To check if abnormal RSSI values are region-specific or if there is an indoor distribution system, repeaters or engineering in a region where abnormal RSSIs are reported.



Procedure

Analyze the geographic distribution diagram of abnormal RSSIs, focusing on their relation with time, carrier distribution, traffic, main/diversity antenna distribution and/or geographical location.

1. Check if abnormal RSSIs are time-variant. That is to say, whether abnormal RSSI values occur in a fixed period or in the period when some special events take place, e.g. entrance examination or construction of indoor distribution system.

2. Check if the RSSIs of one or all carriers are abnormal.

3. Check if abnormal RSSI values are mainly a result of traffic change.

4. Check main and diversity RSSIs to see if both of them or either of them is abnormal.

5. Check to see if the cells with abnormal RSSIs are in the same region or in a region near to troops' camps.

Example

The following figure shows the distribution of abnormal RSSIs of a region.

Figure 6 Distribution of Abnormal RSSIs in a Region

Note: The circles represent the indoor distribution systems.


By analyzing the characteristics of abnormal RSSIs, the reasons for the problem can be roughly determined.

Table 4 lists typical abnormal RSSI phenomena and their possible reasons, which can be used as a reference in troubleshooting of an RSSI alarm.



Table 4 Typical Abnormal RSSI Phenomena and Possible Reasons

Phenomenon Possible Reasons

Only main RSSIs are high

1. The power is too large;2. Something is wrong with feeder connection, feeder, antenna, repeater or indoor distribution system;3. There is interference.

Both main and diversity RSSIs are high

1. There is external interference;2. Engineering quality is satisfied.

Only diversity RSSIs are high There is external interference.

Both main and diversity RSSIs in a region are high There is external interference.

High RSSIs are reported in a fixed period on each day There is external interference.

RSSIs of several days are high There is external interference.

RSSIs fluctuate sharply There is periodical external interference.RSSIs stay at the noise floor level

The connection between the feeder and the antenna is interrupted.

RSSI are very low1. RFE and/or TRX modules have been damaged.2. The module is not properly inserted.

5.3 Checking Relation between Abnormal RSSIs and OMC / Engineering / Optimization OperationBased on the analysis of characteristics of abnormal RSSIs, you can locate the reasons by checking related devices or systems. First, you can check to see if there is any OMC, engineering or optimization operation in the region where abnormal RSSIs are reported.

5.3.1 OMC Operation

Objective

To check if abnormal RSSIs are caused by improper OMC operations.

Procedure

1. Check whether DO carriers are configured and commissioned at the BTS.

Note: Transmission at full power, engineering quality problem, and performance degrading of antenna feeder devices or passive/active devices may lead to intermodulation due to non-linearity, thus bringing abnormal RSSI values. Therefore, A DO network often impose higher requirements for engineering quality and device performance than other networks.



2. Check to see if any hardware or software has been upgraded.

3. Check to see if carriers or hardware of the BTS have been added, deleted or replaced.

4. Check to see if any parameter's setting has been changed.

5.3.2 Engineering and Optimization Operation

Objective

To check whether abnormal RSSIs are a result of engineering or optimization operation.

Procedure

1. Check to see if RF optimization has been done for the sector with abnormal RSSIs and its neighboring sectors.

2. Check to see if any power splitter, indoor distribution system or repeater has been installed or adjusted.

3. Conduct analysis via OMC tools.


For details about the reverse spectrum scanning method, please refer to A.2.

5.3.3 Forwarding the Problem to Related Departments

If analyses show the problem (e.g. module damage, indoor distribution system problem) is the responsibility of other departments, it should be forwarded to other departments for further processing. However, you should follow up the processing progress and result.

5.4 Checking BTS Devices

5.4.1 BTS Running Status

Objective

To make sure BTS running status is consistent with that displayed in the OMC.

Procedure

Check to see if there any BTS alarm in the OMC;



Check the communication between the BTS and the OMC to see if it is through.

5.4.2 BTS Type


Currently, ZTE provides the following types of BTSs: CBTSI2, BTSBI4, BS8800, BBU+RRU, and BTSAE.

