Best Practices for Achieving Low PIM Performance in DAS Networks

Slide 1

Agenda

What is Passive Intermodulation (PIM)

Sources of PIM in a DAS environment

Reasons why PIM is particularly problematic in DAS

How a PIM tester works

Best practices for mitigating PIM

Anritsu MW82119A product features

Slide 2

Passive Intermodulation (PIM)

Slide 3

F1 F2

TX Signals at site

Passive Intermodulation (PIM)Passive Intermodulation (PIM)

PIM = interference

PIM = new frequencies generated by TX Signals at a cell site when they encounter non-linear junctions or materials in the RF path

PIM falling in an operator’s uplink can elevate the noise floor:

▪ Dropped calls ▪ Access failures ▪ Slower data rates

2*F2–1*F1

3*F2–2*F1

4*F2–3*F1

5*F2–4*F1

2*F1–1*F2

3*F1–2*F2

4*F1–3*F2

5*F1–4*F2

IM 3IM 5IM 7IM 9 IM 3 IM 5 IM 7 IM 9

What does PIM look like at the site?

Slide 4

PIM

Mobile uplink signal

What does PIM look like to the operator?

Slide 5

High average noise level

Lower average noise level

QU

IET

BUSY

QU

IET

BUSY

PIM Repair

What is a non-linear junction?

Current increases linearly with applied voltage

High pressure, metal-to-metal contacts

Welded or soldered connectionsCurr

ent

Voltage

Linear junctions

Non-linear junctions

Curr

ent

Voltage

Current does not increase linearly with voltage.

Low pressure, metal-to-metal contacts

Oxide layers on metal surfaces

Arcing across small air gaps or cracks

What is non-linear in a DAS?

Slide 7

Damaged / poorly made components

Broken cracked solder joints

Loose internal fasteners

Braided cables with crimp connectors

Nickel plating

Shipping damage

What is non-linear in a DAS?

Slide 8

High power RF terminations

BTS #1 Input

Out

Out Notorious for poor PIM Impact depends on frequencies

being combined

BTS #2 Input

What is non-linear in a DAS?

Slide 9

Metal flakes inside RF connectors

Worse when touching inner or outer conductor

What is non-linear a DAS?

Slide 10

Poor cable termination

Loose metal flakes

Rough / irregular metal edges

What is non-linear a DAS?

Slide 11

Metal flakes inside cables

Plenum rated cables have no foam to prevent metal flakes from falling inside

What is non-linear in a DAS?

Slide 12

Loose RF connectors

Must be torqued with a torque wrench

What is non-linear in a DAS?

Slide 13

Type-N connectors

Easy to damage contacting surfaces if over torqued

Tend to loosen over time

7/16 DIN connectors better

4.1/9.5 or 4.3/10 “mini DIN” connectors also better

What is non-linear in a DAS?

Slide 14

External PIM Sources

Fire suppression pipes

Air handling ductwork

Metal hangers

Lighting fixtures

Ceiling tile frames

Etc., etc., etc.

Antennas flush

mounted to ceiling

And… there are many opportunities for PIM!

Floor 1

Slide 15

Radio 1 Radio 2Floor 2

Floor 3

63 RF connections

31 cable assemblies

15 antennas

14 power dividers

1 hybrid combiner

1 RF termination

In this simple example:

Where does PIM occur?

F1 F2

IM 3IM 5IM 7IM 9 IM 3 IM 5 IM 7 IM 9

2*F2–1*F1

3*F2–2*F1

4*F2–3*F1

5*F2–4*F1

2*F1–1*F2

3*F1–2*F2

4*F1–3*F2

5*F1–4*F2

PIM occurs at mathematical combinations of the Tx frequencies

F1 = 1930 MHz F2 = 1945 MHz

• IM3 = (2*1930) – (1*1945) = 1915 MHz IM3 = (2*1945) – (1*1930) = 1960 MHz

• IM5 = (3*1930) – (2*1945) = 1900 MHz IM5 = (3*1945) – (2*1930) = 1975 MHz

• IM7 = (4*1930) – (3*1945) = 1885 MHz IM7 = (4*1945) – (3*1930) = 1990 MHz

• IM9 = (5*1930) – (4*1945) = 1870 MHz IM9 = (5*1945) – (4*1930) = 2005 MHz

BTS DownlinkBTS Uplink

Slide 16

Where does PIM occur? (the easy way)

F1 F2

IM 3IM 5IM 7IM 9 IM 3 IM 5 IM 7 IM 9

15 MHz

15 MHz

15 MHz15 MHz15 MHz

15 MHz15 MHz

15 MHz

15 MHz

BTS DownlinkBTS Uplink

Slide 17

Where does PIM occur? (the easy way)

F1 F2

IM 3IM 5 IM 3 IM 5

30 MHz

30 MHz30 MHz

30 MHz30 MHz

BTS DownlinkBTS Uplink

Slide 18

Wide frequency spacing moves IM products farther apart

Increases probability that low order IM product will fall in uplink band

Neutral Host Systems Increase Probability that IM Products Will Fall in Rx Band

Slide 19

Multiple operators / bands:

Different story!

IM 3 falls in E / F block uplink

IM 5 falls in A-block

Single PCS operator:

FCC did a good job!

IM 11 first product that falls in A-block uplink

What is the bandwidth of PIM signals?

