When to Use TMA Guideline

7/31/2019 When to Use TMA Guideline

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TOWER MOUNTED AMPLIFIER GUIDELINE

2(20) RSA 100 56 - 102 Uen Rev A 2002-05-28

Ericsson AB 2002

The contents of this product are subject to revision without notice due tocontinued progress in methodology, design and manufacturing.

Ericsson assumes no legal responsibility for any error or damage resultingfrom usage of this product.

This product is classified as Ericsson Commercial In Confidence


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Contents

1Revision history ..................................................................5

2 Introduction.........................................................................5

3TMA products......................................................................5

4System aspects...................................................................7

4.1 Benefits from introducing TMA...............................................................7

4.2 Considerations when introducing TMA...................................................7

5Link budget improvement ..................................................9

5.1 Link balance and parameter variations ..................................................9

5.2 TMA benefits ........................................................................................10

5.3 Nominal figures for sensitivity and output power..................................10

5.4Alternative parameter values................................................................12

5.5 Power balance calculations..................................................................12

5.6 Link budget improvements ...................................................................14

6Conclusion ........................................................................19

7References ........................................................................20


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1 Revision history

Revision Date Description

2 IntroductionA Tower Mounted Amplifier (TMA) is mounted in the antenna tower close to

the receiving antenna where it amplifies the received signal before it enters the

antenna feeder. The benefit of using TMAs is an improved uplink

performance. Whether it is recommended to use TMAs depends mainly on

which type of Combining and Distribution Unit (CDU) the Radio Base Station

(RBS) is equipped with, but also what area type that is to be covered and the

network quality ambitions the operator has.

This document shall serve as a short guideline describing when it is

appropriate to use TMA in the Ericsson GSM system.

The document describes the different TMA products, the system aspects of

using TMAs and presents the potential link budget improvement by using

TMAs. The document only deals with RBS 2000.

3 TMA productsThere are two different types of TMAs: duplex and dual duplex, see Figure 1.

TMA Duplex contains one duplex filter so that the TX and RX feeder can

be connected to the same antenna.

TMA Dual Duplex contains two duplex filters, one before the LNA and

one behind. This makes it possible to use only one feeder (TX/RX)

between the RBS and the TMA and to use the same antenna for TX/RX.

Today, virtually all TMAs sold are Dual Duplex ones. There are two

reasons for this:

A/ The number of feeders is reduced

B/ Only Dual Duplex TMAs are future proof for RBS2106/2206

installations/upgrades.


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DPX

RXTX

Duplex

DPX

DPX

TX/RX

Dual Duplex

DPX : Duplex Filter

: Low Noise Amplifier

Figure 1. Duplex and dual duplex TMA.

The current TMA product range includes the following frequency options:

Table 1. TMA products.

Duplex Dual Duplex

Frequency

band

[MHz]

Band

width

[MHz]

Frequency

band

[MHz]

Band

width

[MHz]

GSM800, RBS2000 N/A N/A 824-849 25

GSM 900, RBS 2000 N/A N/A 880-905

or

890-915

25

GSM 1800, RBS 2000 1710-1785 25, 75 1710-1785 30, 75

GSM 1900, RBS 2000 1850-1910 25, 60 1850-1910 30, 60


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4 System aspects

4.1 Benefits from introducing TMA

The TMA is mounted in the antenna tower close to the receiving antennas,

where it amplifies the received signal before it enters the antenna feeder.

Thanks to the additional amplification, the uplink RX sensitivity is improved.

There are two reasons for the improvement. Firstly, the feeder loss on the

uplink is neutralized. Secondly, the noise figure for the uplink will decrease.

In areas where noise (C/N) will limit the cell range, the improved RX

sensitivity has a potential of improving the coverage or decreasing the number

of sites required for coverage. Also the uplink speech quality and the dropped

call rate may be improved. More details under paragraph 5.1.

Improvements in speech quality and dropped call rates are often rewarded byan increase in traffic volume and billing.

The improved RX sensitivity will decrease the power consumption of the MS.