If a sector has two links, one is used for transmitting signals, which is the main link; while the other is for receiving signals, which is called the diversity link. If both links are used for transmitting signals, they act as main and diversity links respectively.

Often, if two or more carriers are configured for BTSAE, two antennas of the same sector are used for transmitting signals, so they act as main and diversity antennas respectively. In CBTSI2, BTSBI4, BS8800 and BBU+RRU, one antenna of a sector is assigned the main one, the other antenna the diversity one. In some applications, two-line transmission links can be configured, where the two antennas are main and diversity antennas respectively, as in BTSAE.

Check BTS type and its configuration to see if two-line transmission is configured and the antennas acts as main and diversity antennas respectively. And analyze their relation with abnormal RSSIs.

5.4.3 External or Internal Interference

Objective

To check the interference is internal or external.

Procedure

1. Record RSSIs in BTS Data Observation and then lower the power via the OMC to see if RSSI values decrease.

2. Disable the power amplifier and measure RSSIs again. If the RSSIs decrease to its normal range, it means the interference is internal, that is, caused by a BTS device or antenna feeder system problem. If RSSI keeps unchanged after the power amplifier is disabled, it means the interference is external.

Note: If the sector with abnormal RSSIs has been configured with an optical repeater or trunk amplifier, the disabling of the power amplifier may not be enough. In this case, it is required to disable the repeater or trunk amplifier to determine if the interference is external.

3. If the BTS has a reverse signal test interface, connect a spectrum analyzer to this interface and analyze the reverse spectrum to determine if there is any external interference.



4. Use the BTS's spectrum scanning tool to analyze abnormal RSSIs, determining if there is any external interference.

5. In case of external interference, please refer to Section 5 for the troubleshooting method. Frequency scanning may be needed to locate the interference source.


Many reasons may result in abnormal RSSIs and they can be divided into two categories: internal interference and external interference. The internal and external interference are defined as follows:

Internal Interference refers to the interference caused by a device or connection problem of the BTS and its antenna feeder system.

External Interference refers to the interference caused by wireless signals from other BTSs or systems (including wireless repeaters), which comes to the antenna via the air interface.

5.4.4 BTS Problem or Other Device Problem

In case of internal interference, first check the BTS. Often, one of the two methods can be used: antenna swapping and dummy load connection.

5.4.4.1 Antenna Swapping

Introduction

The antenna swapping method is to exchange the antennas of the same sector or different sectors and see if abnormal RSSIs are caused internally or externally.

Procedure

1. This method is applicable to the following two cases:

i. Main or diversity RSSIs are abnormal

a) Swap the feeders of main and diversity antennas at the cabinet-top interface;

b) Observe if the RSSIs change;

c) If yes, it means the abnormal RSSI problem is not caused by BTS devices; otherwise, it is caused by BTS devices.



Figure 7 Antenna Swapping Method: Main or Diversity RSSIs Are Abnormal

ii. Both main and diversity RSSIs are abnormal

a) Swap the feeder of the sector with normal RSSIs and that with abnormal RSSIs at the cabinet-top interface;

b) Observe if the RSSIs change;

c) If yes, it means the abnormal RSSI problem is not caused by BTS devices; otherwise, it is caused by BTS devices.



Figure 8 Antenna Swapping Method: Main and Diversity RSSIs Are Abnormal


1. The procedure of antenna swapping method is illustrated in the figure below.

Figure 9 Procedure of Antenna Swapping Method

2. In case of a BTS device problem, check related modules (e.g. RFE, TRX), power amplifiers to see if there is any alarm on them, the modules are properly inserted or the parameters are correctly set.

3. In case of a non-BTS device problem, refer to Section 5.5, 5.6 and 5.7 for the troubleshooting procedure.



5.4.4.2 Dummy Load Connection

Introduction

If related test devices are available, you can use dummy load connection method to determine abnormal RSSIs are caused externally or internally.

Preparation

Before using this method, you should prepare the following devices:

A 250 W load with an N-F or DIN-F connector

One 1/2" cable with an N-M or DIN_M connector

Several DIN-N and M-F adapters

Procedure

1. Block the carriers of the sector with abnormal RSSIs;

2. Disconnect the jumpers of main and diversity antennas of the sector from the output ports TX/RX and RX on top of the cabinet respectively.

