TTA Operating Principles and Problem Handling Guide-20050628-B-1.1

Document No.

Product name GBSS

Used by Engineers of Huawei, cooperation

partners, and local staff

Product version

Written by

Wireless Technical Support

Department

Document version

V1.0

TTA Operating Principles and Problem Handling Guide

Prepared by Chen Xinting Date 2004-7-13

Reviewed by Chen Yuan, Fan Kai Date 2005-6-28

Reviewed by Date

Approved by Date

Huawei Technologies Co., Ltd. All rights reserved

2005-06-29 Hauwei Confidential no spreading without permission

Page 1 of 32

2005-06-29 Hauwei Confidential no spreading without permission

Page 2 of 32

Revision record

Date Revision version

Description Author

2004-07-13 Initial draft, Chinese version Chen Xinting

2005-6-28 Reviewing English version Fan Kai

TTA Operating Principles and Problem Handling Guide Internal

2005-06-29 Huawei Confidential No spreading without permission

Page 3 of 32 pages

Table of Contents

Chapter 1 TTA Operating Principles and Types ........................................................................ 5

1.1 Basic Concepts of TTA......................................................................................................... 5 1.1.1 Overview .................................................................................................................... 5 1.1.2 Operating Principles of TTA ....................................................................................... 5 1.1.3 Types of TTA.............................................................................................................. 8

1.2 Settings of Switches of CDU Rear Panels Related to TTA................................................ 11 1.2.1 Setting of Switch of KMW CDU Rear Panel............................................................. 11 1.2.2 Setting of Switch of COM DEV CDU Rear Panel..................................................... 12 1.2.3 Setting of SPL Switch............................................................................................... 14

1.3 Precautions for TTA Data Configuration ............................................................................ 15 1.3.1 TTA Configured........................................................................................................ 15 1.3.2 TTA Not Configured ................................................................................................. 15

Chapter 2 TTA Alarm Handling................................................................................................ 16

2.1 Testing Active Part of the TTA ........................................................................................... 17 2.2 Testing Passive Part of the TTA......................................................................................... 17

Chapter 3 VSWR Test ............................................................................................................. 18

3.1 Definition of VSWR and Its Algorithm Method ................................................................... 18 3.2 VSWR Problems................................................................................................................. 20 3.3 VSWR Test When TTA Not in Operation ........................................................................... 20 3.4 VSWR Test When TTA in Operation.................................................................................. 21

Chapter 4 TTA Current Test .................................................................................................... 24

Chapter 5 Cases...................................................................................................................... 25

5.1 All Level 2 Interference Band on Traffic Management Console due to CDU Attenuation Factor Unconfigured ................................................................................................................. 25

5.2 MS Call Failure due to Incorrect Configuration of Power Attenuation Factor in BSC Data Configuration............................................................................................................................. 26

5.3 One Way Audio After TTA Removed due to Failure to Modify With TTA to Without TTA in Antenna and Feeder Configuration Table ................................................................................ 28

5.4 Tributary TTA Alarm due to Lightning Arrester of the Relocated BTS Not Supporting Feed29 5.5 All Idle Channels at Level 2 Interference Band due to Incorrect Setting of CDU Power Attenuation Factor..................................................................................................................... 32



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Key words: TTA, CDU, SPL, TTA alarm

Abstract: This document introduces the operating principles of the TTA and methods to handle frequently-occurring problems. It also provides some cases for reference.

List of Abbreviations and Acronyms:

CDU Combiner Distribution Unit

SPL SPL board

TTA Tower top amplifier



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Chapter 1

1.1.1

1.1.2

TTA Operating Principles and Types

1.1 Basic Concepts of TTA

Overview

The tower top amplifier (TTA) is installed close to the antenna and consists of duplexer,

low noise amplifier, and feeder.

The duplexer filters the signals received from the antenna to remove external

interference. Then the low noise amplifier amplifies the weak signals received and

sends them to the indoor equipment through low-loss cable.

The tower top low noise amplifier lowers thermal noise greatly without affecting the

carrier-to-interference ratio. This helps improve the transmission quality of uplink

signals.

Because the amplifier is installed on tower top, the signals it amplifies do not get lost

by passing through feeder. In addition, the TTA noise figure (NF) is low with enough

gain. This helps enhance the input level of the signals received by the BTS, reduce the

impact of NF, and improve the quality of signal demodulation.

Operating Principles of TTA

How to improve the receiving sensitivity of the BTS system is a hard task. The reason

lies in the thermal noises caused by the electronic thermal motion of the active parts of

the BTS receiving system and RF conductors, such as feeder and jumper in the

receiving loop, received branch unit and high-frequency amplifier inside the BTS.

These thermal noises lower the signal noise ratio (S/N) of the system, which lowers

the receiving sensitivity of the BTS and the conversation quality.

NF measures the capability of RF parts to process small signals. It is usually defined

as shown in the following figure:

Si Ni SO NO



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NF can also be expressed in the following formula:

NF = (Si/Ni)/ (So/No)

In which,

Si: power of input signals

Ni: power of input noises

So: power of output signals

No: power of output noise

For a multi-level amplification system, its NF is:

NF = F1 + (F2-1)/G1 + (F3-1)/G1*G2 + (1-1) In which,

F1, F2, and F3: NFs of level 1, 2, and 3

Gn: gain of every level (including loss of every level)

Fn: NF of every level

For passive parts, the NF equals loss and the gain is the reciprocal of the loss.

It can be inferred from formula (1-1) that if G1, G2, Gn is large enough, the noise of the

multi-level amplification system depends on F1, NF of level 1.

When formula (1-1) is used, all parameters adopt linear values. Then the linear value

of F is converted into log value.

To summarize the rules of impact of TTA upon the system, two examples are given as

follows:

[Example 1]

Suppose:

F1 = 2.5 dB (1.7783) (NF of the TTA)

F2 = 4.5 dB (2.8184) (NF of the BTS)

G = 12 dB (15.849) (gain of the TTA)

Loss of the feeder and other passive parts: 3 dB (2)

G0 = -3 dB (1/2)

FN of the feeder and other passive parts: F0 = 1/G0

In case of TTA uninstalled, FN of the BTS receiving system with antenna output port

as reference point is:

F = F0 + (F2 - 1)/G0 = 10 Log [2 + (2.8184 - 1)/0.5] = 7.5 dB



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In case of TTA installed, FN of the BTS receiving system with antenna output port as

reference point is:

F = F1 + (F0 1)/G + (F2-1)/ (G*G0) = 10 Log [1.7783 + (2 -1)/15.849 + (2.8184-1)/

(15.849*0.5)] = 3.2dB

Therefore, when a TTA is installed, NF is lowered by 4.3 (7.5-3.2) dB. Namely, uplink

gain is lowered by 4.3 dB.

[Example 1]

Suppose:

F1 = 2.2 dB (1.6596) (NF of the TTA)

F2 = 2.3 dB (1.6982) (NF of the BTS)



G0 = -3 dB (1/2)


In case of TTA uninstalled, FN of the BTS receiving system with antenna output port

as reference point is:

F = F0 + (F2 - 1)/G0 = 10 Log [2 + (1.6982 - 1)/0.5] = 5.3 dB

In case of TTA installed, FN of the BTS receiving system with antenna output port as

reference point is:

F = F1 + (F0 - 1)/G + (F2 - 1)/ (G*G0) = 10 Log [1.6596 + (2 - 1)/15.849 + (1.6982 - 1)/

(15.849*0.5)] = 2.6 dB

Therefore, when a TTA is installed, NF is lowered by 2.7 (5.3 2.6) dB. Namely, uplink

gain is lowered by 2.7 dB.

From the two examples above, we can see:

z The TTA lowers the NF of the BTS receiving system, to improve the receiving sensitivity of the BTS system.

z The TTA improves the receiving sensitivity of uplink signals. z The TTA gain lowers FN.



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z The longer the feeder, the greater the feeder loss. After the TTA is installed, the more NF of the BTS receiving system is lowered, the more uplink gain is improved.

z When the NF of the TTA is very small, the NF of the BTS receiving system is lowered greatly after the TTA is installed. If the NF of the TTA is too large, the NF of

the BTS receiving system may deteriorate after the TTA is installed.

z After the receiving sensitivity of the BTS is improved by the TTS, the BTS becomes more sensitive to external interference.