A TMA will however not help against low C/I. This is due to the fact that the

TMA will amplify the own signal (C) as well as the interference (I) and thus

not increase C/I.

In case of limited bandwidth, high traffic areas such as dense city

environments will call for tight frequency re-use and reduced cell ranges. The

deployment of TMAs under such conditions requires some extra thought.

However, if sufficient bandwidth allows TMA deployment withoutinterference constraints, network improvement can also be gained in dense

urban environments, including improving indoor coverage quality.

4.2 Considerations when introducing TMA

4.2.1 General

Placing active devices in the antenna tower puts extreme requirements on

reliability. The Ericsson TMA is designed for extremely high MTBF (Mean

Time Between Failure) and has dual LNAs and an optional LNA by-passfunctionality, to ensure a problem-free operation.

For RBS2106/2206 compatibility and to minimize the number of feeders, the

dual duplex TMA has to be used.

Todays TMA product range includes full band versions for all GSM bands

and all TMA types. Thus, TMA deployment is possible for all operators no

matter their frequency allocation from the regulators.


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4.2.2 RXLEV Compensation

Due to its amplification, the TMA will also affect the RXLEV values sent to

the BSC. This has to be taken into account during radio network optimization.

For example a received signal that without a TMA is measured to be RXLEV

= 10 (-100 dBm) would with a TMA having 12 dB amplification be measuredas RXLEV = 22. This is an undesired behavior since it would affect parameter

settings in the BSC to a large extent. The desired behavior is that the RXLEV

values sent to the BSC are the ones corresponding to the locating reference

point for sensitivity. If a TMA is used the reference point is defined at the

antenna connector of the TMA, see Figure 2.

RBS

TMA

Reference point

without TMA

Rx antenna

Feeder and jumpers

Reference point

with TMA

Figure 2. Locating reference point for sensitivity with and without TMA.

To transform the RXLEV values from the usual reference point at the RBS

cabinet to a reference point at the antenna connector, the values for the TMA

amplification and the antenna feeder loss must be specified in the Installation

Data Base (IDB) of the RBS. Information on how to do this can be found in

the RBS Site Test Manual.

4.2.3 BSC parameters affected by TMA introduction

For detailed information on BSC parameters influence by the TMA

introduction, please refer to the applicable system release documentation.


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5 Link budget improvement

5.1 Link balance and parameter variations

The RF performance in a cell depends on many factors involved, as will be

outlined later in this section.

By initially assigning these parameter nominal values, a Nominal Cell Plan,

i.e. the first site deployment draft, can be generated.

However, it is essential to understand that real-life site performance including

the Uplink/Downlink relation follows from actual variations of these

parameters and inevitably varies over time for any cell and site. (Ref. Figure

3)

Therefore, successive planning must take parameter tolerances and site-

specific aspects etc into account, to generate a realistic cell plan targeted to adesired radio network quality level.

No. of samples

Downlink superiority vs Uplink (dB)

Downlink > UplinkUplink > Downlink

X Y Z-Z -Y -X

TMA Improvement potential zone

Figure 3. Typical Uplink/Downlink balance distribution

The reasons for the cell-specific link balance variations include:

Variations in the MS populations performance. MS output is

usually lower than nominal values etc.

Variations in real antenna diversity gain, due to relative MS

positions, indoor MS usage etc.

Downlink slant loss is only to be expected for downlink paths with

little or no reflections.

Non-stationary reflection patterns

Different fading patterns for the uplink compared to the downlink


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5.2 TMA benefits

The benefit from deploying TMAs will depend on whether the site is

primarily downlink or uplink limited.

Dropped calls appear in areas with marginal coverage, such as:

Areas in the cell peripheries

Areas suffering from relative RF shadowing

Indoor environments

In-vehicle communication, where MS is not connected to an external

vehicle-mounted antenna

5.2.1 Potential TMA benefits in uplink limited sites:

Improving the geographic area covered, which facilitates the locationof suitable site space and ultimately reduces the number of sites

required. Up-front investment may be reduced.