3. Connect dummy loads to the output ports respectively, making sure the dummy loads and their connections work well.

4. Ask the persons in the equipment room to unblock related carriers via the OMC.

5. Observe reverse RSSIs in the OMC.

6. Compare observed RSSIs with its normal range. If they are in the range, it means the abnormal RSSI problem is not caused by BTS devices; otherwise, it is caused by BTS devices.

Note: In this method, the dummy load and the cable should meet test requirements and be reliably connected.


1. The procedure of dummy load connection method is illustrated in the figure below.



Figure 10 Procedure of Dummy Load Connection Method

2. In case of a BTS device problem, check related modules (e.g. RFE, TRX), power amplifiers to see if there is any alarm on them, the modules are properly inserted or the parameters are correctly set.

3. In case of a non-BTS device problem, refer to Section 5.5, 5.6 and 5.7 for the troubleshooting procedure.

5.5 Checking Passive/Active PartsObjective

To check if abnormal RSSIs are caused by active/passive parts that are connected to the BTS.



Background Information

Nonlinearity of active/passive devices may lead to signal intermodulation. When intermodulated signals fall within the bandwidth of received signals, RSSIs rise up. Besides, if the parameters of repeaters or trunk amplifiers are incorrectly set, the gain of reverse link is extremely high or self-excitation occurs, the RSSIs of reverse links may rise too.

Figure 11 Indoor Coverage of Active/Passive Devices

Procedure

1. Check power splitter: Use a jumper to replace the splitter and observe if RSSIs return normal. If yes, it means the power splitter is faulty; otherwise, go to the next step.

2. Check the coupler: Use a jumper to replace the coupler and observe if RSSIs return normal. If yes, it means the coupler is faulty. Otherwise, proceed to the next step.

3. Check the repeater: If there is an optical repeater connected to the BTS, disconnect the repeater from the coupler and observe RSSIs. If RSSIs return normal, it means the optical repeater brings interference. In this case, it is required to adjust the reverse gain parameter or the repeater. For details about troubleshooting with wireless repeaters, please refer to Section 5.7.



4. Check the trunk amplifier: Checking a trunk amplifier is similar to checking a repeater. First, disconnect the amplifier and observe RSSIs. If RSSIs return normal, it means the amplifier brings interference. In this case, it is required to adjust the reverse gain parameter or the amplifier.

5. Check tower-mounted amplifier: You can use a jumper to replace the amplifier and observe if RSSIs return normal. If yes, it means the abnormal RSSI problem is caused by the amplifier. Otherwise, it means the amplifier works well.


A power splitter is often used in an indoor distribution system or when a sector is split into several sectors.

A coupler is often used when there is a repeater or indoor distribution system.

A trunk amplifier is often used in an indoor distribution system, for complementing the signal loss during transmission.

A tower-mounted amplifier is often used in the antenna feeder system of a BTS.

5.6 Checking Antenna Feeder SystemIf abnormal RSSIs are caused by internal interference but BTS devices and active/passive parts work well, you should turn to the antenna feeder system to find the reasons. In this case, follow this sequence to check the antenna feeder system:

1. The feeder interfaces on the top of the cabinet;

2. 1/2" jumpers on top of the cabinet;

3. Lightning arresters;

4. 7/8" feeders;

5. 1/2" jumper at the antenna side;

6. Connectors

The "dummy load connection" and/or "swapping" methods can be used to check the antenna feeder system.

Procedure

1. 1/2" jumper on top of the cabinet

Figure 12 illustrates the swapping of the jumpers.



To check the 1/2" jumpers, first, make sure the jumper is properly connected to the cabinet-top interface. Then connect 1/2" jumpers and the lightning arresters in a cross way, as shown in Figure 12.

Figure 12 Checking 1/2" jumpers on top of the cabinet

2. Lightning Arrester

If the 1/2" jumpers on the top of cabinet are found normal, resume their connections with the lightning arresters and connect the lightning arresters with 7/8" feeders of main and diversity antennas in a cross way, as shown in Figure 13.