1.1.3

1.

Types of TTA

TTAs can be grouped into:

z Triplex TTAs z Duplex TTAs z Simplex TTAs

Triplex TTAs

Triplex TTAs are often used in CDU solution, where a sector uses a dual polarization

antenna. Thus, the numbers of antennas, feeders, and jumpers decrease.

Figure 1-1 shows a triplex TTA.

Figure 1-1 Triplex TTA

In Figure 1-1, three filters ensure the separation between the receiving and



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transmitting bands. When the amplifier is faulty, the bypass switch is automatically

connected to ensure the continuity of transmission loop (about -2 dB receiving gain

and about 0.6 dB transmitting insertion loss). The offset interface is used to separate

RF from DC and provides DC voltage for the amplifier.

Technical specifications (1800 M) Receive path: Receiving frequency range 1710 MHz 1755 MHz

NF 2.5 dB (max)

Gain 120.5 dB

Gain fluctuation 0.5 dB

Insertion loss in case of bypass 2.0 dB (max)

Output 1 dB compression point 12 dBm (min)

Maximum output power (continuous) 0 dBm

Attenuation 90 dB (min) (@ Tx Band)

90 dB (@GSM-band)

Transmit path: Transmitting frequency range 1805 MHz 1850 MHz

Insertion loss 0.5 dB (max)

Insertion loss fluctuation 0.1 dB

Maximum power capacity (continuous) 200 W

Attenuation 40 dB (min) (@Rx Band)

80 dB (@GSM-band)

Other requirements: Return loss (all port) 18 dB (min)

Connector 7/16 DIN-Female

Operating temperature -40 + 60 Humidity 0 -100%

Protection requirement IP65

DC power supply (@150mA nominal) +12 V DC

Installation Pole, 30mm 100 mm (OD)

Figure 1-2 shows the appearance of triplex TTA.



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Figure 1-2 Appearance of triplex TTA

2. Duplex TTAs

Duplex TTAs are used in the solution where one antenna is shared by transmit and

main.

Figure 1-3 shows a duplex TTA.

Figure 1-3 Duplex TTA

3. Simplex TTAs

Simplex TTAs are used in the solution where a sector uses three antennas (one for

transmit and two for receive). The two receiving antennas use simplex TTAs. The

simplex TTA is applicable to BTS20 combiner-divider cabinets.



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Figure 1-4 shows a simplex TTA.

Figure 1-4 Simplex TTA

1.2 Settings of Switches of CDU Rear Panels Related to TTA

1.2.1 Setting of Switch of KMW CDU Rear Panel

Figure 1-5 shows the TTA option switch on the rear panel of the KMW CDU.

Figure 1-5 TTA option switch of (KMW)CDU rear panel

(state of the switch when TTA is not configured)

When the base station system is not configured with TTA, TTAM and TTAD must be

set to OFF.

When the base station system is configured with TTA,

z The TTA power switches of the CDU are set to ON.



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z The TTA current option switches of the CDU are set to a level, which depends upon the range of nominal working current configured for the TTA.

Note:

The TTA power switches and TTA current options switches of the CDU have main and

diverse receive paths. The states of the two paths must be checked respectively.

When one path, such as diverse receive path, is not used, consider it as a case when

the TTA is not configured, namely, TTAM and TTAD are set to OFF.

Table 1-1 and Table 1-2 list the alarm conditions for KMW CDU main and diverse

receive TTA current. Table 1-1 Alarm conditions for KMW CDU main receive TTA current

Undercurrent alarm Over current alarm Position

of the

option

switch

Rated

current Minimum Nominal

value

Maximum Minimum Nominal

value

Maximum

1 100 mA 45 50 55 160 165 170

2 107 mA 45 50 55 155 170 185

3 205 mA 135 150 165 245 260 275

Table 1-2 Alarm conditions for KMW CDU diversity receive TTA current


of the

option

switch

Rated


value


value

Maximum

1 65 mA

2 107 mA 45 50 55 155 170 185

3 205 mA 135 150 165 245 260 275

1.2.2 Setting of Switch of COM DEV CDU Rear Panel



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Figure 1-6 TTA option switch of (COM DEV)CDU rear panel

(State of the switch when TTA is not configured) When the base station system is not configured with TTA, TTAM and TTAD must be set to level 0 (OFF).

When the base station system is configured with TTA, set the TTA current option

switches of the CDU to a level, which depends upon the range of nominal working

current configured for the TTA. Note:

The TTA power switches and TTA current options switches of the CDU have main and

diverse receive paths. The states of the two paths must be checked respectively.

When one path, such as diverse receive path, is not used, consider it as a case when

the TTA is not configured, namely, TTAM and TTAD are set to level 0 (OFF).

Table 1-3 lists the alarm conditions for COM DEV CDU main/diverse receive TTA

current. Table 1-3 Alarm conditions for COM DEV CDU main/diverse receive TTA current


of the

option

switch

Rated


value


value

Maximum

0 OFF

1 100mA 45 50 55 160 165 170

2 107mA 45 50 55 155 170 185

3 205mA 135 150 165 245 260 275



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1.2.3 Setting of SPL Switch

SPLITTER (SPL) is only used for BTS21. The SPL provides TTA power supply

function. When currents of TTA or SPL exceed normal level, SPL reports TTA or SPL

alarm signals.

The SPL power indicator is the indicator for TTA power supply instead of that for SPL

working power. When the indicator is off, it is possible that the feeder connected with

the TTA is short-circuited or the SPL is faulty.

The SPL DIP switch has four positions. Positions 1, 2, and 3 correspond to 1 dB, 2 dB,

and 4 dB attenuation. Namely, when position 1 of the DIP switch is dialed to OFF, the

SPL attenuation is 1 dB. When position 2 is dialed to OFF, the SPL attenuation is 2 dB.

When position 3 is dialed to OFF, the SPL attenuation is 4 dB. When positions 1, 2,

and 3 are all dialed to OFF, the SPL attenuation is 7 dB. Position 4 is straight through

position and is usually dialed to ON. When a single SPL is used, positions 1, 2, 3, and

4 are all dialed to ON. When SPLs are cascaded, positions 1, 2, 3, and 4 of the DIP

switch of the first SPL are all dialed to ON. The attenuation of the second cascaded

SPL should be 7 dB. Namely, positions 1, 2, 3 are dialed to OFF and position 4 dialed

to ON.

Table 1-4 lists the control attenuation of SPL DIP switch S1.



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Table 1-4 Control attenuation of SPL DIP switch S1

S1.1 S1.2 S1.3 S1.4 Attenuation (dB)

OFF OFF ON ON 1

ON OFF ON ON 2

OFF ON ON ON 3

ON ON OFF ON 4

OFF OFF OFF ON 5

ON OFF OFF ON 6

OFF OFF OFF ON 7

1.3 Precautions for TTA Data Configuration

1.3.1

1.3.2

TTA Configured

When the BTS is configured with TTA, during BSC data configuration, configure the

following based on the actual situation in the Antenna and Feeder Configuration

table:

z CDU z SPL z Combiner z TTA z Power attenuation factor The BTS adjusts CDU gain based on parameters With TTA? and Power attenuation

factor.

Suppose TTA gain is G dB,

z The CDU power attenuation factor should be set to G 4 dB. z The CDU power attenuation factor should be set to 0 when TTA is not configured. z The uplink gain should be set to 255 dB. If TTA gain is 12 dB, the CDU power attenuation factor should be set to 8 dB.

TTA Not Configured

When the BTS is not configured with TTA, during BSC data configuration, configure

the following based on the actual situation in the Antenna and Feeder Configuration

table:

z CDU



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Chapter 2

z SPL z Combiner z TTA The parameter Power attenuation factor is set to 0.

The receive power attenuation factor of the CDU is set to 0 dB by default.

TTA Alarm Handling

When the antenna and feeder system is improperly connected, or water permeates in

the TTA, a TTA alarm occurs.