Also the uplink speech quality and the dropped call rate may be

improved. The improved sensitivity can also be used to decrease the

power consumption of the MS.

5.2.2 Potential TMA benefits in downlink limited sites:

By further strengthening the uplink, call quality and dropped call rate

may be further improved, by minimizing the T_DR_SS_UL (Droppedcall rate related to low uplink signal strength).

NOTE: Operator experience has proven that quality improvements and

dropped call rate reductions can be expected also in such cells, where the

nominal uplink is stronger than the nominal downlink. The reason for this is

that nominal parameter figures are an approximation of the radio scenario at

hand.

5.3 Nominal figures for sensitivity and output power

In Table 2, sensitivity figures for different CDU types are presented with andwithout TMA. The improvement at the reference point is approximately 1.5

dB when using the TMA. Note that the reference point of this improved

sensitivity is defined at the antenna connector of the TMA (see Figure 2). For

an RBS without TMA the reference point is where the feeder cable is

connected to the RBS cabinet. This means that the sensitivity improvement by

using a TMA is 1.5 dB plus the attenuation in the feeder, i.e. the total

sensitivity improvement is typically 3-5 dB.


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Table 2. Nominal sensitivity levels with and without TMA, with reference

points according to Figure 2.

CDU Sensitivity

GSM 800

[dBm with/withou

t TMA

Sensitivity

GSM 900

[dBm with/withou

t TMA

Sensitivity

GSM 1800

dBm with/withou

t TMA

Sensitivity

GSM 1900

dBm with/withou

t TMA

CDU-A n/a -111.5/-110 -111.5/-110 -111.5/ N/A

CDU-C+ n/a -111.5/-110 -111.5/-110 -111.5/-110

CDU-D n/a -111.5/-110 -111.5/-110 n/a

CDU-F n/a -111.5/-110 -111.5/-110 n/a

CDU-G -111.5/-110 -111.5/-110 -111.5/-110 -111.5/-110

The sensitivity figures presented in Table 2 are only valid if the loss in the

feeder between the TMA and the RBS is less or equal to 4 dB. If the loss is

higher the sensitivity will deteriorate according to Table 3. For example if the

feeder loss is 8 dB, the sensitivity of an uplink equipped with CDU-A will be -

111.5 + 1.5 = -110 dBm.

Table 3 Sensitivity deterioration when the loss between the TMA and the RBS

exceeds 4 dB. Note that the figures are measured at 12 dB TMA gain.

Loss dB Sensitivity deterioration dB

4 0

6 0.5

8 1.5

10 2.5

Table 4 shows the TX output power of the RBS for different CDU types.

These values are required to analyze whether the RBS should be equipped

with a TMA or not.


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Table 4. TX output power defined at the RBS cabinet. Figures excluding the

optional software power boost and Coherent Combining features which

increase the output power.

CDU Output

powerGSM 800

[dBm

Output

powerGSM 900

[dBm

Output

powerGSM 1800

dBm

Output

powerGSM 1900

dBm

CDU-A n/a 44.5 43.5 43.5

CDU-C+ n/a 41.0 40.0 40.0

CDU-D n/a 42.0 41.0 N/A

CDU-F n/a 43.0 42.0 N/A

CDU-G 42.0 / 45.5 1/ 42.0 / 45.5 1/ 41.0 / 44.5 1/ 41.0 / 44.5 1/

1/Output power is 3.5 dB lower when CDU-G is used in Capacity Mode

5.4 Alternative parameter values

Many operators use alternative values for some of the parameters in the power

balance calculations (ref. Paragraph 5.5). The reason is to allow for equipment

related, site related and MS population related tolerances and in some cases to

further improve the network quality.

Based on own practical experience, these operators assess the relative uplink

strength to be weaker than in this documents nominal parameter results. By

doing so, they profit from the TMAs in cases, where a nominal parameter

calculation suggest no benefit would be attainable.

Paragraph 5.1 outlines why this is possible.

