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Best Practices for Achieving Low PIM Performance in DAS Networks

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

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Best Practices for Achieving Low PIM Performance in DAS Networks

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  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) • 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 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*F2–4*F1 5*F1–4*F2 IM 9 IM 9 IM 7 IM 5 IM 3 IM 7 IM 3 IM 5

  4. What does PIM look like at the site? PIM 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 • Current increases linearly with applied voltage • High pressure, metal-to-metal contacts • Welded or soldered connections 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 Current Voltage

  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? High power RF terminations BTS #1 Input Out Out • Notorious for poor PIM • Impact depends on frequencies being combined BTS #2 Input

  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 • Fire suppression pipes • Air handling ductwork • Metal hangers • Lighting fixtures • Ceiling tile frames • Etc., etc., etc. Antennas flush mounted to ceiling

  15. And… there are many opportunities for PIM! Floor 1 Floor 2 Floor 3 Radio 2 Radio 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 2*F1–1*F2 2*F2–1*F1 3*F1–2*F2 3*F2–2*F1 4*F2–3*F1 4*F1–3*F2 5*F2–4*F1 5*F1–4*F2 IM 5 IM 3 IM 7 IM 9 IM 9 IM 7 IM 3 IM 5 BTS Uplink BTS Downlink • 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

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

  18. Where does PIM occur? (the easy way) F2 F1 30 MHz 30 MHz 30 MHz 30 MHz 30 MHz IM 5 IM 3 IM 5 IM 3 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 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

  20. What is the bandwidth of PIM signals? F1 F2 200 KHz 200 KHz 600 KHz 600 KHz 1 MHz 1 MHz 1.4 MHz 1.4 MHz 1.8 MHz 1.8 MHz IM 5 IM 3 IM 7 IM 9 IM 9 IM 7 IM 3 IM 5 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 Eliminate non-linearity so that multiple frequencies can peacefully co-exist! GSM UMTS CDMA

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

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

  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-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 )

  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 Antenna location tests Branch test Floortest Sector test System test Radio 1 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 (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! 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 * - Weight varies by frequency option

  34. Battery Operation = Enhanced Portability

  35. 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 seePIM beyond antenna • 6 markers + marker table to identify multiple sources

  37. Wide Range of Test Accessories 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)

  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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