TTA alarms may be caused by:

z Erroneous alarm of TTA z CDU fault or erroneous alarm z Fault with lightning arrester and feeder z Improper connection of the antenna and feeder system z TTA fault or water-permeated Troubleshooting procedures:

1) Power on and reset the CDU. Observe whether the alarm disappears to judge

whether it is erroneous alarm.

2) Check whether the connectors of the receive tributaries get loose. If yes, fasten

them.

3) Use a multimeter to measure whether CDU output is normal. If not, check whether

the TTA and its connector are water-permeated or replace the TTA.

4) Measure the TTA current after uninstalling the connector between the jumper and

the TTA. If the current exceeds the normal range, a TTA alarm is reported. Otherwise,

the TTA alarm is caused by the lightning arrester or feeder.

5) Use a multimeter to measure the current from the jumper on cabinet top to the

lightning arrester. If no exception happens, it means that TTA alarm is caused by

feeder fault.

6) Measure the main feeder. If any exception happens, check the connector between



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the outdoor main feeder and the jumper.

Note:

The normal working current of self-made TTA is 45 mA 90 mA and that of imported

TTA is 50 mA 170 mA.

2.1 Testing Active Part of the TTA

The SPL conducts a real time test of the working current of the TTA. When it exceeds

the normal working range, the SPL generates a TTA alarm signal, which indicates that

the active circuit of the TTA is faulty.

The normal working current of self-made TTA is 45 mA 90 mA and that of imported

TTA is 50 mA 170 mA.

The power supply of the TTA is from the feeder at the input interface of the SPL. The

feeder is powered on as long as the power supply of the SPL is ON.

When testing the active part of the TTA, you should choose the equipment room as the

testing site. If 12 V DC regulated power supply is available, you can also choose other

places for the test.

Test procedures:

1) Remove the jumper on cabinet top.

2) Connect the receive interface of the TTA with a jumper to make the ground of the

TTA be connected with that of the BTS (the ground of the jumper connector getting

touch with that of the socket on cabinet top).

3) Connect a DC ammeter between the core wire of the socket on cabinet top and the

core wire of the jumper of the TTA. Then test the current.

4) Judge whether the active part of the TTA is in good condition based on the

recorded current value.

If 12 V DC regulated power supply is used, connect the positive electrode to the core

wire of the jumper of the TTA to test the current.

2.2 Testing Passive Part of the TTA

To test the passive part of the TTA, you do not need to power on the TTA.



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The standing wave of a simplex TTA at the receiving band should be less than 2.

The standing wave of a duplex TTA at the transmitting band should be less than 1.8

and that at the receiving band less than 2.

When testing the passive part of the TTA, you should choose either the equipment

room or other places as the testing site.

Test procedures:

1) Connect the 50 ohm matching load to the antenna port.

2) Connect the receive interface of the TTA with a jumper and test the standing wave

at the receiving band with SITMARST.

3) Connect the transmitting interface of the TTA with a jumper and test the standing

wave at the transmitting band with SITMARST. This step is not required in case of

simplex TTAs.

4) Judge whether the passive part of the TTA is in good condition based on the

recorded value of the standing wave.

Chapter 3

1.

2.

VSWR Test

3.1 Definition of VSWR and Its Algorithm Method Definition of VSWR

Voltage standing wave ratio (VSWR) reflects the impedance matching between the

near end and remote end. The greater the VSWR is, the worse the impedance

matching is. The worse the impedance matching is, the smaller the energy that the

remote end obtains from the near end is. The direct impact is that:

z The remote end cannot obtain all the energy from the near end. The gain on the transmission line is smaller than the idealized value. The line loss is greater than

expected.

z Some signals are reflected. They shake on the transmission line and superimpose with the subsequent signals transmitted, which damages the quality of signals.

Algorithm Method for VSWR

Figure 3-1 shows the VSWR relations.

z1z0

PinPre

Figure 3-1 VSWR relations



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3.

4.

5.

6.

7.

In Figure 3-1, Pre stands for reflected power, Pin for incident power, Z1 for load

impedance, and Z0 for input impedance.

Reflection Factor

Formula for the reflection factor (indicating the reflection factor of the voltage):

= (Z1 Z0)/ (Z1 + Z0) VSWR

VSWR = (1 + ||)/ (1 ||)

Return Loss

RTL = 20Lg|| = 20Lg ((VSWR - 1)/ (VSWR + 1))

Significance of VSWR Test

Testing the VSWR of the antenna and feeder system level by level can help judge

whether open circuit, short circuit, or bad contact occurs to the signal path. Improving

system impedance matching based on the test result can enhance the quality of

signals and coverage.

Impact of Feeder and Amplifier upon VSWR Test

When a tester is used for VSWR test, it is VSWR of the tested point connected to the

instrument output port that is displayed on the tester. The impedance matching of the

middle and other ports of the tested system cannot be accurately reflected.

Example 1:

A 100-meter-long 7/8" feeder is tested. Its loss at 900 MHz is 4 dB and that at 1800

MHz is 6 dB. When open connection occurs to the other end of the tested cable, the

return loss at 900 MHz should be -8 dB and that at 1800 MHz -12 dB. The return

losses are 2.33 and 1.67 respectively when converted into VSWR.

Example 2:

Suppose the other end of the 100-meter-long cable is connected with an antenna

whose characteristic impedance is 50 ohm and the return loss of the antenna is 10

dB. The return loss at 900 MHz should be 18 dB ((-10) + 2*(- 4)) and that at 1800

MHz 22 dB.

Through this method, you can infer the impedance matching at the other end of the

cable.

Example 3:



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If there is an amplifier and isolator on the transmission line, the signal gain from the

input to the output differs greatly from that from the output to the input. Methods in

Examples 1 and 2 cannot be used. You have to measure them respectively.

3.2 VSWR Problems VSWR problems may be caused by:

z Bad contact Connectors of the antenna, feeder, TTA, or lightning arrester are not:

Properly prepared (such as dry joint) Reliably connected (such as loose, distortion, and sliding filament) Applied with good waterproof measurement (such as accumulated water and stain)

z Devices The CDU, EDU, TTA, or SPL is damaged or generates erroneous alarm.

3.3 VSWR Test When TTA Not in Operation To conduct VSWR test when the TTA is not in operation, you need to prepare the following:

z Antenna analyzer S331A z Cables (RF coaxial cables) z Open-circuit/short-circuit Figure 3-2 shows the connections between the tested devices when the TTA is not in operation.

Figure 3-2 Connections between the tested devices when the TTA is not in operation

Test procedures:

1) Prepare test tools and accessories.

2) Use the open-circuit/short-circuit to correct the VSWR of S331A.



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3) Cut off power to the TTA of the CDU or the EDU.

4) Connect the bypass jumper of the TTA to the signal path.

Conduct the test as shown in . If only the antenna is tested, omit the part not required.

Note:

In case of conducting VSWR test when the TTA is not in operation; remember to connect the bypass jumper of the TTA to the signal path.

3.4 VSWR Test When TTA in Operation To conduct VSWR test when the TTA is in operation, you need to prepare the following:

z Antenna analyzer S331A z Cables (RF coaxial cables) z Open-circuit/short-circuit z Block module

From , it can be seen that to ensure the normal operation of the TTA, the CDU and the lightning arrester cannot be disconnected. The 12 V DC power supply should be prevented from being cascaded with S331A.

Two test methods are available:

Test method 1: use block module

Test procedures:


2) Power off the CDU/SPL.

3) Connect the antenna properly. Note that the input and output directions of N female connectors shown in must be correctly connected. Otherwise, the antenna analyzer is burned.

4) Re-check and power on the CDU/SPL.

5) Set the test menu of the antenna analyzer.

Test method 2: test the transmitting path and receiving path separately

Figure 3-3 shows the connections between the tested devices when the TTA is in operation



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Figure 3-3 Connections between the tested devices when the TTA is in operation

Test procedures:



3) Test the VSWR of the antenna and feeder on the transmitting path.