Figure 13 Checking Lightning Arresters

3. 7/8” Feeder

If the lightning arresters are found normal, resume their connections with 7/8” feeders and connect 7/8" feeders with the 1/2" jumpers at the antenna side in a cross way, as shown in Figure 14.



Figure 14 Checking 7/8” Feeders

4. 1/2" jumper at the antenna side

If 7/8" feeders are found normal, resume their connections with the 1/2" jumpers at the antenna side and connect the 1/2" jumpers at the antenna side with two antennas (or two ports of a dipolarized antenna) in a cross way, as shown in Figure 15.



Figure 15 Checking the 1/2" jumpers at the antenna side


1. Figure 16 illustrates the procedure of dummy load connection method for checking the antenna feeder system.



Figure 16 Procedure of Dummy Load Connection Method for Checking Antenna Feeder System

2. Figure 17 illustrates the procedure of swapping method for checking the antenna feeder system.

The swapping method can be used when main or diversity RSSIs become abnormal.



Figure 17 Procedure of Swapping Method for Checking Antenna Feeder System

5.7 Finding External InterferenceObjective

To check if abnormal RSSIs are a result of external interference.

Procedure

1. First, check if there are any wireless repeaters connected to the BTS. Shut down the repeaters that bring interference for certain and then check other repeaters by shutting them one by one. If RSSIs return normal after one repeater is shut down, it means this repeater brings interference and need to be adjusted.

2. Check other external interference sources: scan the frequencies of the wireless network to determine the locations of interference sources. For details about the



frequency scanning method, please refer to Wireless Network Electromagnetic Environment Test and Interference Checking.


The common external interference that may cause abnormal RSSIs includes:

Interference from other communication systems, such as army’s AMPS system, and the interphone system of a hotel

Interference from wireless repeaters

Interference from illegal terminals, such as wireless fixed stations that do not meet the specifications

Television receivers

Conference jamming systems

6 Case Study

6.1 Abnormal RSSI Arisen from External InterferenceDescription

In a commercial office, about 40 BTSs had suffered abnormal RSSIs for a long time: 14 BTSs in Region A, 10 in Region B and 3 in Region C.

The interference source of Region A was a television & broadcasting transmitting station, which transmitted signals with high spurious strengths, raising the noise floor level of uplink band of the CDMA network to -64 dBm (the test result at the foot of the station).

The interference of Region B raised the noise floor to -80 ~ -90 dBm. As this interference disappeared in a few days, the source had not been found out.

The interference source of Region C is the jammers installed in the buildings of municipal and provincial national security bureaus.

Solution

At the BTS sites, YBT250 and Yagi antenna were used to measure the environmental noise floor, which were higher than normal, so a CDMA filter was applied to filter uplink outbound signals out of the signals received by the Yagi antenna.



Summary

The RSSI alarms caused by external interference often have the following features:

Both main and diversity RSSIs are abnormal;

All carriers of main and diversity sectors report RSSI alarms;

The disabling/enabling PA operation does not change main and diversity RSSIs.

6.2 Abnormal RSSI Arisen from Repeater ProblemDescription

In a region, 12 BTSs were reported with high RSSIs. Analyses showed there were repeaters on the branch links and their uplink gains were set too large, As a result, the RSSIs rose up.

Solution

RSSIs returned normal after the repeaters on the branch links were disabled.

Summary

The high RSSI alarms caused by repeater problems have the following features:

The main RSSIs remain high, while the diversity RSSIs are normal;

All carriers on the main link report high RSSI alarms and their RSSIs are approximate;

After the PA is disabled, the RSSIs still keep at a high level.

6.3 Abnormal RSSI Arisen from Loose Link ConnectionDescription

In a region, 11 BTSs were reported with high RSSIs. Analyses showed the reason lied in loose connections between 1/2" jumper and RFE output port as well as between 1/2" jumper and 7/8" feeder.

Experience demonstrates that if the connections of main link are in poor condition, enabling PA will raise the noise floor of uplink, but the poor contact of connectors on the diversity link has little impact on RSSIs.



