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Best Practices for Achieving Low PIM Performance in DAS Networks

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Presentation on theme: "Best Practices for Achieving Low PIM Performance in DAS Networks"— Presentation transcript:

1 Best Practices for Achieving Low PIM Performance in DAS Networks
Slide 1

2 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

3 Passive Intermodulation (PIM)
TX Signals at site Passive Intermodulation (PIM) Passive Intermodulation (PIM) F1 F2 2*F1–1*F2 2*F2–1*F1 3*F1–2*F2 3*F2–2*F1 4*F1–3*F2 4*F2–3*F1 5*F1–4*F2 5*F2–4*F1 IM 9 IM 7 IM 5 IM 3 IM 3 IM 5 IM 7 IM 9 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

4 What does PIM look like at the site?
Mobile uplink signal

5 What does PIM look like to the operator?
PIM Repair High average noise level BUSY QUIET BUSY QUIET Lower average noise level

6 What is a non-linear junction?
Linear junctions Current Voltage Current increases linearly with applied voltage High pressure, metal-to-metal contacts Welded or soldered connections Current Voltage Non-linear junctions 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

7 What is non-linear in a DAS?
Damaged / poorly made components Broken cracked solder joints Loose internal fasteners Braided cables with crimp connectors Nickel plating Shipping damage

8 What is non-linear in a DAS?
Out BTS #1 Input High power RF terminations BTS #2 Input Out Notorious for poor PIM Impact depends on frequencies being combined

9 What is non-linear in a DAS?
Metal flakes inside RF connectors Worse when touching inner or outer conductor

10 What is non-linear a DAS?
Poor cable termination Loose metal flakes Rough / irregular metal edges

11 What is non-linear a DAS?
Metal flakes inside cables Plenum rated cables have no foam to prevent metal flakes from falling inside

12 What is non-linear in a DAS?
Loose RF connectors Must be torqued with a torque wrench

13 What is non-linear in a DAS?
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

14 What is non-linear in a DAS?
External PIM Sources Antennas flush mounted to ceiling Fire suppression pipes Air handling ductwork Metal hangers Lighting fixtures Ceiling tile frames Etc., etc., etc.

15 And… there are many opportunities for PIM!
Radio 1 Radio 2 Floor 3 Floor 2 Floor 1 In this simple example: 63 RF connections 31 cable assemblies 15 antennas 14 power dividers 1 hybrid combiner 1 RF termination

16 Where does PIM occur? F1 F2 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 BTS Uplink BTS Downlink PIM occurs at mathematical combinations of the Tx frequencies F1 = 1930 MHz F2 = 1945 MHz IM3 = (2*1930) – (1*1945) = MHz IM3 = (2*1945) – (1*1930) = MHz IM5 = (3*1930) – (2*1945) = MHz IM5 = (3*1945) – (2*1930) = MHz IM7 = (4*1930) – (3*1945) = MHz IM7 = (4*1945) – (3*1930) = MHz IM9 = (5*1930) – (4*1945) = MHz IM9 = (5*1945) – (4*1930) = MHz

17 Where does PIM occur? (the easy way)
F1 F2 IM 3 IM 5 IM 7 IM 9 15 MHz BTS Uplink BTS Downlink

18 Where does PIM occur? (the easy way)
F1 F2 IM 3 IM 5 30 MHz BTS Uplink BTS Downlink Wide frequency spacing moves IM products farther apart Increases probability that low order IM product will fall in uplink band

19 Neutral Host Systems Increase Probability that IM Products Will Fall in Rx Band
Single PCS operator: FCC did a good job! IM 11 first product that falls in A-block uplink Multiple operators / bands: Different story! IM 3 falls in E / F block uplink IM 5 falls in A-block

20 What is the bandwidth of PIM signals?
200 KHz 600 KHz 1 MHz 1.4 MHz 1.8 MHz BTS Uplink BTS Downlink PIM bandwidth increases as carrier bandwidth increases PIM bandwidth increase with PIM order

21 Can one wide band carrier generate PIM?
5 MHz 5 MHz 5 MHz 5 MHz 5 MHz 5 MHz 5 MHz 5 MHz 5 MHz IM 3 IM 5 IM 7 IM 9 BTS Uplink BTS Downlink YES ! Signal is composed of individual sub-carrier frequencies

22 What is the solution? LTE GSM UMTS CDMA Eliminate non-linearity so that multiple frequencies can peacefully co-exist!

23 How do we measure linearity?
F1, F2 Test lead Load IM products PIM PIM tester PIM 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

24 Reducing IM3 Reduces all IM Products
F1 F2 IM 3 IM 5 IM 7 IM 9 IM 11 BTS Uplink (Rx) BTS Downlink (Tx) Noise Floor Low IM3 = good linearity Low IM3 drives higher order products below the noise floor

25 Best Practices for Achieving Low PIM performance in a DAS

26 1) Start with high quality components
Only use RF components that: Are designed for low PIM performance Proper material selection No loose metal-to-metal junctions IEC 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 )

27 2) Use crews that are PIM certified
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

28 3) PIM test as you build Radio 1 Radio 2
Antenna location tests Branch test Floor test Sector test System test Radio 2

29 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)

30 Antenna Location Testing
Place antenna as close to design location as possible using low PIM pole Perform PIM test Low test power ( 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! PIM tester

31 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

32 PIM Master MW82119A Features

33 Key Specifications / Capabilities for DAS
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 2x 43dBm Distance-to-PIM™ YES PIM vs. Time Remote Control * - Weight varies by frequency option

34 Battery Operation = Enhanced Portability

35 Tapping on RF connections
PIM vs. Time Capability 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 Tapping on RF connections Limit Line

36 Distance-to-PIM (DTP) Capability
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

37 Wide Range of Test Accessories
R - Backpack Accessory Kit R – Transit case (Holds MW82119A only) R – Transit case (Holds MW82119A plus accessories) (accessories not included) R - Hard Case Accessory Kit

38 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

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