The filter in the duplexer is not directional, except the isolator at the output end. The return loss of the duplexer is generally over 18 dB. The VSWR of the transmitting path can be measured at TX-DUP. For the duplexer, the insertion loss is about 1.5 dB. The return loss minus 3 dB is the VSWR at the transmitting band of the output end of the CDU.

4) Test the VSWR of the antenna and feeder on the main receive path (not suggested).

(1) Power off the CDU.

(2) Remove the CDU panel.

(3) Disconnect the duplexer from the feeding device of the TTA.

(4) Lead out the antenna and feeder of the receive path with proper connector and cable.

(5) Power on the CDU and TTA and test the VSWR.

This method is also applicable to testing the VSWR of the antenna and feeder on the transmitting path

5) Test the VSWR of the antenna and feeder on the diverse receive path (not suggested).



(3) Disconnect the filter from the feeding device of the TTA.



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Precautions:

Put the removed CDU panel in a safe and clean place to avoid getting lost.

Remember to check whether DC power supply is available at the port of the access instrument.

Because the TTA is directional, the VSWR between the TTA and antenna is hard to estimate.



Page 24 of 32 pages

Chapter 4 TTA Current Test

If TTA current is not tested before installation, you can perform the test after BTS

power-on. Here, TTA current test is conducted based on the situation that TTA is not

removed.

Test procedures:


2) Connect a DC ammeter between the core wire of the socket on cabinet top and the

core wire of the jumper. Then test the current.

3) Judge whether the active part of the TTA is in good condition based on the

recorded current value.

For CDU-type BTS, the two switches on the CDU rear panel should be set correctly.

The power switch is ON (no current output if the switch is OFF). Different current levels

are selected for TTA current option switch based on the types of TTA. When TTA

current exceeds the specified range, a current alarm is generated.

Before test, ensure that the equipment works normally. Connect a multimeter in the

path to be tested. You can also connect a multiple with the cabinet top or between the

tower top feeder and TTA to test TTA current according to different requirements.

When connecting a multimeter for on-site test, power off the cabinet and then power

on.



Page 25 of 32 pages

Chapter 5

Cases

5.1 All Level 2 Interference Band on Traffic Management Console due to CDU Attenuation Factor Unconfigured

[Fault Description]

Description: It was viewed on the traffic management console that for some cells, their

interference bands were of level 2 day and night and there was no interference band of

level 1.

[Alarm Information]

None

[Fault Analysis]

Interference bands viewed on the traffic management console are measured based on

uplink. Generally, according to the settings of data management console, interference

band level 1 corresponds to 105 dBm 98 dBm interference signal, level 2 98

dBm 92 dBm, level 3 92 dBm 87 dBm, level 4 87 dBm 85 dBm,

and level 5 greater than 85 dBm. Normally, interference band level should be as low

as possible.

For the fault described above, reasons may be that:

z There is uplink interference for the BTS. z One part of the BTS is faulty, such as the TRX or CDU. z Traffic measurement is inaccurate due to some reason. z Data configurations of these cells are unreasonable. z A repeater or TTA is added in the cell. They are not operated as required. For example, inconsistent data, low quality, or nonstandard installation.

[Troubleshooting]

(1) It was found out after careful check of the traffic management console that the

interference bands of these cells were of level 2 day and night and there was no



Page 26 of 32 pages

interference band of level 1. This case is abnormal. If there is interference,

interference at night should be less than that during the day. In addition, there must be

interference band of level 1 except that there is a fixed external interference or one

board of the BTS is faulty.

(2) Such fault happened to 15 cells, which were in suburbs and a bit far from each

other. If there is an external interference, there should be more than one interference

source, which is, however, impossible for suburbs.

(3) The maintenance engineer of the customer said that a set of TTAs were installed

recently. Their power supply was not from BTA CDU but from themselves. Therefore,

there was no corresponding data configured on the data configuration console.

(4) Generally, the TTA gain is 12 dB 14 dB. TTAs compensate feeder loss by about

4 dB. Therefore, it was doubted that the fault was caused by no attenuation factor

added in data configuration.

(5) On the data management console, set cell configuration in Antenna and Feeder

Configuration table to With TTA and CDU attenuation factor to 8 (there was no TTA

configured originally). The fault was cleared.

[Suggestions and Summary]

Currently, some customers purchase and install TTAs to enhance BTS coverage

capability without configuring data, which tends to cause problems. Huawei engineers

should guide the customers to operate according to the specifications.

5.2 MS Call Failure due to Incorrect Configuration of Power Attenuation Factor in BSC Data Configuration

[Fault Description]

A Huawei BTS312 failed to access a call when the signal leve was less than 85

dBm.

[Alarm Information]

None

[Fault Analysis]



Page 27 of 32 pages

The MS voice access path is:

MSRadio link (including antenna and feeder system)BTSE1

BTS_DDFTrunk

transmissionBSC_DDFE132BIEHWNETOPTOptical

fiberFBICTNE3ME1 or transmission equipmentMSMFTCMSC

Resons for the fault described above may be that:

z An individual MS may cannot make a call when the signal level is less than -85 dBm.

z Multipath effect causes some signals to land outside the delay window, which results in false intra-frequency interference and normal conversation impossible.

z The reduced performance of the TRX of the BTS causes reduced uplink receiving sensitivity. As a result, a call cannot be accessed when the signal level is less than

85 dBm.

z A TTA is not used for 80 W large-power BTS, which causes unbalance between uplink and downlink signals.

z Bit error occurs to the transmission equipment, which results in reduced access performance.

z The hardware equipment of the BSC and the MSC is faulty, which results in decreased service performance.

z Unreasonable data of network planning or external interference of the network causes great interference.

z Error of hardware data configuration causes decrease in service performance. [Troubleshooting]

(1) On-site information collection found out that multiple MSs cannot make calls when

the signal level was less than -85 dBm. Therefore, it was not a problem of an individual

MS.

(2) Test multiple BTSs and find out such problem was available for every BTS.

Therefore, it was not a problem of an individual BTS or multipath effect. In addition,



Page 28 of 32 pages

this problem occurred to both 40 W and 80 W BTSs. Therefore, using PBU instead of

TTA was not the reason for the fault.

(3) It was found that through drive test that the frequency plan was reasonable.

Interference was small after analysis of interference band on the traffic management

console. Therefore, interference and multipath effect did not cause the fault.

(4) Trace transmission error and fine no error.

(5) Check all boards of the BSC and no faulty board was found.

(6) Register unlink and downlink balance performance measurement and trace. It was

found out that problematic BTS was at level 11, which meant that grave unlink and

downlink unbalance existed. When one cell of the BTS used a TTA and the other two

cells did not use TTAs, the cell installed with TTA had good uplink and downlink

balance performance. The cells not installed with TTAs were at level 11.

(7) Check the Antenna and Feeder Configuration table and find that power attenuation

factor was set to 10 no matter whether a TTA was installed. Modify the value of power

attenuation factor of the BTS not installed with a TTA to 0 and then conduct a test. A

MS could make a call when the downlink signal level was 100 dBm. Modify all

settings of power attenuation factor and conduct a test. The fault was cleared.


When a TTA is not installed, values of power attenuation factor are set to 0. When a

TTA is installed, if the TTA gain is dB, the value of power attenuation factor is G 4.

5.3 One Way Audio After TTA Removed due to Failure to Modify With TTA to Without TTA in Antenna and Feeder Configuration

Table

[Fault Description]

A dialing test was conducted after the experiment of large power reconstruction of

three cells of BTSA (S111), modification of data configuration, replacement of EDU

with CDU, and removal of two tributary TTAs. The MS of the called party rang. One

way audio occurred when the call was connected.



Page 29 of 32 pages

[Alarm Information]

Alarm of TRX9 one way audio.

[Fault Analysis]

In case of S111 configuration, after modified data reset, there should be no description

of the TRX in data configuration information as that in case of large power

reconstruction. Check the data and find no error. All TRX9s were modified to TRX8. It

must have been that TRX9 was not changed to TRX8 in some tables during data

setting, which resulted in host and BAM data inconsistency.

[Troubleshooting]

(1) Check the data and find that there was no description of TRX9 in data

configuration of the BTS. Reset all related tables and apply fourth level reset to the

BTS. One way audio remained. Continue checking the data.