Since dropped calls may be further reduced and since no significant negative

effects are generated by uplink superiority, it is always good to evaluate the

potential benefits of a stronger uplink. In paragraph 5.6, an optional parameter

margin to stress this potential is included in Tables 5, 6, 7 and 8.

Suggestions on how to perform trial evaluation of TMA benefits are available

from Ericsson (ref. 3).

5.5 Power balance calculations

To see whether it is beneficial to use a TMA one can check the power balance

of the system assuming that there is no TMA. This can be done using

equation (1). 45 polarized antennas and equal feeder loss uplink and

downlink are assumed throughout this document. For more information about

link budget equations please refer to ref. 1.


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sensslantdivMSbalRBS LGPP +++= (max))( (1)

where

PRBS(bal)

is the RBS output power at the TX reference point to be used in

order to achieve a power balance between the uplink and the

downlink. The TX reference point is where the feeder is

connected to the RBS cabinet. The RBS out put power can be

found in Table 4.

PMS(max) is the maximum MS output power. Depends on the power class.

Gdiv is the average diversity gain (usually 3.5 dB)

Lslant is the downlink propagation loss due to 45 polarized antennas

(usually 1 dB).

sens is the difference in sensitivity between the MS and RBS, i.e.MSsens - RBSsens.Note that the reference point at the RBS

cabinet should be used (see Figure 2). The recommended figure

for MS sensitivity is 104 dBm.

If the maximum output power of the RBS is higher than the balanced one (see

equation (1)), the uplink is the limiting link and the link budget can be

improved by using a TMA. The link budget improvements calculated

according to equation (1) are summarized in section 5.6.

If it is decided to use a TMA the balanced RBS output power is given by:

TMAjfsensslantdivMSbalRBS LLLGPP +++++= +(max))( (2)

where

Lf+j is the loss in feeders and jumpers between the RBS and the TMA

LTMA is the TX loss in the TMA. For TMA Duplex and Dual Duplex

this loss is 0.3 dB. For TMA Simplex there is no TX loss.

sens is the difference in sensitivity between the MS and RBS, i.e.

MSsens - RBSsens.Note that the sensitivity reference point of the

RBS now is situated at the antenna connector of the TMA.


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5.6 Link budget improvements

5.6.1 GSM800

In Table 5, the link budget improvement of using a TMA in a GSM 800 cell is

calculated for the available CDU types. The improvement is calculated

according to equation (1) and that network planning must be based on the

lower powered mobiles at 29 dBm (0.8 W).

To accommodate for equipment related, site related and MS population

related tolerances, an uplink limiting adjustment parameter the chart below

includes some tolerances. The higher network quality requirements, the more

attention should be given to the effect of these tolerances.

Table 5. Link budget improvement of using TMAs for GSM800.

CDU-G

Capacity

CDU-G

Coverage

PMS(max)[dBm] 29 29

Gdiv [dB] 3.5 3.5

Lslant[dB] 11/

11/

MSsens [dBm] -104 -104

RBSsens [dBm] -110 -110

PRBS(bal) [dBm] 39.5 39.5

PRBS(max) [dBm] 42.01/

45.51/

Nominal TMA potential dB 3.5 6.5

Uplink adjustment2/

dB 2-4 2-4

Adjusted TMA potential2/ dB 5.5-7.5 8.5-10.5

1/If the features Software Power Boost or Coherent Combining are used, each

giving an additional 3 dB downlink power or if space diversity (no downlink

slant loss) is used, the link budget calculations should be modified accordingly.

2/Proposed uplink adjustment, as per paragraph 5.4, to capture the full potential

in improved call quality and better in-door penetration.


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5.6.2 GSM900

In Table 6, the link budget improvement of using a TMA in a GSM 900 cell is

calculated for the available CDU types. The improvement is calculated

according to equation (1).

To accommodate for equipment related, site related and MS populationrelated tolerances, an uplink limiting adjustment parameter the chart below

includes some tolerances. The higher network quality requirements, the more

attention should be given to the effect of these tolerances.