Solution

Lower the power to decrease RSSIs. After the PA is turned off, RSSIs return normal.

Find the loose connections and tighten them.

Summary

The RSSI alarms caused by loose link connections have the following features:

The main RSSIs are abnormal, while the diversity ones are normal;

All carriers of the main link report high RSSI alarms, that is, the noise floors within 10 MHz bandwidth are relatively high;

The alarms are continuously raised.

6.4 Abnormal RSSI Arisen from Hardware ProblemDescription

In a region, 1 BTS was reported with abnormal RSSIs. Analyses showed the problem is caused by TRX problem.

Solution

1. The test results at RFE test port show the uplink noise floors are in normal range. (The noise floor is less than -70 dBm at 1.23 MHz bandwidth.)

2. The alarm disappears with the TRX module being exchanged with that of a neighbor cell.

Summary

The RSSI alarms caused by hardware problems have the following features:

Either main or diversity RSSIs or both of them are abnormal;

The alarms may be reported continuously or from time to time;

One or several carriers may report the RSSI alarms.

6.5 Abnormal RSSI Arisen from Terminal ProblemDescription

In a region, a BTS raised high RSSI alarm. Analyses showed this is because of a terminal problem.



Normally, a terminal has good power control performance, enabling it to control the transmit power based on specific environment so as to reduce its impact on other terminals. As a result, a normal terminal will not have great impact on the BTS's RSSIs. But if the terminal's power control function fails, it will send the signals at a high power, thus leading to high RSSIs.

Solution

During the tests at RFE test port of the BTS, a high CDMA signal is found. The test results show the uplink noise floor is in normal range. (The noise floor is less than -70 dBm at 1.23 MHz bandwidth.)

Summary

The RSSI alarms caused by terminal problems have the following features:

The RSSIs of one carrier of main or diversity link stay high, while the other carriers’ RSSIs are normal.

Scanning the carrier with abnormal RSSIs cannot find any narrowband interference signal.



AppA References

A.1 RSSI Query Method

For ZTE CDMA BTSs, their RSSIs can be queried in the OMC. The operations are as follows:

1. In the OMC system, choose [Views] --> [Performance Management] to display the Performance Management window.

2. Choose [Performance Management] --> [Original Data Query].

3. In the dialog box that pops up, choose [IP RF Data Object] or [Hirs RF Data Object] for the [Select Performance Object].

4. Choose [Query by Group] in query condition and [30 minutes] in the period, and set the start and end times.

5. In the query condition, choose the BTSs whose RSSIs are to be queried.

6. In the Attribute filed, choose correct options. By default, all options are chosen.

7. Upon completion of query, click Excel icon to save the query result as an Excel file.

A.2 Reverse Spectrum Scanning

ZTE's CBTS I2 and BTSB I4 have reverse spectrum scanning function, which can be used to scan the reverse received spectrum of a sector. By analyzing the scanning result, you can see if there is any interference signal as well as the characteristics of the interference signal, such as band (narrow or wide), frequency and amplitude. To perform the spectrum scanning function, do the following in the OMC system:

1. Choose [Views] --> [System Tools] --> [BTS Data Observation] to open BTS Data Observation window.

2. Choose [Real-time Observation] --> [Spectrum Scanning].

3. Choose [Data Operation] --> [Set Observation Object] and in the interface that displays, select corresponding BTS, cells and main/diversity

4. Choose [Data Operation] --> [Start Observation] to start the observation.



5. After the Scanning Successful message is displayed, double-click the desired line (cell) and you can see the reverse spectrum.

6. Or you can select one or more frequencies to see their spectrums.

The following figures show spectrum scanning results obtained in the OMC. From these figures, you can see the difference between main and diversity spectrums as well as the narrowband interference signals in main and diversity bandwidths.

Figure 18 Reverse Spectrum Scanning: Main RSSIs Are Normal, while Diversity RSSIs Are Low

Figure 19 Reverse Spectrum Scanning: Narrowband Interference Signals Present in Main and Diversity Bandwidth


zxc10 bssb rssi alarm troubleshooting guide_r1.1

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