(2) The last two items in the Antenna and Feeder Configuration table are

With/without TTA and Power attenuation factor. With TTA and Power attenuation

factor is 12 4 = 8 are specified in case of large power configuration to suppress

uplink out-band noise. In case of PBU and EDU removed, Without TTA and Power

attenuation factor = 0 should be specified. During data check, it was found that

Without TTA and Power attenuation factor = 0 were specified. This was the source

of the fault. Such data configuration would amplify useful uplink signals and out-band

noises by 8 dB, which caused decline in signal noise ratio and one way audio as a

result.

(3) The fault was cleared after data modification and BTS fourth level reset.


Pay close attention to the descriptions in the Antenna and Feeder Configuration table.

5.4 Tributary TTA Alarm due to Lightning Arrester of the Relocated BTS Not Supporting Feed

[Fault Description]



Page 30 of 32 pages

A relocated BTS312 (S111, V06) was made by N. The old antennas and feeders were

used by the relocated BTS. The equipment operated normally after the BTS started to

work. The configuration of the third cell was modified to large power configuration (1

PBU + 1 EDU + 2 TTAs) to increase its coverage. After such configuration, an alarm of

EDU tributary TTA was generated and alarms occurred to two tributaries of the EDU.

[Alarm Information]

Alarm of EDU tributary TTA

Alarms occurred to two tributaries of the EDU.

[Fault Analysis]

An alarm of EDU tributary TTA was generated when the feeding current of the EDU

tributary exceeded the normal value. The possible reasons were that:

z The corresponding tributary TTA was damaged. z The part between the EDU tributary to TTA was not properly connected. Or some parts (including the jumper, feeder, lighting arrester) were damaged.

z The EDU alarm detection circuit was faulty. During the large power reconstruction, one PBU, one EDU, and two TTAs were added.

Because it was of small possibility that two TTS were faulty simultaneously, the

possible reason that the TTA was damaged was cleared. Conduct an on-site antenna

and feeder standing wave test. The VSWR was less than 1.3. The possible reason of

damaged parts or improper connection was cleared. Such alarm also occurred when

an EDU that worked normally on other BTSs was used for this BTS. The EDU worked

normally on Huawei newly-built large power BTSs. The possible that the EDU was

faulty was cleared.

After comparison of this relocated BTS with other large power BTSs, there were no

differences between the jumpers and feeders. The antenna used by the relocated BTS

was accepted by Huawei. Only the lightning arrester was made by N. Special attention

was then paid to the lightning arrester.

The CS72640 lightning arrester made by N was of 1/4 wavelength short-circuited



Page 31 of 32 pages

T-type. For 890 MHz 960 MHz current, its inner conductor was connected and so

was the external conductor. For low frequency and DC, its inner and external

conductors were connected at the lightning arrester. It meant that it was not feed-type

lighting arrester, which caused TTA over current alarm.

For Huawei, lightning arrester is of feed-type lighting arrester by default. It works

normally with TTA. The TTA alarm disappeared after the lightning arrester was

uninstalled.

[Troubleshooting]

(1) Only jumpers were added during the installation of TTAs. Check that the jumpers

were properly prepared, the connection between the jumpers to the TTA and to the

feeder were properly connected, and that VSWR was normal.

(2) Replace the EDU with an EDU working normally. Apply the original EDU to other

BTSs and it worked normally. Therefore, the fault was not caused by the EDU.

(3) It was less likely that VSWR alarms occurred to both TTAs and both TTAs were

damaged. Apply other TTAs to the relocated BTS. The fault also occurred. Therefore,

the fault was not caused by TTAs.

(4) After comparison of this relocated BTS with other large power BTSs, there were

no differences between the jumpers and feeders. The antenna used by the relocated

BTS was accepted by Huawei. Only the lightning arrester was made by N. Uninstall

the lightning arrester. Alarms of EDU tributary TTAs disappeared.

(5) Replace the lightning arrester with Huawei lighting arrester. No EDU tributary

alarm occurred. Therefore, it was confirmed that the alarm of EDU tributary TTA was

generated because the CS72640 lightning arrester made by N did not support TTA.


Note the compatibility between the additional TTA and PBU with the original

equipment.

Note the differences between the site under discussion and other normal sites when

problems occurred.



Page 32 of 32 pages

5.5 All Idle Channels at Level 2 Interference Band due to Incorrect Setting of CDU Power Attenuation Factor

[Fault Description]

It was found after system loading that the idle channels of all cells are at level 2

interference band. This system was 1800 network. Frequency sweep found no signals

at this frequency band.

[Fault Analysis]

Interference comes from internal and external reasons. It is of little possibility that

external reason works when the whole system is interfered. Even if there is

interference source, interference in different cells should vary. Similarly, it is of little

possibility that BTS performance fault works when interference band of the whole

system is abnormal. Therefore, the interference must come from antenna. Only

Antenna and Feeder Configuration table is related to the data of antenna.

In the Antenna and Feeder Configuration table, Power attenuation factor of CDU

uplinks was set to all 0. Power attenuation factor functions to attenuate TTA gain

properly when TTA is installed. Otherwise, too high gain will heighten extra low noise,

which causes rise of system interference band.

[Troubleshooting]

For BTS using CDU, adjust CDU gain based on the two parameters With/without

TTA and Power attenuation factor. In the CDU, gain is fixed to 10.

Set uplink based on the actual situation of TTA:

z Power attenuation factor: 8 in case of With TTA (indicating CDU attenuation 8 dB, supposing feeder loss 4 dB)

z Power attenuation factor: 0 in case of Without TTA

Table of Contents

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Document No.

Product name

GBSS

Used by

Engineers of Huawei, cooperation partners, and local staff

Product version

Written by

Wireless Technical Support Department

Document version

V1.0

TTA Operating Principles and Problem Handling Guide

Prepared by

Chen Xinting

Date

2004-7-13

Reviewed by

Chen Yuan, Fan Kai

Date

2005-6-28

Reviewed by

Date

Approved by

Date

Huawei Technologies Co., Ltd.

All rights reserved

Revision record

Date

Revision version

Description

Author

2004-07-13

Initial draft, Chinese version

Chen Xinting

2005-6-28

Reviewing English version

Fan Kai

Table of Contents

5Chapter 1 TTA Operating Principles and Types


51.1.1 Overview

51.1.2 Operating Principles of TTA

81.1.3 Types of TTA






151.3.1 TTA Configured

151.3.2 TTA Not Configured

16Chapter 2 TTA Alarm Handling



18Chapter 3 VSWR Test

183.1 Definition of VSWR and Its Algorithm Method

203.2 VSWR Problems

203.3 VSWR Test When TTA Not in Operation

213.4 VSWR Test When TTA in Operation

24Chapter 4 TTA Current Test

25Chapter 5 Cases



285.3 One Way Audio After TTA Removed due to Failure to Modify With TTA to Without TTA in Antenna and Feeder Configuration Table

295.4 Tributary TTA Alarm due to Lightning Arrester of the Relocated BTS Not Supporting Feed

325.5 All Idle Channels at Level 2 Interference Band due to Incorrect Setting of CDU Power Attenuation Factor

Key words: TTA, CDU, SPL, TTA alarm

Abstract: This document introduces the operating principles of the TTA and methods to handle frequently-occurring problems. It also provides some cases for reference.

List of Abbreviations and Acronyms:

CDU Combiner Distribution Unit

SPL SPL board

TTA Tower top amplifier

Chapter 1 TTA Operating Principles and Types


1.1.1 Overview

The tower top amplifier (TTA) is installed close to the antenna and consists of duplexer, low noise amplifier, and feeder.

The duplexer filters the signals received from the antenna to remove external interference. Then the low noise amplifier amplifies the weak signals received and sends them to the indoor equipment through low-loss cable.

The tower top low noise amplifier lowers thermal noise greatly without affecting the carrier-to-interference ratio. This helps improve the transmission quality of uplink signals.

Because the amplifier is installed on tower top, the signals it amplifies do not get lost by passing through feeder. In addition, the TTA noise figure (NF) is low with enough gain. This helps enhance the input level of the signals received by the BTS, reduce the impact of NF, and improve the quality of signal demodulation.