CDU-A CDU-C+

(CDU-C)

CDU-D CDU-G

Capacity

CDU-G

Coverage

CDU-F

PMS(max)[dBm] 33 33 33 33 33 33

Gdiv [dB] 3.5 3.5 3.5 3.5 3.5 3.5

Lslant[dB] 11/

11/

11/

11/

11/

11/

MSsens [dBm] -104 -104 -104 -104 -104 -104

RBSsens [dBm] -110 -110 -110 -110 -110 -110

PRBS(bal) [dBm] 43.5 43.5 43.5 43.5 43.5 43.5


411/

42 42.01/

45.51/

43.0

Nominal TMA potentialdB

1.0 0 0 0 2.0 0

Uplink adjustment2/

dB 2-4 2-4 2-4 2-4 2-4 2-4

Adjusted TMA potential2/ dB 3 - 5 0 - 1.5 0.5 2.5 0.5 2.5 4-6 1.5-3.5

1/If the features Software Power Boost or Coherent Combining are used, each giving an

additional 3 dB downlink power or if space diversity (no downlink slant loss) is used, the link

budget calculations should be modified accordingly. Software power boost is not possible for

configurations using CDU-D or CDU-F. Coherent Combining is only available for CDU-G

configurations.2/

Proposed uplink adjustment, as per paragraph 5.4, to capture the full potential in improved

call quality and better in-door penetration. For GSM900/1800/1900, this adjustment to the

theoretical model is necessary, to explain the well-proven TMA network benefits also for

CDU types where the Nominal TMA potential is zero.

One of many examples of the validity of the uplink adjustment is a German

trial, which led up to a full scale GSM900 TMA deployment onto the Ericsson

GSM radio network. Figure 4 below shows this trials Dropped-Call-Rate and


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Traffic as a function of the TMA deployment as well as a change in TX output

power.

The conclusion that the TMA deployment generates an approximately 50%

reduction in the dropped call rate already with the TX output power limited by

4 dB states the case for the Uplink adjustment parameter.

Figure 4. Recorded dropped call rate & Traffic volume as a function ofGSM900 TMA deployment and TX output power

Field Trials: Coverage & Quality Improvement at Rural Omni-Site

0

1

2

3

4

5

1 4 710

13

16

19

22

25

28

31

34

37

40

43

46

49

52

Dropped CallRate [%]

TCH Traffic[Erlang]

Day

Date 1:

TMAs installed

Date 2:

BS Tx Power

increased by 2 dB

Date 3:

BS Tx Power

increased by 4 dB


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5.6.3 GSM1800

In Table 7, link budget improvement of using a TMA in a GSM 1800 cell is

calculated for various CDU types. The improvement is calculated according to

equation (1).


CDU-A CDU-C+

(CDU-C)

CDU-D CDU-G

Capacity

CDU-G

Coverage

CDU-F

PMS(max)[dBm] 30 30 30 30 30 30

Gdiv [dB] 3.5 3.5 3.5 3.5 3.5 3.5

Lslant[dB] 11/

11/

11/

11/

11/

11/

MSsens[dBm

]

-104 -104 -104 -104 -104 -104

RBSsens [dBm] -110 -110 -110 -110 -110 -110

PRBS(bal) [dBm] 40.5 40.5 40.5 40.5 40.5 40.5


401/

411/

41 44.5 42

Nominal TMA potential

dB

3.0 0 0.5 0.5 4 1.5

Uplink adjustment2/

dB 2-4 2-4 2-4 2-4 2-4 2-4

Adjusted TMA potential2/ dB 5 - 7 1.5 3.5 2.5 4.5 2.5-4.5 6-8 3.5-5.5

1/If the features Software Power Boost or Coherent Combining are used, each giving an

additional 3 dB downlink power or if space diversity (no downlink slant loss) is used, the link

budget calculations should be modified accordingly. Software power boost is not possible for

configurations using CDU-D or CDU-F. Coherent Combining is only available for CDU-G

configurations.