F1 F2

IM 3IM 5IM 7IM 9 IM 3 IM 5 IM 7 IM 9

200 KHz200 KHz

600 KHz

1 MHz

1.4 MHz

1.8 MHz

600 KHz

1 MHz

1.4 MHz

1.8 MHz

PIM bandwidth increases as carrier bandwidth increases

PIM bandwidth increase with PIM order

BTS DownlinkBTS Uplink

Slide 20

Can one wide band carrier generate PIM?

IM 3

IM 5IM 7

IM 9

5 MHz

5 MHz

5 MHz5 MHz5 MHz

5 MHz5 MHz

5 MHz

5 MHz

YES !

Signal is composed of individual sub-carrier frequencies

BTS DownlinkBTS Uplink

Slide 21

What is the solution?

Slide 22

Eliminate non-linearity so that multiple frequencies can peacefully co-exist!

LTE

GSM

UM

TS

CDMA

Slide 23

How do we measure linearity?

With a PIM tester!

Inject two CW test signals at a known magnitude

Measure 3rd order intermodulation product (IM3)

IM3 “characterizes” the linearity of the system

If IM3 is low = linearity is good

If IM3 is high = linearity is poor

Load

IM products

F1, F2

PIM

Test lead

PIM tester

PIM

Low IM3 = good linearity

Low IM3 drives higher order products below the noise floor

Slide 24

Reducing IM3 Reduces all IM Products

A A

F1 F2

IM 3

IM 5IM 7IM 9IM 11

IM 3

IM 5 IM 7

BTS Uplink (Rx) BTS Downlink (Tx)

Noise Floor

Best Practices for Achieving Low PIM performance in a DAS

Slide 25

1) Start with high quality components

Slide 26

Only use RF components that:

Are designed for low PIM performance

Proper material selection

No loose metal-to-metal junctions

IEC-62037-1 provides more extensive list of design guidelines

From companies that:

Own PIM test equipment

Have their manufacturing processes under control

100% test to verify performance (-150dBc with 2x 20W test tones )

2) Use crews that are PIM certified

Slide 27

Understand the importance of cleanliness

Use alcohol swabs to clean mated pairs of connectors

Vacuum end of cables before attaching connectors

Understand the importance of proper cable preparation

Cut plenum rated cables with razor blade cutter (not saw)

Use sharp cutting tools

Use the correct tools for the type of cable in use

Understand the importance of tight connections

Always use a torque wrench (DIN)

Do not over/under tighten (Type-N)

Have experience operating PIM test equipment

3) PIM test as you build

Antenna location tests

Branch test

Floor test

Slide 28

Radi

o 1

Radi

o 2

Sector test

System test

3) PIM test as you build(con’t)

Problems are identified and corrected before being replicated throughout the DAS

Faster to locate PIM sources when testing smaller sections

Easier access to antennas / splitters to troubleshoot and correct problems

Tools, materials, man-lifts, still on hand

Reduced re-work at antenna locations (when antenna locations are pre-tested)

Slide 29

Antenna Location Testing

Place antenna as close to design location as possible using low PIM pole

Perform PIM test

Low test power (15 - 30 dBm typical)

Lowest frequency only (700 or 850 MHz)

Pass/Fail limit (depends on test power)

Find passing location within 1 m of design location

Small movements = big changes in PIM!

Slide 30

PIM tester

Things to Avoid Around Antennas:

For every rule there is an exception

This is why it is important to test!

Try to avoid placing antennas within 1m of:

Metal seams (ductwork, etc.)

Concrete with obvious signs of rust

Lighting fixtures

Electronic devices

Products containing RF ID tags

Slide 31

PIM Master MW82119A Features

Slide 32

Key Specifications / Capabilities for DAS

Slide 33

Parameter Specification

Small size 350 x 314 x 152mm(13.8 x 12.4 x 6.0in)

Light weight 9 kg to 12 kg *(20 lb to 27 lb)

Battery operation > 3.0 hours

Wide power range 25dBm to 46dBm(0.3W to 39.8W)

Low residual PIM -117 dBm @ 2x 43dBm

Distance-to-PIM™ YES

PIM vs. Time YES

Remote Control YES

* - Weight varies by frequency option

Battery Operation = Enhanced Portability

Slide 34

PIM magnitude vs. time

Tap on all RF connections while

performing the PIM test

Visual indication of PIM stability

Peak PIM held for Pass/Fail

Slide 35

PIM vs. Time Capability

Tapping on RF connections Limit Line

Distance-to-PIM (DTP) Capability

Slide 36

The fastest way to locate PIM

PIM magnitude vs. distance

Eliminates guess-work

Able to see PIM beyond antenna

6 markers + marker table to identify

multiple sources

Wide Range of Test Accessories

Slide 37

2000-1746-R - Hard Case Accessory Kit

2000-1745-R - Backpack Accessory Kit

760-265-R – Transit case

(Holds MW82119A plus accessories)

(accessories not included)

760-259-R – Transit case

(Holds MW82119A only)

Conclusion

PIM is a challenge in DAS environments

Many potential sources

More harmful frequency combinations

Best practices for mitigating PIM include:

Using high quality components

Using trained installation crews

PIM testing as you build (starting with antenna locations)

Anritsu PIM Master is well suited for PIM testing in a DAS environments

Exceptional portability

Fully integrated, Distance-to-PIM (DTP) technology

Slide 38