1.1.2 Operating Principles of TTA

How to improve the receiving sensitivity of the BTS system is a hard task. The reason lies in the thermal noises caused by the electronic thermal motion of the active parts of the BTS receiving system and RF conductors, such as feeder and jumper in the receiving loop, received branch unit and high-frequency amplifier inside the BTS. These thermal noises lower the signal noise ratio (S/N) of the system, which lowers the receiving sensitivity of the BTS and the conversation quality.

NF measures the capability of RF parts to process small signals. It is usually defined as shown in the following figure:

NF can also be expressed in the following formula:

NF = (Si/Ni)/ (So/No)

In which,

Si: power of input signals

Ni: power of input noises

So: power of output signals

No: power of output noise

For a multi-level amplification system, its NF is:

NF = F1 + (F2-1)/G1 + (F3-1)/G1*G2 + (1-1)

In which,

F1, F2, and F3: NFs of level 1, 2, and 3

Gn: gain of every level (including loss of every level)

Fn: NF of every level

For passive parts, the NF equals loss and the gain is the reciprocal of the loss.

It can be inferred from formula (1-1) that if G1, G2, Gn is large enough, the noise of the multi-level amplification system depends on F1, NF of level 1.

When formula (1-1) is used, all parameters adopt linear values. Then the linear value of F is converted into log value.

To summarize the rules of impact of TTA upon the system, two examples are given as follows:

[Example 1]

Suppose:

F1 = 2.5 dB (1.7783) (NF of the TTA)

F2 = 4.5 dB (2.8184) (NF of the BTS)



G0 = -3 dB (1/2)


In case of TTA uninstalled, FN of the BTS receiving system with antenna output port as reference point is:

F = F0 + (F2 - 1)/G0 = 10 Log [2 + (2.8184 - 1)/0.5] = 7.5 dB

In case of TTA installed, FN of the BTS receiving system with antenna output port as reference point is:

F = F1 + (F0 1)/G + (F2-1)/ (G*G0) = 10 Log [1.7783 + (2 -1)/15.849 + (2.8184-1)/ (15.849*0.5)] = 3.2dB

Therefore, when a TTA is installed, NF is lowered by 4.3 (7.5-3.2) dB. Namely, uplink gain is lowered by 4.3 dB.

[Example 1]

Suppose:

F1 = 2.2 dB (1.6596) (NF of the TTA)

F2 = 2.3 dB (1.6982) (NF of the BTS)



G0 = -3 dB (1/2)


In case of TTA uninstalled, FN of the BTS receiving system with antenna output port as reference point is:

F = F0 + (F2 - 1)/G0 = 10 Log [2 + (1.6982 - 1)/0.5] = 5.3 dB

In case of TTA installed, FN of the BTS receiving system with antenna output port as reference point is:

F = F1 + (F0 - 1)/G + (F2 - 1)/ (G*G0) = 10 Log [1.6596 + (2 - 1)/15.849 + (1.6982 - 1)/ (15.849*0.5)] = 2.6 dB

Therefore, when a TTA is installed, NF is lowered by 2.7 (5.3 2.6) dB. Namely, uplink gain is lowered by 2.7 dB.

From the two examples above, we can see:

The TTA lowers the NF of the BTS receiving system, to improve the receiving sensitivity of the BTS system.

The TTA improves the receiving sensitivity of uplink signals.

The TTA gain lowers FN.

The longer the feeder, the greater the feeder loss. After the TTA is installed, the more NF of the BTS receiving system is lowered, the more uplink gain is improved.

When the NF of the TTA is very small, the NF of the BTS receiving system is lowered greatly after the TTA is installed. If the NF of the TTA is too large, the NF of the BTS receiving system may deteriorate after the TTA is installed.

After the receiving sensitivity of the BTS is improved by the TTS, the BTS becomes more sensitive to external interference.

1.1.3 Types of TTA

TTAs can be grouped into:

Triplex TTAs

Duplex TTAs

Simplex TTAs

1. Triplex TTAs

Triplex TTAs are often used in CDU solution, where a sector uses a dual polarization antenna. Thus, the numbers of antennas, feeders, and jumpers decrease.

Figure 1-1 shows a triplex TTA.

Figure 1-1 Triplex TTA

In Figure 1-1, three filters ensure the separation between the receiving and transmitting bands. When the amplifier is faulty, the bypass switch is automatically connected to ensure the continuity of transmission loop (about -2 dB receiving gain and about 0.6 dB transmitting insertion loss). The offset interface is used to separate RF from DC and provides DC voltage for the amplifier.

Technical specifications (1800 M)

Receive path:

Receiving frequency range 1710 MHz 1755 MHz

NF 2.5 dB (max)

Gain 120.5 dB

Gain fluctuation 0.5 dB

Insertion loss in case of bypass 2.0 dB (max)

Output 1 dB compression point 12 dBm (min)

Maximum output power (continuous) 0 dBm

Attenuation 90 dB (min) (@ Tx Band)

90 dB (@GSM-band)

Transmit path:

Transmitting frequency range 1805 MHz 1850 MHz

Insertion loss 0.5 dB (max)

Insertion loss fluctuation 0.1 dB

Maximum power capacity (continuous) 200 W

Attenuation 40 dB (min) (@Rx Band)

80 dB (@GSM-band)

Other requirements:

Return loss (all port) 18 dB (min)

Connector 7/16 DIN-Female

Operating temperature -40 + 60

Humidity 0 -100%

Protection requirement IP65

DC power supply (@150mA nominal) +12 V DC

Installation Pole, 30mm 100 mm (OD)

Figure 1-2 shows the appearance of triplex TTA.

Figure 1-2 Appearance of triplex TTA

2. Duplex TTAs

Duplex TTAs are used in the solution where one antenna is shared by transmit and main.

Figure 1-3 shows a duplex TTA.

Figure 1-3 Duplex TTA

3. Simplex TTAs

Simplex TTAs are used in the solution where a sector uses three antennas (one for transmit and two for receive). The two receiving antennas use simplex TTAs. The simplex TTA is applicable to BTS20 combiner-divider cabinets.

Figure 1-4 shows a simplex TTA.

Figure 1-4 Simplex TTA



Figure 1-5 shows the TTA option switch on the rear panel of the KMW CDU.

Figure 1-5 TTA option switch of (KMW)CDU rear panel

(state of the switch when TTA is not configured)

When the base station system is not configured with TTA, TTAM and TTAD must be set to OFF.

When the base station system is configured with TTA,

The TTA power switches of the CDU are set to ON.

The TTA current option switches of the CDU are set to a level, which depends upon the range of nominal working current configured for the TTA.

Note:

The TTA power switches and TTA current options switches of the CDU have main and diverse receive paths. The states of the two paths must be checked respectively. When one path, such as diverse receive path, is not used, consider it as a case when the TTA is not configured, namely, TTAM and TTAD are set to OFF.

Table 1-1 and Table 1-2 list the alarm conditions for KMW CDU main and diverse receive TTA current.

Table 1-1 Alarm conditions for KMW CDU main receive TTA current

Position of the option switch

Rated current

Undercurrent alarm

Over current alarm

Minimum

Nominal value

Maximum

Minimum

Nominal value

Maximum

1

100 mA

45

50

55

160

165

170

2

107 mA

45

50

55

155

170

185

3

205 mA

135

150

165

245

260

275

Table 1-2 Alarm conditions for KMW CDU diversity receive TTA current


Rated current

Undercurrent alarm

Over current alarm

Minimum

Nominal value

Maximum

Minimum

Nominal value

Maximum

1

65 mA

2

107 mA

45

50

55

155

170

185

3

205 mA

135

150

165

245

260

275


Figure 1-6 TTA option switch of (COM DEV)CDU rear panel

(State of the switch when TTA is not configured)

When the base station system is not configured with TTA, TTAM and TTAD must be set to level 0 (OFF).

When the base station system is configured with TTA, set the TTA current option switches of the CDU to a level, which depends upon the range of nominal working current configured for the TTA.