2/Proposed uplink adjustment, as per paragraph 5.4, to capture the full potential in improved

call quality and better in-door penetration. For GSM900/1800/1900, this adjustment to the

theoretical model is necessary, to explain the well-proven TMA network benefits also for

CDU types where the Nominal TMA potential is zero.


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5.6.4 GSM1900

In Table 8, the link budget improvement of using a TMA in a GSM 1900 cell.

The improvement is calculated according to equation (1).

Table 8 Link budget improvement of using TMAs for CDU C and CDU-C+ at

GSM1900. For CDU-A TMA is mandatory.

CDU-C+

(CDU-C)

CDU-D CDU-G

Capacity

CDU-G

Coverage

PMS(max) [dBm] 30 30 30 30

Gdiv [dB] 3.5 3.5 3.5 3.5

Lslant[dB] 11/

11/

11/

11/

MSsens[dBm

]

-104 -104 -104 -104

RBSsens [dBm] -110 -110 -110 -110

PRBS(bal) [dBm] 40.5 40.5 40.5 40.5

PRBS(max) [dBm] 401/

411/

41 44.5

Nominal TMA potential

dB

0 0.5 0.5 4

Uplink adjustment2/

dB

2-4 2-4 2-4 2-4

Adjusted TMA potential2/ dB 1.53.5 2.54.5 2.54.5 6-8

1/If the features Software Power Boost or Coherent Combining are used, each

giving an additional 3 dB downlink power or if space diversity (no downlink

slant loss) is used, the link budget calculations should be modified accordingly.

Software power boost is not possible for configurations using CDU-D or CDU-F.

Coherent Combining is only available for CDU-G configurations.

2/Proposed uplink adjustment, as per paragraph 5.4, to capture the full potential in

improved call quality and better in-door penetration. For GSM900/1800/1900,

this adjustment to the theoretical model is necessary, to explain the well-provenTMA network benefits also for CDU types where the Nominal TMA potential is

zero.


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6 ConclusionThe Rayleigh fading is different on the uplink and the downlink. In a non-

frequency hopping cell it could occasionally happen that only the uplink

suffers from a fading dip. In these situations the improved sensitivity of the

TMA would be beneficial even if it according to strict link budget calculationswould be superfluous.

Another aspect is that the link budget calculations are based on an MS

sensitivity of -104 dBm and MS output power of 33 dBm and 30 dBm for

GSM900 and GSM800/1800/1900 respectively. Given todays MS featuring

dual and triple band capability, built-in antenna technology and the race for

the best stand-by and talk-time performance, it is to be assumed that a modern

MS population will deviate from these values.

In the process ofcell planning, all mobiles (old as well as newer ones) should

be considered. Thus by adopting the uplink adjustment calculations in

paragraph 5.6, we can understand why many operators install TMAs for allCDU types.

Note that the link budgets are calculated for standard configurations. If the

feature Software Power Boost is used, the calculation s should be modified

according to footnotes 1/. To capture the full potential in improved call quality

and better in-door penetration, calculation modification according to foot

notes 2/ is advisable.

Lastly, remember that a TMA does not improve C/I. Thus, in areas where it is

interference rather than noise that limits the system performance (for example

in cities with tight frequencyre-use) it is questionable whether to use TMA.

Also note that in these types of environment it has shown that it is thedownlink and not the uplink that suffers from the worst quality. Efforts to

improve the uplink will therefore not contribute so much to the overall speech

quality.


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7 References

ref. 1 RF Guidelines GSM900 (1800, 1900) MHz

16 (17,18) /100 56-HSC 103 12 Rev B, 2001

ref. 2 Sensitivity figures and output power for RBS2000 Macro

LRN/X-98:033 Rev H, 2001

ref. 3 TMA Field Trial Recommendations Guideline

RSA 100 56 - 102 Uen Rev A 2002-05-28

ref. 4 Tower Mounted Amplifiers Guideline The Ericsson GSM System R7

5/100 56 HSC 103 12 Uen Rev B, 1999

When to Use TMA Guideline

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