Note:

The TTA power switches and TTA current options switches of the CDU have main and diverse receive paths. The states of the two paths must be checked respectively. When one path, such as diverse receive path, is not used, consider it as a case when the TTA is not configured, namely, TTAM and TTAD are set to level 0 (OFF).

Table 1-3 lists the alarm conditions for COM DEV CDU main/diverse receive TTA current.

Table 1-3 Alarm conditions for COM DEV CDU main/diverse receive TTA current


Rated current

Undercurrent alarm

Over current alarm

Minimum

Nominal value

Maximum

Minimum

Nominal value

Maximum

0

OFF

1

100mA

45

50

55

160

165

170

2

107mA

45

50

55

155

170

185

3

205mA

135

150

165

245

260

275


SPLITTER (SPL) is only used for BTS21. The SPL provides TTA power supply function. When currents of TTA or SPL exceed normal level, SPL reports TTA or SPL alarm signals.

The SPL power indicator is the indicator for TTA power supply instead of that for SPL working power. When the indicator is off, it is possible that the feeder connected with the TTA is short-circuited or the SPL is faulty.

The SPL DIP switch has four positions. Positions 1, 2, and 3 correspond to 1 dB, 2 dB, and 4 dB attenuation. Namely, when position 1 of the DIP switch is dialed to OFF, the SPL attenuation is 1 dB. When position 2 is dialed to OFF, the SPL attenuation is 2 dB. When position 3 is dialed to OFF, the SPL attenuation is 4 dB. When positions 1, 2, and 3 are all dialed to OFF, the SPL attenuation is 7 dB. Position 4 is straight through position and is usually dialed to ON. When a single SPL is used, positions 1, 2, 3, and 4 are all dialed to ON. When SPLs are cascaded, positions 1, 2, 3, and 4 of the DIP switch of the first SPL are all dialed to ON. The attenuation of the second cascaded SPL should be 7 dB. Namely, positions 1, 2, 3 are dialed to OFF and position 4 dialed to ON.

Table 1-4 lists the control attenuation of SPL DIP switch S1.

Table 1-4 Control attenuation of SPL DIP switch S1

S1.1

S1.2

S1.3

S1.4

Attenuation (dB)

OFF

OFF

ON

ON

1

ON

OFF

ON

ON

2

OFF

ON

ON

ON

3

ON

ON

OFF

ON

4

OFF

OFF

OFF

ON

5

ON

OFF

OFF

ON

6

OFF

OFF

OFF

ON

7


1.3.1 TTA Configured

When the BTS is configured with TTA, during BSC data configuration, configure the following based on the actual situation in the Antenna and Feeder Configuration table:

CDU

SPL

Combiner

TTA

Power attenuation factor

The BTS adjusts CDU gain based on parameters With TTA? and Power attenuation factor.

Suppose TTA gain is G dB,

The CDU power attenuation factor should be set to G 4 dB.

The CDU power attenuation factor should be set to 0 when TTA is not configured.

The uplink gain should be set to 255 dB.

If TTA gain is 12 dB, the CDU power attenuation factor should be set to 8 dB.

1.3.2 TTA Not Configured

When the BTS is not configured with TTA, during BSC data configuration, configure the following based on the actual situation in the Antenna and Feeder Configuration table:

CDU

SPL

Combiner

TTA

The parameter Power attenuation factor is set to 0.

The receive power attenuation factor of the CDU is set to 0 dB by default.

Chapter 2 TTA Alarm Handling

When the antenna and feeder system is improperly connected, or water permeates in the TTA, a TTA alarm occurs.

TTA alarms may be caused by:

Erroneous alarm of TTA

CDU fault or erroneous alarm

Fault with lightning arrester and feeder

Improper connection of the antenna and feeder system

TTA fault or water-permeated

Troubleshooting procedures:

1) Power on and reset the CDU. Observe whether the alarm disappears to judge whether it is erroneous alarm.

2) Check whether the connectors of the receive tributaries get loose. If yes, fasten them.

3) Use a multimeter to measure whether CDU output is normal. If not, check whether the TTA and its connector are water-permeated or replace the TTA.

4) Measure the TTA current after uninstalling the connector between the jumper and the TTA. If the current exceeds the normal range, a TTA alarm is reported. Otherwise, the TTA alarm is caused by the lightning arrester or feeder.

5) Use a multimeter to measure the current from the jumper on cabinet top to the lightning arrester. If no exception happens, it means that TTA alarm is caused by feeder fault.

6) Measure the main feeder. If any exception happens, check the connector between the outdoor main feeder and the jumper.

Note:

The normal working current of self-made TTA is 45 mA 90 mA and that of imported TTA is 50 mA 170 mA.


The SPL conducts a real time test of the working current of the TTA. When it exceeds the normal working range, the SPL generates a TTA alarm signal, which indicates that the active circuit of the TTA is faulty.

The normal working current of self-made TTA is 45 mA 90 mA and that of imported TTA is 50 mA 170 mA.

The power supply of the TTA is from the feeder at the input interface of the SPL. The feeder is powered on as long as the power supply of the SPL is ON.

When testing the active part of the TTA, you should choose the equipment room as the testing site. If 12 V DC regulated power supply is available, you can also choose other places for the test.

Test procedures:


2) Connect the receive interface of the TTA with a jumper to make the ground of the TTA be connected with that of the BTS (the ground of the jumper connector getting touch with that of the socket on cabinet top).

3) Connect a DC ammeter between the core wire of the socket on cabinet top and the core wire of the jumper of the TTA. Then test the current.

4) Judge whether the active part of the TTA is in good condition based on the recorded current value.

If 12 V DC regulated power supply is used, connect the positive electrode to the core wire of the jumper of the TTA to test the current.


To test the passive part of the TTA, you do not need to power on the TTA.

The standing wave of a simplex TTA at the receiving band should be less than 2.

The standing wave of a duplex TTA at the transmitting band should be less than 1.8 and that at the receiving band less than 2.

When testing the passive part of the TTA, you should choose either the equipment room or other places as the testing site.

Test procedures:

1) Connect the 50 ohm matching load to the antenna port.

2) Connect the receive interface of the TTA with a jumper and test the standing wave at the receiving band with SITMARST.

3) Connect the transmitting interface of the TTA with a jumper and test the standing wave at the transmitting band with SITMARST. This step is not required in case of simplex TTAs.

4) Judge whether the passive part of the TTA is in good condition based on the recorded value of the standing wave.

Chapter 3 VSWR Test

3.1 Definition of VSWR and Its Algorithm Method

1. Definition of VSWR

Voltage standing wave ratio (VSWR) reflects the impedance matching between the near end and remote end. The greater the VSWR is, the worse the impedance matching is. The worse the impedance matching is, the smaller the energy that the remote end obtains from the near end is. The direct impact is that:

The remote end cannot obtain all the energy from the near end. The gain on the transmission line is smaller than the idealized value. The line loss is greater than expected.

Some signals are reflected. They shake on the transmission line and superimpose with the subsequent signals transmitted, which damages the quality of signals.

2. Algorithm Method for VSWR

Figure 3-1 shows the VSWR relations.

Figure 3-1 VSWR relations

In Figure 3-1, Pre stands for reflected power, Pin for incident power, Z1 for load impedance, and Z0 for input impedance.

3. Reflection Factor

Formula for the reflection factor (indicating the reflection factor of the voltage):

= (Z1 Z0)/ (Z1 + Z0)

4. VSWR

VSWR = (1 + ||)/ (1 ||)

5. Return Loss

RTL = 20Lg|| = 20Lg ((VSWR - 1)/ (VSWR + 1))

6. Significance of VSWR Test

Testing the VSWR of the antenna and feeder system level by level can help judge whether open circuit, short circuit, or bad contact occurs to the signal path. Improving system impedance matching based on the test result can enhance the quality of signals and coverage.

7. Impact of Feeder and Amplifier upon VSWR Test

When a tester is used for VSWR test, it is VSWR of the tested point connected to the instrument output port that is displayed on the tester. The impedance matching of the middle and other ports of the tested system cannot be accurately reflected.

Example 1:

A 100-meter-long 7/8" feeder is tested. Its loss at 900 MHz is 4 dB and that at 1800 MHz is 6 dB. When open connection occurs to the other end of the tested cable, the return loss at 900 MHz should be -8 dB and that at 1800 MHz -12 dB. The return losses are 2.33 and 1.67 respectively when converted into VSWR.

Example 2:

Suppose the other end of the 100-meter-long cable is connected with an antenna whose characteristic impedance is 50 ohm and the return loss of the antenna is 10 dB. The return loss at 900 MHz should be 18 dB ((-10) + 2*(- 4)) and that at 1800 MHz 22 dB.

Through this method, you can infer the impedance matching at the other end of the cable.

Example 3:

If there is an amplifier and isolator on the transmission line, the signal gain from the input to the output differs greatly from that from the output to the input. Methods in Examples 1 and 2 cannot be used. You have to measure them respectively.

3.2 VSWR Problems

VSWR problems may be caused by:

Bad contact

Connectors of the antenna, feeder, TTA, or lightning arrester are not:

Properly prepared (such as dry joint)

Reliably connected (such as loose, distortion, and sliding filament)

Applied with good waterproof measurement (such as accumulated water and stain)

Devices

The CDU, EDU, TTA, or SPL is damaged or generates erroneous alarm.

3.3 VSWR Test When TTA Not in Operation

To conduct VSWR test when the TTA is not in operation, you need to prepare the following:

Antenna analyzer S331A

Cables (RF coaxial cables)

Open-circuit/short-circuit

Figure 3-2 shows the connections between the tested devices when the TTA is not in operation.

Figure 3-2 Connections between the tested devices when the TTA is not in operation

Test procedures:



3) Cut off power to the TTA of the CDU or the EDU.

4) Connect the bypass jumper of the TTA to the signal path.

Conduct the test as shown in . If only the antenna is tested, omit the part not required.

Note:

In case of conducting VSWR test when the TTA is not in operation; remember to connect the bypass jumper of the TTA to the signal path.

3.4 VSWR Test When TTA in Operation

To conduct VSWR test when the TTA is in operation, you need to prepare the following:

Antenna analyzer S331A

Cables (RF coaxial cables)

Open-circuit/short-circuit

Block module

From , it can be seen that to ensure the normal operation of the TTA, the CDU and the lightning arrester cannot be disconnected. The 12 V DC power supply should be prevented from being cascaded with S331A.

Two test methods are available:

Test method 1: use block module

Test procedures:


2) Power off the CDU/SPL.

3) Connect the antenna properly. Note that the input and output directions of N female connectors shown in must be correctly connected. Otherwise, the antenna analyzer is burned.

4) Re-check and power on the CDU/SPL.

5) Set the test menu of the antenna analyzer.

Test method 2: test the transmitting path and receiving path separately

Figure 3-3 shows the connections between the tested devices when the TTA is in operation

Figure 3-3 Connections between the tested devices when the TTA is in operation

Test procedures:



3) Test the VSWR of the antenna and feeder on the transmitting path.

The filter in the duplexer is not directional, except the isolator at the output end. The return loss of the duplexer is generally over 18 dB. The VSWR of the transmitting path can be measured at TX-DUP. For the duplexer, the insertion loss is about 1.5 dB. The return loss minus 3 dB is the VSWR at the transmitting band of the output end of the CDU.

4) Test the VSWR of the antenna and feeder on the main receive path (not suggested).



(3) Disconnect the duplexer from the feeding device of the TTA.



This method is also applicable to testing the VSWR of the antenna and feeder on the transmitting path

5) Test the VSWR of the antenna and feeder on the diverse receive path (not suggested).



(3) Disconnect the filter from the feeding device of the TTA.



Precautions:

Put the removed CDU panel in a safe and clean place to avoid getting lost.

Remember to check whether DC power supply is available at the port of the access instrument.

Because the TTA is directional, the VSWR between the TTA and antenna is hard to estimate.

Chapter 4 TTA Current Test

If TTA current is not tested before installation, you can perform the test after BTS power-on. Here, TTA current test is conducted based on the situation that TTA is not removed.

Test procedures:


2) Connect a DC ammeter between the core wire of the socket on cabinet top and the core wire of the jumper. Then test the current.

3) Judge whether the active part of the TTA is in good condition based on the recorded current value.

For CDU-type BTS, the two switches on the CDU rear panel should be set correctly. The power switch is ON (no current output if the switch is OFF). Different current levels are selected for TTA current option switch based on the types of TTA. When TTA current exceeds the specified range, a current alarm is generated.

Before test, ensure that the equipment works normally. Connect a multimeter in the path to be tested. You can also connect a multiple with the cabinet top or between the tower top feeder and TTA to test TTA current according to different requirements.

When connecting a multimeter for on-site test, power off the cabinet and then power on.

Chapter 5 Cases


[Fault Description]

Description: It was viewed on the traffic management console that for some cells, their interference bands were of level 2 day and night and there was no interference band of level 1.

[Alarm Information]

None

[Fault Analysis]

Interference bands viewed on the traffic management console are measured based on uplink. Generally, according to the settings of data management console, interference band level 1 corresponds to 105 dBm 98 dBm interference signal, level 2 98 dBm 92 dBm, level 3 92 dBm 87 dBm, level 4 87 dBm 85 dBm, and level 5 greater than 85 dBm. Normally, interference band level should be as low as possible.

For the fault described above, reasons may be that:

There is uplink interference for the BTS.

One part of the BTS is faulty, such as the TRX or CDU.

Traffic measurement is inaccurate due to some reason.

Data configurations of these cells are unreasonable.

A repeater or TTA is added in the cell. They are not operated as required. For example, inconsistent data, low quality, or nonstandard installation.

[Troubleshooting]

(1) It was found out after careful check of the traffic management console that the interference bands of these cells were of level 2 day and night and there was no interference band of level 1. This case is abnormal. If there is interference, interference at night should be less than that during the day. In addition, there must be interference band of level 1 except that there is a fixed external interference or one board of the BTS is faulty.

(2) Such fault happened to 15 cells, which were in suburbs and a bit far from each other. If there is an external interference, there should be more than one interference source, which is, however, impossible for suburbs.

(3) The maintenance engineer of the customer said that a set of TTAs were installed recently. Their power supply was not from BTA CDU but from themselves. Therefore, there was no corresponding data configured on the data configuration console.

(4) Generally, the TTA gain is 12 dB 14 dB. TTAs compensate feeder loss by about 4 dB. Therefore, it was doubted that the fault was caused by no attenuation factor added in data configuration.

(5) On the data management console, set cell configuration in Antenna and Feeder Configuration table to With TTA and CDU attenuation factor to 8 (there was no TTA configured originally). The fault was cleared.


Currently, some customers purchase and install TTAs to enhance BTS coverage capability without configuring data, which tends to cause problems. Huawei engineers should guide the customers to operate according to the specifications.


[Fault Description]

A Huawei BTS312 failed to access a call when the signal leve was less than 85 dBm.

[Alarm Information]

None

[Fault Analysis]

The MS voice access path is:

MSRadio link (including antenna and feeder system)BTSE1 BTS_DDFTrunk transmissionBSC_DDFE132BIEHWNETOPTOptical fiberFBICTNE3ME1 or transmission equipmentMSMFTCMSC

Resons for the fault described above may be that:

An individual MS may cannot make a call when the signal level is less than -85 dBm.

Multipath effect causes some signals to land outside the delay window, which results in false intra-frequency interference and normal conversation impossible.

The reduced performance of the TRX of the BTS causes reduced uplink receiving sensitivity. As a result, a call cannot be accessed when the signal level is less than 85 dBm.

A TTA is not used for 80 W large-power BTS, which causes unbalance between uplink and downlink signals.

Bit error occurs to the transmission equipment, which results in reduced access performance.

The hardware equipment of the BSC and the MSC is faulty, which results in decreased service performance.

Unreasonable data of network planning or external interference of the network causes great interference.

Error of hardware data configuration causes decrease in service performance.

[Troubleshooting]

(1) On-si

Documents

TTA Operating Principles and Problem Handling Guide-20050628-B-1.1